Abstract:
An image display apparatus for enhancing contrast is provided. The apparatus includes a tunable illumination mask and/or a tunable image mask. According to the light path in the image display apparatus, the tunable illumination mask dynamically controls the area through which the light passes to block noise such as scattering or diffraction light and thereby enhances contrast.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This Application claims priority to Taiwan Patent Application No. 92122351 filed on Aug. 14, 2003.  
       FIELD OF INVENTION  
       [0002]     The present application generally relates to an image display apparatus for enhancing the contrast, and more particularly to an image display apparatus to block light of noise-type for enhancing the contrast.  
       BACKGROUND OF THE INVENTION  
       [0003]     In parallel with the progress of business activities and the development of interactive learning, projectors have become indispensable image display apparatuses in many fields. The image displaying technology is advancing from the liquid crystal display (LCD) to digital light processing (DLP).  
         [0004]     The digital light processing technology employs reflected light, which is modulated by the spatial light modulator (SLM), such as the generally known digital micromirror device (DMD). The DMD is a bistable spatial light modulator consisting of multiple arrays of many pixels. Each pixel has a micromirror.  FIG. 1  illustrates a single pixel of DMD. By individually controlling the tilt angle of each micromirror  10 , every micromirror  10  can be selectively arranged in two states, namely an “on” state (+θ degrees)  10   a  and an “off” state (−θ degrees)  10   b . Light source is denoted by reference numeral  14 . Light reflected by micromirrors  10   a  in the “on” state passes through the projection lens  16  onto a screen. Light reflected by micromirrors  10  in the “off” state  10   b  reaches an integrator  18  and a dark field is created. Images are created by gray-scale modulation between the “on”  10   a  and “off”  10   b  states. The flat state  10   c  occurs when the micromirrors  10  are not landed (no deflection). The flat state  10   c  is not a stable state (not tristable).  
         [0005]     Contrast, brightness, resolution, weight, light source lifetime are the indices for determining the quality of a projector. Scattering and diffraction are the dominant mechanisms that determine the contrast. Contrast is defined as the ratio of the light intensities between “on”  10   a  and “off”  10   b  states of the spatial light modulator device. Contrast can be enhanced by either increasing the light intensity of the on-state  10   a , or by decreasing the light intensity of the off-state  10   b . As the brightness of the off-state approaches zero, a small absolute drop in off-state brightness results in a higher impact to the overall contrast. However, owing to scattering and diffraction from the flat state  10   c , the brightness of the off-state doesn&#39;t actually approach zero. So far, the conventional techniques do not have relatively satisfactory solutions. Thus, the contrast-improving techniques described in this application concentrate on enhancing the contrast by lowering the brightness of the off-state.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention provides an image display apparatus to dynamically block light of noise-type, such as light from scattering and diffraction, for enhancing the contrast.  
         [0007]     Firstly, the image display apparatus of the present invention includes a light source, an illumination module and a tunable illumination mask. The light source is for projecting light onto the illumination module. The illumination module includes an illumination stop. The tunable illumination mask includes an illumination hole, which is positioned at the location of the illumination stop. The size of the illumination hole is adjustable so as to effectively block light of noise-type from the illumination module. In order to further enhance the effect, the illumination module defines a centerline. The illumination module contains lenses and optical elements aligning with the centerline. The tunable illumination mask is capable of moving two-dimensionally to make the center of the illumination hole deviate from the centerline to an optimal position to substantially block light of noise-type. At the same time, the size of the illumination hole is adjusted to block light of noise-type, such as scattering and diffraction from the illumination module.  
         [0008]     Secondly, the present invention also provides another image display apparatus including a light source, an image module, a tunable image mask and a spatial light modulator. The image module includes a projection-lens stop. The tunable image mask includes an image hole, which is positioned at the location of the projection-lens stop. The size of the image hole is adjustable so as to block light of noise-type from the image module. In order to further enhance the effect, the spatial light modulator and the image module define a centerline. Lenses and optical elements in the spatial light modulator and the image module all align with the centerline. The tunable image mask, which has a function similar to that of the tunable illumination mask, is able to block light of noise-type such as scattering and diffraction. The tunable image mask positioned at the location of the projection-lens stop dynamically adjusts the size of the image hole according to the modulation result of the spatial light modulator, and is capable of moving two-dimensionally to an optimal position to substantially reduce light of noise-type on the screen, so as to enhance the contrast.  
         [0009]     In addition, the two above-mentioned image display apparatuses may be integrated into one to include a light source, an illumination module, an image module, a tunable illumination mask, a tunable image mask and a spatial light modulator. The image display apparatus is better able to block light of noise-type because both the tunable illumination mask and the tunable image mask are present. The tunable illumination mask and the tunable image mask can substantially block light of noise-type such as scattering and diffraction by dynamically adjusting their positions and the areas that allow light to pass through according to the direction of the incoming light in the apparatus, and thereby enhance the contrast of the apparatus. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  illustrates a single pixel of a conventional DMD;  
         [0011]      FIG. 2  illustrates an image display apparatus of Example 1 of the present invention;  
         [0012]      FIG. 3  illustrates the tunable illumination mask and the tunable image mask of the present invention;  
         [0013]      FIG. 4  illustrates an image display apparatus of Example 2 of the present invention;  
         [0014]      FIG. 5  illustrates an image display apparatus of Example 3 of the present invention. 
     
    
     DETAILED DESCRIPTION  
     EXAMPLE 1  
       [0015]      FIG. 2  illustrates the image display apparatus of the present invention, including a light source  14 , an illumination module  202  and a tunable illumination mask  204 . The light source  14  is for projecting light onto the illumination module  202 . The illumination module  202  includes an illumination stop  206 . The tunable illumination mask  204  includes an illumination hole  302  (as shown in  FIG. 3 ), which is positioned at the location of the illumination stop  206  indicated by the direction of the arrow shown in  FIG. 2 . The size of the illumination hole  302  is adjustable so as to effectively block light of noise-type from the illumination module  202 .  
         [0016]     The above-mentioned tunable illumination mask  204  consists of a plurality of movable diaphragms  300  that overlap with one another to form the illumination hole  302  for the light to pass through. The size of the illumination hole  302  can be adjusted by adjusting the movable diaphragms  302 , so that the light passing through the illumination hole  302  can be adjusted as well. Thus, the tunable illumination mask  204  blocks light of noise-type such as scattering and diffraction and only allows the desirable light to pass through.  
         [0017]     Even though the tunable illumination mask  204  alone may block light of noise-type, it would be better if the position of the tunable illumination mask  204  itself is adjustable according to the direction of the incoming light. The present invention provides a tunable illumination mask that is further capable of moving two-dimensionally. The illumination module  202  defines a centerline  1  and contains lenses and optical elements aligning with the centerline  1 . The tunable illumination mask  204  is capable of moving two-dimensionally to make the center of the illumination hole  302  deviate from the centerline  1  to an optimal position to substantially block light of noise-type such as scattering and diffraction from the illumination module  202 . Specifically speaking, the center of the light overlaps with the centerline  1  but the center of the illumination hole  302  deviates from the centerline  1 . Accordingly, the light passing through the illumination hole  302  is in a shape of a “cat eye” and the tunable illumination mask  204  therefore blocks light of noise-type such as scattering and diffraction.  
       EXAMPLE 2  
       [0018]     The present invention further provides a second image display apparatus (as shown in  FIG. 4 ) including a light source  14 , an image module  402 , a tunable image mask  404  and a spatial light modulator  406 . The difference between EXAMPLE 2 and EXAMPLE 1 is that EXAMPLE 2 includes a spatial light modulator  406 , which can be a digital micromirror device (DMD). The spatial light modulator  406  as shown in  FIG. 1  may have an “on” state  10   a , a “flat” state  10   c  and an “off” state  10   b  for selectively modulating the light to form an image on the screen.  
         [0019]     The image module  402  includes a projection-lens stop  408 . The tunable image mask  404  includes an image hole that is structurally similar to the image hole  302  in  FIG. 3 . The tunable image mask  404  is positioned at the location of the projection-lens stop  408 , which is indicated by the direction of the arrow in  FIG. 4 . The function of the tunable image mask  404  is similar to that of the tunable illumination mask  204  in  FIG. 2 . They all block light of noise-type such as scattering and diffraction. The tunable image mask  404  also consists of a plurality of movable diaphragms  300  and includes an adjustable image hole that acts like the image hole  302 . To further enhance the results, the tunable image mask  404  is capable of moving two-dimensionally. The spatial light modulator  406  and the image module  402  define a centerline  1  and contain lenses and optical elements aligning with the centerline  1 . Based on the modulation result of the spatial light modulator  406 , the tunable image mask  404  is capable of moving two-dimensionally according to the direction of the light, to an optimal position to substantially diminish the light of noise-type on the screen to enhance the contrast.  
       EXAMPLE 3  
       [0020]     This example combines all the necessary elements (shown in  FIG. 5 ) that are disclosed in EXAMPLE 1 and EXAMPLE 2, including a light source  14 , an illumination module  502 , an image module  504 , a tunable illumination mask  510 , a tunable image mask  512  and a spatial light modulator  514 . The spatial light modulator  514  lies between the illumination module  502  and the image module  504 . The illumination module  502 , the spatial light modulator  514  and the image module  504  define a centerline  1  and contain lenses and optical elements aligning with the centerline  1 . In this image display apparatus, the tunable illumination mask  510  and the tunable image mask  512  (according to the direction of the arrow illustrated in  FIG. 5 ) are located in the illumination stop  506  and in the projection-lens stop  508  to more effectively block the light of noise-type.  
         [0021]     The spatial light modulator  514  may still be a digital micromirror device. Following the conventional techniques of the mechanism of the digital micromirror, the tunable illumination mask  510  and the tunable image mask  512  may dynamically block the light of noise-type in the “flat” state  10   c . In the illumination module  502 , according to the tilt angle of the “on” state (+θ degrees)  10   a  and the “off” state (−θ degrees)  10   b  of the digital micromirror device  514 , the light passing through the projection-lens stop  508  in the “flat” state  10   c  can be calculated. Based on this result, the area on the illumination stop  506  that the light passes through is determined, and then the tunable illumination mask  510  can be used to block in advance the light of noise-type that may potentially interfere with the digital micromirror device  514 . By adjusting the size of the illumination hole  302  and the two-dimensional position of the tunable illumination mask  510  to block the light of noise-type, the interference in the spatial light modulator  514  is decreased and the contrast is enhanced. In the image module  504 , the tunable image mask  512  is positioned at the location of the projection-lens stop  508 , and the size of the image hole is dynamically adjusted according to the modulation result of the spatial light modulator  514  to control the lighted area on the screen. Simultaneously, the tunable image mask  512  is capable of moving two-dimensionally in accordance with the direction of the light to an optimal position to block the diffraction from the “flat” state  10   c  and the “off” state  10   b  to diminish the light of noise-type on the screen and to enhance the contrast.  
         [0022]     By means of the detailed descriptions of what is presently considered to be the most practical and preferred embodiments of the subject invention, it is the expectation that the features and the gist thereof are plainly revealed. Nevertheless, these above-mentioned illustrations are not intended to be construed in a limiting sense. Instead, it should be well understood that any analogous variation and equivalent arrangement is supposed to be covered within the spirit and scope to be protected and that the interpretation of the scope of the subject invention would therefore as much as broadly apply.