Device and method for color adjustment and gamma correction and display panel driver using the same

This application claims priority to Japanese Patent Application No. 2014-153918, filed on Jul. 29, 2014, the disclosure which is incorporated herein by reference.

The present invention relates to a display device, display panel driver, image processing device, and method of driving a display panel, and more particularly to digital arithmetic processing of image data for color adjustment.

Image data are often subject to digital arithmetic processing to display an image with a desired image quality. One known digital arithmetic processing technology is color adjustment. Image data often include data indicating the grayscale values of respective subpixels (such as red subpixels, green subpixels and blue subpixels) of respective pixels and the colors of the respective pixels in an actual display image can be adjusted by adjusting the grayscale values of the respective subpixels through a color adjustment technology.

One example of a color adjustment technology is color gamut adjustment. A display panel (such as a liquid crystal display panel) may be insufficient in the color reproducibility and this may make it impossible to represent all the colors in a desired color gamut (for example, the color gamut defined in the sRGB standard or the NTSC (National Television System Committee) standard). In such a case, a color adjustment technology helps representing the colors in a color gamut as similar as possible to the desired color gamut.

Although various technologies have been proposed for color adjustment, the inventors find room for improvement in conventional color adjustment technologies with respect to the circuit size reduction, while achieving an appropriate color adjustment. The situation may be severe, especially when color adjustment and different image processing (such as gamma correction) are performed in serial.

Discussed below is an example in which gamma correction is performed on image data obtained by color adjustment, as illustrated in FIG. 1 . In order to effectively perform color adjustment, it is desired that the bit width of the output image data obtained by the color adjustment is larger than that of the input image data. This aims to avoid gradation collapse in the color adjustment. In one example, when input image data of color adjustment represent the grayscale value of each of the red, green and blue colors with eight bits, image data which represent the grayscale value of each of the red, green and blue colors with 10 bits may be generated as the output of the color adjustment.

When gamma correction is further performed on the image data obtained as the output of the color adjustment, it is further desired that the bit width of the image data obtained as the output of the gamma correction is further increased. When image data which represent the grayscale value of each of the red, green and blue colors with 10 bits are generated as the output of the color adjustment, for example, image data which represent the grayscale value of each of the red, green and blue colors with 12 bits may be generated as the output of the gamma correction. The increase in the bit widths of the input and output image data of the gamma correction, however, undesirably increases the circuit size of a circuit used for the color adjustment.

In an aspect of the present invention, a display device includes: a display panel and a display panel driver driving the display panel. The display panel driver includes: a processing circuit configured to perform digital arithmetic processing on R, G and B grayscale values of input image data to calculate R, G and B grayscale values of output image data, respectively; a driver circuit configured to drive the display panel in response to the output image data; and a control point data generation circuit. The control point data generation circuit is configured to: generate first control point data indicating a shape of a gamma curve of a desired gamma value; calculate R control point data indicating an input-output curve of digital arithmetic processing performed on the R grayscale value of the input image data by correcting the first control point data in response to a position of a corresponding point corresponding to the input image data in a color space; calculate G control point data indicating an input-output curve of digital arithmetic processing performed on the G grayscale value of the input image data by correcting the first control point data in response to the position of the corresponding point in the color space; and calculate B control point data indicating an input-output curve of digital arithmetic processing performed on the B grayscale value of the input image data by correcting the first control point data in response to the position of the corresponding point in the color space. The processing circuit is configured to: calculate the R grayscale value of the output image data in response to the R control point data, calculate the G grayscale value of the output image data in response to the G control point data, and calculate the B grayscale value of the output image data in response to the B control point data.

In another aspect of the present invention, a display panel driver for driving a display panel includes: a processing circuit configured to perform digital arithmetic processing on R, G and B grayscale values of input image data to calculate R, G and B grayscale values of output image data, respectively; a driver circuit configured to drive the display panel in response to the output image data; and a control point data generation circuit. The control point data generation circuit is configured to: generate first control point data indicating a shape of a gamma curve of a desired gamma value; calculate R control point data indicating an input-output curve of digital arithmetic processing performed on the R grayscale value of the input image data by correcting the first control point data in response to a position of a corresponding point corresponding to the input image data in a color space; calculate G control point data indicating an input-output curve of digital arithmetic processing performed on the G grayscale value of the input image data by correcting the first control point data in response to the position of the corresponding point in the color space; and calculate B control point data indicating an input-output curve of digital arithmetic processing performed on the B grayscale value of the input image data by correcting the first control point data in response to the position of the corresponding point in the color space. The processing section is configured to: calculate the R grayscale value of the output image data in response to the R control point data, calculate the G grayscale value of the output image data in response to the G control point data, and calculate the B grayscale value of the output image data in response to the B control point data.

In still another aspect of the present invention, an image processing device includes: a processing circuit configured to perform digital arithmetic processing on R, G and B grayscale values of input image data to calculate R, G and B grayscale values of output image data, respectively; a control point data generation circuit. The control point data generation circuit is configured to: generate first control point data indicating a shape of a gamma curve of a desired gamma value; calculate R control point data indicating an input-output curve of digital arithmetic processing performed on the R grayscale value of the input image data by correcting the first control point data in response to a position of a corresponding point corresponding to the input image data in a color space; calculate G control point data indicating an input-output curve of digital arithmetic processing performed on the G grayscale value of the input image data by correcting the first control point data in response to the position of the corresponding point in the color space; and calculate B control point data indicating an input-output curve of digital arithmetic processing performed on the B grayscale value of the input image data by correcting the first control point data in response to the position of the corresponding point in the color space. The processing section is configured to: calculate the R grayscale value of the output image data in response to the R control point data, calculate the G grayscale value of the output image data in response to the G control point data, and calculate the B grayscale value of the output image data in response to the B control point data.

In still another aspect of the present invention, a method of driving a display panel includes: calculating R, G and B grayscale values of output image data by performing digital arithmetic processing on R, G and B grayscale values of input image data, respectively; and driving the display panel in response to the output image data. The step of calculating the R, G and B grayscale values of the output image data includes: generating first control point data indicating a shape of a gamma curve of a desired gamma value; calculating R control point data indicating an input-output curve of digital arithmetic processing performed on the R grayscale value of the input image data by correcting the first control point data in response to a position of a corresponding point corresponding to the input image data in a color space; calculating G control point data indicating an input-output curve of digital arithmetic processing performed on the G grayscale value of the input image data by correcting the first control point data in response to the position of the corresponding point in the color space; calculating B control point data indicating an input-output curve of digital arithmetic processing performed on the B grayscale value of the input image data by correcting the first control point data in response to the position of the corresponding point in the color space; calculating the R grayscale value of the output image data in response to the R control point data; calculating the G grayscale value of the output image data in response to the G control point data; and calculating the B grayscale value of the output image data in response to the B control point data.

The present invention effectively provides a device and method for achieving digital image processing including color adjustment and gamma correction with a reduced circuit size and a display panel driver and display device using the same.

The above and other advantages and features of the present invention will be more apparent from the following description taken in conjunction with the accompanied drawings, in which:

FIG. 1 is an exemplary configuration of an image processing circuit performing color adjustment and gamma correction in serial;

FIG. 2 is a conceptual diagram illustrating gamma correction and color adjustment performed on input image data in one embodiment of the present invention;

FIG. 3A illustrates an example of a desired color gamut and intrinsic color gamut of a liquid crystal display panel for which color adjustment is to be performed;

FIG. 3B illustrates an example of the positions of the white point, the vertices corresponding to three elementary colors and the vertices corresponding to the complementary colors of the three elementary colors;

FIG. 4 is a block diagram illustrating an exemplary configuration of a display device in a first embodiment of the present invention;

FIG. 5 is a circuit diagram conceptually illustrating the configuration of each subpixel;

FIG. 6 is a block diagram illustrating an example of the configuration of a driver IC in the first embodiment of the present invention;

FIG. 7 is a block diagram illustrating an example of the configuration of an approximate gamma correction circuit;

FIG. 8 is a graph illustrating the relation between control point data and the shape of an input-output curve of arithmetic processing performed on the R, G and B grayscale values D IN R , D IN G and D IN B of input image data D IN ;

FIG. 9 is a block diagram illustrating an example of the configuration of a control point data calculation circuit in the first embodiment;

FIG. 10 is a block diagram illustrating an example of a correction amount calculation circuit in the first embodiment;

FIG. 11A is a flowchart illustrating digital arithmetic processing performed on input image data D IN in the first embodiment;

FIG. 11B is a graph illustrating the relation among an APL, a gamma value γ_VALUE and control point data set CP_sel in one embodiment;

FIG. 11C is a graph illustrating the relation among an APL, a gamma value γ_VALUE and control point data set CP_sel in another embodiment;

FIG. 11D is a graph conceptually illustrating the shapes of gamma curves corresponding to control point data set CP#q and CP#(q+1) and the shape of a gamma curve corresponding to control point data set CP_sel;

FIG. 12A is a flowchart illustrating an exemplary calculation procedure of correction amounts ΔCP_R, ΔCP_G and ΔCP_B in one embodiment of the present invention;

FIG. 12B is a table illustrating settings used in one example of calculation of correction amounts ΔCP_R, ΔCP_G and ΔCP_B;

FIG. 13 is a graph illustrating the relation between R, G and B grayscale values of input image data D IN and those of output image data D OUT ;

FIG. 14 is a flowchart illustrating an exemplary calculation procedure of correction amounts for the white point and the vertices corresponding to the respective elementary colors and complementary colors;

FIG. 15A is a table illustrating an example of the measurement result of panel characteristics;

FIG. 15B is a table illustrating the result of transformation from chromaticity coordinates (u′, v′) to (x, y) with respect to the measured values of the chromaticity coordinates of the white point (WP) and the R, G, B, C, M and Y vertices illustrated in FIG. 15A ;

FIG. 16 is a table illustrating an example of settings of desired values of adjustment;

FIG. 17A is a table illustrating an example of 50%-saturation panel characteristics;

FIG. 17B is a table illustrating an example of 50%-saturation desired values;

FIG. 18A is a table illustrating the result of transformation from chromaticity coordinates (u′, v′) to (x, y) with respect to the chromaticity coordinates of the white point (WP) and the 50%-saturation panel characteristics values of the respective elementary colors and complementary colors illustrated in FIG. 17A ;

FIG. 18B is a table illustrating the result of transformation from chromaticity coordinates (u′, v′) to (x, y) with respect to desired values of the chromaticity coordinates of the white point and the 50%-saturation desired values of the respective elementary colors and complementary colors illustrated in FIG. 17B ;

FIG. 18C is a table illustrating the result of transformation from chromaticity coordinates (x, y) to (X, Y, Z) with respect to the chromaticity coordinates of the white point and the 50%-saturation panel characteristics values of the respective elementary colors and complementary colors illustrated in FIG. 18A ;

FIG. 18D is a table illustrating the result of transformation from chromaticity coordinates (x, y) to (X, Y, Z) with respect to desired values of the chromaticity coordinates of the white point and the 50%-saturation desired values of the respective elementary colors and complementary colors illustrated in FIG. 18B ;

FIG. 19A is a table illustrating an example of the ratio among R, G and B grayscale values of 50%-saturation panel characteristics values of the respective elementary colors and complementary colors;

FIG. 19B is a table illustrating an example of the ratio among R, G and B grayscale values of 50%-saturation desired values of the respective elementary colors and complementary colors;

FIG. 19C is a table illustrating an example of R, G and B grayscale values of 50%-saturation panel characteristics values of the respective elementary colors and complementary colors;

FIG. 19D is a table illustrating an example of R, G and B grayscale values of 50%-saturation desired values of the respective elementary colors and complementary colors;

FIG. 20A is a table illustrating correction amounts of R, G and B grayscale values obtained for 50% saturation;

FIG. 20B is a table illustrating an example of correction amounts ΔCP_R, ΔCP_G and ΔCP_B obtained for the respective elementary color and complementary colors;

FIG. 21 is a block diagram illustrating an exemplary configuration of a driver IC in a second embodiment;

FIG. 22 is a block diagram illustrating an exemplary configuration of a control point data calculation circuit in the second embodiment;

FIG. 23 is a flowchart illustrating digital arithmetic processing performed on input image data D IN in the second embodiment;

FIG. 24A is a table illustrating an example of settings of correction amounts for the white point and the vertices corresponding to the respective elementary colors and complementary colors in the second embodiment;

FIG. 24B is a table illustrating an example of the relation among the grayscale values of input image data D IN , the intrinsic panel characteristics of a liquid crystal display panel (panel brightness characteristics) and desired values of brightness adjustment;

FIG. 25A is a table illustrating an example of the values of control point data CP 0 _P to CP 5 _P in digital arithmetic processing in the second embodiment;

FIG. 25B is a table illustrating an example of the values of control point data CP 0 _sel to CP 5 _sel in digital arithmetic processing in the second embodiment; and

FIG. 26 is a table illustrating an example of the finally-obtained values of control point data CP 0 _R to CP 5 _R, CP 0 _G to CP 5 _G and CP 0 _B to CP 5 _B.

Embodiments of the present invention provide a device and method for digital image processing including color adjustment and gamma correction with a reduced circuit size and a display panel driver and display device using the same. Other aspects of the present invention would be understood by a person skilled in the art from the following disclosure.

The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art would recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposed. It should be noted that the same or similar components may be denoted by the same or corresponding reference numerals.

FIGS. 2, 3A and 3B schematically illustrate color adjustment processing performed in one embodiment of the present invention. In the present embodiment, as illustrated in FIG. 2 , gamma correction and color adjustment are performed on input image data D IN through digital arithmetic processing to generate gamma-corrected and color-adjusted output image data D OUT .

In the present embodiment, output image data D OUT are calculated by performing arithmetic processing on input image data D IN in accordance with given arithmetic expressions. In detail, the R grayscale value D OUT R of output image data D OUT is calculated by using an arithmetic expression in which the R grayscale value D IN R of input image data D IN is defined as a variable. Correspondingly, the G grayscale value D OUT G of output image data D OUT is calculated by using an arithmetic expression in which the G grayscale value D IN G of input image data D IN is defined as a variable, and the B grayscale value D OUT B of output image data D OUT is calculated by using an arithmetic expression in which the B grayscale value D IN B of input image data D IN is defined as a variable.

The upper row of FIG. 2 illustrates curves indicating the input-output relations of the digital arithmetic processing achieved by the arithmetic expressions (that is, the relation between the values of input image data D IN and the values of output image data D OUT ). In the following, a curve indicating an input-output relation may be referred to as “input-output curve”. An input-output curve is specified for each of the R, G and B grayscale values.

In the present embodiment, the shapes of the input-output curves are specified by the positions of control points (CPs) and the coefficients defined in the arithmetic expressions used for calculating the output image data D OUT are determined depending on the positions of the control points to allow the input-output curves to be shaped as desired. More specifically, the shape of each input-output curve is specified with the positions of six control points CP 0 to CP 5 in the present embodiment. The positions of the ends of the input-output curve are specified with the control points CP 0 and CP 5 , respectively, and the shape of the intermediate portion of the input-output curve is specified with the control points CP 1 to CP 4 . The control points CP 2 and CP 3 specify the two positions that the input-output curve passes through near the midpoint of the input-output curve. The control point CP 1 indicates the degree of curvature in the portion between the control points CP 0 and CP 2 and the control point CP 4 indicates the degree of curvature in the portion between the control points CP 3 and CP 5 . It should be noted that, in the example illustrated in FIG. 2 , the control points CP 1 and CP 4 are not defined at positions that the input-output curve passes through. The control points CP 0 to CP 5 are each defined as a point in a coordinate system in which the first coordinate axis corresponds to the grayscale values (which may be any of the R, G and B grayscale values) of input image data D IN and the second coordinate axis corresponds to the grayscale values of output image data D OUT . It should be noted however that the number and/or definition of the control points may be variously modified.

Additionally, as illustrated in the lower row of FIG. 2 , gamma correction and color adjustment are concurrently achieved by controlling the shapes of the input-output curves of the respective colors in the present invention. More specifically, the shapes of the input-output curves, that is, the positions of the control points CP 0 to CP 5 are first determined to make the input-output curves approximate to the gamma curves of desired gamma values. Furthermore, color adjustment is achieved by correcting (adjusting) the shapes of the input-output curves, that is, the positions of the control points CP 0 to CP 5 individually for the respective colors.

The color adjustment is performed so that a desired color gamut is achieved in a targeted display panel (in the present embodiment, a liquid crystal display panel). FIG. 3A illustrates a desired color gamut and the intrinsic color gamut of a display panel for which color adjustment is to be performed. Even when the desired color gamut and the intrinsic color gamut of a display panel is different, it is possible to make the color gamut of an actually displayed image approximate to a desired color gamut through color adjustment in a pseudo manner.

Schematically, such color adjustment can be achieved as described below. First, appropriate correction amounts of control points CP 0 to CP 5 are calculated for the white point, the vertices corresponding to the respective elementary colors and the vertices corresponding to the complementary colors. FIG. 3B illustrates an example of the positions of the white point (W), the vertices corresponding to the three elementary colors and the vertices corresponding to the complementary colors of the three elementary colors in the color space. It should be noted that, in the present embodiment, the three elementary colors are defined as R (red), G (green) and B (blue) and the complementary colors of the three elementary colors are defined as C (cyan), M (magenta) and Y (yellow). The vertex of a certain elementary color means the point at which the saturation of the elementary color is maximum (the point at which the saturation is 100%) in the color space. Correspondingly, the vertex of a certain complementary color means the point at which the saturation of the complementary color is maximum (the point at which the saturation is 100%) in the color space. In the following, the vertices corresponding to the elementary color R, G and B are referred to as R, G and B vertices, respectively, and the vertices corresponding to the complementary color C, M and Y are referred to as C, M and Y vertices, respectively.

It should be noted that appropriate correction amounts of control points CP 0 to CP 5 suitable for the write point, the vertices corresponding to the respective elementary colors and the respective complementary colors are parameters to be determined on the characteristics of the display panel. It is possible to calculate approximate correction amounts for the write point, the vertices corresponding to the respective elementary colors and the complementary color, respectively, from measured values of the characteristics of the display panel, and the calculated correction amounts are stored in a proper storage means (such as a register). Details will be described later.

The correction amounts of control points CP 0 to CP 5 for each pixel are determined the position of the point corresponding to the input image data D IN in the color space. In the following, the point corresponding to the input image data D IN in the color space may be referred to as “corresponding point”, hereinafter.

More specifically, in the present embodiment, six areas A 1 to A 6 are defined in the color space with the write point, the vertices corresponding to the three elementary colors and the vertices corresponding to the three complementary colors as follows:

Area A 1 : the triangular area defined by the R vertex, the Y vertex and the white point

Area A 2 : the triangular area defined by the Y vertex, the G vertex and the white point

Area A 3 : the triangular area defined by the G vertex, the C vertex and the white point

Area A 4 : the triangular area defined by the C vertex, the B vertex and the white point

Area A 5 : the triangular area defined by the B vertex, the M vertex and the white point

Area A 6 : the triangular area defined by the M vertex, the R vertex and the white point

It should be noted that the areas A 1 to A 6 are each defined with the write point, a vertex corresponding to one elementary color and a vertex corresponding to one complementary color.

In the color adjustment of the present embodiment, for input image data D IN corresponding to a certain pixel, it is determined which of the six areas A 1 to A 6 the corresponding point of the input image data D IN belongs to in the color space. Furthermore, the following three “distances” are calculated for the area which the corresponding point of the input image data D IN is determined as belonging to (which may be referred to as “belonging area”, hereinafter):

(1) Distance d ELM between the vertex corresponding to the elementary color by which the belonging area is defined and the corresponding point of the input image data D IN ;

(2) Distance d CMP between the vertex corresponding to the complementary color by which the belonging area is defined and the corresponding point of the input image data D IN ; and

(3) Distance d W between the white point and the corresponding point of the input image data D IN .

In the present embodiment, the correction amounts of control points CP 0 to CP 5 are calculated for input image data D IN corresponding to each pixel on the basis of: the correction amounts determined for the elementary color which defines the belonging area; the correction amounts determined for the complementary color which defines the belonging area; the correction amounts determined for the white point; and the three calculated distances d ELM , d CMP and d W . The color adjustment is achieved by performing digital arithmetic processing on the input image data D IN in accordance with the input-output curves with the shapes determined by the control points CP 0 to CP 5 corrected with the calculated correction amounts. It should be noted that any parameters defined to indicate the degree of separation of two points in the color space may be used as the “distance”. Specific examples of the “distance” will be described later.

The above-described method allows performing digital arithmetic processing including gamma correction and color adjustment with a reduced circuit size, because the gamma correction and color adjustment are concurrently performed. Described in the following are specific configurations and operations of a display device, a display panel driver and an image processing circuit for performing the above-described color adjustment.

First Embodiment

FIG. 4 is a block diagram illustrating an exemplary configuration of a display device in a first embodiment of the present invention. The display device of the present embodiment is configured as a liquid crystal display device 1 which includes a liquid crystal display panel 2 and a driver IC (integrated circuit) 3 .

The liquid crystal display panel 2 includes a display region 5 and a gate line drive circuit 6 (also referred to as GIP (gate-in-panel) circuit). Arranged in the display region 5 are a plurality of gate lines (also referred to as scan lines or address lines), a plurality of data lines 8 (also referred to as signal lines or source lines) and a plurality of pixels 9 . In the present embodiment, the number of the gate lines 7 is v and the number of the data lines 8 is 3 h, where v and h are each an integer equal to or more than two. The pixels 9 are arranged in v rows and h columns in the display region 5 , where v and h are integers equal to or more than two.

In the present embodiment, each pixel 9 includes three subpixels: an R subpixel 11 R, a G subpixel 11 G and a B subpixel 11 B. The R subpixel 11 R is a subpixel corresponding to the red color (that is, displaying the red color), the G subpixel 11 G is a subpixel corresponding to the green color (that is, displaying the green color), and the B subpixel 11 B is a subpixel corresponding to the blue color (that is, displaying the blue color). The R, G and B subpixels 11 R, 11 G and 11 B may be collectively referred to as subpixels 11 , if not distinguished from one another. In the present embodiment, the subpixels 11 are arrayed in v rows and 3 h columns in the liquid crystal display panel 2 . Each subpixel 11 is connected to a corresponding gate line 7 and a corresponding data line 8 . In driving the respective subpixels 11 of the liquid crystal display panel 2 , the gate lines 7 are sequentially selected and desired drive voltages are written into the subpixels 11 connected to the selected gate line 7 through the data lines 8 . This allows setting the respective subpixels 11 to desired grayscale levels and displaying a desired image in the display region 5 of the liquid crystal display panel 2 .

FIG. 5 is a circuit diagram conceptually illustrating the configuration of each subpixel 11 . Each subpixel 11 includes a TFT (thin film transistor) 12 and a pixel electrode 13 . The TFT 12 has a gate connected to a gate line 7 , a source connected to a data line 8 and a drain connected to the pixel electrode 13 . The pixel electrode 13 is disposed opposed to the counter electrode (also referred to as common electrode) 14 of the liquid crystal display panel 2 and Liquid crystal is filled between the pixel electrode 13 and the counter electrode 14 . It should be noted that, although the counter electrode 14 is illustrated as being prepared for each subpixel 11 in FIG. 5 , a person skilled in the art would appreciate that one counter electrode is shared by a plurality of subpixels 11 (in a typical configuration, one common counter electrode 14 is disposed in the liquid crystal display panel 2 ).

Referring back to FIG. 4 , the driver IC 3 drives the data lines 8 and also generates gate line control signals S GIp which control the gate line drive circuit 6 . The data lines 8 are driven in response to input image data D IN and synchronization data D SYNC , which are received from the processor 4 . The input image data D IN are data corresponding to an image to be displayed in the display region 5 of the liquid crystal display panel 2 . More specifically, the input image data D IN are data specifying the grayscale level of each subpixel 11 of each pixel 9 . As described above, the input image data D IN include an R grayscale value D IN R , a G grayscale value D IN G and a B grayscale value D IN B . The grayscale level of the R subpixel 11 R is specified by the R grayscale value D IN R , the grayscale level of the G subpixel 11 G is specified by the G grayscale value D IN G , and the grayscale level of the B subpixel 11 B is specified by the B grayscale value D IN B . In the present embodiment, the R, G and B grayscale values D IN R , D IN G and D IN B are all 8-bit data. In other words, the input image data D IN are data indicating the grayscale levels of the respective subpixels of each pixel 9 of the liquid crystal display panel 2 with 24 bits. The synchronization data D SYNC , which are used to control the operation timing of the driver IC 3 , control the generation timing of timing control signals generated in the driver IC 3 , including the vertical sync signal V SYNC , the horizontal sync signal H SYNC and so on. The gate line control signals S GIP are generated in response to the synchronization data D SYNC . The driver IC 3 is mounted on the liquid crystal display panel 2 with a surface mounting technology such as a COG (chip-on-glass) technology.

FIG. 6 is a block diagram illustrating an exemplary configuration of the driver IC 3 . The driver IC 3 includes an interface circuit 21 , an approximate gamma correction circuit 22 , a color reduction circuit 23 , a latch circuit 24 , a grayscale voltage generator circuit 25 , a data line drive circuit 26 , a gamma value setting circuit 27 , a correction amount calculation circuit 28 and a control point data calculation circuit 29 .

The interface circuit 21 receives the input image data D IN from the processor 4 and forwards the received input image data D IN to the approximate gamma correction circuit 22 .

The approximate gamma correction circuit 22 performs the above-described digital arithmetic processing for color adjustment and gamma correction. The approximate gamma correction circuit 22 performs the digital arithmetic processing on the input image data D IN to generate output image data D OUT . The output image data D OUT , which specify the grayscale level of each subpixel 11 of each pixel 9 similarly to the input image data D IN , include an R grayscale value D OUT R , a G grayscale value D OUT G and a B grayscale value D OUT B .

FIG. 7 is a block diagram illustrating an exemplary configuration of the approximate gamma correction circuit 22 . The approximate gamma correction circuit 22 includes approximate gamma correction circuits 30 R, 30 G and 30 B, which are prepared to process the R grayscale value D IN R , the G grayscale value D IN G and the B grayscale value D IN B of the input image data D IN , respectively. The approximate gamma correction circuit 30 R performs correction processing on the R grayscale value D IN R of the input image data D IN in accordance with an arithmetic expression to generate the R grayscale value D OUT R of the output image data D OUT . As illustrated in FIG. 7 , the approximate gamma correction circuit 30 R is supplied with control point data CP 0 _R to CP 5 _R. As illustrated in FIG. 8 , the control point data CP 0 _R to CP 5 _R specify the shape of the input-output curve of the arithmetic processing performed on the R grayscale value D IN R of the input image data D IN , and indicate the positions of the control points CP 0 to CP 5 that specify the shape of the input-output curve. The coefficients of the arithmetic expression used by the approximate gamma correction circuit 30 R for the arithmetic processing are determined from the control point data CP 0 _R to CP 5 _R and this allows performing digital arithmetic processing on the R grayscale value D IN R in accordance with the input-output curve with the desired shape. In the following, the control point data CP 0 _R to CP 5 _R may be collectively referred to as correction point data set CP_R.

Correspondingly, the approximate gamma correction circuits 30 G and 30 B perform correction processing on the G grayscale value D IN G and B grayscale value D IN B of the input image data D IN in accordance with arithmetic expressions to generate the G grayscale value D OUT G and B grayscale value D OUT B of the output image data D OUT . As illustrated in FIG. 7 , the approximate gamma correction circuit 30 G is supplied with control point data CP 0 _G to CP 5 _G, and the approximate gamma correction circuit 30 B is supplied with control point data CP 0 _B to CP 5 _B. As illustrated in FIG. 8 , the control point data CP 0 _G to CP 5 _G specify the shape of the input-output curve of the arithmetic processing performed on the G grayscale value D IN G of the input image data D IN , and indicate the positions of the control points CP 0 to CP 5 that specify the shape of the input-output curve. Correspondingly, the control point data CP 0 _B to CP 5 _B specify the shape of the input-output curve of the arithmetic processing performed on the B grayscale value D IN B of the input image data D IN , and indicate the positions of the control points CP 0 to CP 5 that specify the shape of the input-output curve. The coefficients of the arithmetic expression used by the approximate gamma correction circuit 30 G for the arithmetic processing are determined from the control point data CP 0 _G to CP 5 _G and this allows performing digital arithmetic processing on the G grayscale value D IN G in accordance with the input-output curve with the desired shape. Correspondingly, the coefficients of the arithmetic expression used by the approximate gamma correction circuit 30 B for the arithmetic processing are determined from the control point data CP 0 _B to CP 5 _B and this allows performing digital arithmetic processing on the B grayscale value D IN B in accordance with the input-output curve with the desired shape. In the following, the control point data CP 0 _G to CP 5 _G may be collectively referred to as correction point data set CP_G, and the control point data CP 0 _B to CP 5 _B may be collectively referred to as correction point data set CP_B.

The number of bits of the R grayscale value D OUT R , G grayscale value D OUT G and B grayscale value D OUT B of the output image data D OUT is larger than that of the R grayscale value D IN R , G grayscale value D IN G and B grayscale value D IN B of the input image data D IN . This effectively avoids loss of grayscale level information of each pixel in the digital arithmetic processing for the color adjustment and gamma correction. In the present embodiment, the R grayscale value D IN R , G grayscale value D IN G and B grayscale value D IN B of the input image data D IN are each 8-bit data and the R grayscale value D OUT R , G grayscale value D OUT G and B grayscale value D OUT B of the output image data D OUT are each 10-bit data.

The color reduction circuit 23 , the latch circuit 24 , the grayscale voltage generator circuit 25 and the data line drive circuit 26 function as drive circuitry that drives the data lines 8 of the display region 5 of the liquid crystal display panel 2 in response to the output image data D OUT received from the approximate gamma correction circuit 22 . More specifically, the color reduction circuit 23 performs color reduction on the output image data D OUT generated by the approximate gamma correction circuit 22 to generate color-reduced image data D OUT _ D . The color-reduced image data D OUT _ D are generated to represent the grayscale level of each subpixel 11 of each pixel 9 with eight bits. The latch circuit 24 latches the color-reduced image data D OUT _ D from the color reduction circuit 23 in response to a latch signal S STB received from a timing control circuit (not illustrated) and forwards the latched color-reduced image data D OUT _ D to the data line drive circuit 26 . The grayscale voltage generator circuit 25 feeds a set of grayscale voltages to the data line drive circuit 26 . In the present embodiment, in which the color-reduced image data D OUT _ D represent the grayscale level of each subpixel 11 of each pixel 9 with eight bits, the number of grayscale voltages fed from the grayscale voltage generator circuit 25 is 256 (=2 8 ). The data line drive circuit 26 drives the data lines 8 of the display region 5 of the liquid crystal display panel 2 in response to the color-reduced image data D OUT _ D received from the latch circuit 24 . In detail, the data line drive circuit 26 selects desired grayscale voltages from among the grayscale voltages received from the grayscale voltage generator circuit 25 in response to the color-reduced image data D OUT _ D and drives the corresponding data lines 8 of the liquid crystal display panel 2 to the selected grayscale voltages.

The gamma value setting circuit 27 , the correction amount calculation circuit 28 and the control point data calculation circuit 29 operate as control point data generation circuitry that calculates the control point data CP 0 _R to CP 5 _R, CP 0 _G to CP 5 _G and CP 0 _B to CP 5 _B and feeds the control point data CP 0 _R to CP 5 _R, CP 0 _G to CP 5 _G and CP 0 _B to CP 5 _B to the approximate gamma correction circuit 22 . More specifically, the gamma value setting circuit 27 determines the gamma value γ_VALUE of the gamma correction to be performed in the approximate gamma correction circuit 22 and sends the determined gamma value γ_VALUE to the control point data calculation circuit 29 . In the present embodiment, the gamma value γ_VALUE is determined on the basis of the APL (average picture level) of each frame image (the image displayed in the display region 5 of the liquid crystal display panel 2 in each frame period). The APL of each frame image is calculated from the input image data D IN . In the present embodiment, the gamma value γ_VALUE is commonly used for processing of R grayscale value D IN R , G grayscale value D IN G and B grayscale value D IN B of the input image data D IN .

It should be noted that the gamma value γ_VALUE may be determined on the basis of parameters other than the APL of the each frame image. It should be also noted that it is not necessary to determine the gamma value γ_VALUE in each frame period; the gamma value γ_VALUE may be fixed to a predetermined value. In this case, the gamma value γ_VALUE may be preset to a register prepared in the gamma value setting circuit 27 . When the gamma value γ_VALUE is preset to a register, it is preferable that the register, which holds the gamma value γ_VALUE, is rewritable from the outside of the driver IC 3 .

The correction amount calculation circuit 28 calculates correction amounts ΔCP_R of the control point data CP 0 _R to CP 5 _R, correction amounts ΔCP_G of the control point data CP 0 _G to CP 5 _G, and correction amounts ΔCP_B of the control point data CP 0 _B to CP 5 _B. In detail, the correction amount calculation circuit 28 selects the belonging area which the point corresponding to the input image data D IN (the corresponding point) belongs to in the color space, from among the above-described areas A 1 to A 6 (refer to FIG. 3B ) and calculates the three distances d ELM , d CMP and d W , where: d ELM is the distance between the vertex corresponding to the elementary color that defines the belonging area and the corresponding point of the input image data D IN ; d CMP is the distance between the vertex corresponding to the complementary color that defines the belonging area and the corresponding point of the input image data D IN ; and d W is the distance between the white point and the corresponding point of the input image data D IN . The correction amount calculation circuit 28 calculates the correction amounts ΔCP_R, ΔCP_G and ΔCP_B in response to the distances d ELM , d CMP and d W . The configuration and operation of the correction amount calculation circuit 28 will be described later in detail.

The control point data calculation circuit 29 calculates the control point data CP 0 _R to CP 5 _R, CP 0 _G to CP 5 _G and CP 0 _B to CP 5 _B, which are fed to the approximate gamma correction circuit 22 , on the basis of the gamma value γ_VALUE received from the gamma value setting circuit 27 and the correction amounts ΔCP_R, ΔCP_G and ΔCP_B received from the correction amount calculation circuit 28 . As described later, the control point data calculation circuit 29 calculates the control point data CP 0 _R to CP 5 _R, CP 0 _G to CP 5 _G and CP 0 _B to CP 5 _B by calculating the control point data that specify the shape of the gamma curve in accordance with the gamma value γ_VALUE and modifying the control point data on the basis of the correction amounts ΔCP_R, ΔCP_G and ΔCP_B received from the correction amount calculation circuit 28 .

Next, a description is given in detail of the configurations of the control point data calculation circuit 29 and the correction amount calculation circuit 28 . FIG. 9 is a block diagram illustrating a preferred example of the configuration of the control point data calculation circuit 29 . In the example illustrated in FIG. 9 , the control point data calculation circuit 29 includes a control point data set storage register 31 , an interpolation/selection circuit 32 and a control point data adjustment circuit 33 .

The control point data set storage register 31 stores therein a plurality of control point data sets CP# 1 to CP#m. The control point data sets CP# 1 to CP#m are used as initial data used for determining the above-described control point data set CP_R, CP_G and CP_B. The control point data sets CP# 1 to CP#m respectively correspond to different gamma values γ, and each control point data set CP#j (j is an integer from one to m) includes control point data CP 0 # j to CP 5 # j.

The interpolation/selection circuit 32 determines a control point data set CP_sel corresponding to the gamma value γ_VALUE received from the gamma value setting circuit 27 . The control point data set CP_sel includes control point data CP 0 _sel to CP 5 _sel. In one embodiment, the interpolation/selection circuit 32 may determine the control point data set CP_sel by selecting the control point data set CP_sel from among the control point data sets CP# 1 to CP#m in response to the gamma value γ_VALUE. Alternatively, the interpolation/selection circuit 32 may determine the control point data set CP_sel by selecting two of the control point data sets CP# 1 to CP#m in response to the gamma value γ_VALUE and performing an interpolation on the selected two control point data sets. Details of the determination of the control point data set CP_sel will be described later. The control point data set CP_sel determined by the interpolation/selection circuit 32 is transmitted to the control point data adjustment circuit 33 .

The control point data adjustment circuit 33 calculates the control point data CP 0 _R to CP 5 _R, CP 0 _G to CP 5 _G and CP 0 _B to CP 5 _B, which are to be fed to the approximate gamma correction circuit 22 , by modifying the control point data CP 0 _sel to CP 5 _sel in response to the correction amounts ΔCP_R, ΔCP_G and ΔCP_B received from the correction amount calculation circuit 28 . As described above, the approximate gamma correction unit 30 R of the approximate gamma correction circuit 22 performs arithmetic processing on the R grayscale value D IN R of the input image data D IN in accordance with the input-output curve specified by the control point data CP 0 _R to CP 5 _R. Correspondingly, the approximate gamma correction circuit 30 G performs arithmetic processing on the G grayscale value D IN G of the input image data D IN in accordance with the input-output curve specified by the control point data CP 0 _G to CP 5 _G and the approximate gamma correction circuit 30 B performs arithmetic processing on the B grayscale value D IN B of the input image data D IN in accordance with the input-output curve specified by the control point data CP 0 _B to CP 5 _B.

FIG. 10 is a block diagram illustrating a preferred example of the configuration of the correction amount calculation circuit 28 . The correction amount calculation circuit 28 includes: a maximum-and-minimum values calculation circuit 41 , an elementary color vertex distance calculation circuit 42 , an R vertex correction amount register 43 R, a G vertex correction amount register 43 G, a B vertex correction amount register 43 B, a selector 44 , a multiplier 45 , a complementary color vertex distance calculation circuit 46 , a C vertex correction amount register 47 C, an M vertex correction amount register 47 M, a Y vertex correction amount register 47 Y, a selector 48 , a multiplier 49 , a white point distance calculation circuit 50 , a white point correction amount register 51 , a multiplier 52 and an adder 53 .

The maximum-and-minimum values calculation circuit 41 finds which of the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN are maximum and minimum for each pixel. This operation is equivalent to determining which of the areas A 1 to A 6 illustrated in FIG. 3B the corresponding point of the input image data D IN belongs to in the color space. This is because the belonging area of the corresponding point of the input image data D IN can be determined as the area defined with the white point, the vertex of the elementary color corresponding to the largest one of the R, G and B grayscale values D IN R , D IN G and D IN B and the vertex of the complementary color of the elementary color corresponding to the smallest one of the R, G and B grayscale values D IN R , D IN G and D IN B . When the R grayscale value D IN R is the largest and the B grayscale value D IN B is the smallest, for example, the belonging area of the corresponding point of the input image data D IN can be determined as the area A 1 (that is, the area defined with the R vertex, the Y vertex and the while point); it should be noted here that Y (yellow) is the complementary color of B (blue). The maximum-and-minimum values calculation circuit 41 generates a selection signal SEL RGB selecting one of R, G and B on the basis of which of the R, G and B grayscale values D IN R , D IN G and D IN B is maximum and further generates a selection signal SEL CMY selecting one of C, M and Y on the basis of which of the R, G and B grayscale values D IN R , D IN G and D IN B is minimum. The selection signal SEL RGB is generated to select the elementary color corresponding to the largest one of the R, G and B grayscale values D IN R , D IN G and D IN B and the selection signal SEL CMY is generated to select the complementary color of the elementary color corresponding to the smallest one of the R, G and B grayscale values D IN R , D IN G and D IN B .

The elementary color selected by the maximum-and-minimum values calculation circuit 41 may be referred to as “selected elementary color” and the vertex corresponding to the selected elementary color may be referred to as “selected elementary color vertex”. Correspondingly, the complementary color selected by the maximum-and-minimum values calculation circuit 41 may be referred to as “selected complementary color” and the vertex corresponding to the selected complementary color may be referred to as “selected complementary color vertex”.

The elementary color vertex distance calculation circuit 42 calculates the distance d ELM between the selected elementary color vertex (the vertex corresponding to the selected elementary color selected by the selection signal SEL RGB ) and the corresponding point of the input image data D IN . Any parameters determined to indicate the degree of separation between the vertex corresponding to the elementary color selected by the selection signal SEL RGB and the corresponding point of the input image data D IN in the color space may be used as the distance d ELM . A specific example of the definition of the distance d ELM will be described later.

The R vertex correction amount register 43 R stores therein R vertex correction amounts ΔCP_R R , ΔCP_G R and ΔCP_B R . The R vertex correction amounts ΔCP_R R , ΔCP_G R and ΔCP_B R are values that are appropriate as the correction amounts ΔCP_R, ΔCP_G and ΔCP_B for the R vertex, that is, values to be set as the correction amounts ΔCP_R, ΔCP_G and ΔCP_B when the corresponding point of the input image data D IN coincides with the R vertex in the color space. As described later, the R vertex correction amounts ΔCP_R R , ΔCP_G R and ΔCP_B R can be calculated from measurement results of the characteristics of the liquid crystal display panel 2 , and the R vertex correction amounts ΔCP_R R , ΔCP_G R and ΔCP_B R may be set in the R vertex correction amount register 43 R in advance (for example, when the driver IC 3 is booted).

Correspondingly, the G vertex correction amount register 43 G stores therein G vertex correction amounts ΔCP_R G , ΔCP_G G and ΔCP_B G . The G vertex correction amounts ΔCP_R G , ΔCP_G G and ΔCP_B G are values that are appropriate as the correction amounts ΔCP_R, ΔCP_G and ΔCP_B for the G vertex, that is, values to be set as the correction amounts ΔCP_R, ΔCP_G and ΔCP_B when the corresponding point of the input image data D IN coincides with the G vertex in the color space. The G vertex correction amounts ΔCP_R G , ΔCP_G G and ΔCP_B G may be set in the G vertex correction amount register 43 G in advance (for example, when the driver IC 3 is booted).

Also, the B vertex correction amount register 43 B stores therein B vertex correction amounts ΔCP_R B , ΔCP_G B and ΔCP_B B . The B vertex correction amounts ΔCP_R B , ΔCP_G B and ΔCP_B B are values that are appropriate as the correction amounts ΔCP_R, ΔCP_G and ΔCP_B for the B vertex, that is, values to be set as the correction amounts ΔCP_R, ΔCP_G and ΔCP_B when the corresponding point of the input image data D IN coincides with the B vertex in the color space. The B vertex correction amounts ΔCP_R B , ΔCP_G B and ΔCP_B B may be set in the B vertex correction amount register 43 B in advance (for example, when the driver IC 3 is booted).

The selector 44 selects correction amounts corresponding to the selected elementary color selected by the selection signal SEL RGB from among the correction amounts stored in the R, G and B vertex correction amount registers 43 R, 43 G and 43 B and outputs the selected correction amounts. Hereinafter, the correction amounts output from the selector 44 are referred to as selected elementary color correction amounts ΔCP_R ELM , ΔCP_G ELM and ΔCP_B ELM . It should be noted that ΔCP_R ELM is the correction amount used in the calculation of the control point data CP 0 _R to CP 5 _R and determined as one of ΔCP_R R , ΔCP_R G and ΔCP_R B . Correspondingly, ΔCP_G ELM is the correction amount used in the calculation of the control point data CP 0 _G to CP 5 _G and determined as one of ΔCP_G R , ΔCP_G G and ΔCP_G B . Similarly, ΔCP_B ELM is the correction amount used in the calculation of the control point data CP 0 _B to CP 5 _B and determined as one of ΔCP_B R , ΔCP_B G and ΔCP_B B .

The multiplier 45 calculates elementary-color-distance dependent correction amounts ΔCP_R ELM-d , ΔCP_G ELM-d and ΔCP_B ELM-d from the distance d ELM and the selected elementary color correction amounts ΔCP_R ELM , ΔCP_G ELM and ΔCP_B ELM , respectively, which are output from the selector 44 . The elementary-color-distance dependent correction amount ΔCP_R ELM-d is calculated from ΔCP_R ELM and the distance d ELM so that the elementary-color-distance dependent correction amount ΔCP_ ELM-d is closer to ΔCP_R ELM as the point corresponding to the input image data D IN is closer to the elementary color vertex with which the belonging area of the input image data D IN is defined. Correspondingly, the elementary-color-distance dependent correction amount ΔCP_G ELM-d is calculated from ΔCP_G ELM and the distance d ELM so that the elementary-color-distance dependent correction amount ΔCP_G ELM-d is closer to ΔCP_G ELM as the point corresponding to the input image data D IN is closer to the elementary color vertex with which the belonging area of the input image data D IN is defined. The elementary-color-distance dependent correction amount ΔCP_B ELM-d is calculated from ΔCP_B ELM and the distance d ELM so that the elementary-color-distance dependent correction amount ΔCP_G ELM-d is closer to ΔCP_G ELM as the point corresponding to the input image data D IN is closer to the elementary vertex with which the belonging area of the input image data D IN is defined.

In the present embodiment, in which the distance d ELM is defined so that the distance d ELM is increased as the corresponding point of the input image data D IN is closer to the vertex corresponding to the elementary color with which the belonging area of the corresponding point of the input image data D IN is defined, the multiplier 45 calculates the elementary-color-distance dependent correction amount ΔCP_R ELM-d so that the elementary-color-distance dependent correction amount ΔCP_R ELM-d is proportional to the product of the selected elementary color correction amount ΔCP_R ELM and the distance d ELM . Correspondingly, the multiplier 45 calculates the elementary-color-distance dependent correction amount ΔCP_G ELM-d so that the elementary-color-distance dependent correction amount ΔCP_G ELM-d is proportional to the product of the selected elementary color correction amount ΔCP_G ELM and the distance d ELM , and calculates the elementary-color-distance dependent correction amount ΔCP_B ELM-d so that the elementary-color-distance dependent correction amount ΔCP_B ELM-d is proportional to the product of the selected elementary color correction amount ΔCP_B ELM and the distance d ELM .

The complementary color vertex distance calculation circuit 46 calculates the distance d CMP between the vertex corresponding to the complementary color selected by the selection signal SEL CMY and the corresponding point of the input image data D IN in the color space. Any parameters determined to indicate the degree of separation between the vertex corresponding to the complementary color selected by the selection signal SEL CMY and the corresponding point of the input image data D IN in the color space may be used as the distance d CMP . A specific example of the definition of the distance d CMP will be described later.

The C vertex correction amount register 47 C stores therein C vertex correction amounts ΔCP_R C , ΔCP_G C and ΔCP_B C . The C vertex correction amounts ΔCP_R C , ΔCP_G C and ΔCP_B C are values that are appropriate as the correction amounts ΔCP_R, ΔCP_G and ΔCP_B for the C vertex, that is, values to be set as the correction amounts ΔCP_R, ΔCP_G and ΔCP_B when the corresponding point of the input image data D IN coincides with the C vertex in the color space. As described later, the C vertex correction amounts ΔCP_R C , ΔCP_G C and ΔCP_B C can be calculated from measurement results of the characteristics of the liquid crystal display panel 2 , and the C vertex correction amounts ΔCP_R C , ΔCP_G C and ΔCP_B C may be set in the C vertex correction amount register 47 C in advance (for example, when the driver IC 3 is booted).

Correspondingly, the M vertex correction amount register 47 M stores therein M vertex correction amounts ΔCP_R M , ΔCP_G M and ΔCP_B M . The M vertex correction amounts ΔCP_R M , ΔCP_G M and ΔCP_B M are values that are appropriate as the correction amounts ΔCP_R, ΔCP_G and ΔCP_B for the M vertex, that is, values to be set as the correction amounts ΔCP_R, ΔCP_G and ΔCP_B when the corresponding point of the input image data D IN coincides with the M vertex in the color space. The M vertex correction amounts ΔCP_R M , ΔCP_G M and ΔCP_B M may be set in the M vertex correction amount register 47 M in advance (for example, when the driver IC 3 is booted).

Also, the Y vertex correction amount register 47 Y stores therein Y vertex correction amounts ΔCP_R Y , ΔCP_G Y and ΔCP_B Y . The Y vertex correction amounts ΔCP_R Y , ΔCP_G Y and ΔCP_B Y are values that are appropriate as the correction amounts ΔCP_R, ΔCP_G and ΔCP_B for the Y vertex, that is, values to be set as the correction amounts ΔCP_R, ΔCP_G and ΔCP_B when the corresponding point of the input image data D IN coincides with the Y vertex in the color space. The Y vertex correction amounts ΔCP_R Y , ΔCP_G Y and ΔCP_B Y may be set in the Y vertex correction amount register 47 Y in advance (for example, when the driver IC 3 is booted).

It should be noted that the calculation of the R vertex correction amounts ΔCP_R R , ΔCP_G R , ΔCP_B R , G vertex correction amounts ΔCP_R G , ΔCP_G G , ΔCP_B G , B vertex correction amounts ΔCP_R B , ΔCP_G B , ΔCP_B B , C vertex correction amounts ΔCP_R C , ΔCP_G C , ΔCP_B C , M vertex correction amounts ΔCP_R M , ΔCP_G M , ΔCP_B M , Y vertex correction amounts ΔCP_R Y , ΔCP_G Y , ΔCP_B Y , which are respectively stored in the R vertex correction amount register 43 R, G vertex correction amount register 43 G, B vertex correction amount register 43 B, C vertex correction amount register 47 C, M vertex correction amount register 47 M, Y vertex correction amount register 47 Y and white point correction amount register 5 , will be described later in detail.

The selector 48 selects correction amounts corresponding to the selected complementary color selected by the selection signal SEL CMY from among the correction amounts stored in the C, M and Y vertex correction amount registers 47 C, 47 M and 47 Y and outputs the selected correction amounts. Hereinafter, the correction amounts output from the selector 48 are referred to as selected elementary color correction amounts ΔCP_R CMP , ΔCP_G CMP and ΔCP_B CMP . It should be noted that ΔCP_R CMP is the correction amount used in the calculation of the control point data CP 0 _R to CP 5 _R. Correspondingly, ΔCP_G CMP is the correction amount used in the calculation of the control point data CP 0 _G to CP 5 _G and ΔCP_B CMP is the correction amount used in the calculation of the control point data CP 0 _B to CP 5 _B.

The multiplier 49 calculates complementary-color-distance dependent correction amounts ΔCP_R CMP-d , ΔCP_G CMP-d and ΔCP_B CMP-d from the distance d CMP and the selected complementary color correction amounts ΔCP_R CMP , ΔCP_G CMP and ΔCP_B CMP , respectively, which are output from the selector 47 . The complementary-color-distance dependent correction amount ΔCP_R CMP-d is calculated from ΔCP_R CMP and the distance d CMP so that the complementary-color-distance dependent correction amount ΔCP_R CMP-d is closer to ΔCP_R CMP as the point corresponding to the input image data D IN is closer to the complementary color vertex with which the belonging area of the input image data D IN is defined. Correspondingly, the complementary-color-distance dependent correction amount ΔCP_G CMP-d is calculated from ΔCP_G CMP and the distance d CMP so that the complementary-color-distance dependent correction amount ΔCP_G CMP-d is closer to ΔCP_G CMP as the point corresponding to the input image data D IN is closer to the complementary color vertex with which the belonging area of the input image data D IN is defined, and the complementary-color-distance dependent correction amount ΔCP_B CMP-d is calculated from ΔCP_B CMP and the distance d CMP so that the complementary-color-distance dependent correction amount ΔCP_B CMP-d is closer to ΔCP_B CMP as the point corresponding to the input image data D IN is closer to the complementary color vertex with which the belonging area of the input image data D IN is defined.

In the present embodiment, in which the distance d CMP is defined so that the distance d CMP is increased as the corresponding point of the input image data D IN is closer to the vertex corresponding to the elementary color with which the belonging area of the corresponding point of the input image data D IN is defined, the multiplier 49 calculates the complementary-color-distance dependent correction amount ΔCP_R CMP-d so that the complementary-color-distance dependent correction amount ΔCP_R CMP-d is proportional to the product of the selected complementary color correction amount ΔCP_R CMP and the distance d CMP . Correspondingly, the multiplier 49 calculates the complementary-color-distance dependent correction amount ΔCP_G CMP-d so that the complementary-color-distance dependent correction amount ΔCP_G CMP-d is proportional to the product of the selected complementary color correction amount ΔCP_G CMP and the distance d CMP and calculates the complementary-color-distance dependent correction amount ΔCP_B CMP-d so that the complementary-color-distance dependent correction amount ΔCP_B CMP-d is proportional to the product of the selected complementary color correction amount ΔCP_B CMP and the distance d CMP .

The white point distance calculation circuit 50 calculates the distance d W between the white point and the corresponding point of the input image data D IN in the color space. Any parameters determined to indicate the degree of separation between the white point and the corresponding point of the input image data D IN in the color space may be used as the distance d W . A specific example of the definition of the distance d W will be described later.

The white point correction amount register 51 stores therein white point correction amounts ΔCP_R W , ΔCP_G W and ΔCP_B W . The white point correction amounts ΔCP_R W , ΔCP_G W and ΔCP_B W are values that are appropriate as the correction amounts ΔCP_R, ΔCP_G and ΔCP_B for the white point, that is, values to be set as the correction amounts ΔCP_R, ΔCP_G and ΔCP_B when the corresponding point of the input image data D IN coincides with the white point in the color space. As described later, the white point correction amounts ΔCP_R W , ΔCP_G W and ΔCP_B W can be calculated from measurement results of the characteristics of the liquid crystal display panel 2 , and the white point correction amounts ΔCP_R W , ΔCP_G W and ΔCP_B W may be set in the white point correction amount register 51 in advance (for example, when the driver IC 3 is booted).

The multiplier 52 calculates white-point-distance dependent correction amounts ΔCP_R W-d , ΔCP_G W-d and ΔCP_B W-d from the distance d W and the white point correction amounts ΔCP_R W , ΔCP_G W and ΔCP_B W , respectively, which are output from the white point correction amount register 51 . The white-point-distance dependent correction amount ΔCP_R W-d is calculated from ΔCP_R W and the distance d W so that the white-point-distance dependent correction amount ΔCP_R W-d is closer to ΔCP_R W as the point corresponding to the input image data D IN is closer to the white point. Correspondingly, the white-point-distance dependent correction amount ΔCP_G W-d is calculated from ΔCP_G W and the distance d W so that the white-point-distance dependent correction amount ΔCP_G W-d is closer to ΔCP_G W as the point corresponding to the input image data D IN is closer to the white point, and the white-point-distance dependent correction amount ΔCP_B W-d is calculated from ΔCP_B W and the distance d W so that the white-point-distance dependent correction amount ΔCP_B W-d is closer to ΔCP_B W as the point corresponding to the input image data D IN is closer to the white point.

The adder 53 calculates the correction amounts ΔCP_R, ΔCP_G and ΔCP_B from the elementary-color-distance dependent correction amounts ΔCP_R ELM-d , ΔCP_G ELM-d and ΔCP_B ELM-d that are output from the multiplier 45 , the complementary-color-distance dependent correction amounts ΔCP_R CMP-d , ΔCP_G CMP-d and ΔCP_B CMP-d that are output from the multiplier 49 and the white-point-distance dependent correction amounts ΔCP_R W-d , ΔCP_G W-d and ΔCP_B W-d that are output from the multiplier 52 . In detail, the adder 53 calculates the correction amount ΔCP_R as the sum of ΔCP_R ELM-d , ΔCP_R CMP-d and ΔCP_R W-d . Correspondingly, the adder 53 calculates the correction amount ΔCP_G as the sum of ΔCP_G ELM-d , ΔCP_G CMP-d and ΔCP_G W-d and calculates the correction amount ΔCP_B as the sum of ΔCP_B ELM-d , ΔCP_B CMP-d and ΔCP_B W-d .

It should be noted that, the calculation of the R vertex correction amounts ΔCP_R R , ΔCP_G R , ΔCP_B R , G vertex correction amounts ΔCP_R G , ΔCP_G G , ΔCP_B G , B vertex correction amounts ΔCP_R B , ΔCP_G B , ΔCP_B B , C vertex correction amounts ΔCP_R C , ΔCP_G C , ΔCP_B C , M vertex correction amounts ΔCP_R M , ΔCP_G M , ΔCP_B M and Y vertex correction amounts ΔCP_R Y , ΔCP_G Y , ΔCP_B Y , which are respectively stored in the R vertex correction amount register 43 R, G vertex correction amount register 43 G, B vertex correction amount register 43 B, C vertex correction amount register 47 C, M vertex correction amount register 47 M and Y vertex correction amount register 47 Y, will be described later in detail.

Next, a description is given of digital arithmetic processing performed for the color adjustment and gamma correction in the first embodiment. FIG. 11A is a flowchart illustrating the digital arithmetic processing performed in the first embodiment.

The gamma value γ_VALUE is determined by the gamma value setting circuit 27 . In the present embodiment, the gamma value γ_VALUE is determined for each frame period on the basis of the APL (average picture level) of the frame image displayed in each frame period. The APL of each frame image is calculated from the input image data D IN .

In one embodiment, the gamma value γ_VALUE may be calculated in accordance with the following expression (1), for example:

γ_VALUE=γ_ STD +( APL )·η,  (1)

where γ_STD is a reference gamma value, (APL) is the APL of the frame image, and η is a predetermined positive proportionality constant.

It should be noted that a common gamma value γ_VALUE is determined for the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN , in the present embodiment. The gamma value γ_VALUE may be determined on the basis of other parameters in addition to or instead of the APL of each frame image.

A control point data set CP_sel (which includes control point data CP 0 _sel to CP 5 _sel) is further selected or calculated in response to the gamma value γ_VALUE thus determined. The control point data set CP_sel is initial data used to calculate the control point data set CP_R, CP_G and CP_B finally fed to the approximate gamma correction circuit 22 . The control point data set CP_sel is selected for each frame image.

In one embodiment, the control point data set CP_sel is selected from the control point data sets CP# 1 to CP#m stored in the control point data set storage register 31 of the control point data calculation circuit 29 . As described above, the control point data sets CP# 1 to CP#m correspond to different gamma values γ, and each control point data set CP#j includes control point data CP 0 # j to CP 5 # j.

The control point data CP 0 # j to CP 5 # j of the control point data set CP#j corresponding to a given gamma value γ are determined as follows:

( 1 ) ⁢ ⁢ For ⁢ ⁢ γ < 1 , CP ⁢ ⁢ 0 ⁢ # ⁢ ⁢ j = 0 ⁢

⁢ CP ⁢ ⁢ 1 ⁢ # ⁢ ⁢ j = 4 · Gamma ⁡ [ K / 4 ] - Gamma ⁡ [ K ] 2 ⁢

⁢ CP ⁢ ⁢ 2 ⁢ # ⁢ ⁢ j = Gamma ⁡ [ K - 1 ] ⁢

⁢ CP ⁢ ⁢ 3 ⁢ # ⁢ ⁢ j = Gamma ⁡ [ K ] ⁢

⁢ CP ⁢ ⁢ 4 ⁢ # ⁢ ⁢ j = 2 · Gamma ⁡ [ ( D IN MAX + K - 1 ) / 2 ] - D OUT MAX ⁢

⁢ CP ⁢ ⁢ 5 ⁢ # ⁢ ⁢ j = D OUT MAX ( 2 ⁢ a ) ( 2 ) ⁢ ⁢ For ⁢ ⁢ γ ≥ 1 , CP ⁢ ⁢ 0 ⁢ # ⁢ ⁢ j = 0 ⁢

⁢ CP ⁢ ⁢ 1 ⁢ # ⁢ ⁢ j = 2 · Gamma ⁡ [ K / 2 ] - Gamma ⁡ [ K ] ⁢

⁢ CP ⁢ ⁢ 2 ⁢ # ⁢ ⁢ j = Gamma ⁡ [ K - 1 ] ⁢

⁢ CP ⁢ ⁢ 3 ⁢ # ⁢ ⁢ j = Gamma ⁡ [ K ] ⁢

⁢ CP ⁢ ⁢ 4 ⁢ # ⁢ ⁢ j = 2 · Gamma ⁡ [ ( D IN MAX + K - 1 ) / 2 ] ⁢ D OUT MAX ⁢

⁢ CP ⁢ ⁢ 5 ⁢ # ⁢ ⁢ j = D OUT MAX ( 2 ⁢ b )

In expressions (2a) and (2b), D IN MAX is the allowed maximum value of the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN , depending on the number of bits of the R, G and B grayscale values D IN R , D IN G and D IN B .

D OUT MAX is the allowed maximum value of the R, G and B grayscale values D OUT R , D OUT G and D OUT B of the output image data D OUT , depending on the number of bits of the R, G and B grayscale values D OUT R , D OUT G and D OUT B . K is a constant given by the following expression (3):

K =( D IN MAX +1)/2.  (3)

Gamma [x] is a function representing the strict expression of the gamma correction and defined by the following expression (4):

Gamma[ x ] =D OUT MAX ·( x/D IN MAX ) γ   (4)

In the present embodiment, the control point data sets CP# 1 to CP#m are determined so that the gamma value γ is increased as the index j is increased for the control point data set CP#j, which is allowed to be arbitrarily selected from the control point data sets CP# 1 to CP#m. In other words, it holds:

γ 1 <γ 2 < . . . <γ m−1 <γ m ,  (5)

where γ j is the gamma value determined for the control point data set CP#j.

In one embodiment, the control point data set CP_sel is selected from among the control point data sets CP# 1 to CP#m in response to the gamma value γ_VALUE. A control point data set CP#j with a larger value of j is selected as the gamma value γ_VALUE is increased.

FIG. 11B is a graph illustrating the relation among the APL, γ_VALUE and the control point data set CP_sel in the case when the control point data set CP_sel is thus determined. As the APL is increased, the gamma value γ_VALUE is increased and a control point data set CP#j with a larger value of j is selected.

In an alternative embodiment, the control point data set CP_sel may be calculated as follows: 2 P−(Q−1) control point data sets CP# 1 to CP#m (where m=2 P−(Q−1) ) are stored in the control point data set storage register 31 , where P is the number of bits used to indicate the APL of each frame image and Q is a predetermined integer equal to or more than two and less than P. The control point data sets CP# 1 to CP#m stored in the control point data set storage register 31 may be fed to from the processor 4 to the driver IC 3 is initial settings.

Two control point data sets CP#q and CP#(q+1) are further selected from the control point data sets CP# 1 to CP#m stored in the control point data set storage register 31 in response to the gamma value γ_VALUE, where q is an integer from one to m−1. The control point data sets CP#q and CP#(q+1) are selected to satisfy the following expression (6):

γ q <γ_VALUE<γ q+1 .  (6)

The control point data CP 0 _sel to CP 5 _sel of the control point data set CP_sel are calculated by interpolation of the control point data CP 0 # q to CP 5 # q of the selected control point data set CP#q and the control point data CP 0 #( q+ 1) to CP 5 #( q+ 1) of the selected control point data set CP#( q+ 1), respectively.

More specifically, the control point data CP 0 _sel to CP 5 _sel of the control point data set CP_sel are calculated from the control point data of the selected two control point data CP#q and CP#(q+1) in accordance with the following expression (7):

CPα sel =CPα# q +{(CPα#( q+ 1)−CPα# q )/2 Q }×APL [ Q -1:0],  (7)

where α is an integer from zero to five and APL[Q−1:0] is the value of the lower Q bits of the APL.

FIG. 11C is a graph illustrating the relation among the APL, γ_VALUE and the control point data set CP_sel in the case when the control point data set CP_sel is thus determined. As the APL is increased, the gamma value γ_VALUE is increased and control point data sets CP#q and CP#(q+1) with a larger value of q are selected. The control point data set CP_sel is determined so that the control point data set CP_sel corresponds to a gamma value between the gamma values γ q and γ q+1 , which correspond to the control point data sets CP#q and CP#(q+1).

FIG. 11D is a graph illustrating the shapes of the gamma curves respectively corresponding to the control point data sets CP#q and CP#(q+1) and the shape of the gamma curve corresponding to the control point data set CP_sel. Since the control point data CPα of the control point data set CP_sel is calculated through interpolation of the control point data CPα#q and CPα#(q+1) of the control point data sets CP#q and CP#(q+1) (α is an integer from zero to five), the gamma curve corresponding to the control point data set CP_sel has such a shape that the gamma curve corresponding to the control point data set CP_sel is located between the gamma curves corresponding to the control point data sets CP#q and CP#(q+1). The calculation of the control point data CP 0 _sel to CP 5 _sel of the control point data set CP_sel through the interpolation of the control point data CP 0 to CP 5 of the selected two control point data sets CP#q and CP#(q+1) effectively allows finely adjusting the gamma value used for the gamma correction with a reduced number of the control point data sets CP# 1 to CP#m stored in the control point data set storage register 31 .

The correction amounts ΔCP_R, ΔCP_G and ΔCP_B are further calculated by the correction amount calculation circuit 28 . The correction amounts ΔCP_R, ΔCP_G and ΔCP_B are determined depending on the position of the corresponding point of the input image data D IN in the color space. It should be noted that the correction amounts ΔCP_R, ΔCP_G and ΔCP_B are calculated for each pixel 9 on the basis of the input image data D IN . The correction amounts ΔCP_R, ΔCP_G and ΔCP_B for a certain pixel 9 are calculated on the basis of the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN associated with the pixel 9 . FIG. 12A is a flowchart illustrating the calculation procedure of the correction amounts ΔCP_R, ΔCP_G and ΔCP_B.

First, it is determined by the maximum-and-minimum values calculation circuit 41 which of the areas A 1 to A 6 (see FIG. 3B ) the corresponding point of the input image data D IN belongs to in the color space (at steps S 11 to S 13 ).

More specifically, it is determined by the maximum-and-minimum values calculation circuit 41 which of the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN are maximum and minimum (at step S 11 ). The belonging area of the corresponding point of the input image data D IN is determined as an area defined with the vertex corresponding to the elementary color associated with the largest one of the R, G and B grayscale values D IN R , D IN G and D IN B , the vertex corresponding to the complementary color of the elementary color associated with the smallest one, and the white point. When the R grayscale value D IN R is the largest and the B grayscale value D IN B is the smallest, for example, the belonging area of the corresponding point of the input image data D IN can be determined as the area A 1 (that is, the area defined with the R vertex, the Y vertex and the white point).

The selection signal SEL RGB is generated to select one of R, G and B on the basis of which of the R, G and B grayscale values D IN R , D IN G and D IN B is the largest (at step S 12 ), and the selection signal SEL CMY is generated to select one of C, M and Y on the basis of which of the R, G and B grayscale values D IN R , D IN G and D IN B is the smallest (at step S 13 ). Here, the selection signal SEL RGB is generated to select the elementary color associated with the largest one of the R, G and B grayscale values D IN R , D IN G and D IN B , and the selection signal SEL CMY is generated to select the complementary color of the elementary color associated with the smallest one of the R, G and B grayscale values D IN R , D IN G and D IN B . In the following, the vertex corresponding to the elementary color selected at step S 12 is referred to as “selected elementary color vertex” and the vertex corresponding to the complementary color selected at step S 13 is referred to as “selected complementary color vertex”.

Furthermore, the following three “distances” are calculated for the belonging area of the corresponding point of the input image data D IN (at steps S 14 to S 18 ):

(1) the distance d ELM between the selected elementary color vertex (that is, the vertex corresponding to the elementary color which defines the belonging area) and the corresponding point of the input image data D IN ,

(2) the distance d CMP between the selected complementary color vertex (that is, the vertex corresponding to the complementary color which defines the belonging area) and the corresponding point of the input image data D IN , and

(3) the distance d W between the white point and the corresponding point of the input image data D IN . The distance d ELM is calculated by the elementary color vertex distance calculation circuit 42 , and the distance d CMP is calculated by the complementary color vertex distance calculation circuit 46 . The distance d W is calculated by the white point distance calculation circuit 50 . The above-described distances d ELM , d CMP and d W are calculated as follows:

The difference between the R grayscale value of the selected elementary color vertex and the R grayscale value D IN R of the input image data D IN , the difference between the G grayscale value of the selected elementary color vertex and the G grayscale value D IN G of the input image data D IN and the difference between the B grayscale value of the selected elementary color vertex and the B grayscale value D IN B of the input image data D IN are calculated (at step S 14 ). In the present embodiment, the differences between the R, G and B grayscale values of the selected elementary color vertex and the R, G and B grayscale value D IN R , D IN G and D IN B of the input image data are calculated in accordance with the following expressions (8a) to (8c):

RGB dist_ R=RGB _ R top− D IN R ,  (8a)

RGB dist_ G=RGB _ G top− D IN G , and  (8b)

RGB dist_ B=RGB _ B top− D IN B ,  (8c)

where RGB_Rtop, RGB_Gtop and RGB_Btop are the R, G and B grayscale values of the selected elementary color vertex, respectively. RGBdist_R is the difference between the R grayscale value of the selected elementary color vertex and the R grayscale value D IN R of the input image data D IN . Correspondingly, RGBdist_G is the difference between the G grayscale value of the selected elementary color vertex and the G grayscale value D IN G of the input image data D IN and RGBdist_B is the difference between the B grayscale value of the selected elementary color vertex and the grayscale value D IN B of the input image data D IN .

Correspondingly, the difference between the R grayscale value of the selected complementary color vertex and the R grayscale value D IN R of the input image data D IN , the difference between the G grayscale value of the selected complementary color vertex and the G grayscale value D IN G of the input image data D IN and the difference between the B grayscale value of the selected complementary color vertex and the B grayscale value D IN B of the input image data D IN are calculated (at step S 15 ). In the present embodiment, the differences between the R, G and B grayscale values of the selected complementary color vertex and the R, G and B grayscale value D IN R , D IN G and D IN B of the input image data are calculated in accordance with the following expressions (9a) to (9c):

CMY dist_ R=CMY _ R top− D IN R ,  (9a)

CMY dist_ G=CMY _ G top− D IN G , and  (9b)

CMY dist_ B=CMY _ B top− D IN B ,  (9c)

where CMY_Rtop, CMY_Gtop and CMY_Btop are the R, G and B grayscale values of the selected complementary color vertex, respectively. CMPdist_R is the difference between the R grayscale value of the selected complementary color vertex and the R grayscale value D IN R of the input image data D IN . Correspondingly, CMYdist_G is the difference between the G grayscale value of the selected complementary color vertex and the G grayscale value D IN G of the input image data D IN and CMYdist_B is the difference between the B grayscale value of the selected complementary color vertex and the B grayscale value D IN B of the input image data D IN .

The distance d ELM between the selected elementary color vertex and the corresponding point of the input image data D IN is calculated on the basis of the difference between the maximum and minimum values of the differences RGBdist_R, RGBdist_G and RGBdist_B (at step S 16 ). More specifically, the distance d ELM between the selected elementary color vertex and the corresponding point of the input image data D IN is calculated in accordance with the following expression (10):

d ELM =D IN MAX −(max( RGB dist)−min( RGB dist)),   (10)

where D IN MAX is the allowed maximum value of the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN and determined on the number of bits of the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN . When the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN are each 8-bit data, for example, D IN MAX is 255 (=2 8 −1). max(RGBdist) is the maximum value of the differences RGBdist_R, RGBdist_G and RGBdist_B and min(RGBdist) is the minimum value of the differences RGBdist_R, RGBdist_G and RGBdist_B.

Similarly, the distance d CMP between the selected complementary color vertex and the corresponding point of the input image data D IN is calculated on the basis of the difference between the maximum and minimum values of the differences CMYdist_R, CMYdist_G and CMYdist_B (at step S 17 ). More specifically, the distance d CMP between the selected complementary color vertex and the corresponding point of the input image data D IN is calculated in accordance with the following expression (11):

d CMP =D IN MAX −(max( CMY dist)−min( CMY dist)),   (11)

where max(CMYdist) is the maximum value of the differences CMYdist_R, CMYdist_G and CMYdist_B and min(CMYdist) is the minimum value of the differences CMYdist_R, CMYdist_G and CMYdist_B.

Furthermore, the distance d W between the white point and the input image data D IN is calculated as the minimum value of the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN (at step S 18 ).

In other words, it holds:

d W =min( D IN R ,D IN G ,D IN B )  (12)

It should be noted here that, in the present invention, the distances d ELM , d CMP and d W are defined so that the sum of the d ELM , d CMP and d W is equal to the maximum value of the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN .

Furthermore, the correction amounts ΔCP_R, ΔCP_G and ΔCP_B of the control point data are calculated on the basis of the distances d ELM , d CMP and d W thus calculated (at step S 19 ). The calculation of the correction amounts ΔCP_R, ΔCP_G and ΔCP_B at step S 19 is achieved as follows:

The selected elementary color correction amounts ΔCP_R ELM , ΔCP_G ELM and ΔCP_B ELM (the correction amounts associated with the selected elementary color) are output from the selector 44 in response to the selection signal SEL RGB , and the elementary-color-distance dependent correction amounts ΔCP_R ELM-d , ΔCP_G ELM-d and ΔCP_B ELM-d are calculated from the distance d ELM and the selected elementary color correction amounts ΔCP_R ELM , ΔCP_G ELM and ΔCP_B ELM . The elementary-color-distance dependent correction amount ΔCP_R ELM-d is calculated from ΔCP_R ELM and the distance d ELM so that the elementary-color-distance dependent correction amount ΔCP_R ELM-d is closer to the value of ΔCP_R ELM as the corresponding point of the input image data D IN is closer to the vertex corresponding to the elementary color with which the belonging area of the corresponding point is defined. Correspondingly, the elementary-color-distance dependent correction amount ΔCP_G ELM-d is calculated from ΔCP_G ELM and the distance d ELM so that the elementary-color-distance dependent correction amount ΔCP_G ELM-d is closer to the value of ΔCP_G ELM as the corresponding point of the input image data D IN is closer to the vertex corresponding to the elementary color with which the belonging area of the corresponding point is defined, and the elementary-color-distance dependent correction amount ΔCP_B ELM-d is calculated from ΔCP_B ELM and the distance d ELM so that the elementary-color-distance dependent correction amount ΔCP_B ELM-d is closer to the value of ΔCP_B ELM as the corresponding point of the input image data D IN is closer to the vertex corresponding to the elementary color with which the belonging area of the corresponding point is defined.

In the present embodiment, the elementary-color-distance dependent correction amounts ΔCP_R ELM-d , ΔCP_G ELM-d and ΔCP_B ELM-d are calculated by the multiplier 45 as the products of the selected elementary color correction amounts ΔCP_R ELM , ΔCP_G ELM and ΔCP_B ELM , respectively, and the value obtained by normalizing the distance d ELM with the allowed maximum value D IN MAX . Namely, it holds:

ΔCP_ R ELM-d =ΔCP_ R ELM ×d ELM /D IN MAX ,  (13a)

ΔCP_ G ELM-d =ΔCP_ G ELM ×d ELM /D IN MAX , and  (13b)

ΔCP_ B ELM-d =ΔCP_ B ELM ×d ELM /D IN MAX .  (13c)

Furthermore, the selected complementary color correction amounts ΔCP_R CMP , ΔCP_G CMP and ΔCP_B CMP (the correction amounts associated with the selected complementary color) are output from the selector 48 in response to the selection signal SEL CMY , and the complementary-color-distance dependent correction amounts ΔCP_R CMP-d , ΔCP_G CMP-d and ΔCP_B CMP-d are calculated from the distance d CMP and the selected elementary color correction amounts ΔCP_R CMP , ΔCP_G CMP and ΔCP_B CMP . The complementary-color-distance dependent correction amount ΔCP_R CMP-d is calculated from ΔCP_R CMP and the distance d CMP so that the complementary-color-distance dependent correction amount ΔCP_R CMP-d is closer to the value of ΔCP_R CMP as the corresponding point of the input image data D IN is closer to the vertex corresponding to the complementary color with which the belonging area of the corresponding point is defined. Correspondingly, the complementary-color-distance dependent correction amount ΔCP_G CMP-d is calculated from ΔCF_G CMP and the distance d CMP so that the complementary-color-distance dependent correction amount ΔCP_G CMP-d is closer to the value of ΔCP_G CMP as the corresponding point of the input image data D IN is closer to the vertex corresponding to the complementary color with which the belonging area of the corresponding point is defined, and the complementary-color-distance dependent correction amount ΔCP_B CMP-d is calculated from ΔCP_B CMP and the distance d CMP so that the complementary-color-distance dependent correction amount ΔCP_B CMP-d closer to the value of ΔCP_B CMP as the corresponding point of the input image data D IN is closer to the vertex corresponding to the complementary color with which the belonging area of the corresponding point is defined.

In the present embodiment, the complementary-color-distance dependent correction amounts ΔCP_R CMP-d , ΔCP_G CMP-d and ΔCP_B CMP-d are calculated by the multiplier 49 as the products of the selected complementary color correction amounts ΔCP_R CMP , ΔCP_G CMP and ΔCP_B CMP , respectively, and the value obtained by normalizing the distance d CMP with the allowed maximum value D IN MAX . Namely, it holds:

ΔCP_ R CMP-d =ΔCP_ R CMP ×d CMP /D IN MAX   (14a)

ΔCP_ G CMP-d =ΔCP_ G CMP ×d CMP /D IN MAX , and  (14b)

ΔCP_ B CMP-d =ΔCP_ B CMP ×d CMP /D IN MAX .  (14c)

Furthermore, the white-point-distance dependent correction amounts ΔCP_R W-d , ΔCP_G W-d and ΔCP_B W-d are calculated from the distance d W and the white point correction amounts ΔCP_R W , ΔCP_G W and ΔCP_B W . The white-point-distance dependent correction amount ΔCP_R W-d is calculated from ΔCP_R W and the distance d W so that the white-point-distance dependent correction amount ΔCP_R W-d is closer to the value of ΔCP_R W as the corresponding point of the input image data D IN is closer to the white point. Correspondingly, the white-point-distance dependent correction amount ΔCP_G W-d is calculated from ΔCP_G W and the distance d W so that the white-point-distance dependent correction amount ΔCP_G W-d is closer to the value of ΔCP_G W as the corresponding point of the input image data D IN is closer to the white point, and the white-point-distance dependent correction amount ΔCP_B W-d is calculated from ΔCP_B W and the distance d W so that the white-point-distance dependent correction amount ΔCP_B W-d is closer to the value of ΔCP_B W as the corresponding point of the input image data D IN is closer to the white point.

In the present embodiment, the white-point-distance dependent correction amounts ΔCP_R W-d , ΔCP_G W-d and ΔCP_B W-d are calculated by the multiplier 49 as the products of the white point correction amounts ΔCP_R W , ΔCP_G W and ΔCP_B W , respectively, and the value obtained by normalizing the distance d W with the allowed maximum value D IN MAX . Namely, it holds:

ΔCP_ R W-d =ΔCP_ R W ×d W /D IN MAX ,  (15a)

ΔCP_ G W-d =ΔCP_ G W ×d W /D IN MAX , and  (15b)

ΔCP_ B W-d =ΔCP_ B W ×d W /D IN MAX .  (15c)

The correction amount ΔCP_R is calculated on the basis of the elementary-color-distance dependent correction amount ΔCP_R ELM-d , the complementary-color-distance dependent correction amount ΔCP_R CMP-d and the white-point-distance dependent correction amount ΔCP_R W-d . In the present embodiment, the correction amount ΔCP_R is calculated by the adder 53 as the sum of the elementary-color-distance dependent correction amount ΔCP_R ELM-d , the complementary-color-distance dependent correction amount ΔCP_R CMP-d and the white-point-distance dependent correction amount ΔCP_R W-d .

Namely, it holds:

ΔCP_ R =ΔCP_ R ELM-d +ΔCP_ R CMP-d +ΔCP_ R W-d .  (16a)

Correspondingly, the correction amount ΔCP_G is calculated on the basis of the elementary-color-distance dependent correction amount ΔCP_G ELM-d the complementary-color-distance dependent correction amount ΔCP_G CMP-d and the white-point-distance dependent correction amount ΔCP_G W-d , and the correction amount ΔCP_B is calculated on the basis of the elementary-color-distance dependent correction amount ΔCP_B ELM-d , the complementary-color-distance dependent correction amount ΔCP_B CMP-d and the white-point-distance dependent correction amount ΔCP_B W-d . In the present embodiment, the correction amount ΔCP_G is calculated by the adder 53 as the sum of the elementary-color-distance dependent correction amount ΔCP_G ELM-d , the complementary-color-distance dependent correction amount ΔCP_G CMP-d and the white-point-distance dependent correction amount ΔCP_G W-d , and the correction amount ΔCP_B is calculated as the sum of the elementary-color-distance dependent correction amount ΔCP_B ELM-d , the complementary-color-distance dependent correction amount ΔCP_B CMP-d and the white-point-distance dependent correction amount ΔCP_B W-d .

Namely, it holds:

ΔCP_ G =ΔCP_ G ELM-d +ΔCP_ G CMP-d +ΔCP_ G W-d , and  (16b)

ΔCP_ B =ΔCP_ B ELM-d +ΔCP_ B CMP-d +ΔCP_ B W-d ,  (16b)

The correction amounts ΔCP_R, ΔCP_G and ΔCP_B thus calculated are transmitted to the control point data adjustment circuit 33 of the control point data calculation circuit 29 .

In the following, a description is given of one specific example of the calculation of the correction amounts ΔCP_R, ΔCP_G and ΔCP_B. FIG. 12B illustrates the initial settings used in this example. Discussed below is the case when the R vertex correction amounts ΔCP_R R , ΔCP_G R and ΔCP_B R , the Y vertex correction amounts ΔCP_R Y , ΔCP_G Y and ΔCP_B Y and the white point correction amounts ΔCP_R W , ΔCP_G W and ΔCP_B W are set as illustrated in FIG. 12B . As described above, the R vertex correction amounts ΔCP_R R , ΔCP_G R and ΔCP_B R are set to the R vertex correction amount register 43 R, and the Y vertex correction amounts ΔCP_R Y , ΔCP_G Y and ΔCP_B Y are set to the Y vertex correction amount register 47 Y. The white point correction amounts ΔCP_R W , ΔCP_G W and ΔCP_B W are set to the white point correction amount register 51 .

Additionally, it is assumed in this example that the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN are each 8-bit data and therefore the allowed maximum value D IN MAX is 255.

In the case when the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN are 200, 130 and 100, respectively, the correction amounts ΔCP_R, ΔCP_G and ΔCP_B are calculated as described below.

Among the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN , the largest one is the R grayscale values D IN R , and the smallest one is the B grayscale value D IN B . Area of the corresponding point of the input image data D IN in the color space is the area A 1 , which is defined by the white point, the R vertex and the Y vertex (see FIG. 3B ). The selected elementary color vertex is the R vertex, and the selected complementary color vertex is the Y vertex.

The differences between the R, G and B grayscale values of the selected elementary color vertex (that is, the R vertex) and the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN are calculated in accordance with expressions (8a) to (8c) as follows:

RGB dist_ R= 255−200=55,

RGB dist_ G= 0−130=−130, and

RGB dist_ B= 0−100=−100.

The differences between the R, G and B grayscale values of the selected complementary color vertex (that is, the Y vertex) and the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN are calculated in accordance with expressions (9a) to (9c) as follows:

CMY dist_ R= 255−200=55,

CMY dist_ G= 255−130=125, and

CMY dist_ B= 0−100=−100.

The distance d ELM between the selected elementary color vertex and the corresponding point of the input image data D IN is calculated in accordance with expression (10) as follows:

d ELM =255−{55−(−130)}=70.

The distance d CMP between the selected complementary color vertex and the corresponding point of the input image data D IN is calculated in accordance with expression (11) as follows:

d CMP =255−{55−(−100)}=100.

The distance d W between the white point and the corresponding point of the input image data D IN is calculated in accordance with expression (12) as follows:

d W =100.

The white-point-distance dependent correction amounts ΔCP_R W-d , ΔCP_G W-d and ΔCP_B W-d are calculated in accordance with expressions (15a) to (15c) as follows:

It should be noted that ΔCP_R W-d , ΔCP_G W-d and ΔCP_B W-d are each calculated as a 10-bit value and rounded to a value at increments of 0.25.

Also, the elementary-color-distance dependent correction amounts ΔCP_R ELM-d , ΔCP_G ELM-d and ΔCP_B ELM-d are calculated in accordance with expressions (13a) to (13c) as follows:

Δ ⁢ ⁢ CP_R ELM - d = ⁢ Δ ⁢ ⁢ CP_R R × d ELM / D IN MAX , and = ⁢ 0 × 70 / 255 = 0 , Δ ⁢ ⁢ CP_G ELM - d = ⁢ Δ ⁢ ⁢ CP_G R × d ELM / D IN MAX , = ⁢ - 10 × 70 / 255 = - 2.75 , and Δ ⁢ ⁢ CP_B ELM - d = ⁢ Δ ⁢ ⁢ CP_B R × d ELM / D IN MAX , = ⁢ - 12 × 70 / 255 = - 3.25 .

It should be noted that ΔCP_R ELM-d , ΔCP_G ELM-d and ΔCP_B ELM-d are each calculated as a 10-bit value and rounded to a value at increments of 0.25.

Furthermore, the complementary-color-distance dependent correction amounts ΔCP_R CMP-d , ΔCP_G CMP-d and ΔCP_B CMP-d are calculated in accordance with expressions (14a) to (14c) as follows:

Δ ⁢ ⁢ CP_R CMP - d = ⁢ Δ ⁢ ⁢ CP_R CMP × d CMP / D IN MAX , = ⁢ 0 × 100 / 255 = 0 , Δ ⁢ ⁢ CP_G CMP - d = ⁢ Δ ⁢ ⁢ CP_G CMP × d CMP / D IN MAX , = ⁢ 0 × 100 / 255 = 0 , and Δ ⁢ ⁢ CP_B CMP - d = ⁢ Δ ⁢ ⁢ CP_B CMP × d ⁢ CMP / D IN MAX , = ⁢ - 12 × 100 / 255 = - 4.75 .

It should be noted that ΔCP_R CMP-d , ΔCP_G CMP-d and ΔCP_B CMP-d are each calculated as a 10-bit value and rounded to a value at increments of 0.25.

The correction amounts ΔCP_R, ΔCP_G and ΔCP_B are calculated in accordance with expressions (16a) to (16c) as follows:

Δ ⁢ ⁢ CP_R = ⁢ Δ ⁢ ⁢ CP_R ELM - d + Δ ⁢ ⁢ CP_R CMP - d + Δ ⁢ ⁢ CP_R W - d , = ⁢ 0 , Δ ⁢ ⁢ CP_G = ⁢ Δ ⁢ ⁢ CP_G ELM - d + Δ ⁢ ⁢ CP_G CMP - d + Δ ⁢ ⁢ C ⁢ ⁢ P_G W - d , = ⁢ - 4.25 , and Δ ⁢ ⁢ CP_B = ⁢ Δ ⁢ ⁢ CP_B ELM - d + Δ ⁢ ⁢ CP_B CMP - d + Δ ⁢ ⁢ CP_B W - d , = ⁢ - 11.

Referring back to FIG. 11A , the control point data sets CP_R, CP_G and CP_B to be transmitted to the approximate gamma correction circuit 22 are calculated by the control point data adjustment circuit 33 on the basis of the control point data of the control point data set CP_sel determined by the interpolation/selection circuit 32 and the correction amounts ΔCP_R, ΔCP_G and ΔCP_B calculated by the correction amount calculation circuit 28 . It should be noted that the correction amounts ΔCP_R, ΔCP_G and ΔCP_B are calculated for each pixel 9 and therefore the correction point data sets CP_R, CP_G and CP_B are also calculated for each pixel 9 .

More specifically, the control point data CP 0 _R to CP 5 _R of the control point data set CP_R are calculated by adding the correction amount ΔCP_R to the control point data CP 0 _sel to CP 5 _sel of the control point data set CP_sel, respectively. Namely,

CP0_ R =CP0_sel+ΔCP_ R,

CP1_ R =CP1_sel+ΔCP_ R,

CP2_ R =CP2_sel+ΔCP_ R,

CP3_ R =CP3_sel+ΔCP_ R,

CP4_ R =CP4_sel+ΔCP_ R , and

CP5_ R =CP5_sel+ΔCP_ R,   (17)

Correspondingly, the control point data CP 0 _G to CP 5 _G of the control point data set CP_G are calculated by adding the correction amount ΔCP_G to the control point data CP 0 _sel to CP 5 _sel of the control point data set CP_sel, respectively. Namely,

CP0_ G =CP0_sel+ΔCP_ G,

CP1_ G =CP1_sel+ΔCP_ G,

CP2_ G =CP2_sel+ΔCP_ G,

CP3_ G =CP3_sel+ΔCP_ G,

CP4_ G =CP4_sel+ΔCP_ G , and

CP5_ G =CP5_sel+ΔCP_ G,   (18)

Furthermore, the control point data CP 0 _B to CP 5 _B of the control point data set CP_B are calculated by adding the correction amount ΔCP_B to the control point data CP 0 _sel to CP 5 _sel of the control point data set CP_sel, respectively. Namely,

CP0_ R =CP0_sel+ΔCP_ B,

CP1_ R =CP1_sel+ΔCP_ B,

CP2_ R =CP2_sel+ΔCP_ B,

CP3_ R =CP3_sel+ΔCP_ B,

CP4_ R =CP4_sel+ΔCP_ B , and

CP5_ R =CP5_sel+ΔCP_ B,   (19)

The control point data sets CP_R, CP_G and CP_B thus calculated are transferred to the approximate gamma correction circuit 22 .

Digital arithmetic processing is performed on the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN of each pixel 9 on the basis of the control point data sets CP_R, CP_G and CP_B to generate the R, G and B grayscale values D OUT R , D OUT G and D OUT B of the output image data D OUT associated with each pixel 9 . This arithmetic processing is performed by the approximate gamma correction circuits 30 R, 30 G and 30 B of the approximate gamma correction circuit 22 .

More specifically, in the digital arithmetic processing in the approximate gamma correction circuit 22 of the present embodiment, the R, G and B grayscale values D OUT R , D OUT G and D OUT B of the output image data D OUT are calculated from the R, G and B grayscale values D IN B , D IN G and D IN B of the input image data D IN in accordance with the following expressions:

(1) For the case when D IN k <D IN Center and CP 1 >CP 0 ,

D OUT k = 2 ⁢ ( CP1_k - CP0_k ) · PD INS k K 2 + ( CP3_k - CP0_k ) ⁢ D INS k K + CP0_k ( 20 ⁢ a )

(2) for the case when D IN k <D in Center and CP 1 ≦CP 0 ,

D OUT k = 2 ⁢ ( CP1_k - CP0_k ) · ND INS k K 2 + ( CP3_k - CP0_k ) ⁢ D INS k K + CP0_k ( 20 ⁢ b )

and

(3) for the case when D IN k >D IN Center ,

D OUT k = 2 ⁢ ( CP4_k - CP2_k ) · ND INS k K 2 + ( CP5_k - CP2_k ) ⁢ D INS k K + CP2_k ( 20 ⁢ c )

It should be noted that the index k is any of “R”, “G” and “B”.

In the above, the intermediate data value D IN Center is defined by the following expression (20d)

D IN Center =D IN MAX /2  (20d)

where D IN MAX is the allowed maximum value of the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN . K is the parameter defined by the above-described expression (3); K is given as follows:

K =( D IN MAX +1)/2.

Furthermore, D INS k , PD INS k and ND INS k in expressions (20a) to (20c) are values defined as follows:

(a) D INS k

D INS k is a value determined depending on the grayscale value D IN k (the R, G and B grayscale values D IN R , D IN G and D IN B ) of the input image data D IN and given by the following expression:

D INS k D IN k (for D IN k <D IN Center )

D INS k =D IN k +1 −K (for D IN k >D IN Center )  (21)

(b) PD INS k

PD INS k is defined by expression (22a) with a parameter R k defined by expression (22b) as follows:

PD INS k =( K−R k )· R k   (22a)

R k =K 1/2 ·( D INS k ) 1/2   (22b)

As understood from expressions (22a) and (22b), the parameter R k is a value proportional to a square root of the grayscale value D IN k and

therefore PD INS k is a value calculated by an expression including a term proportional to a square root of the grayscale value D IN k and a term proportional to the grayscale value D IN k to the power of one.

ND INS is given by the following expression (23):

ND INS k =( K−D INS k )· D INS k   (23)

As understood from expressions (21) and (23), ND INS k is a value calculated by an expression including a term proportional to a square of the grayscale value D IN k of the input image data D IN .

FIG. 13 is a graph illustrating the relations between the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN and the R, G and B grayscale values D OUT R , D OUT G and D OUT B of the output image data D OUT in the case when the R, G and B grayscale values D OUT R , D OUT G and D OUT B of the output image data D OUT are calculated in accordance with the above-described arithmetic processing.

The control point data CP 0 _sel to CP 5 _sel are determined to make the input-output curve approximate to the gamma curve of the gamma value γ_VALUE. The control point data CP 0 _R to CP 5 _R used for the calculation of the R grayscale value D OUT R of the output image data D OUT are calculated by adding the correction amount ΔCP_R to the control point data CP 0 _sel to CP 5 _sel thus determined for color adjustment. The R grayscale value D OUT R of the output image data D OUT is calculated from the R grayscale value D IN R of the input image data D IN in accordance with the input-output curve with the shape specified by the control point data CP 0 _R to CP 5 _R.

Correspondingly, the control point data CP 0 _G to CP 5 _G used for the calculation of the G grayscale value D OUT G of the output image data D OUT are calculated by adding the correction amount ΔCP_G to the control point data CP 0 _sel to CP 5 _sel for color adjustment. The G grayscale value D OUT G of the output image data D OUT is calculated from the G grayscale value D IN G of the input image data D IN in accordance with the input-output curve with the shape specified by the control point data CP 0 _G to CP 5 _G. Furthermore, the control point data CP 0 _B to CP 5 _B used for the calculation of the B grayscale value D OUT B of the output image data D OUT are calculated by adding the correction amount ΔCP_B to the control point data CP 0 _sel to CP 5 _sel for color adjustment. The B grayscale value D OUT B of the output image data D OUT is calculated from the B grayscale value D IN B of the input image data D IN in accordance with the input-output curve with the shape specified by the control point data CP 0 _B to CP 5 _B.

The output image data D OUT , which are calculated by the approximate gamma correction circuit 22 in accordance with the expressions described above, are transmitted to the color reduction circuit 23 . In the color reduction circuit 23 , color reduction is performed on the output image data D OUT to generate the color-reduced image data D OUT _ D . The color-reduced image data D OUT _ D are transmitted to the data line drive circuit 26 via the latch circuit 24 and the data lines 8 of the liquid crystal display panel 2 are driven in response to the color-reduced image data D OUT _ D .

The above-described digital arithmetic processing of the present embodiment allows concurrently performing gamma correction and color adjustment with a reduced circuit size.

(Calculation of Correction Amounts for Respective Elementary Color Vertices, Complementary Color Vertices and White Point)

In the following, a description is given of an exemplary calculation method of the R vertex correction amounts ΔCP_R R , ΔCP_G R , ΔCP_B R , the G vertex correction amounts ΔCP_R G , ΔCP_G G , ΔCP_B G , the B vertex correction amounts ΔCP_R B , ΔCP_G B , ΔCP_B B , the C vertex correction amounts ΔCP_R C , ΔCP_G C , ΔCP_B C , the M vertex correction amounts ΔCP_R M , ΔCP_G M , ΔCP_B M , the Y vertex correction amounts ΔCP_R Y , ΔCP_G Y , ΔCP_B Y and the white point correction amounts ΔCP_R W , ΔCP_G W , ΔCP_B W . It should be noted that these correction amounts are respectively set in the R vertex correction amount register 43 R, the G vertex correction amount register 43 G, the B vertex correction amount register 43 B, the C vertex correction amount register 47 C, the M vertex correction amount register 47 M, the Y vertex correction amount register 47 Y and the white point correction amount register 51 .

The R vertex correction amounts ΔCP_R R , ΔCP_G R , ΔCP_B R are values to be set as the correction amounts ΔCP_R, ΔCP_G, ΔCP_B in the case when the corresponding point of the input image data D IN coincides with the R vertex in the color space. As understood from the above-described operation, in the case when the corresponding point of the input image data D IN coincides with the R vertex in the color space, the control point data CP 0 _R to CP 5 _R, which are finally used for the digital arithmetic processing of the input image data D IN , are calculated by adding the correction amount ΔCP_R R to the control point data CP 0 _sel to CP 5 _sel, which are determined on the basis of the gamma value γ_VALUE. Correspondingly, the control point data CP 0 _G to CP 5 _G are calculated by adding the correction amount ΔCP_G R to the control point data CP 0 _sel to CP 5 _sel, and the control point data CP 0 _B to CP 5 _B are calculated by adding the correction amount ΔCP_B R to the control point data CP 0 _sel to CP 5 _sel.

Correspondingly, the G vertex correction amounts ΔCP_R G , ΔCP_G G , ΔCP_B G are values to be set as the correction amounts ΔCP_R, ΔCP_G, ΔCP_B in the case when the corresponding point of the input image data D IN coincides with the G vertex in the color space, and the B vertex correction amounts ΔCP_R B , ΔCP_G B , ΔCP_B B are values to be set as the correction amounts ΔCP_R, ΔCP_G, ΔCP_B in the case when the corresponding point of the input image data D IN coincides with the B vertex in the color space. Furthermore, the C vertex correction amounts ΔCP_R C , ΔCP_G C , ΔCP_B C are values to be set as the correction amounts ΔCP_R, ΔCP_G, ΔCP_B in the case when the corresponding point of the input image data D IN coincides with the C vertex in the color space, and the M vertex correction amounts ΔCP_R M , ΔCP_G M , ΔCP_B M are values to be set as the correction amounts ΔCP_R, ΔCP_G, ΔCP_B in the case when the corresponding point of the input image data D IN coincides with the M vertex in the color space. Finally, the Y vertex correction amounts ΔCP_R Y , ΔCP_G Y , ΔCP_B Y are values to be set as the correction amounts ΔCP_R, ΔCP_G, ΔCP_B in the case when the corresponding point of the input image data D IN coincides with the Y vertex in the color space, and the white point correction amounts ΔCP_R W , ΔCP_G W , ΔCP_B W are values to be set as the correction amounts ΔCP_R, ΔCP_G, ΔCP_B in the case when the corresponding point of the input image data D IN coincides with the white point in the color space.

The R vertex correction amounts ΔCP_R R , ΔCP_G B , ΔCP_B R , the G vertex correction amounts ΔCP_R G , ΔCP_G G , ΔCP_B G , the B vertex correction amounts ΔCP_R B , ΔCP_G B , ΔCP_B B , the C vertex correction amounts ΔCP_R C , ΔCP_G C , ΔCP_B C , the M vertex correction amounts ΔCP_R M , ΔCP_G M , ΔCP_B M , the Y vertex correction amounts ΔCP_R Y , ΔCP_G Y , ΔCP_B Y and the white point correction amounts ΔCP_R W , ΔCP_G W , ΔCP_B W are determined on the basis of the display characteristics of the liquid crystal display panel 2 (the panel characteristics) so that a desired color gamut is achieved by the color adjustment.

FIG. 14 is a flowchart illustrating an exemplary procedure of the calculation of the correction amounts for the vertices corresponding to the respective elementary colors and complementary colors and the white point.

The panel characteristics of the liquid crystal display panel 2 are measured. More specifically, the chromaticity coordinates of the white point, the R, G, B, C, M and Y vertices are measured with respect to the liquid crystal display panel 2 . The chromaticity coordinates of the white point can be obtained by performing a color measurement with respect to an image corresponding to input image data D IN in which the R, G and B grayscale values are set to the allowed maximum value (in the present embodiment, 255) for all the pixels.

The chromaticity coordinates of the R vertex can be obtained by performing a color measurement with respect to an image corresponding to input image data D IN in which the R grayscale value is set to the allowed maximum value (255 in the present embodiment) for all the pixels and the G and B grayscale values are set to zero for all the pixels. Correspondingly, the chromaticity coordinates of the G vertex can be obtained by performing a color measurement with respect to an image corresponding to input image data D IN in which the G grayscale value is set to the allowed maximum value for all the pixels and the B and R grayscale values are set to zero for all the pixels, and the chromaticity coordinates of the B vertex can be obtained by performing a color measurement with respect to an image corresponding to input image data D IN in which the B grayscale value is set to the allowed maximum value for all the pixels and the R and G grayscale values are set to zero for all the pixels.

Furthermore, the chromaticity coordinates of the C vertex can be obtained by performing a color measurement with respect to an image corresponding to input image data D IN in which the G and B grayscale values are set to the allowed maximum value for all the pixels and the R grayscale value is set to zero for all the pixels. Correspondingly, the chromaticity coordinates of the M vertex can be obtained by performing a color measurement with respect to an image corresponding to input image data D IN in which the B and R grayscale values are set to the allowed maximum value for all the pixels and the G grayscale value is set to zero for all the pixels, and the chromaticity coordinates of the Y vertex can be obtained by performing a color measurement with respect to an image corresponding to input image data D IN in which the R and G grayscale values are set to the allowed maximum value for all the pixels and the B grayscale value is set to zero for all the pixels.

FIG. 15A is a table illustrating one example of the measurement result of the panel characteristics obtained at step S 21 . In the present embodiment, the measured chromaticity coordinates of the white point (WP), the R, G, B, C, M and Y vertices are represented by the chromaticity coordinates (u′, v′) defined in a CIE 1976 UCS chromaticity diagram.

A transformation matrix for obtaining R, G and B grayscale values corresponding to a chromaticity coordinates (X, Y, Z) with respect to the liquid crystal display panel 2 , which may be referred to as “panel characteristics transformation matrix”, hereinafter, is calculated from the measurement result of the panel characteristics obtained at step S 21 . The panel characteristics transformation matrix is calculated from the measured chromaticity coordinates (u′, v′) of the white point (WP) and the R, G and B vertices.

First, the chromaticity coordinates (x, y) of the white point (WP) and the R, G and B vertices are calculated by performing a transformation from the chromaticity coordinates (u′, v′) to (x, y). FIG. 15B is a table illustrating the result of the transformation from the chromaticity coordinates (u′, v′) to (x, y) for the measured chromaticity coordinates of the white point (WP), the R, G, B, C, M and Y vertices illustrated in FIG. 15A .

As known in the art, the matrix describing the chromaticity coordinates (X, Y, Z) of the color displayed on a display device for a given set of R, G and B grayscale values is given as follows:

where (Rx, Ry, Rz) are the chromaticity coordinates (x, y, z) of the R vertex of the display device, (Gx, Gy, Gz) are the chromaticity coordinates (x, y, z) of the G vertex and (Bx, By, Bz) are the chromaticity coordinates (x, y, z) of the B vertex. It should be noted that the following holds:

Rz= 1− Rx−Ry,

Gz= 1 −Gx−Gy , and

Bz= 1 −Bx−By,

from the definition of the chromaticity coordinates (x, y, z).

The coefficients r, g and b are obtained as the solutions of the following simultaneous equations:

( Rx / Ry Gx / Gy Bx / By 1 1 1 Rz / Ry Gz / Gy Bz / By ) ⁢ ( r g b ) = ( Wx / Wy 1 Wz / Wy ) ( 25 )

where (Wx, Wy, Wz) is the chromaticity coordinates (x, y, z) of the white point.

It should be noted that it holds:

Wz= 1 −Wx−Wy.

The panel characteristics transformation matrix is obtained with the inverse matrix of the matrix described on the right side of expression (24) as follows:

By calculating the specific values of the respective elements of expression (25) for the chromaticity coordinates of the white point (WP), and the R, G and B vertices illustrated in FIG. 15B , the following is obtained:

(

1.899

0.535

2.908

1

1

1

0.069

0.128

14.208

)

⁢

(

r

g

b

)

=

(

0.960

1

1.044

)

(

27

)

The coefficients r, g and b are obtained from the simultaneous equations (27) as follows:

r =0.197,

g= 0.737, and

b= 0.066.

With respect to the panel characteristics illustrated in FIGS. 15A and 15B , the panel characteristics transformation matrix is finally obtained from the obtained coefficients r, g and b and expression (26) as follows:

( R G B ) = ( 3.700 - 1.900 - 0.623 - 0.992 1.879 0.071 0.046 - 0.161 1.070 ) ⁢ ( X Y Z ) ( 28 )

Desired values of the chromaticity coordinates of the white point and the R, G, B, C, M and Y vertices are determined in accordance with a desired color gamut. When the desired color gamut is determined in accordance with the sRGB standard, for example, the desired values of the chromaticity coordinates (u′, v′) of the white point and the R, G, B, C, M and Y vertices are determined as illustrated in FIG. 16 .

It should be noted that the actually achievable color gamut depends on the characteristics of the liquid crystal display panel and therefore the desired values set at step S 23 may be unachievable. To address this, in the present embodiment, the correction amounts ΔCP_R, ΔCP_G and ΔCP_B are determined so that the chromaticity coordinates at which the saturations of the respective elementary colors and complementary colors are 50% with respect to the panel characteristics of the liquid crystal display panel 2 (hereinafter, referred to as “500-saturation panel characteristics values”) coincide with the desired values determined so that the saturations of the respective elementary colors and complementary colors are 50% (hereinafter, referred to as “50%-saturation desired values”). At steps S 24 to S 26 described below, the correction amounts ΔCP_R, ΔCP_G and ΔCP_B are calculated so that the 50%-saturation panel characteristics values of the respective elementary colors and complementary colors of the liquid crystal display panel 2 coincide with the 50%-saturation desired values of the respective elementary colors and complementary colors. It should be noted that, with respect to the white point, the correction amounts ΔCP_R, ΔCP_G and ΔCP_B are calculated so that the chromaticity coordinates of the white point for the panel characteristics of the liquid crystal display panel 2 coincide with the desired values of the chromaticity coordinates of the white point.

The 50%-saturation panel characteristics values of the respective elementary colors and complementary colors of the liquid crystal display panel 2 and the 50%-saturation desired values of the respective elementary colors and complementary colors are calculated.

The 50%-saturation panel characteristics values of the respective elementary colors and complementary colors of the liquid crystal display panel 2 are calculated as the average values of the measured chromaticity coordinates (u′, v′) of the respective elementary colors and complementary colors and the measured chromaticity coordinates (u′, v′) of the white point. More specifically, the 50%-saturation panel characteristics values of the elementary color R is calculated as the average value of the measured chromaticity coordinates (u′, v′) of the R vertex and the measured chromaticity coordinates (u′, v′) of the white point. With respect to the measurement result of the panel characteristics illustrated in FIG. 15A , for example, the measured chromaticity coordinates (u′, v′) of the R vertex are (0.444, 0.526) and the measured chromaticity coordinates (u′, v′) of the white point are (0.201, 0.471). Accordingly, as illustrated in FIG. 17A , the 50%-saturation panel characteristics values of the elementary color R are calculated as (0.322, 0.499).

Correspondingly, the 50%-saturation panel characteristics values of the elementary color G is calculated as the average value of the measured chromaticity coordinates (u′, v′) of the G vertex and the measured chromaticity coordinates (u′, v′) of the white point, and the 50%-saturation panel characteristics values of the elementary color B is calculated as the average value of the measured chromaticity coordinates (u′, v′) of the B vertex and the measured chromaticity coordinates (u′, v′) of the white point.

Furthermore, the 50%-saturation panel characteristics values of the complementary color C is calculated as the average value of the measured chromaticity coordinates (u′, v′) of the C vertex and the measured chromaticity coordinates (u′, v′) of the white point. Correspondingly, the 50%-saturation panel characteristics values of the complementary color M is calculated as the average value of the measured chromaticity coordinates (u′, v′) of the M vertex and the measured chromaticity coordinates (u′, v′) of the white point, and the 50%-saturation panel characteristics values of the complementary color Y is calculated as the average value of the measured chromaticity coordinates (u′, v′) of the Y vertex and the measured chromaticity coordinates (u′, v′) of the white point.

FIG. 17A illustrates the 50%-saturation panel characteristics values of the respective elementary colors and complementary colors calculated for the measurement result of the panel characteristics illustrated in FIG. 15A . It should be noted that, for the white point, the measurement result obtained at step S 21 are illustrated again in FIG. 17A .

The 50%-saturation desired values of the respective elementary colors and respective complementary colors are calculated as the average values of the desired values of the chromaticity coordinates (u′, v′) of the respective elementary colors and complementary colors and the desired values of the chromaticity coordinates (u′, v′) of the white point. More specifically, the 50%-saturation desired values of the elementary color R are calculated as the average values of the desired values of the chromaticity coordinates (u′, v′) of the R vertex and the desired values of the chromaticity coordinates (u′, v′) of the white point. With respect to the desired values illustrated in FIG. 16 , for example, the desired values of the chromaticity coordinates (u′, v′) of the R vertex are (0.452, 0.523) and the desired values of the chromaticity coordinates (u′, v′) of the white point are (0.198, 0.468). Accordingly, as illustrated in FIG. 17B , 50%-saturation desired values of the elementary color R are calculated as (0.324, 0.496).

Correspondingly, the 50%-saturation desired values of the elementary color G are calculated as the average values of the desired values of the chromaticity coordinates (u′, v′) of the G vertex and the desired values of the chromaticity coordinates (u′, v′) of the white point, and the 50%-saturation desired values of the elementary color B are calculated as the average values of the desired values of the chromaticity coordinates (u′, v′) of the B vertex and the desired values of the chromaticity coordinates (u′, v′) of the white point.

Furthermore, the 50%-saturation desired values of the complementary color C are calculated as the average values of the desired values of the chromaticity coordinates (u′, v′) of the C vertex and the desired values of the chromaticity coordinates (u′, v′) of the white point. Correspondingly, the 50%-saturation desired values of the complementary color M are calculated as the average values of the desired values of the chromaticity coordinates (u′, v′) of the M vertex and the desired values of the chromaticity coordinates (u′, v′) of the white point, and the 50%-saturation desired values of the complementary color Y are calculated as the average values of the desired values of the chromaticity coordinates (u′, v′) of the Y vertex and the desired values of the chromaticity coordinates (u′, v′) of the white point.

FIG. 17B illustrates the 50%-saturation desired values of the respective elementary colors and complementary colors calculated in the case when the desired values of the respective elementary colors and complementary colors are set as illustrated in FIG. 16 . It should be noted that, for the white point, the desired values are illustrated again in FIG. 17B .

Correction amounts of the R, G and B grayscale values are calculated for the 50% saturation. More strictly, calculated at step S 25 are correction amounts determined for correcting R, G and B grayscale values of input image data corresponding to the 50% saturations of the respective elementary colors and complementary colors so that the colors corresponding to the 50%-saturation desired values of the respective elementary colors and complementary colors are actually displayed on the liquid crystal display panel 2 . It should be noted that, for the white point, correction amounts are determined for correcting R, G and B grayscale values of input image data corresponding to the white point so that the color corresponding to the desired values of the white point are actually displayed on the liquid crystal display panel 2 .

The correction amounts for 50% saturation are calculated as follows: First, transformation from chromaticity coordinates (u′, v′) to chromaticity coordinates (X, Y, Z) are performed on the 50%-saturation panel characteristics values of the respective elementary colors and complementary colors of the liquid crystal display panel 2 and the measured chromaticity coordinates of the white point. The transformation from chromaticity coordinates (u′, v′) to chromaticity coordinates (X, Y, Z) can be achieved by performing transformation from chromaticity coordinates (u′, v′) to (x, y) and further performing transformation from chromaticity coordinates (x, y) to (X, Y, Z).

FIG. 18A illustrates the result of transformation from chromaticity coordinates (u′, v′) to (x, y) for the 50%-saturation panel characteristics values of the respective elementary colors and complementary colors and the measured chromaticity coordinates of the white point illustrated in FIG. 17A , and FIG. 18C illustrates the result of further transformation to chromaticity coordinates (X, Y, Z).

Similarly, transformations from chromaticity coordinates (u′, v′) to (x, y) and from (x, y) to (X, Y, Z) are performed on the 50%-saturation desired values of the respective elementary colors and complementary colors and the desired values of the chromaticity coordinates of the white point. FIG. 18B illustrates the result of transformation from chromaticity coordinates (u′, v′) to (x, y) for the 50%-saturation desired values of the respective elementary colors and complementary colors and the desired values of the chromaticity coordinates of the white point illustrated in FIG. 17B , and FIG. 18D illustrates the result of further transformation to chromaticity coordinates (X, Y, Z).

by applying the transformation matrix given by expression (26) to the 50%-saturation panel characteristics values of the respective elementary colors and complementary colors of the liquid crystal display panel 2 represented in the form of chromaticity coordinates (X, Y, Z), it is possible to obtain the ratio among the R, G and B grayscale values corresponding to the 50%-saturation panel characteristics values of the respective elementary colors and complementary colors of the liquid crystal display panel 2 . In the case when the values of the respective elements of the transformation matrix are given by expression (28) and the 50%-saturation panel characteristics values of the respective elementary colors and complementary colors of the liquid crystal display panel 2 and the measured chromaticity coordinates (X, Y, Z) of the white point are given as illustrated in FIG. 18C , the ratio among the R, G and B grayscale values corresponding to the 50%-saturation panel characteristics values of the respective elementary colors and complementary colors are calculated as illustrated in FIG. 19A .

Furthermore, by applying the transformation matrix given by expression (26) to the 50%-saturation desired values of the respective elementary colors and complementary colors and the desired values of the chromaticity coordinates of the white point represented in the form of chromaticity coordinates (X, Y, Z), it is possible to obtain the ratio among the R, G and B grayscale values of the 50%-saturation desired values of the respective elementary colors and complementary colors and the desired values of the white point. In the case when the values of the respective elements of the transformation matrix are given by expression (28) and the 50%-saturation desired values of the respective elementary colors and complementary colors and the desired values of the chromaticity coordinates (X, Y, Z) of the white point are given as illustrated in FIG. 18D , the ratio among the R, G and B grayscale values corresponding to the 50%-saturation desired values of the respective elementary colors and complementary colors and the desired values of the chromaticity coordinates of the white point are calculated as illustrated in FIG. 19B .

The R, G and B grayscale values corresponding to the 50%-saturation panel characteristics values of the respective elementary colors and complementary colors of the liquid crystal display panel 2 are calculated by normalizing the thus-calculated ratio among the R, G and B grayscale values corresponding to the 50%-saturation panel characteristics values of the respective elementary colors and complementary colors of the liquid crystal display panel 2 with a specific value (for example, the allowed maximum value D IN MAX of the R, G and B grayscale values). FIG. 19C illustrates the R, G and B grayscale values normalized with the allowed maximum values D IN MAX (=255) for the case when the ratio among the R, G and B grayscale values corresponding to the 50%-saturation panel characteristics values of the respective elementary colors and complementary colors and the white point of the liquid crystal display panel 2 are given as illustrated in FIG. 19A .

Correspondingly, the R, G and B grayscale values corresponding to the 50%-saturation desired values of the respective elementary colors and complementary colors and the desired values of the chromaticity coordinates of the white point of are calculated by normalizing the thus-calculated ratio among the R, G and B grayscale values corresponding to the 50%-saturation desired values of the respective elementary colors and complementary colors and the desired values of the chromaticity coordinates of the white point with a specific value (for example, the allowed maximum value D IN MAX of the R, G and B grayscale values). FIG. 19D illustrates the R, G and B grayscale values normalized with the allowed maximum values D IN MAX (=255) for the case when the ratio among the R, G and B grayscale values corresponding to the 50%-saturation desired values of the respective elementary colors and complementary colors and the desired values of the chromaticity coordinates of the white point are given as illustrated in FIG. 19B .

The correction amounts of the R, G and B grayscale values for 50% saturation are respectively calculated as the differences between the R, G and B grayscale values corresponding to the 50%-saturation panel characteristics values of the respective elementary colors and complementary colors of the liquid crystal display panel 2 and those corresponding to the 50%-saturation desired values of the respective elementary colors and complementary colors.

Also, the correction amounts of the R, G and B grayscale values for the white point are respectively calculated as the differences between the R, G and B grayscale values of the white point of the liquid crystal display panel 2 and the R, G and B grayscale values corresponding to the desired values of the chromaticity coordinates of the white point. The correction amounts of the R, G and B grayscale values for the white point thus obtained are used as the white point correction amounts ΔCP_R W , ΔCP_G W and ΔCP_B W . The obtained white point correction amounts ΔCP_R W , ΔCP_G W and ΔCP_B W are stored in advance in the white point correction amount register 51 .

FIG. 20A illustrates the correction amounts of R, G and B grayscale values for 50% saturation and the correction amounts of the white point in the case when the R, G and B grayscale values corresponding to the 50%-saturation panel characteristics values of the respective elementary colors and complementary colors of the liquid crystal display panel 2 are given as illustrated in FIG. 19C and the R, G and B grayscale values corresponding to the 50%-saturation desired values of the respective elementary colors and complementary colors and the desired values of the chromaticity coordinates of the white point are given as illustrated in FIG. 19D .

The correction amounts ΔCP_R, ΔCP_G and ΔCP_B for the vertices corresponding to the respective elementary colors and complementary colors (that is, the points at which the saturations of the respective elementary colors and complementary colors are 100%) are calculated. The correction amounts ΔCP_R, ΔCP_G and ΔCP_B for the vertices corresponding to the respective elementary colors and complementary colors are calculated through linear extrapolation of the correction amounts of the R, G and B grayscale values for the white point (that is, the point at which the saturations of all the elementary colors and complementary colors are 0%) and the correction amounts of the R, G and B grayscale values for 50% saturations of the respective elementary colors and complementary colors.

It should be noted that the control point data CP 0 and CP 5 , which indicate the positions of the end points of the input-output curves of R, G and B grayscale values, are data specifying the positions of the vertices corresponding to the elementary colors and complementary colors with R, G and B grayscale values, while the correction amounts ΔCP_R, ΔCP_G and ΔCP_B are added to the control point data CP 0 _sel and CP 5 _sel determined on the gamma value γ_VALUE. Accordingly, the correction amounts ΔCP_R, ΔCP_G and ΔCP_B for the respective vertices are to be determined as such correction amounts of R, G and B grayscale values that the 50%-saturation panel characteristics values coincide with the 50%-saturation desired values.

For example, the R vertex correction amounts ΔCP_R R , ΔCP_G R and ΔCP_B R are calculated in accordance with the following expression (29a):

Δ ⁢ ⁢ CP_R R = D IN MAX · ( Δ ⁢ ⁢ R R ⁢ ⁢ 50 - Δ ⁢ ⁢ CP_R W ) min ⁡ ( R R ⁢ ⁢ 50 , G R ⁢ ⁢ 50 , B R ⁢ ⁢ 50 ) + Δ ⁢ ⁢ CP_R W ⁢

⁢ Δ ⁢ ⁢ CP_G R = D IN MAX · ( Δ ⁢ ⁢ G R ⁢ ⁢ 50 - Δ ⁢ ⁢ CP_G W ) min ⁡ ( R R ⁢ ⁢ 50 , G R ⁢ ⁢ 50 , B R ⁢ ⁢ 50 ) + Δ ⁢ ⁢ CP_G W ⁢

⁢ Δ ⁢ ⁢ CP_B R = D IN MAX · ( Δ ⁢ ⁢ B R ⁢ ⁢ 50 - Δ ⁢ ⁢ CP_B W ) min ⁡ ( R R ⁢ ⁢ 50 , G R ⁢ ⁢ 50 , B R ⁢ ⁢ 50 ) + Δ ⁢ ⁢ CP_B W ( 29 ⁢ a )

where ΔR R50 is the correction amount of the R grayscale value for the elementary color R which is calculated for 50% saturation at step S 25 , ΔG R50 is the correction amount of the G grayscale value for the elementary color R which is calculated for 50% saturation at step S 25 , and ΔB R50 is the correction amount of the B grayscale value for the elementary color R which is calculated for 50% saturation at step S 25 . R R50 is the R grayscale value of the 50%-saturation panel characteristics values of the elementary color R calculated at step S 25 , G R50 is the G grayscale value of the 50%-saturation panel characteristics values of the elementary color R and B R50 is the B grayscale value of the 50%-saturation panel characteristics values of the elementary color R. min (a, b, c) is the minimum value of a, b and c.

The R vertex correction values ΔCP_R R , ΔCP_G R and ΔCP_B R thus obtained are stored in advance in the R vertex correction amount register 43 R.

Also, the G vertex correction amounts ΔCP_R G , ΔCP_G G and ΔCP_B G are calculated in accordance with the following expression (29b):

Δ ⁢ ⁢ CP_R G = D IN MAX · ( Δ ⁢ ⁢ R G ⁢ ⁢ 50 - Δ ⁢ ⁢ CP_R W ) min ⁡ ( R G ⁢ ⁢ 50 , G G ⁢ ⁢ 50 , B G ⁢ ⁢ 50 ) + Δ ⁢ ⁢ CP_R W ⁢

⁢ Δ ⁢ ⁢ CP_G G = D IN MAX · ( Δ ⁢ ⁢ G G ⁢ ⁢ 50 - Δ ⁢ ⁢ CP_G W ) min ⁡ ( R G ⁢ ⁢ 50 , G G ⁢ ⁢ 50 , B G ⁢ ⁢ 50 ) + Δ ⁢ ⁢ CP_G W ⁢

⁢ Δ ⁢ ⁢ CP_B G = D IN MAX · ( Δ ⁢ ⁢ B G ⁢ ⁢ 50 - Δ ⁢ ⁢ CP_B W ) min ⁡ ( R G ⁢ ⁢ 50 , G G ⁢ ⁢ 50 , B G ⁢ ⁢ 50 ) + Δ ⁢ ⁢ CP_B W ( 29 ⁢ b )

where ΔR G50 is the correction amount of the R grayscale value for the elementary color G which is calculated for 50% saturation at step S 25 , AG G50 is the correction amount of the G grayscale value for the elementary color G which is calculated for 50% saturation at step S 25 , and AB G50 is the correction amount of the B grayscale value for the elementary color G which is calculated for 50% saturation at step S 25 . R R50 is the R grayscale value of the 50%-saturation panel characteristics values of the elementary color G calculated at step S 25 , G G50 is the G grayscale value of the 50%-saturation panel characteristics values of the elementary color G, and B G50 is the B grayscale value of the 50%-saturation panel characteristics values of the elementary color G.

The G vertex correction values ΔCP_R G , ΔCP_G G and ΔCP_B G thus obtained are stored in advance in the G vertex correction amount register 43 G.

Also, the B vertex correction amounts ΔCP_R B , ΔCP_G B and ΔCP_B B are calculated in accordance with the following expression (29c):

Δ ⁢ ⁢ CP_R B = D IN MAX · ( Δ ⁢ ⁢ R B ⁢ ⁢ 50 - Δ ⁢ ⁢ CP_R W ) min ⁡ ( R B ⁢ ⁢ 50 , G B ⁢ ⁢ 50 , B B ⁢ ⁢ 50 ) + Δ ⁢ ⁢ CP_R W ⁢

⁢ Δ ⁢ ⁢ CP_G B = D IN MAX · ( Δ ⁢ ⁢ G B ⁢ ⁢ 50 - Δ ⁢ ⁢ CP_G W ) min ⁡ ( R B ⁢ ⁢ 50 , G B ⁢ ⁢ 50 , B B ⁢ ⁢ 50 ) + Δ ⁢ ⁢ CP_G W ⁢

⁢ Δ ⁢ ⁢ CP_B B = D IN MAX · ( Δ ⁢ ⁢ B B ⁢ ⁢ 50 - Δ ⁢ ⁢ CP_B W ) min ⁡ ( R B ⁢ ⁢ 50 , G B ⁢ ⁢ 50 , B B ⁢ ⁢ 50 ) + Δ ⁢ ⁢ CP_B W ( 29 ⁢ c )

where ΔR B50 is the correction amount of the R grayscale value for the elementary color B which is calculated for 50% saturation at step S 25 , AG B50 is the correction amount of the G grayscale value for the elementary color B which is calculated for 50% saturation at step S 25 , and AB B50 is the correction amount of the B grayscale value for the elementary color B which is calculated for 50% saturation at step S 25 . R B50 is the R grayscale value of the 50%-saturation panel characteristics values of the elementary color B calculated at step S 25 , G B50 is the G grayscale value of the 50%-saturation panel characteristics values of the elementary color B, and B B50 is the B grayscale value of the 50%-saturation panel characteristics values of the elementary color B.

The B vertex correction values ΔCP_R B , ΔCP_G B and ΔCP_B B thus obtained are stored in advance in the B vertex correction amount register 43 B.

Furthermore, the C vertex correction amounts ΔCP_R C , ΔCP_G C and ΔCP_B C are calculated in accordance with the following expression (29d):

Δ ⁢ ⁢ CP_R C = D IN MAX · ( Δ ⁢ ⁢ R C ⁢ ⁢ 50 - Δ ⁢ ⁢ CP_R W ) min ⁡ ( R C ⁢ ⁢ 50 , G C ⁢ ⁢ 50 , B C ⁢ ⁢ 50 ) + Δ ⁢ ⁢ CP_R W ⁢

⁢ Δ ⁢ ⁢ CP_G C = D IN MAX · ( Δ ⁢ ⁢ G C ⁢ ⁢ 50 - Δ ⁢ ⁢ CP_G W ) min ⁡ ( R C ⁢ ⁢ 50 , G C ⁢ ⁢ 50 , B C ⁢ ⁢ 50 ) + Δ ⁢ ⁢ CP_G W ⁢

⁢ Δ ⁢ ⁢ CP_B C = D IN MAX · ( Δ ⁢ ⁢ B C ⁢ ⁢ 50 - Δ ⁢ ⁢ CP_B W ) min ⁡ ( R C ⁢ ⁢ 50 , G C ⁢ ⁢ 50 , B C ⁢ ⁢ 50 ) + Δ ⁢ ⁢ CP_B W ( 29 ⁢ d )

where ΔR C50 is the correction amount of the R grayscale value for the complementary color C which is calculated for 50% saturation at step S 25 , ΔG C50 is the correction amount of the G grayscale value for the complementary color C which is calculated for 50% saturation at step S 25 , AB C50 is the correction amount of the B grayscale value for the complementary color C which is calculated for 50% saturation at step S 25 . R C50 is the R grayscale value of the 50%-saturation panel characteristics values of the complementary color C calculated at step S 25 , G C50 is the G grayscale value of the 50%-saturation panel characteristics values of the complementary color C, and B C50 is the B grayscale value of the 50%-saturation panel characteristics values of the complementary color C.

The C vertex correction values ΔCP_R C , ΔCP_G C and ΔCP_B C thus obtained are stored in advance in the C vertex correction amount register 47 C.

Furthermore, the M vertex correction amounts ΔCP_R M , ΔCP_G M and ΔCP_B M are calculated in accordance with the following expression (29e):

Δ ⁢ ⁢ CP_R M = D IN MAX · ( Δ ⁢ ⁢ R M ⁢ ⁢ 50 - Δ ⁢ ⁢ CP_R W ) min ⁡ ( R M ⁢ ⁢ 50 , G M ⁢ ⁢ 50 , B M ⁢ ⁢ 50 ) + Δ ⁢ ⁢ CP_R W ⁢

⁢ Δ ⁢ ⁢ CP_G M = D IN MAX · ( Δ ⁢ ⁢ G M ⁢ ⁢ 50 - Δ ⁢ ⁢ CP_G W ) min ⁡ ( R M ⁢ ⁢ 50 , G M ⁢ ⁢ 50 , B M ⁢ ⁢ 50 ) + Δ ⁢ ⁢ CP_G W ⁢

⁢ Δ ⁢ ⁢ CP_B M = D IN MAX · ( Δ ⁢ ⁢ B M ⁢ ⁢ 50 - Δ ⁢ ⁢ CP_B W ) min ⁡ ( R M ⁢ ⁢ 50 , G M ⁢ ⁢ 50 , B M ⁢ ⁢ 50 ) + Δ ⁢ ⁢ CP_B W ( 29 ⁢ e )

where ΔR M50 is the correction amount of the R grayscale value for the complementary color M which is calculated for 50% saturation at step S 25 , ΔG M50 is the correction amount of the G grayscale value for the complementary color M which is calculated for 50% saturation at step S 25 , and ΔB M50 is the correction amount of the B grayscale value for the complementary color M which is calculated for 50% saturation at step S 25 . R M50 is the R grayscale value of the 50%-saturation panel characteristics values of the complementary color M calculated at step S 25 , G M50 is the G grayscale value of the 50%-saturation panel characteristics values of the complementary color M, and B M50 is the B grayscale value of the 50%-saturation panel characteristics values of the complementary color M.

The M vertex correction values ΔCP_R M , ΔCP_G M and ΔCP_B M thus obtained are stored in advance in the M vertex correction amount register 47 M.

Furthermore, the Y vertex correction amounts ΔCP_R Y , ΔCP_G Y and ΔCP_B Y are calculated in accordance with the following expression (29f):

Δ ⁢ ⁢ CP_R Y = D IN MAX · ( Δ ⁢ ⁢ R Y ⁢ ⁢ 50 - Δ ⁢ ⁢ CP_R W ) min ⁡ ( R Y ⁢ ⁢ 50 , G Y ⁢ ⁢ 50 , B Y ⁢ ⁢ 50 ) + Δ ⁢ ⁢ CP_R W ⁢

⁢ Δ ⁢ ⁢ CP_G Y = D IN MAX · ( Δ ⁢ ⁢ G Y ⁢ ⁢ 50 - Δ ⁢ ⁢ CP_G W ) min ⁡ ( R Y ⁢ ⁢ 50 , G Y ⁢ ⁢ 50 , B Y ⁢ ⁢ 50 ) + Δ ⁢ ⁢ CP_G W ⁢

⁢ Δ ⁢ ⁢ CP_B Y = D IN MAX · ( Δ ⁢ ⁢ B Y ⁢ ⁢ 50 - Δ ⁢ ⁢ CP_B W ) min ⁡ ( R Y ⁢ ⁢ 50 , G Y ⁢ ⁢ 50 , B Y ⁢ ⁢ 50 ) + Δ ⁢ ⁢ CP_B W ( 29 ⁢ f )

where ΔR Y50 is the correction amount of the R grayscale value for the complementary color Y which is calculated for 50% saturation at step S 25 , ΔG Y50 is the correction amount of the G grayscale value for the complementary color Y which is calculated for 50% saturation at step S 25 , and AB Y50 is the correction amount of the B grayscale value for the complementary color Y which is calculated for 50% saturation at step S 25 . R Y50 is the R grayscale value of the 50%-saturation panel characteristics values of the complementary color Y calculated at step S 25 , G Y50 is the G grayscale value of the 50%-saturation panel characteristics values of the complementary color Y, and B Y50 is the B grayscale value of the 50%-saturation panel characteristics values of the complementary color Y.

The Y vertex correction values ΔCP_R Y , ΔCP_G Y and ΔCP_B Y thus obtained are stored in advance in the Y vertex correction amount register 47 Y.

Second Embodiment

In a second embodiment, a technique for individually performing color adjustment and brightness adjustment is provided. The technology disclosed in the first embodiment, in which the gamma correction is performed on the basis of the control point data CP 0 _sel to CP 5 _sel determined in accordance with the gamma value γ_VALUE, undesirably causes changes in the input-output characteristics, that is, the gamma characteristics of the respective elementary colors and complementary colors of the liquid crystal display device 1 as a whole from the intrinsic gamma characteristics of the liquid crystal display panel 2 . Presented in the second embodiment is a technology that achieves brightness adjustment through gamma correction while reducing a change in the gamma characteristics of the respective elementary colors and complementary colors from the intrinsic gamma characteristics of the liquid crystal display panel 2 .

FIG. 21 is a block diagram illustrating an exemplary configuration of a driver IC 3 A in the second embodiment. The configuration of the driver IC 3 A in the second embodiment is similar to that of the driver IC 3 in the first embodiment. It should be noted that, the calculation method of the control point data CP 0 _R to CP 5 _R, CP 0 _G to CP 5 _G and CP 0 _B to CP 5 _B are modified in the second embodiment. In connection with this, in the second embodiment, the driver IC 3 A includes a control point data calculation circuit 29 A, the configuration and operation of which are different from those of the control point data calculation circuit 29 used in the first embodiment.

The configuration of the correction amount calculation circuit 28 in the second embodiment is similar to that in the first embodiment. It should be noted however that, in the second embodiment, the correction amount calculation circuit 28 is configured to feed, in addition to the correction amounts ΔCP_R, ΔCP_G and ΔCP_B, the distances d ELM , d CMP , d W , max(D IN R , D IN G , D IN B ) (which is the maximum value of the R, G and B grayscale values of the input image data D IN ), and the selection signals SEL RGB and SEL CMY , which are calculated in the calculation procedure of the correction amounts ΔCP_R, ΔCP_G and ΔCP_B, to the control point data calculation circuit 29 A. As described above, the distance d ELM is the distance between the corresponding point of the input image data D IN and the vertex corresponding to the elementary color with which the belonging area of the corresponding point of the input image data D IN is defined, and the distance d CMP is the distance between the corresponding point of the input image data D IN and the vertex corresponding to the complementary color with which the belonging area of the corresponding point of the input image data D IN is defined. The distance d W is the distance between the white point and the corresponding point of the input image data D IN . The selection signal SEL RGB indicates the selected elementary color vertex, that is, which of the R, G and B vertices defines the belonging area, and the selection signal SEL CMY indicates the selected complementary color vertex, that is, which of the C, M and Y vertices defines the belonging area.

The control point data calculation circuit 29 A calculates the control point data CP 0 _R to CP 5 _R, CP 0 _G to CP 5 _G and CP 0 _B to CP 5 _B on the basis of the gamma value γ_VALUE received from the gamma value setting circuit 27 , and the correction amounts ΔCP_R, ΔCP_G and ΔCP_B, the distances d ELM , d CMP , d W , the maximum value max(D IN R , D IN G , D IN B ) of the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN and the selection signals SEL RGB and SEL CMY , which are received from the correction amount calculation circuit 28 . In the present embodiment, the gamma value γ_VALUE indicates the gamma value of gamma correction to be performed on the brightness of each pixel.

FIG. 22 is a block diagram illustrating an exemplary configuration of the control point data calculation circuit 29 A in the second embodiment. The configuration of the control point data calculation circuit 29 A in the second embodiment is similar to that of the control point data calculation circuit 29 illustrated in FIG. 9 . It should be noted however that the control point data calculation circuit 29 A additionally includes R, G, B, C, M and Y panel characteristics control point data registers 34 R, 34 G, 34 B, 34 C, 34 M and 34 Y and a control point data color interpolation circuit 35 in the second embodiment. In the following, the R, G, B, C, M and Y panel characteristics control point data registers 34 R, 34 G, 34 B, 34 C, 34 M and 34 Y may be collectively referred to as “panel characteristics control point data registers 34 ”, if they are not distinguished from one another.

The R panel characteristics control point data register 34 R stores therein control point data CP 0 _P R to CP 5 _P R corresponding to the intrinsic gamma characteristics of the elementary color R of the liquid crystal display panel 2 . When the gamma value of the intrinsic gamma characteristics of the elementary color R of the liquid crystal display panel 2 is 2.1, for example, the control point data CP 0 _P R to CP 5 _P R are determined to specify the gamma curve with a gamma value of 2.1. The values of the control point data CP 0 _P R to CP 5 _P R can be calculated with the same expressions as those used for calculating CP 0 # j to CP 5 # j of the control point data set CP#j. Namely, the expressions for calculating the control point data CP 0 _P R to CP 5 _P R can be obtained by replacing CP 0 # j to CP 5 # j with CP 0 _P R to CP 5 _P R , respectively, in expressions (2a) and (2b). In this case, the gamma value of the gamma characteristics of the liquid crystal display panel 2 is used as the gamma value γ in expression (4).

Correspondingly, the G panel characteristics control point data register 34 G stores therein control point data CP 0 _P G to CP 5 _P G corresponding to the intrinsic gamma characteristics of the elementary color G of the liquid crystal display panel 2 , and the B panel characteristics control point data register 34 B stores therein control point data CP 0 _P B to CP 5 _P B corresponding to the intrinsic gamma characteristics of the elementary color G of the liquid crystal display panel 2 .

Furthermore, the C panel characteristics control point data register 34 C stores therein control point data CP 0 _P C to CP 5 _P C corresponding to the intrinsic gamma characteristics of the complementary color C of the liquid crystal display panel 2 , and the M panel characteristics control point data register 34 M stores therein control point data CP 0 _P M to CP 5 _P M corresponding to the intrinsic gamma characteristics of the complementary color M of the liquid crystal display panel 2 . Finally, the Y panel characteristics control point data register 34 Y stores therein control point data CP 0 _P Y to CP 5 _P Y corresponding to the intrinsic gamma characteristics of the complementary color Y of the liquid crystal display panel 2 .

Although FIG. 22 illustrates the configuration in which the panel characteristics control point data registers 34 are respectively provided for the respective elementary colors and complementary colors, a common panel characteristics control point data register 34 storing common control point data may be provided for elementary and/or complementary colors with which the gamma values of the intrinsic gamma characteristics of the liquid crystal display panel 2 are the same.

The control point data color interpolation circuit 35 calculates control point data CP 0 _L to CP 5 _L through interpolation of the control point data CP 0 _sel to CP 5 _sel determined by the interpolation/selection circuit 32 , the control point data CP 0 _P ELM to CP 5 _P ELM corresponding to the selected elementary color (the elementary color specified by the selection signal SEL RGB ) and the control point data CP 0 _P CMP to CP 5 _P CMP corresponding to the selected complementary color (the complementary color specified by the selection signal SEL CMP ). The control point data CP 0 _P ELM to CP 5 _P ELM corresponding to the selected elementary color correspond to the intrinsic gamma characteristics of the selected elementary color of the liquid crystal display panel 2 , and are selected from the control point data stored in the R, G and B panel characteristics control point data registers 34 R, 34 G and 34 B in response to the selection signal SEL RGB . On the other hand, the control point data CP 0 _P CMP to CP 5 _P CMP corresponding to the selected complementary color correspond to the intrinsic gamma characteristics of the selected complementary color of the liquid crystal display panel 2 , and are selected from the control point data stored in the C, M and Y panel characteristics control point data registers 34 C, 34 M and 34 Y in response to the selection signal SEL CMY . The distances d ELM , d CMP , d W and the maximum value max(D IN R , D IN G , D IN B ) are used in the interpolation for the calculation of the control point data CP 0 _L to CP 5 _L.

The control point data CP 0 _L to CP 5 _L calculated by the control point data color interpolation circuit 35 are transmitted to the control point data adjustment circuit 33 . In the present embodiment, the control point data adjustment circuit 33 calculates the control point data CP 0 _R to CP 5 _R, CP 0 _G to CP 5 _G and CP 0 _B to CP 5 _B, which are to be transmitted to the approximate gamma correction circuit 22 , through modifying the control data CP 0 _L to CP 5 _L received from the control point data color interpolation circuit 35 in response to the correction amounts ΔCP_R, ΔCP_G and ΔCP_B received from the correction amount calculation circuit 28 .

Next, a description is given of the digital arithmetic processing performed for color adjustment and gamma correction in the second embodiment. FIG. 23 is a flowchart illustrating the digital arithmetic processing performed on the input image data D IN in the second embodiment.

Steps S 01 to S 03 :

The setting of the gamma value γ_VALUE (step S 01 ), the determination of the control point data set CP_sel (control point data CP 0 _sel to CP 5 _sel) based on the gamma value e γ_VALUE (step S 02 ) and the calculation of the correction amounts ΔCP_R, ΔCP_G and ΔCP_B (step S 03 ) are performed in the same way as the first embodiment. It should be noted that the gamma value γ_VALUE are determined to indicate the gamma value of gamma correction to be performed on the brightness of each pixel in the present embodiment. It should be also noted that the distances d ELM , d CMP , d W and the maximum value max(D IN R , D IN G , D IN B ) of the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN are calculated in the calculation of the correction amounts ΔCP_R, ΔCP_G and ΔCP_B.

The control point data CP 0 _L to CP 5 _L are calculated through interpolation of the control point data CP 0 _sel to CP 5 _sel determined by the interpolation/selection circuit 32 , the control point data CP 0 _P ELM to CP 5 _P ELM corresponding to the selected elementary color (the elementary color with which the belonging area is defined, or the elementary color indicated by the selection signal SEL RGB ) and the control point data CP 0 _P CMP to CPS_P CMP corresponding to the selected complementary color (the complementary color with which the belonging area is defined, or the complementary color indicated by the selection signal SEL CMY ). As described above, the control point data CP 0 _L to CP 5 _L are calculated by the control point data color interpolation circuit 35 .

The interpolation performed in the control point data color interpolation circuit 35 aims at individually performing color adjustment and brightness adjustment. In the present embodiment, gamma correction is performed on the brightness of each pixel, keeping the gamma characteristics of the respective colors of the liquid crystal display panel 2 unchanged. In other words, the gamma correction is performed on the basis of the control point data CP 0 _sel to CP 5 _sel determined on the basis of the gamma value γ_VALUE when the input image data D IN correspond to the white point in the color space. When the input image data D IN correspond to the selected elementary color in the color space, on the other hand, the gamma correction is performed on the basis of the control point data corresponding to the intrinsic gamma characteristics of the selected elementary color of the liquid crystal display panel 2 , that is, the control point data CP 0 _P ELM to CP 5 _P ELM . When the selected elementary color is the elementary color R, for example, the control point data CP 0 _P R to CP 5 _P R are selected as the control point data CP 0 _P ELM to CP 5 _P ELM and the gamma correction is performed on the control point data CP 0 _P R to CP 5 _P R . Similarly, when the input image data D IN correspond to the selected complementary color in the color space, the gamma correction is performed on the basis of the control point data corresponding to the intrinsic gamma characteristics of the selected complementary color of the liquid crystal display panel 2 , that is, the control point data CP 0 _P CMP to CP 5 _P CMP When the input image data D IN correspond to a point distant from any of the white point and the vertices corresponding to the elementary colors and complementary colors, the gamma correction is performed on the basis of the control point data CP 0 _L to CP 5 _L, that is, the control point data obtained through interpolation of the control point data CP 0 _sel to CP 5 _sel, CP 0 P ELM to CP 5 _P ELM and CP 0 _P CMP to CP 5 _P CMP depending on the distances d ELM , d CMP and d W .

In order to exclude the components of the brightness, the values obtained by normalization of the distances d ELM , d CMP and d W are used in this interpolation. It should be noted that the distances d ELM , d CMP and d W are calculated so that the sum of the distances d ELM , d CMP and d W is equal to the maximum value max(D IN R , D IN G , D IN B ) of the R, G and B grayscale values D IN R , D IN G and D IN B , as understood from the description of the first embodiment. In this embodiment, the distances d ELM , d CMP and d W are normalized with the maximum value max(D IN R , D IN G , D IN B ).

In one embodiment, the interpolation at step S 34 is performed in accordance with the following expressions (30):

CP0_ L =CP0_ P ELM ·<d ELM >+CP0_ P CMP ·<d CMP >+CP0 sel ·<d W >,

CP1_ L =CP1_ P ELM ·<d ELM >+CP1_ P CMP ·<d CMP >+CP0 sel ·<d W >,

CP2_ L =CP2_ P ELM ·<d ELM >+CP2_ P CMP ·<d CMP >+CP0 sel ·<d W >,

CP3_ L =CP3_ P ELM ·<d ELM >+CP3_ P CMP ·<d CMP >+CP0 sel ·<d W >,

CP4_ L =CP4_ P ELM ·<d ELM >+CP4_ P CMP ·<d CMP >+CP0 sel ·<d W >, and

CP5_ L =CP5_ P ELM ·<d ELM >+CP5_ P CMP ·<d CMP >+CP0 sel ·<d W >.   (30)

Here, <d ELM >, <d CMP > and <d W > are the values obtained by normalizing the distances d ELM , d CMP and d W . In the present embodiment, <d ELM >, <d CMP > and <d W > are calculated in accordance with the following expressions:

< d ELM >=d ELM /max( D IN R ,D IN G ,D IN B ),

< d ELM >=d CMP /max( D IN R ,D IN G ,D IN B ), and

< d W >=d W /max( D IN R ,D IN G ,D IN B ),

The control point data CP 0 _L to CP 5 _L thus calculated are transmitted to the control point data adjustment circuit 33 .

The control point data set CP_R, CP_G and CP_B, which are to be transmitted to the approximate gamma correction circuit 22 , are calculated by the control point data adjustment circuit 33 from the control point data of the control point data set CP_L determined by the control point data color interpolation circuit 35 and the correction amounts ΔCP_R, ΔCP_G and ΔCP_B calculated by the correction amount calculation circuit 28 .

More specifically, the control point data CP 0 _R to CP 5 _R of the control point data set CP_R are calculated by adding the correction amount ΔCP_R to the control point data CP 0 _L to CP 5 _L, respectively.

Namely,

CP0_ R =CP0_ L +ΔCP_ R,

CP1_ R =CP1_ L +ΔCP_ R,

CP2_ R =CP2_ L +ΔCP_ R,

CP3_ R =CP3_ L +ΔCP_ R,

CP4_ R =CP4_ L +ΔCP_ R , and

CP5_ R =CP5_ L +ΔCP_ R,   (31)

Correspondingly, the control point data CP 0 _G to CP 5 _G of the control point data set CP_G are calculated by adding the correction amount ΔCP_G to the control point data CP 0 _L to CP 5 _L, respectively.

Namely,

CP0_ G =CP0_ L +ΔCP_ G,

CP1_ G =CP1_ L +ΔCP_ G,

CP2_ G =CP2_ L +ΔCP_ G,

CP3_ G =CP3_ L +ΔCP_ G,

CP4_ G =CP4_ L +ΔCP_ G , and

CP5_ G =CP5_ L +ΔCP_ G.   (32)

Furthermore, the control point data CP 0 _B to CP 5 _B of the control point data set CP_B are calculated by adding the correction amount ΔCP_B to the control point data CP 0 _L to CP 5 _L, respectively.

Namely,

CP0_ G =CP0_ L +ΔCP_ B,

CP1_ G =CP1_ L +ΔCP_ B,

CP2_ G =CP2_ L +ΔCP_ B,

CP3_ G =CP3_ L +ΔCP_ B,

CP4_ G =CP4_ L +ΔCP_ B , and

CP5_ G =CP5_ L +ΔCP_ B.   (33)

The control point data set CP_R, CP_G and CP_B thus calculated are transmitted to the approximate gamma correction circuit 22 .

Digital arithmetic processing is performed on the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN for each pixel 9 by using the control point data sets CP_R, CP_G and CP_B, and thereby the R, G and B grayscale values D OUT R , D OUT G and D OUT B of the output image data D OUT for each pixel 9 are calculated. The calculation of the R, G and B grayscale values D OUT R , D OUT G and D OUT B of the output image data D OUT in the second embodiment are achieved through the same processing as the first embodiment.

In the following, a description is given of a specific example of calculations of the correction amounts ΔCP_R, ΔCP_G and ΔCP_B and the control point data sets CP_R, CP_G and CP_B. In this example, it is assumed that the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN are each 8-bit data and therefore the allowed maximum value D IN MAX is 255. It is also assumed that the R, G and B grayscale values D OUT R , D OUT G and D OUT B of the output image data D OUT are 10-bit data. The correction amounts for the white point and the vertices corresponding to the respective elementary colors and complementary colors are preset as illustrated in FIG. 24A . It should be noted that the correction amounts are given as 10-bit data in FIG. 24A .

In the example discussed below, the correction amounts ΔCP_R, ΔCP_G, ΔCP_B and the control point data sets CP_R, CP_G and CP_R are calculated for the case when the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN are 100, 40 and 20, respectively. It should be noted that the grayscale value D IN R is the largest among the R, G and B grayscale values D IN R , D IN G and D IN B and the B grayscale value D IN B is the smallest. Accordingly, the belonging area of the corresponding point of the input image data D IN in the color space is the area A 1 which is defined with the white point, the R vertex and the Y vertex (see FIG. 3B ). The selected elementary color vertex is the R vertex and the selected complementary color vertex is the Y vertex.

The differences between the R, G and B grayscale values of the selected elementary color vertex (that is, the R vertex) and the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN are calculated in accordance with expressions (8a) to (8c) as follows:

RGB dist_ R= 255−100=155,

RGB dist_ G= 0−40=−40, and

RGB dist_ B= 0−20=−20.

The differences between the R, G and B grayscale values of the selected complementary color vertex (that is, the Y vertex) and the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN are calculated in accordance with expressions (9a) to (9c) as follows:

CMY dist_ R= 255−100=155,

CMY dist_ G= 255−40=215, and

CMY dist_ B= 0−20=−20.

The distance d ELM between the selected elementary color vertex and the corresponding point of the input image data D IN is calculated in accordance with expression (10) as follows:

d ELM =255−{155−(−40)}=60.

The distance d CMP between the selected complementary color vertex and the corresponding point of the input image data D IN is calculated in accordance with expression (11) as follows:

d CMP =255−{155−(−20)}=20.

The distance d W between the white point and the corresponding point of the input image data D IN is calculated in accordance with expression (12) as follows:

d m =20.

It should be noted that the sum of the distances d ELM , d CMP and d W thus obtained is equal to the R grayscale value D IN R (=100) of the input image data D IN , which is the largest among the R, G and B grayscale values D IN R , D IN G and D IN B of the input image data D IN .

The elementary-color-distance dependent correction amounts ΔCP_R ELM-d , ΔCP_G ELM-d and ΔCP_B ELM-d are calculated in accordance with expressions (13a) to (13c) as follows:

The complementary-color-distance dependent correction amounts ΔCP_R CMP-d , ΔCP_G CMP-d and ΔCP_B CMP-d are calculated in accordance with expressions (14a) to (14c) as follows:

The white-point-distance dependent correction amounts ΔCP_R W-d , ΔCP_G W-d and ΔCP_B W-d are calculated in accordance with expressions (15a) to (15c) as follows:

The correction amounts ΔCP_R, ΔCP_G and ΔCP_B are calculated in accordance with expressions (16a) to (16c) as follows:

Δ ⁢ ⁢ CP_R = ⁢ Δ ⁢ ⁢ CP_R ELM - d + Δ ⁢ ⁢ CP_R CMP - d + Δ ⁢ ⁢ CP_R W - d , = ⁢ { 69 × 60 + 20 × 20 + ( - 50 ) × 20 } / 255 = ⁢ 13 Δ ⁢ ⁢ CP_G = ⁢ Δ ⁢ ⁢ CP_G ELM - d + Δ ⁢ ⁢ CP_G CMP - d + Δ ⁢ ⁢ CP_G W - d , = ⁢ { 0 × 60 + 7 × 20 + ( - 16 ) × 20 } / 255 , = ⁢ - 1 , and Δ ⁢ ⁢ CP_B = ⁢ Δ ⁢ ⁢ CP_B ELM - d + Δ ⁢ ⁢ CP_B CMP - d + Δ ⁢ ⁢ CP_B W - d , = ⁢ ( 28 × 60 + 44 × 20 + 0 × 20 ) / 255 , = ⁢ 10.

It should be noted that the correction amounts ΔCP_R, ΔCP_G and ΔCP_B are 10-bit data obtained by rounding to integers.

Discussed below is the case when the gamma value γ_VALUE of the gamma correction for brightness adjustment is set to 2.2 by the gamma value setting circuit 27 . FIG. 24B is illustrates the relation among the grayscale values of the input image data D IN , the intrinsic panel characteristics of the liquid crystal display panel 2 (panel brightness characteristics) and the desired values of the brightness adjustment (that is, the brightness characteristics to be achieved by the gamma correction). In FIG. 24B , “W 0 ” indicates that all of the R, G and B grayscale values are zero, and “W 64 ” indicates that all of the R, G and B grayscale values are 64. The similar applies to “W 127 ”, “W 128 ”, “W 192 ” and “W 255 ”.

It is further assumed that the gamma values of the intrinsic gamma characteristics of the liquid crystal display panel 2 for the elementary color R and the complementary color Y are both 2.1. When the gamma value of the intrinsic gamma characteristics of the liquid crystal display panel 2 for the elementary color R is 2.1, the control point data CP 0 _P R to CP 5 _P R to be stored in the R panel characteristics control point data register 34 R are obtained from expressions (2b) and (3) by substituting 2.1 for γ into expression (4). Correspondingly, the gamma value of the intrinsic gamma characteristics of the liquid crystal display panel 2 for the complementary color Y is 2.1, the control point data CP 0 _P Y to CP 5 _P Y to be stored in the Y panel characteristics control point data register 34 Y are obtained from expressions (2b) and (3) by substituting 2.1 for γ into expression (4). In this example, the values of the control point data CP 0 _P Y to CP 5 _P Y are equal to the values of the control point data CP 0 _P R to CP 5 _P R , respectively, since the gamma values of the gamma characteristics for the elementary color R and the complementary color Y are the same. FIG. 25A is a table illustrating the values of the control point data CP 0 _P R to CP 5 _P R and the control point data CP 0 _P Y to CP 5 _P Y thus obtained.

The values of the control point data CP 0 _sel to CP 5 _sel, which are determined on the basis of the gamma value γ_VALUE, are obtained from expressions (2b) and (3) by substituting 2.2 for γ into expression (4). FIG. 25B is a table illustrating the values of the control point data CP 0 _sel to CP 5 _sel thus obtained.

The control point data CP 0 _L to CP 5 _L are calculated through interpolation of the control point data CP 0 _P R to CP 5 _P R stored in the R panel characteristics control point data register 34 R, the control point data CP 0 _P Y to CP 5 _P Y stored in the Y panel characteristics control point data register 34 Y, and the control point data CP 0 _sel to CP 5 _sel determined on the basis of the gamma value γ_VALUE. The control point data CP 0 _L to CP 5 _L are calculated in accordance with expression (30) as follows:

CP0_L = ⁢ ( 0 × 60 + 0 × 20 + 0 × 20 ) / 100 , = ⁢ 0 , CP1_L = ⁢ ( 0 × 60 + 0 × 20 + ( - 16 ) × 20 ) / 100 , = ⁢ - 3 , CP2_L = ⁢ ( 508 × 60 + 508 × 20 + 491 × 20 ) / 100 , = ⁢ 505 , CP3_L = ⁢ ( 512 × 60 + 512 × 20 + 496 × 20 ) / 100 , = ⁢ 508 CP4_L = ⁢ ( 508 × 60 + 508 × 20 + 486 × 20 ) / 100 , = ⁢ 504 , and CP5_L = ⁢ ( 1020 × 60 + 1020 × 20 + 1020 × 20 ) / 100 , = ⁢ 1020.

It should be noted that the control point data CP 0 _L to CP 5 _L are calculated as 10-bit data rounded to integers.

The control point data CP 0 _R to CP 5 _R, CP 0 _G to CP 5 _G and CP 0 _B to CP 5 _B, which are finally used for the digital arithmetic processing performed on the input image data D IN , are calculated from the control point data CP 0 _L to CP 5 _L and correction amounts ΔCP_R, ΔCP_G and ΔCP_B thus obtained. FIG. 26 illustrates the finally-obtained values of the control point data CP 0 _R to CP 5 _R, CP 0 _G to CP 5 _G and CP 0 _B to CP 5 _B.

Although specific embodiments of the present invention are described above, it would be apparent to a person skilled in the art that the present invention is not limited to the above-described embodiment; the present invention may be implemented with various modifications. Although embodiments of the liquid crystal display device 1 including the liquid crystal display panel 2 are described above, the digital arithmetic processing performed in the above-described embodiments can be implemented in an image processing device. It should be also noted that the present invention is applicable to panel display devices including different display panels (such as display devices including OLED (organic light emitting diode) display panels).