Method of using a pixel to display an image

1. Field of the Invention

The present invention relates to a method of using pixels to display an image, and more particularly, to a method of using pixels with various brightness to display an image.

2. Description of the Prior Art

Due to the low luminous efficiency of materials for generating blue light in existing AMOLED display panels, the thin film transistor (TFT) driver in the driving circuit has to supply a large driving current to enable the AMOLED display panel providing sufficient blue light. However, this may reduce the lifetime of the materials for generating blue light and increase the power consumption of the AMOLED display, consequently damaging the AMOLED display.

In accordance with one embodiment of the present invention, a method of using a pixel to display an image is disclosed. The pixel comprises a first sub-pixel, a second sub-pixel, a third sub-pixel and a fourth sub-pixel. The third sub-pixel and the fourth sub-pixel are used to display a substantially same color. The method includes providing a first brightness of the first sub-pixel and a first brightness of the second sub-pixel in a first display mode; providing a second brightness of the first sub-pixel and a second brightness of the second sub-pixel in a second display mode; inputting an image signal having a chromaticity coordinate; generating a first comparison relationship according to the first brightness of the first sub-pixel and the second brightness of the first sub-pixel; generating a second comparison relationship according to the first brightness of the second sub-pixel and the second brightness of the second sub-pixel; if the chromaticity coordinate of the image signal is within a chromaticity range capable of being displayed by the first sub-pixel, the second sub-pixel and the third sub-pixel, processing the image signal according to the first comparison relationship, the second comparison relationship and the chromaticity coordinate of the image signal; and displaying the processed image signal in the first display mode. The first display mode is performed by using the first sub-pixel, the second sub-pixel, and the third sub-pixel to display an image. The second display mode is performed by using the first sub-pixel, the second sub-pixel, and the fourth sub-pixel to display the image.

In accordance with another embodiment of the present invention, a method of using a pixel to display an image is disclosed. The pixel comprises a first sub-pixel, a second sub-pixel, a third sub-pixel and a fourth sub-pixel. The third sub-pixel and the fourth sub-pixel are used to display a substantially same color. The method includes providing a first brightness of the first sub-pixel and a first brightness of the second sub-pixel in a first display mode; providing a second brightness of the first sub-pixel and a second brightness of the second sub-pixel in a second display mode; inputting an image signal having a chromaticity coordinate; generating a first comparison relationship according to the first brightness of the first sub-pixel and the second brightness of the first sub-pixel; generating a second comparison relationship according to the first brightness of the second sub-pixel and the second brightness of the second sub-pixel; if the chromaticity coordinate of the image signal is outside a chromaticity range capable of being displayed by the first sub-pixel, the second sub-pixel and the third sub-pixel, processing the image signal according to the first comparison relationship, the second comparison relationship and the chromaticity coordinate of the image signal; and displaying the processed image signal in the second display mode. The first display mode is performed by using the first sub-pixel, the second sub-pixel, and the third sub-pixel to display an image. The second display mode is performed by using the first sub-pixel, the second sub-pixel, and the fourth sub-pixel to display the image.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

FIG. 1A to FIG. 1H are diagrams illustrating various pixel arrangements of a pixel in a display according to an embodiment of the present invention.

FIG. 2 is a flowchart illustrating how to display an image with a pixel according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating how to generate a brightness ratio according to an embodiment of the present invention.

FIG. 1A to FIG. 1H are diagrams illustrating various pixel arrangements of a pixel in a display (i.e., an active matrix organic light emitting diode AMOLED) according to an embodiment of the present invention. The AMOLED display has a plurality of pixels arranged as an array (i*j), and each of the pixels has a first sub-pixel (i.e., a red sub-pixel R), a second sub-pixel (i.e., a green sub-pixel G), a third sub-pixel (i.e. a first blue sub-pixel B 1 ), a fourth sub-pixel (i.e. a second blue sub-pixel B 2 ). The pixel arrangements of the above four color sub-pixels are illustrated as shown in FIG. 1A to FIG. 1H , but are not limited as such. In the present embodiment, the red, green, first blue (light blue), and second blue (dark blue) sub-pixels in each pixel of the AMOLED display can be arranged as a 2 by 2 matrix or a 1 by 4 matrix.

Because the luminous efficiency of the material for generating cyan light is at least four times that of the material for generating blue light, in the present embodiment, each pixel is formed by four sub-pixels. And materials for generating red, green, first blue (light blue), and second blue (dark blue) light are used to form red, green, first blue and second blue sub-pixels of the pixel respectively. Further, only one of the first blue and second blue sub-pixels is used with the red and green sub-pixels to display an image of the pixel in each frame. The dark blue sub-pixel has higher color saturation and the light blue sub-pixel has higher luminous efficiency. If the chromaticity coordinate of an image signal is within a chromaticity range capable of being displayed by the first sub-pixel, the second sub-pixel and the third sub-pixel and within a chromaticity range capable of being displayed by the first sub-pixel, the second sub-pixel and the fourth sub-pixel, the image signal is displayed by using the first sub-pixel, the second sub-pixel, and the third sub-pixel. Accordingly, the luminous efficiency of the AMOLED is improved, and the power consumption of the entire AMOLED display is reduced.

Please refer to FIG. 2 which shows a flowchart of a method of using a pixel to display an image. The method 200 comprises the following steps:

Step S 210 : Provide a first brightness B 1 max1 of the first sub-pixel and a first brightness B 2 max1 of the second sub-pixel in a first display mode and providing a second brightness B 1 max2 of the first sub-pixel and a second brightness B 2 max2 of the second sub-pixel in a second display mode;

Step S 212 : Generate a first comparison relationship according to the first brightness B 1 max1 of the first sub-pixel and the second brightness B 1 max2 of the first sub-pixel and generate a second comparison relationship according to the first brightness B 2 max1 of the second sub-pixel and the second brightness B 2 max2 of the second sub-pixel;

Step S 213 : Determine whether the chromaticity coordinate of the image signal is within a chromaticity range capable of being displayed by the first sub-pixel, the second sub-pixel and the third sub-pixel, if yes, perform Step S 214 , if not, perform Step S 218 ;

Step S 214 : Process the image signal according to the first comparison relationship, the second comparison relationship and the chromaticity coordinate of the image signal, if the first brightness B 1 max1 of the first sub-pixel is greater than/equal to the second brightness B 1 max2 of the first sub-pixel and the first brightness B 2 max1 of the second sub-pixel is greater than/equal to the second brightness B 2 max2 of the second sub-pixel, transmit the image signal without transforming the image signal and perform step S 223 , if the first brightness B 1 max1 of the first sub-pixel is smaller than the second brightness B 1 max2 of the first sub-pixel and the first brightness B 2 max1 of the second sub-pixel is greater than/equal to the second brightness B 2 max2 of the second sub-pixel, perform step S 215 , if the first brightness B 1 max1 of the first sub-pixel is greater than/equal to the second brightness B 1 max2 of the first sub-pixel and the first brightness B 2 max1 of the second sub-pixel is smaller than the second brightness B 2 max2 of the second sub-pixel, perform step S 216 , if the first brightness B 1 max1 of the first sub-pixel is smaller than the second brightness B 1 max2 of the first sub-pixel and the first brightness B 2 max1 of the second sub-pixel is smaller than the second brightness B 2 max2 of the second sub-pixel, perform step S 217 ;

Step S 215 : Transform the image signal according to a first brightness ratio β 1 , and perform step S 223 , in which the first brightness ratio β 1 is the ratio of the first brightness B 1 max1 of the first sub-pixel and the second brightness B 1 max2 of the first sub-pixel;

Step S 216 : Transform the image signal according to a second brightness ratio β 2 , and perform step S 223 , in which the second brightness ratio β 2 is the ratio of the first brightness B 2 max1 of the second sub-pixel and the second brightness B 2 max2 of the second sub-pixel;

Step S 217 : Transform the image signal according to a first brightness ratio β 1 and a second brightness ratio β 2 , and perform step S 223 , in which the first brightness ratio β 1 is the ratio of the first brightness B 1 max1 of the first sub-pixel and the second brightness B 1 max2 of the first sub-pixel and the second brightness ratio β 2 is the ratio of the first brightness B 2 max1 of the second sub-pixel and the second brightness B 2 max2 of the second sub-pixel;

Step S 218 : Process the image signal according to the first comparison relationship, the second comparison relationship and the chromaticity coordinate of the image signal, if the first brightness B 1 max1 of the first sub-pixel is smaller than the second brightness B 1 max2 of the first sub-pixel and the first brightness B 2 max1 of the second sub-pixel is smaller than the second brightness B 2 max2 of the second sub-pixel, transmit the image signal without transforming the image signal, and perform step S 224 , if the first brightness B 1 max1 of the first sub-pixel is greater than/equal to the second brightness B 1 max2 of the first sub-pixel and the first brightness B 2 max1 of the second sub-pixel is smaller than the second brightness B 2 max2 of the second sub-pixel, perform step S 219 , if the first brightness B 1 max1 of the first sub-pixel is smaller than the second brightness B 1 max2 of the first sub-pixel and the first brightness B 2 max1 of the second sub-pixel is greater than/equal to the second brightness B 2 max2 of the second sub-pixel, perform step S 220 , if the first brightness B 1 max1 of the first sub-pixel is greater than/equal to the second brightness B 1 max2 of the first sub-pixel and the first brightness B 2 max1 of the second sub-pixel is greater than/equal to the second brightness B 2 max2 of the second sub-pixel, perform step S 221 ;

Step S 219 : Transform the image signal according to a third brightness ratio β 3 , and perform step S 224 , in which the third brightness ratio β 3 is the ratio of the second brightness B 1 max2 of the first sub-pixel and the first brightness B 1 max1 of the first sub-pixel;

Step S 220 : Transform the image signal according to a fourth brightness ratio β 4 , and perform step S 224 , in which the fourth brightness ratio β 4 is the ratio of the second brightness B 2 max2 of the second sub-pixel and the first brightness B 2 max1 of the second sub-pixel;

Step S 221 : Transform the image signal according to a third brightness ratio β 3 and a fourth brightness ratio β 4 , and perform step S 224 , in which the third brightness ratio β 3 is the ratio of the second brightness B 1 max2 of the first sub-pixel and the first brightness B 1 max1 of the first sub-pixel and the fourth brightness ratio β 4 is the ratio of the second brightness B 2 max2 of the second sub-pixel and the first brightness B 2 max1 of the second sub-pixel;

Step S 223 : Display an image with the first sub-pixel, the second sub-pixel, and the third sub-pixel according to the image signal or the transformed image signal.

Step S 224 : Display an image with the first sub-pixel, the second sub-pixel, and the fourth sub-pixel according to the image signal or the transformed image signal.

In step S 210 , the first sub-pixel (i.e., a red sub-pixel R), the second sub-pixel (i.e., a green sub-pixel G) and the third sub-pixel (i.e., a first blue sub-pixel B 1 ) are used to generate a first white image, i.e. displaying the white image in a first display mode. When the first white image is generated, measure the first brightness B 1 max1 of the red sub-pixel and the first brightness B 2 max1 of the green sub-pixel. Then the first sub-pixel (i.e., a red sub-pixel R), the second sub-pixel (i.e., a green sub-pixel G) and the fourth sub-pixel (i.e., a second blue sub-pixel B 2 ) are used to generate a second white image, i.e. displaying the white image in the second display mode. The second white image has the same chromaticity coordinate as the first white image. When the second white image is generated, measure the second brightness B 1 max2 of the red sub-pixel and the second brightness B 2 max2 of the green sub-pixel. In step S 212 , the first brightness B 1 max1 of the red sub-pixel is compared with the second brightness B 1 max2 of the red sub-pixel to generate the first comparison relationship. The first brightness B 2 max1 of the green sub-pixel is compared with the second brightness B 2 max2 of the green sub-pixel to generate the second comparison relationship. Step S 213 is used to determine if step S 214 or step S 218 should be performed according to whether the chromaticity coordinate of the image signal is within a chromaticity range capable of being displayed by the first sub-pixel, the second sub-pixel and the third sub-pixel or not.

In step S 214 , the image signal is processed according to the first comparison relationship, the second comparison relationship and the chromaticity coordinate of the image signal. The processing scheme of the image signal may be simply transmitting the image signal or transforming the image signal. If B 1 max1 ≧B 1 max2 , B 2 max1 ≧B 2 max2 , and the chromaticity coordinate of the image signal is within a chromaticity range capable of being displayed by the red, green and first blue sub-pixels, the image signal is transmitted without transforming the image signal and then the step S 223 is performed to display an image with the red, green and first blue sub-pixels according to the image signal. For example, when using the red sub-pixel R, the green sub-pixel G and the first blue sub-pixel B 1 to generate the first white image, the measured B 1 max1 is 1398 lumen, B 1 max2 is 3055 lumen, and the chromaticity coordinate of the first white image is (0.28, 0.33) in CIE 1931 color space. When using the red sub-pixel R, the green sub-pixel G and the second blue sub-pixel B 2 to generate the second white image having the same chromaticity coordinate as the first white image (0.28, 0.33) in CIE 1931 color space, the measured B 2 max1 is 1191 lumen and B 2 max2 is 1989 lumen. If the chromaticity coordinate of the image signal (i.e. R=255 G=200 B=220) is within a chromaticity range capable of being displayed by the red, green and first blue sub-pixels, the image is displayed by the red, green and first blue sub-pixels according to the image signal (R=255 G=200 B=220) without transforming the image signal because B 1 max1 ≧B 1 max2 and B 2 max1 ≧B 2 max2 .

In step S 214 , if B 1 max1 <B 1 max2 , B 2 max1 ≧B 2 max2 and the chromaticity coordinate of the image signal is within a chromaticity range capable of being displayed by the red, green and first blue sub-pixels, the step S 215 is performed to transform the image signal according to the first brightness ratio β 1 , and then the step S 223 is performed to display an image with the red, green and first blue sub-pixels according to the transformed image signal. If B 1 max1 ≧B 1 max2 and B 2 max1 <B 2 max2 and the chromaticity coordinate of the image signal is within a chromaticity range capable of being displayed by the red, green and first blue sub-pixels, the step S 216 is performed to transform the image signal according to the second brightness ratio β 2 , and then the step S 223 is performed to display an image with the red, green and first blue sub-pixels according to the transformed image signal. If B 1 max1 <B 1 max2 , B 2 max1 <B 2 max2 and the chromaticity coordinate of the image signal is within a chromaticity range capable of being displayed by the red, green and first blue sub-pixels, the step S 217 is performed to transform the image signal according to the first brightness ratio β 1 and the second brightness ratio β 2 , and then the step S 223 is performed to display an image with the red, green and first blue sub-pixels according to the transformed image signal.

In step S 215 , if B 1 max1 <B 1 max2 , B 2 max1 ≧B 2 max2 and the chromaticity coordinate of the image signal is within a chromaticity range capable of being displayed by the red, green and first blue sub-pixels, a red brightness ratio β 1 is generated according to B 1 max1 and B 1 max2 , the image signal is transformed according to β 1 , and an image is displayed according to the transformed image signal by using the red, green, and first blue sub-pixels. β 1 is generated according to the following equation 1:

In equation 1, x 11 is a grayscale of the red sub-pixel when the red, green and first blue sub-pixels are used to generate a first predetermined brightness Bx. x 12 is a grayscale of the red sub-pixel when the red, green and the second blue sub-pixels are used to generate the first predetermined brightness Bx. B 1 max1 is the first brightness of the red sub-pixel, B 1 max2 is the second brightness of the red sub-pixel and γ 1 is a gamma value of the red sub-pixel (i.e., γ 1 =2.2). Please refer to FIG. 3 , which is a diagram illustrating how to generate the red brightness ratio β 1 according to an embodiment of the present invention. The relationship between B 1 max1 , B 1 max2 and β 1 is derived as follow:

In equation 2, N is the maximum grayscale of the image signal (i.e., N is 255). For example, when using the red sub-pixel R, the green sub-pixel G and the first blue sub-pixel B 1 to generate the first white image having a chromaticity coordinate (0.28, 0.33) in CIE 1931 color space, the measured first brightness of the red sub-pixel B 1 max1 is 1191 lumen, and the measured first brightness of the green sub-pixel B 2 max1 is 3055 lumen. When using the red sub-pixel R, the green sub-pixel G and the second blue sub-pixel B 2 to generate the second white image having the same chromaticity coordinate as the first white image, the measured second brightness of the red sub-pixel B 1 max2 is 1398 lumen, and the measured second brightness of the green sub-pixel B 2 max2 is 1989 lumen. If the chromaticity coordinate of the image signal (i.e. R=255 G=200 B=220) is within a chromaticity range capable of being displayed by the red sub-pixel, the green sub-pixel and the first blue sub-pixel, the red brightness ratio β 1 is generated according to B 1 max1 and B 1 max2 because B 1 max1 <B 1 max2 and B 2 max1 ≧B 2 max2 , the red signal of the image signal is transformed according to the red brightness ratio β 1 , and the image is displayed according to the transformed image signal (R′, G′, B′) by using the red sub-pixel, the green sub-pixel, and the first blue sub-pixel. In this example, β 1 is:

The transformed image signal (R′, G′, B′) is calculated as follows:

R′= 255×β 1 =255×0.929=236

G′=G= 200

B′=B= 220

In step S 216 , if B 1 max1 ≧B 1 max2 , B 2 max1 <B 2 max2 and the chromaticity coordinate of the image signal is within a chromaticity range capable of being displayed by the red, green and first blue sub-pixels, a green brightness ratio β 2 is generated according to B 2 max1 and B 2 max2 , the image signal is transformed according to β 2 , and then the image is displayed according to the transformed image signal by using the red, green, and first blue sub-pixels. β 2 is generated according to the following equation 3:

In equation 3, x 21 is a grayscale of the green sub-pixel when the red, green and first blue sub-pixels are used to generate a second predetermined brightness Bx. x 22 is a grayscale of the green sub-pixel when the red, green and second blue sub-pixels are used to generate the second predetermined brightness Bx. B 2 max1 is the first brightness of the green sub-pixel, B 2 max2 is the second brightness of the green sub-pixel and γ 2 is a gamma value of the green sub-pixel (i.e., γ 2 =2.2). The derivation of equation 3 is similar to equation 1. In the present embodiment, when using the red sub-pixel R, the green sub-pixel G and the first blue sub-pixel B 1 to generate the first white image having a chromaticity coordinate (0.28, 0.33) in CIE 1931 color space, the measured first brightness of the red sub-pixel B 1 max1 is 1398 lumen and the measured first brightness of the green sub-pixel B 2 max1 is 1989 lumen. When using the red sub-pixel R, the green sub-pixel G and the second blue sub-pixel B 2 to generate the second white image having the same chromaticity coordinate as the first white image, the measured second brightness of the red sub-pixel B 1 max2 is 1191 lumen, and the measured second brightness of the green sub-pixel B 2 max2 is 3055 lumen. If the chromaticity coordinate of the image signal (i.e. R=255 G=200 B=220) is within a chromaticity range capable of being displayed by the red sub-pixel, the green sub-pixel and the first blue sub-pixel, the green brightness ratio β 2 is generated according to B 2 max1 and B 2 max2 because B 1 max1 ≧B 1 max2 and B 2 max1 <B 2 max2 , the green signal of the image signal is transformed according to the green brightness ratio β 2 , and the image is displayed according to the transformed image signal (R′, G′, B′) by using the red sub-pixel, the green sub-pixel, and the first blue sub-pixel. In this example, β 2 is:

The transformed image signal (R′, G′, B′) is calculated as follows:

R′=R= 255

G′= 200×β 2 =200×0.822=164

B′=B= 220

In step S 217 , if B 1 max1 <B 1 max2 , B 2 max1 <B 2 max2 and the chromaticity coordinate of the image signal is within a chromaticity range capable of being displayed by the red, green and first blue sub-pixels, a red brightness ratio β 1 is generated according to the B 1 max1 and B 1 max2 , a green brightness ratio β 2 is generated according to the B 2 max1 and B 2 max2 , the image signal is transformed according to β 1 and β 2 , and then the image is displayed according to the transformed image signal by using the red, green, and first blue sub-pixels. β 1 and β 2 are generated according to the following equations respectively:

For example, when using the red sub-pixel R, the green sub-pixel G and the first blue sub-pixel B 1 to generate the first white image having a chromaticity coordinate (0.28, 0.33) in CIE 1931 color space, the measured first brightness of the red sub-pixel B 1 max1 is 1191 lumen, and the measured first brightness of the green sub-pixel B 2 max1 is 1989 lumen. When using the red sub-pixel R, the green sub-pixel G and the second blue sub-pixel B 2 to generate the second white image having the same chromaticity coordinate as the first white image, the measured second brightness of the red sub-pixel B 1 max2 is 1398 lumen and the measured second brightness of the green sub-pixel B 2 max2 is 3055 lumen. If the chromaticity coordinate of the image signal (i.e. R=255 G=200 B=220) is within a chromaticity range capable of being displayed by the red sub-pixel, the green sub-pixel and the first blue sub-pixel, the red brightness ratio β 1 is generated according to B 1 max1 and B 1 max2 , the green brightness ratio β 2 is generated according to the B 2 max1 and B 2 max2 because B 1 max1 <B 1 max2 and B 2 max1 <B 2 max2 , the red signal of the image signal is transformed according to the red brightness ratio β 1 and the green signal of the image signal is transformed according to the green brightness ratio β 2 . Then the image is displayed according to the transformed image signal (R′, G′, B′) by using the red sub-pixel, the green sub-pixel, and the first blue sub-pixel. In this example, β 1 is:

In this example, β 2 is:

The transformed image signal (R′, G′, B′) is calculated as follows:

R′= 255×β 1 =255×0.929=236

G′= 200×β 2 =200×0.822=164

B′=B= 220

In step S 218 , the image signal is processed according to the first comparison relationship, the second comparison relationship and the chromaticity coordinate of the image signal. The processing scheme of the image signal may be simply transmitting the image signal or transforming the image signal. If B 1 max1 <B 1 max2 , B 2 max1 <B 2 max2 , and the chromaticity coordinate of the image signal is outside a chromaticity range capable of being displayed by the red, green and first blue sub-pixels, the image signal is transmitted without transforming the image signal and the step S 224 is performed to display an image with the red, green and second blue sub-pixels according to the image signal. For example, when using the red sub-pixel R, the green sub-pixel G and the first blue sub-pixel B 1 to generate the first white image, the measured B 1 max1 is 1191 lumen, B 1 max2 is 1398 lumen, and the chromaticity coordinate of the first white image is (0.28, 0.33) in CIE 1931 color space. When using the red sub-pixel R, the green sub-pixel G and the second blue sub-pixel B 2 to generate the second white image having the same chromaticity coordinate as the first white image (0.28, 0.33) in CIE 1931 color space, the measured B 2 max1 is 1989 lumen and B 2 max2 is 3055 lumen. If the chromaticity coordinate of the image signal (i.e. R=255 G=200 B=220) is outside a chromaticity range capable of being displayed by the red, green and first blue sub-pixels, the step S 224 is performed to display the image according to the image signal with the red, green and second blue sub-pixels without transforming the image signal because B 1 max1 <B 1 max2 and B 2 max1 <B 2 max2 .

In step S 218 , if B 1 max1 ≧B 1 max2 , B 2 max1 <B 2 max2 and the chromaticity coordinate of the image signal is outside a chromaticity range capable of being displayed by the red, green and first blue sub-pixels, the step S 219 is performed to transform the image signal according to the third brightness ratio β 3 , and the step S 224 is performed to display an image with the red, green and second blue sub-pixels according to the transformed image signal. If B 1 max1 <B 1 max2 and B 2 max1 ≧B 2 max2 and the chromaticity coordinate of the image signal is outside a chromaticity range capable of being displayed by the red, green and first blue sub-pixels, the step S 220 is performed to transform the image signal according to the fourth brightness ratio β 4 , and the step S 224 is performed to display an image with the red, green and second blue sub-pixels according to the transformed image signal. If B 1 max1 ≧B 1 max2 , B 2 max1 ≧B 2 max2 and the chromaticity coordinate of the image signal is outside a chromaticity range capable of being displayed by the red, green and first blue sub-pixels, the step S 221 is performed to transform the image signal according to the third brightness ratio β 3 and the fourth brightness ratio β 4 , and the step S 224 is performed to display an image with the red, green and second blue sub-pixels according to the transformed image signal.

In step S 219 , if B 1 max1 ≧B 1 max2 , B 2 max1 <B 2 max2 and the chromaticity coordinate of the image signal is outside a chromaticity range capable of being displayed by the red, green and first blue sub-pixels, a red brightness ratio β 3 is generated according to B 1 max1 and B 1 max2 , the image signal is transformed according to β 3 , and the image is displayed according to the transformed image signal by using the red, green, and second blue sub-pixels. β 3 is generated according to the following equation 4:

In equation 4, x 11 is a grayscale of the red sub-pixel when the red, green and first blue sub-pixels are used to generate a first predetermined brightness Bx. x 12 is a grayscale of the red sub-pixel when the red, green and the second blue sub-pixels are used to generate the first predetermined brightness Bx. B 1 max1 is the first brightness of the red sub-pixel, B 1 max2 is the second brightness of the red sub-pixel and γ 1 is a gamma value of the red sub-pixel (i.e., γ 1 =2.2). For example, when using the red sub-pixel R, the green sub-pixel G and the first blue sub-pixel B 1 to generate the first white image having a chromaticity coordinate (0.28, 0.33) in CIE 1931 color space, the measured first brightness of the red sub-pixel B 1 max1 is 1398 lumen, and the measured first brightness of the green sub-pixel B 2 max1 is 1989 lumen. When using the red sub-pixel R, the green sub-pixel G and the second blue sub-pixel B 2 to generate the second white image having the same chromaticity coordinate as the first white image, the measured second brightness of the red sub-pixel B 1 max2 is 1191 lumen, and the measured second brightness of the green sub-pixel B 2 max2 is 3055 lumen. If the chromaticity coordinate of the image signal (i.e. R=5 G=10 B=240) is outside a chromaticity range capable of being displayed by the red sub-pixel, the green sub-pixel and the first blue sub-pixel, the red brightness ratio β 3 is generated according to B 1 max1 and B 1 max2 because B 1 max1 ≧B 1 max2 and B 2 max1 <B 2 max2 , the red signal of the image signal is transformed according to the red brightness ratio β 3 , and the image is displayed according to the transformed image signal (R′, G′, B′) by using the red sub-pixel, the green sub-pixel, and the second blue sub-pixel. In this example, β 3 is:

The transformed image signal (R′, G′, B′) is calculated as follows:

R′= 5×β 1 =5×0.929=4

G′=G= 10

B′=B= 240

In step S 220 , if B 1 max1 <B 1 max2 , B 2 max1 ≧B 2 max2 and the chromaticity coordinate of the image signal is outside a chromaticity range capable of being displayed by the red, green and first blue sub-pixels, a green brightness ratio β 4 is generated according to B 2 max1 and B 2 max2 , the image signal is transformed according to β 4 , and then the image is displayed according to the transformed image signal by using the red, green, and second blue sub-pixels. β 4 is generated according to the following equation 5:

In equation 5, x 21 is a grayscale of the green sub-pixel when the red, green and first blue sub-pixels are used to generate a second predetermined brightness Bx. x 22 is a grayscale of the green sub-pixel when the red, green and second blue sub-pixels are used to generate the second predetermined brightness Bx. B 2 max1 is the first brightness of the green sub-pixel, B 2 max2 is the second brightness of the green sub-pixel and γ 2 is a gamma value of the green sub-pixel (i.e., γ 2 =2.2). When using the red sub-pixel R, the green sub-pixel G and the first blue sub-pixel B 1 to generate the first white image having a chromaticity coordinate (0.28, 0.33) in CIE 1931 color space, the measured first brightness of the red sub-pixel B 1 max1 is 1989 lumen and the measured first brightness of the green sub-pixel B 2 max1 is 1398 lumen. When using the red sub-pixel R, the green sub-pixel G and the second blue sub-pixel B 2 to generate the second white image having the same chromaticity coordinate as the first white image, the measured second brightness of the red sub-pixel B 1 max2 is 3055 lumen, and the measured second brightness of the green sub-pixel B 2 max2 is 1191 lumen. If the chromaticity coordinate of the image signal (i.e. R=5 G=10 B=240) is outside a chromaticity range capable of being displayed by the red sub-pixel, the green sub-pixel and the first blue sub-pixel, the green brightness ratio β 4 is generated according to B 2 max1 and B 2 max2 because B 1 max1 <B 1 max2 and B 2 max1 ≧B max2 , the green signal of the image signal is transformed according to the green brightness ratio β 4 , and the image is displayed according to the transformed image signal (R′, G′, B′) with the red sub-pixel, the green sub-pixel, and the second blue sub-pixel. In this example, β 4 is:

The transformed image signal (R′, G′, B′) is calculated as follows:

R′=R= 5

G′= 10×β 2 =200×0.822=8

B′=B= 240

In step S 221 , if B 1 max1 ≧B 1 max2 , B 2 max1 ≧B 2 max2 and the chromaticity coordinate of the image signal is outside a chromaticity range capable of being displayed by the red, green and first blue sub-pixels, a red brightness ratio β 3 is generated according to the B 1 max1 and B 1 max2 , a green brightness ratio β 4 is generated according to the B 2 max1 and B 2 max2 , the image signal is transformed according to β 3 and β 4 , and then the image is displayed according to the transformed image signal by using the red, green, and second blue sub-pixels.

For example, when using the red sub-pixel R, the green sub-pixel G and the first blue sub-pixel B 1 to generate the first white image having a chromaticity coordinate (0.28, 0.33) in CIE 1931 color space, the measured first brightness of the red sub-pixel B 1 max1 is 1398 lumen, and the measured first brightness of the green sub-pixel B 2 max1 is 3055 lumen. When using the red sub-pixel R, the green sub-pixel G and the second blue sub-pixel B 2 to generate the second white image having the same chromaticity coordinate as the first white image, the measured second brightness of the red sub-pixel B 1 max2 is 1191 lumen and the measured second brightness of the green sub-pixel B 2 max2 is 1989 lumen. If the chromaticity coordinate of the image signal (i.e. R=5 G=10 B=240) is outside a chromaticity range capable of being displayed by the red sub-pixel, the green sub-pixel and the first blue sub-pixel, the red brightness ratio β 3 is generated according to B 1 max1 and B 1 max2 , the green brightness ratio β 4 is generated according to B 2 max1 and B 2 max2 because B 1 max1 ≧B 1 max2 and B 2 max1 ≧B 2 max2 , the red signal of the image signal is transformed according to the red brightness ratio β 3 and the green signal of the image signal is transformed according to the green brightness ratio β 4 . Then the image is displayed according to the transformed image signal (R′, G′, B′) with the red sub-pixel, the green sub-pixel, and the second blue sub-pixel. In this example, β 3 is:

In this example, β 4 is:

The transformed image signal (R′, G′, B′) is calculated as follows:

R′= 5×β 1 =5×0.929=4

G′= 10×β 2 =10×0.822=8

B′=B= 240

In the present invention, only one of the light blue and dark blue sub-pixels of a pixel is used to generate image data with the red sub-pixel and the green sub-pixel. The dark blue sub-pixel has higher color saturation and the light blue sub-pixel has higher luminous efficiency. If the chromaticity coordinate of the image signal is both within a chromaticity range capable of being displayed by the first sub-pixel, the second sub-pixel and the third sub-pixel and within a chromaticity range capable of being displayed by the first sub-pixel, the second sub-pixel and the fourth sub-pixel, the processed image data is displayed by using the first sub-pixel, the second sub-pixel, and the third sub-pixel. Accordingly, the luminous efficiency of the AMOLED is improved, and the power consumption of the AMOLED display is reduced.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.