Projection type display apparatus

This invention relates to a projection type display apparatus normally called liquid crystal projector in which a liquid crystal light valve is used.

A projection type display apparatus in which a liquid crystal light valve is used is conventionally configured in such a manner as shown in FIG. 11 .

Referring to FIG. 11, the projection type display apparatus 90 shown includes an illumination unit (illumination optical system) 10 wherein part of non-polarized white light from a white light source 11 directly passes, but the remaining part of the non-polarized white light is first reflected by a reflector 12 and then passes, through a pair of multi-lens arrays 13 and 14 disposed in an opposing relationship to each other so that they are converted into a light flux which has an intensity distribution uniform within a fixed region on a plane perpendicular to the center axis of the light flux. Further, the light flux is converted from non-polarized light into linearly polarized light by a polarizing conversion element 15 and goes out from the illumination unit 10 through a condenser lens 16 .

The light flux going out from the illumination unit 10 is decomposed into red color light 3 R, green and blue color light 3 GB by a dichroic mirror 21 , and the red color light 3 R is reflected by a mirror 22 and introduced into a liquid crystal light valve 30 R for red through a condenser lens 28 R.

Meanwhile, the green and blue color light 3 GB is decomposed into green color light 3 G and blue color light 3 B by a dichroic mirror 23 , and the green color light 3 G is introduced into a liquid crystal light valve 30 G for green through a condenser lens 28 G while the blue color light 3 B is introduced into a liquid crystal light valve 30 B for blue through a relay lens 24 , a mirror 25 , another relay lens 26 , another mirror 27 and a condenser lens 28 B.

The liquid crystal light valves 30 R, 30 G and 30 B are each formed from a liquid crystal panel of the transmission type, and images are written into the liquid crystal light valves 30 R, 30 G and 30 B with red, green and blue color signals, respectively.

The decomposed color lights 3 R, 3 G and 3 B of red, green and blue are modulated and converted into image lights 4 R, 4 G and 4 B of red, green and blue by the liquid crystal light valves 30 R, 30 G and 30 B, respectively. The image lights 4 R, 4 G and 4 B of red, green and blue are synthesized by a dichroic prism 40 , and the image light 5 after the synthesis is projected in an enlarged scale on a screen 110 by a projection lens 50 .

While FIG. 11 shows a display apparatus of the front projection type wherein the optical units from the illumination unit 10 to the projection lens 50 form the projection type display apparatus 90 separately from the screen 110 , also optical units of a display apparatus of the back projection type wherein the optical units from the illumination unit to the projection lens and the screen are disposed in a cabinet are formed similarly as in the projection type display apparatus 90 of FIG. 11 .

With the conventional projection type display apparatus described above, however, the contrast on the screen cannot be raised higher than a certain fixed value from a view angle of a liquid crystal panel which composes each of the liquid crystal light valves as described below.

FIG. 12 illustrates a manner wherein a light flux from the illumination unit 10 in the projection type display apparatus 90 of FIG. 11 is introduced into a liquid crystal light valve 30 in principle with the decomposition optical system omitted. Here, the liquid crystal light valve 30 is the liquid crystal light valve 30 R, 30 G or 30 B for red, green or blue.

It is to be noted, however, that, while, in the projection type display apparatus 90 of FIG. 11, the lengths of the optical paths from the illumination unit 10 to the liquid crystal light valves 30 R, 30 G and 30 B are set such that the optical paths for the red color light 3 R and the green color light 3 G are equal to each other but the optical path for the blue color light 3 B is longer than those for the red color light 3 R and the green color light 3 G so that the length is unequal with regard to the blue color, it is assumed that, in FIG. 12, the optical path lengths from the illumination unit 10 to the liquid crystal light valve 30 are equal for the red, green and blue color lights for the convenience of description.

Usually, the size of the light exit of the illumination unit 10 is relatively greater than the aperture size of the liquid crystal light valve 30 . Therefore, light emitted from the illumination unit 10 is introduced into the liquid crystal light valve 30 while being condensed, and as viewed from the liquid crystal light valve 30 , the light is introduced from every direction within a certain angular range with respect to the direction of a normal 32 to the liquid crystal light valve 30 .

However, since TN (Twisted Nematic) liquid crystal of the twisted light mode wherein the major axis of a liquid crystal molecule is twisted by 90° between the top and the bottom of the liquid crystal layer is used for a liquid crystal panel which composes the liquid crystal light valve 30 , the light shutter characteristic differs depending upon the view angle.

As regards the view angle, as shown in FIG. 13, the angle φ of outgoing light 33 b from the liquid crystal panel 31 originating from incoming light 33 a to the liquid crystal panel 31 with respect to a reference azimuth on an outgoing face 34 of the liquid crystal panel 31 is defined as an azimuth angle, and an angle θ of the outgoing light 33 b with respect to the normal 32 to the liquid crystal panel 31 is defined as a polar angle. As viewed on the display screen on the outgoing face 34 , φ=0° corresponds to the rightward direction; φ=90° corresponds to the upward direction; φ=180° corresponds to the leftward direction; and φ=270° corresponds to the downward direction.

FIG. 14 illustrates a result of measurement of the view angle dependency of the light cutoff rate which was performed while a certain liquid crystal panel was placed in an all-black state. The center of concentric circles corresponds to θ=0; the circle denoted by numeral 5 corresponds to θ=5°; the circle denoted by numeral 10 corresponds to θ=10°; and the circle denoted by numeral 15 corresponds to θ=15°.

The region indicated as “99% ˜” is a view angle range within which light less then 1% is transmitted; the region indicated as “90% ˜” is a view angle range within which light less than 10% is transmitted; the region indicated as “80% ˜” and surrounded by a thick line is a view angle range within which light less than 20% is transmitted; and the region indicated as “70% ˜” and surrounded by a broken line is a view angle range within which light less than 30% is transmitted.

Accordingly, with the liquid crystal panel shown, a sufficient light shutter function is exhibited and a high contrast is exhibited for any light flux 37 which penetrates the liquid crystal panel upwardly from below when the liquid crystal panel is viewed downwardly from above as indicated by an arrow mark 35 of FIG. 12 as viewed from the outgoing face 34 side shown in FIG. 13 . However, the light shutter function is inferior and the contrast is low for any light flux 38 which penetrates the liquid crystal panel downwardly from above when the liquid crystal panel is viewed upwardly from below as indicated by an arrow mark 36 of FIG. 12 .

Since the contrast on the screen is given by an arithmetic mean of contrasts of light fluxes introduced into the liquid crystal light valve 30 , with the conventional projection type display apparatus described above, the contrast on the screen cannot be raised higher than a certain fixed value.

In order to solve the problem just described, it is disclosed to use an optical film having an optical anisotropy in Japanese Patent Laid-Open No. 222213. However, the optical film having an optical anisotropy is disadvantageous in that it is complicated in a method of production and is expensive and that the optical anisotropy changes if it is illuminated with intense light.

It is an object of the present invention to provide a projection type display apparatus which can maintain a high contrast for a long period of time and can be produced simply and at a low cost.

In order to attain the object described above, according to the present invention, there is provided a projection type display apparatus, including an illumination optical system for emitting light from a white light source as a light flux whose intensity distribution is uniformed, a decomposition optical system for decomposing the emitted light flux into color lights of red, green and blue, a plurality of liquid crystal light valves for the colors into which the decomposed color lights of the colors are introduced individually, a synthesis optical system for synthesizing the image lights of the colors emitted from the liquid crystal light valves for the colors, and a projection optical system for projecting the synthesized image lights to a screen, wherein a first optical path from the illumination optical system to one of the liquid crystal light valves for a predetermined one color through the decomposition optical system is formed longer than second optical paths to the liquid crystal light valves for the other two colors, and a filter is disposed at one of positions opposing to each other across the center of the light flux between the white light source and the decomposition optical system for attenuating or cutting off light of a wavelength region different from that of light which passes the other of the positions.

The projection type display apparatus is advantageous in that a high contrast can be maintained for a long period of time and it can be produced simply at a low cost.

The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols.

FIG. 1 is a schematic view showing a projection type display apparatus to which the present invention is applied;

FIG. 2 is a schematic and diagrammatic view illustrating operation of the projection type display apparatus of FIG. 1;

FIG. 3 is a schematic view showing another projection type display apparatus to which the present invention is applied;

FIG. 4 is a schematic and diagrammatic view illustrating operation of the projection type display apparatus of FIG. 3;

FIG. 5 is a view showing a modification to the projection type display apparatus of FIGS. 1 and 3;

FIGS. 6 and 7 are diagrams illustrating different examples of spectral characteristics of optical filters in the projection type display apparatus of FIG. 5;

FIG. 8 is a schematic view illustrating operation of the projection type display apparatus of FIG. 5;

FIG. 9 is a schematic view showing an example of a projection type display apparatus of the front projection type;

FIG. 10 is a schematic view showing an example of a projection type display apparatus of the rear projection type;

FIG. 11 is a schematic view showing an example of a conventional projection type display apparatus.

FIG. 12 is a view illustrating operation of the projection type display apparatus of FIG. 11;

FIG. 13 is a schematic diagrammatic view illustrating a definition of a view angle; and

FIG. 14 is a diagrammatic view showing an example of a view angle characteristic of a liquid crystal panel.

[First Embodiment: FIGS. 1 and 2 ]

FIG. 1 shows a projection type display apparatus to which the present invention is applied.

Referring to FIG. 1, the projection type display apparatus 100 of the present embodiment has a similar configuration to that of the projection type display apparatus 90 shown in FIG. 11 except that an optical filter 17 is disposed in such a manner as hereinafter described. In particular, the projection type display apparatus 100 includes an illumination unit 10 wherein part of non-polarized white light from a white light source 11 directly passes, but the remaining part of the non-polarized white light is first reflected by a reflector 12 and then passes, as a light flux 1 through a pair of multi-lens arrays 13 and 14 disposed in an opposing relationship to each other so that the light flux 1 is converted into a light flux which has an intensity distribution uniform within a fixed region on a plane perpendicular to the center axis 1 a of the light flux. Further, the light flux is converted from non-polarized light into linearly polarized light by a polarizing conversion element 15 and goes out from the illumination unit 10 through a condenser lens 16 .

The light flux 2 going out from the illumination unit 10 is decomposed into red color light 3 R and green and blue color light 3 GB by a dichroic mirror 21 , and the red color light 3 R is reflected by a mirror 22 and introduced into a liquid crystal light valve 30 R for red through a condenser lens 28 R.

Meanwhile, the green and blue color light 3 GB is decomposed into green color light 3 G and blue color light 3 B by a dichroic mirror 23 , and the green color light 3 G is introduced into a liquid crystal light valve 30 G for green through a condenser lens 28 G while the blue color light 3 B is introduced into a liquid crystal light valve 30 B for blue through a relay lens 24 , a mirror 25 , another relay lens 26 , another mirror 27 and a condenser lens 28 B.

The decomposed color lights 3 R, 3 G and 3 B of red, green and blue are modulated and converted into image lights 4 R, 4 G and 4 B of red, green and blue by the liquid crystal light valves 30 R, 30 G and 30 B, respectively. The image lights 4 R, 4 G and 4 B of red, green and blue are synthesized by a dichroic prism 40 , and the image light 5 after the synthesis is projected in an enlarged scale on a screen 110 by a projection lens 50 .

A liquid crystal panel which composes each of the liquid crystal light valves 30 R, 30 G and 30 B exhibits a sufficient light shutter function for any light flux which penetrates the liquid crystal panel upwardly from below when the liquid crystal panel is viewed downwardly from above, but exhibits an inferior light shutter function for any light flux which penetrates the liquid crystal panel downwardly from above when the liquid crystal panel is viewed upwardly from below, like the view angle characteristic of FIG. 14 .

In the projection type display apparatus 100 of the present embodiment, as the optical filter 17 , a filter which cuts off the wavelength region λb of blue of an unequal length but transmits therethrough the wavelength region λg of green and the wavelength region λr of red as indicated by a spectral characteristic 7 B of FIG. 2 is disposed at a lower position adjacent a light exit of the illumination unit 10 . Here, the optical filter 17 may otherwise attenuate part of the wavelength region λb of blue in place of cutting off the wavelength region λb of blue.

FIG. 2 illustrates a manner wherein a light flux from the illumination unit 10 in the projection type display apparatus 100 of FIG. 1 is introduced into the liquid crystal light valves 30 R, 30 G and 30 B in principle with the decomposition optical system omitted. A lens 29 corresponds to the relay lenses 24 and 26 of FIG. 1 . Incidentally, the lens 29 (relay lenses 24 and 26 ) introduces light from the illumination unit 10 so that the range within which the liquid crystal light valve 30 B is illuminated by the illumination unit 10 may be substantially equal to those of the liquid crystal light valves 30 R and 30 G.

As shown in FIG. 2, in the projection type display apparatus 100 of FIG. 1, a light flux emitted from an upper position of the light exit of the illumination unit 10 is introduced as light fluxes 3 Rd and 3 Gd, which penetrate downwardly from above, into the liquid crystal light valves 30 R and 30 G for red and green, but introduced as a light flux 3 Bu, which penetrates upwardly from below in a reversed vertical relationship, into the liquid crystal light valve 30 B for blue. Meanwhile, a light flux emitted from a lower position of the light exit of the illumination unit 10 is introduced as light fluxes 3 Ru and 3 Gu, which penetrate upwardly from below, into the liquid crystal light valves 30 R and 30 G for red and green, but introduced, if the optical filter 17 is not present, as a light flux 3 Bd, which penetrates downwardly from above in a reversed vertical relationship, into the liquid crystal light valve 30 B for blue.

However, the optical filter 17 for cutting off only the wavelength region λb of blue is disposed at the lower position adjacent the light exit of the illumination unit 10 .

Therefore, blue light components in the light flux emitted from the lower position of the light exit of the illumination unit 10 are cut off, and consequently, the blue color light 3 B is prevented from being introduced as a light flux 3 Bd, which penetrates downwardly from above and gives rise to a drop of the contrast, into the liquid crystal light valve 30 B for blue.

Since blue light components in the light flux emitted from the upper position of the light exit of the illumination unit 10 are not cut off by the optical filter 17 , the blue color light 3 B is introduced as a light flux 3 Bu, which penetrates upwardly from below and increases the contrast, into the liquid crystal light valve 30 B for blue.

Accordingly, the contrast of blue on the screen as an arithmetic mean of contrasts of the light fluxes introduced into the liquid crystal light valve 30 B is improved. In this instance, although the amount of incoming light to the liquid crystal light valve 30 B decreases, the decreasing amount can be suppressed to the minimum.

Red right components and green light components in the light flux emitted from the lower position of the light exit of the illumination unit 10 are not influenced by the optical filter 17 , and the contrasts of red and green on the screen do not vary.

The optical filter 17 can be formed in multiple layers including low refraction factor material layers and high refraction factor material layers layered alternately on a transparent substrate and can be manufactured simply and at a low cost. Besides, an inorganic material which is stable against light such as SiO2 or TiO2 can be used as the material for the optical filter 17 , and even if intense light is irradiated on the optical filter 17 for a long period of time, the spectral characteristic of the optical filter 17 does not vary.

Accordingly, with the projection type display apparatus of the present embodiment, a high contrast can be maintained for a long period of time and the projection type display apparatus 100 can be manufactured simply at a low cost.

[Second Embodiment: FIGS. 3 and 4 ]

FIG. 3 shows another projection type display apparatus to which the present invention is applied.

The projection type display apparatus 100 of the present embodiment has a similar configuration to that of the projection type display apparatus 100 of FIG. 1 except that an optical filter 18 is disposed in place of the optical filter 17 of FIG. 1 .

In the projection type display apparatus 100 of the present embodiment, a filter for cutting off the wavelength region λg of green but transmitting therethrough the wavelength region λb of blue and the wavelength region λr of red as indicated by a spectral characteristic 8 G of FIG. 4 or another filter for cutting off the wavelength region λr of red but transmitting therethrough the wavelength region λb of blue and the wavelength region λg of green as indicated by a spectral characteristic 8 R of FIG. 4 is disposed as the optical filter 18 at an upper position adjacent the light exit of the illumination unit 10 . Here, the filter for cutting off the wavelength region λg of green as indicated by the spectral characteristic 8 G may be replaced by a filter which attenuates part of the wavelength region λg of green. Further, the filter for cutting off the wavelength region λr of red as indicated by the spectral characteristic 8 R may be replaced by a filter which attenuates part of the wavelength region λr of red.

FIG. 4 illustrates, similarly to FIG. 2, a manner wherein a light flux from the illumination unit 10 in the projection type display apparatus 100 of FIG. 3 is introduced into the liquid crystal light valves 30 R, 30 G and 30 B in principle with the decomposition optical system omitted.

As shown in FIG. 4, in the projection type display apparatus 100 of FIG. 3, a light flux emitted from a lower position of the light exit of the illumination unit 10 is introduced as light fluxes 3 Ru and 3 Gu, which penetrate upwardly from below, into the liquid crystal light valves 30 R and 30 G for red and green, but introduced as a light flux 3 Bd, which penetrates downwardly from above in a reversed vertical relationship, into the liquid crystal light valve 30 B for blue. Meanwhile, a light flux emitted from an upper position of the light exit of the illumination unit 10 is introduced as light fluxes 3 Rd and 3 Gd, which penetrate downwardly from above, into the liquid crystal light valves 30 R and 30 G for red and green, but introduced as a light flux 3 Bu, which penetrates upwardly from below in a reversed vertical relationship, into the liquid crystal light valve 30 B for blue.

However, the optical filter 18 for cutting off only the wavelength region λg of green or the wavelength region λr of red is disposed at the upper position adjacent the light exit of the illumination unit 10 .

Accordingly, where a filter for cutting off only the wavelength region λg of green is disposed as the optical filter 18 , then green light components in the light flux emitted from the upper position of the light exit of the illumination unit 10 are cut off, and consequently, the green color light 3 G is prevented from being introduced as a light flux 3 Gd, which penetrates downwardly from above and gives rise to a drop of the contrast, into the liquid crystal light valve 30 G for green.

Since green light components in the light flux emitted from the lower position of the light exit of the illumination unit 10 are not cut off by the optical filter 18 , the green color light 3 G is introduced as a light flux 3 Gu, which penetrates upwardly from below and increases the contrast, into the liquid crystal light valve 30 G for green.

Accordingly, the contrast of green on the screen as an arithmetic mean of contrasts of the light fluxes introduced into the liquid crystal light valve 30 G is improved. Also in this instance, the decreasing amount of incoming light to the liquid crystal light valve 30 G can be suppressed to the minimum.

Blue right components and red light components in the light flux emitted from the upper position of the light exit of the illumination unit 10 are not influenced by the optical filter 18 , and the contrasts of blue and red on the screen do not vary.

Where a filter for cutting off only the wavelength region λr of red is disposed as the optical filter 18 , the contrast of red on the screen is improved similarly as described hereinabove.

The projection type display apparatus of the present embodiment may be modified such that a filter for cutting off the wavelength region λg of green and the wavelength region λr of red but transmitting therethrough the wavelength region λb of blue is disposed as the optical filter 18 . In this instance, as apparent from the foregoing description, the contrasts of green and red on the screen are improved.

[Third Embodiment: FIGS. 5 to 8 ]

FIG. 5 shows a further projection type display apparatus to which the present invention is applied.

Referring to FIG. 5, the projection type display apparatus 100 is a modification to both of the projection type display apparatus of the first and second embodiments described hereinabove with reference to FIGS. 1 and 3. More particularly, the projection type display apparatus 100 of the present embodiment is a combination of the projection type display apparatus of the first and second embodiments wherein the optical filter 17 is disposed at a lower position and the optical filter 18 are disposed at an upper position adjacent the light exit of the illumination unit 10 .

As an example, a filter for cutting off only the wavelength region λb of blue as indicated by a spectral characteristic 7 B of FIG. 6 is disposed as the optical filter 17 while another filter for cutting off only the wavelength region λg of green or the wavelength region λr of red as indicated by a spectral characteristic 8 G or 8 R of FIG. 6 is disposed as the optical filter 18 .

As another example, a filter for cutting off only the wavelength region λb of blue as indicated by a spectral characteristic 7 B of FIG. 7 is disposed as the optical filter 17 while another filter for cutting off the wavelength region λg of green and the wavelength region λr of red as indicated by a spectral characteristic 8 GR of FIG. 7 is disposed as the optical filter 18 .

FIG. 8 illustrates, similarly to FIGS. 2 and 4, a manner wherein a light flux from the illumination unit 10 in the projection type display apparatus 100 of FIG. 5 is introduced into the liquid crystal light valves 30 R, 30 G and 30 B in principle with the decomposition optical system omitted.

With the projection type display apparatus 100 of the present embodiment, the contrast of blue on the screen is improved similarly as with the projection type display apparatus 100 of the embodiment of FIG. 1, and the contrast of green or red or the contrasts of green and red on the screen are improved in accordance with the spectral characteristic of the optical filter 18 similarly as with the projection type display apparatus 100 of the embodiment of FIG. 3 .

Particularly where a filter for cutting off the wavelength region λg of green and the wavelength region λr of red is disposed as the optical filter 18 , the contrast on the screen is improved with regard to all of blue, green and red.

[Other Embodiments]

The optical filter 17 or 18 may not be disposed adjacent the light exit of the illumination unit 10 , but be disposed as such a multi-layer film as described above formed on the light emitting face of the condenser lens 16 or be disposed otherwise on the light incoming side of the multi-lens array 13 , between the multi-lens array 13 and the multi-lens array 14 , between the multi-lens array 14 and the polarizing conversion element 15 , or between the polarizing conversion element 15 and the condenser lens 16 , or the like.

Where the optical filters 17 and 18 are disposed in such a manner as in the projection type display apparatus 100 of the embodiment of FIG. 5, they may be disposed in an opposing relationship to each other in an oblique direction across the light flux center axis 1 a such that one of them is disposed adjacent the light exit of the illumination unit 10 while the other is disposed on the light incoming side of the multi-lens array 13 .

Where a liquid crystal panel which composes each of the liquid crystal light valves 30 R, 30 G and 30 B has such a view angle characteristic that, conversely to that of the projection type display apparatus 100 of the embodiments described hereinabove, it exhibits a sufficient light shutter function for any light flux which penetrates the liquid crystal panel downwardly from above when the liquid crystal panel is viewed upwardly from below, but exhibits an inferior light shutter function for any light flux which penetrates the liquid crystal panel upwardly from below when the liquid crystal panel is viewed downwardly from above, the optical filter 17 is disposed at a higher position than the light flux center axis 1 a such as an upper position adjacent the light exit of the illumination unit 10 while the optical filter 18 is disposed at a lower position than the light flux center axis 1 a such as a lower position adjacent the light exit of the illumination unit 10 conversely to those in the projection type display apparatus 100 of the embodiments described hereinabove.

On the other hand, when the liquid crystal panel is viewed from the light emitting face, where a liquid crystal panel which composes each of the liquid crystal light valves 30 R, 30 G and 30 B has such a view angle characteristic that it exhibits a sufficient light shutter function for any light flux which penetrates the liquid crystal panel leftwardly from the right when the liquid crystal panel is viewed rightwardly from the left, but exhibits an inferior light shutter function for any light flux which penetrates the liquid crystal panel rightwardly from the left when the liquid crystal panel is viewed leftwardly from the right, or has an opposite view angle characteristic, the optical filter 17 is disposed at a leftward position or a rightward position with respect to the light flux center axis 1 a while the optical filter 18 is disposed at a rightward position or a leftward position with respect to the light flux center axis 1 a conversely.

While the projection type display apparatus 100 of the embodiments described above has an unequal length for the optical path for blue, alternatively the optical path for green or for red may have an unequal length.

Further, while the embodiments described above are directed to a front projection type display apparatus wherein the projection type display apparatus 100 and the screen 110 are formed separately from each other as shown in FIG. 9, the present invention can be applied also to a back projection type display apparatus wherein a display apparatus unit 102 , reflecting mirror 103 and screen 104 which correspond to the projection type display apparatus 100 of FIG. 9 are disposed in a cabinet 101 as shown as a projection type display apparatus 100 in FIG. 10 .

[Verification of the Invention]

With regard to a comparative example wherein none of the optical filter 17 and the optical filter 18 is disposed in the projection type display apparatus 100 shown in FIG. 1, 3 or 5 and embodiments wherein the optical filter 17 or 18 or the optical filters 17 and 18 are disposed in the projection type display apparatus 100 shown in FIGS. 1, 3 and 5 , the contrast on the screen was measured to verify effects of the present invention.

For the measurement of the contrast, signals were inputted to the liquid crystal light valves 30 R, 30 G and 30 B to project an all-white state image and an all-black state mage on the screen, and the luminance Yw in the all-white state and the luminance Yk in the all-black state were measured at the position of the center of the screen by a luminance meter to determine a contrast ratio (Yw:Yk) to calculate a contrast value (Yw/Yk). It is determined that the higher the contrast value, the higher the contrast and the better the picture quality.

With the comparative example, the contrast value was 400.

IMPLEMENTATION EXAMPLE 1

In the implementation example 1, the optical filter 17 in the projection type display apparatus 100 of the embodiment of FIG. 1 cuts off only the wavelength region λb of blue. In this instance, the contrast value was 450.

IMPLEMENTATION EXAMPLE 2

In the implementation example 2, the optical filter 18 in the projection type display apparatus 100 of the embodiment of FIG. 3 cuts off only the wavelength region λg of green. In this instance, the contrast value was 500.

IMPLEMENTATION EXAMPLE 3

In the implementation example 3, the optical filter 18 in the projection type display apparatus 100 of the embodiment of FIG. 3 cuts off only the wavelength region λr of red. In this instance, the contrast value was 470.

IMPLEMENTATION EXAMPLE 4

In the implementation example 4, the optical filter 17 in the projection type display apparatus 100 of the embodiment of FIG. 5 cuts off only the wavelength region λb of blue and the optical filter 18 cuts off only the wavelength region λg of green. In this instance, the contrast value was 550.

IMPLEMENTATION EXAMPLE 5

In the implementation example 5, the optical filter 17 in the projection type display apparatus 100 of the embodiment of FIG. 5 cuts off only the wavelength region λb of blue and the optical filter 18 cuts off the wavelength region λg of green and the wavelength region λr of red. In this instance, the contrast value was 600.

While preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.