Light modulating unit and image projection apparatus

A light modulating unit includes first and second light modulating sections each of which modulates an illumination light on the basis of a video signal to generate a projection light that is a linearly polarized light, a light path synthesizing section which synthesizes the projection lights generated by the first and second light modulating sections using the nature that directions of polarizations of the projection lights cross at right angles, and a beam shifting section which sets beams of the projection lights synthesized by the light path synthesizing section, in a shifted state or a non-shifted state on the basis of the directions of polarizations of the projection lights, the beam shifting section switching the shifted state and the non-shifted state synchronously with modulation timings for the first and second light modulating sections.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2004-050213, filed Feb. 25, 2004, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light modulating unit and an image projection apparatus using the light modulating unit.

2. Description of the Related Art

With the recent increase in the resolution of imaging devices, there has also been a growing demand for an increase in the resolution of image projection apparatuses that display images taken. Accordingly, much effort has been made to develop display devices (light modulating devices) with a large number of pixels. However, the display device does not have a sufficient resolution compared to the imaging device. The light modulating device is sometimes called a spatial modulation device.

A proposal described below has been made as a technique to realize a high resolution using a light modulating device (LCD or the like) with a limited number of pixels.

However, this proposal simply synthesizes the images generated by the two light modulating devices, using the PBS. Because of its nature, the PBS can synthesize only two images, a P-polarized light image and an S-polarized light image. This technique can thus realize only two-point pixel shifts. That is, this proposal cannot realize three-or-more-point pixel shifts. Therefore, with this proposal, it is difficult to sufficiently increase the resolution.

Jpn. Pat. Appln. KOKAI Publication No. 2002-268014 proposes that a two- or four-point pixel shift be realized by using one light modulating device and supplying an image from the light modulating device to a beam shifting section (wobbling unit) through a PBS. However, if a four-point pixel shift is carried out, four points are temporally sequentially shifted, so that a light intensity per pixel is one-fourth of a normal value. It is thus difficult obtain a sufficient light intensity. Further, since the four points are temporally sequentially shifted, a time lag may occur, resulting in a flickering image.

Thus, disadvantageously, with the conventionally proposed techniques to increase the resolution, it is difficult to sufficiently increase the resolution, to obtain a sufficient light intensity, and to obtain images free from flickering. Accordingly, it has been difficult to increase the resolution and to obtain images with an excellent display quality.

It is an object of the present invention to provide a light modulating unit and an image projection apparatus that enable the resolution and display quality to be improved.

BRIEF SUMMARY OF THE INVENTION

A first aspect of the present invention, there is provided a light modulating unit which modulates an illumination light on the basis of an inputted video signal, the light modulating unit comprising: first and second light modulating sections each of which modulates an illumination light on the basis of a video signal to generate a projection light that is a linearly polarized light; a light path synthesizing section which synthesizes the projection lights generated by the first and second light modulating sections using the nature that directions of polarizations of the projection lights cross at right angles; and a beam shifting section which sets beams of the projection lights synthesized by the light path synthesizing section, in a shifted state or a non-shifted state on the basis of the directions of polarizations of the projection lights, the beam shifting section switching the shifted state and the non-shifted state synchronously with modulation timings for the first and second light modulating sections.

In the light modulating unit, a positional relationship between the first and second light modulating sections may be determined so that pixel positions of the projection lights generated by the first and second light modulating sections and synthesized by the light path synthesizing section are adjacent to each other in a predetermined direction.

In the light modulating unit, the beam shifting section may include a liquid crystal panel which can rotate the direction of polarization of the projection light and a birefringence plate which generates a transmission light which is offset from an extension of an incident light if the incident light has a particular direction of polarization, and the liquid crystal panel may rotate the direction of polarization of the projection light synchronously with the modulation timings for the first and second light modulating sections.

In the light modulating unit, the light modulating unit may comprise a plurality of sets each composed of the first and second light modulating sections and the light path synthesizing section, the first and second light modulating sections in each set generating projection lights of the same color, colors of the projection lights being different between the sets, and the light modulating unit may further comprise a color synthesizing prism which synthesizes the projection lights from the respective sets, and the beam shifting section may shift the beams of the projection lights synthesized by the color synthesizing prism on the basis of the directions of polarizations of the projection lights.

In the light modulating unit, the number of sets may be three and the colors of the projection lights in the respective sets may be red, blue, and green.

In the light modulating unit, the light path synthesizing section may be composed of a polarization beam splitter having a first to sixth planes and a polarization plane, and the first and second light modulating sections may be composed of first and second light modulating devices, respectively, arranged opposite the first and second planes that are not perpendicular to the polarization plane of the polarization beam splitter, and when the illumination light is incident on the third plane which is not perpendicular to the polarization plane and which is different from the first and second planes, the first light modulating device may be illuminated by an S-polarized light component of the illumination light reflected by the polarization plane, and the second light modulating device may be illuminated by a P-polarized light component of the illumination light passing through the polarization plane.

In the light modulating unit, each of the first and second light modulating sections may include a plurality of light modulating devices which generate projection lights having different colors and a color synthesizing prism which synthesizes the projection lights generated by the plurality of light modulating devices, and the direction of polarization of the projection light emitted by the color synthesizing prism of the first light modulating section may be orthogonal to the direction of polarization of the projection light emitted by the color synthesizing prism of the second light modulating section.

In the light modulating unit, one of the first and second light modulating sections may have a λ/2 plate which makes the direction of polarization of the projection light emitted by the first light modulating section orthogonal to the direction of polarization of the projection light emitted by the second light modulating section.

In the light modulating unit, the light path synthesizing section may be composed of a polarization beam splitter, and a projection light of a P-polarized light and a projection light of an S-polarized light may be incident on the beam shifting section.

In the light modulating unit, if an amount of input image information contained in the video signal is larger than an amount of display image information which can be displayed by each of the first and second light modulating sections, the liquid crystal panel may sequentially assume two states in which the liquid crystal panel rotates or does not rotate the direction of polarization of the projection light through 90°, and if the amount of input image information is smaller than the amount of display image information, the liquid crystal panel may maintain one state in which the liquid crystal panel rotates the direction of polarization of the projection light through 45°.

In the light modulating unit, if an amount of input image information contained in the video signal is larger than an amount of display image information which can be displayed by each of the first and second light modulating sections, the beam shifting section may sequentially set the projection lights generated by the first and second light modulating sections, in the shifted state and the non-shifted state in a direction orthogonal to the predetermined direction, and if the amount of input image information is smaller than the amount of display image information, the beam shifting section may apply a spatial low pass filter action to the projection lights generated by the first and second light modulating sections, in the direction orthogonal to the predetermined direction.

A second aspect of the present invention, there is provided an image projection apparatus comprising: the light modulating unit, a light source which supplies an illumination light to the first and second light modulating sections, and a projection optical section which projects the projection light from the beam shifting section on a screen.

In the image projection apparatus, the positional relationship between the first and second light modulating sections may be determined so that a pixel position of the projection light generated by the first light modulating section and synthesized by the light path synthesizing section is offset from a pixel position of the projection light generated by the second light modulating section and synthesized by the light path synthesizing section by half a pixel pitch in a predetermined direction, and the beam shifting section may be configured so that a pixel position of the projection light in the shifted state is offset from a pixel position of the projection light in the non-shifted state by half a pixel pitch in a direction orthogonal to the predetermined direction.

In the image projection apparatus, the light path synthesizing section may be composed of a polarization beam splitter, and one of beams of the projection lights generated by the first and second light modulating sections may be shifted by the beam shifting section, and the other beam may not be shifted by the beam shifting section.

In the image projection apparatus, the image projection apparatus may further comprise an extracting section which extracts, from the video signal, a signal corresponding to a projection light for each pixel emitted by the beam shifting section, and the first and second light modulating sections may modulate the illumination light on the basis of the signal extracted by the extracting section.

A third aspect of the present invention, there is provided an image projection apparatus which uses the light modulating unit to project images based on right and left eye video signals on a screen in order to allow a three-dimensional image to be observed using a pair of polarization glasses in which a direction of polarization for a right eye and a direction of polarization for a left eye cross at right angles, wherein if one of the first and second light modulating sections modulates an illumination light on the basis of the right eye video signal, the other of the first and second light modulating sections modulates the illumination light on the basis of the left eye video signal, the positional relationship between the first and second light modulating sections is determined so that a pixel position of the projection light generated by the first light modulating section and synthesized by the light path synthesizing section is offset from a pixel position of the projection light generated by the second light modulating section and synthesized by the light path synthesizing section by half a pixel pitch in a predetermined direction, and the beam shifting section is configured so that a pixel position of the projection light in the shifted state is offset from a pixel position of the projection light in the non-shifted state by half a pixel pitch in a direction orthogonal to the predetermined direction.

In the image projection apparatus, the image projection apparatus may further comprise an extracting section which extracts, from the video signal, a signal corresponding to a projection light for each pixel emitted by the beam shifting section, and the first and second light modulating sections may modulate the illumination light on the basis of the signal extracted by the extracting section.

A fourth aspect of the present invention, there is provided a light modulating unit which modulates an illumination light on the basis of an inputted video signal, the light modulating unit comprising: at least one light modulating section which modulates an illumination light on the basis of a video signal to generate a projection light that is a linearly polarized light; and a beam shifting section which sets a beam of the projection light generated by the light modulating section, in a shifted state or a non-shifted state on the basis of a direction of polarization of the projection light, the beam shifting section switching the shifted state and the non-shifted state synchronously with a modulation timing for the light modulating section, wherein if an amount of input image information contained in the video signal is larger than an amount of display image information which can be displayed by the light modulating section, the beam shifting section sequentially sets the beam of the projection light in the shifted state and the non-shifted state, and if the amount of input image information is smaller than the amount of display image information, the beam shifting section does not sequentially set the beam of the projection light in the shifted state and the non-shifted state but fixes the beam in one state.

In the light modulating unit, the beam shifting section may include a liquid crystal panel which can rotate the direction of polarization of the projection light and a birefringence plate which generates a transmission light which is offset from an extension of an incident light if the incident light has a particular direction of polarization, and if the amount of input image information is larger than the amount of display image information, the liquid crystal panel may sequentially assume two states in which the liquid crystal panel rotates or does not rotate the direction of polarization of the projection light through 90°, and if the amount of input image information is smaller than the amount of display image information, the liquid crystal panel may maintain one state in which the liquid crystal panel rotates the direction of polarization of the projection light through 45°. Advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a view schematically showing an image projection apparatus using a light modulating unit according to a first embodiment of the present invention.

A light source110is a very high pressure mercury lamp, a xenon lamp, an LED, or the like. An illumination light from the light source110is incident, via an illumination optical system120, on a projection unit composed of a light path synthesizing section200, a first light modulating device301, and a second light modulating device302.

The light path synthesizing section200has a polarization converting function and a light path synthesizing function. The light path synthesizing section200is a PBS (Polarization Beam Splitter) prism. The PBS prism is a hexahedron structure. When an illumination light is incident on a polarization plane205through a constituent plane201of the PBS prism, a P-polarized light component of the illumination light is transmitted through the polarization plane205. On the other hand, an S-polarized light component of the illumination light is reflected by the polarization plane205.

The S-polarized light component separated by the light path synthesizing section200is emitted from a constituent plane202of the PBS prism. The S-polarized light component is then incident on a first light modulating device301placed opposite the constituent plane202. The P-polarized light component separated by the light path synthesizing section200is emitted from a constituent plane203of the PBS prism. The P-polarized light component is then incident on a second light modulating device302placed opposite the constituent plane203.

Each of the first light modulating device301and second light modulating device302is composed of a reflection type liquid crystal display device (reflection type LCD) and spatially modulate the incident light in accordance with a video signal to generate a projection light that is a linearly polarized light. Specifically, the light modulating device301rotates the incident S-polarized light component in accordance with the video signal. The light modulating device301thus emits a P-polarized light component to the constituent plane202of the PBS prism. The light modulating device302rotates the incident P-polarized light component in accordance with the video signal. The light modulating device302thus emits an S-polarized light component to the constituent plane203of the PBS prism. The P-polarized light component from the light modulating device301is transmitted through the polarization plane205of the PBS prism200. The P-polarized light component is then emitted from a constituent plane204of the prism200. The S-polarized light component from the light modulating device302is reflected by the polarization plane205of the PBS prism200. The S-polarized light component is then emitted from the constituent plane204of the prism200. In other words, the light path synthesizing section200synthesizes the P-polarized light from the light modulating device301and the S-polarized light from the light modulating device302using the nature that their directions of polarization cross at right angles. In this case, a wavelength plate may be placed between the light path synthesizing section (PBS prism) and the light modulating device (reflection type LCD).

FIGS. 2A and 2Bare diagrams showing the positional relationship between the first light modulating device301and the second light modulating device302.FIG. 2Ais a plan view andFIG. 2Bis a side view.FIG. 3is a diagram showing an array of pixels in each of the first light modulating device301and second light modulating device302.FIG. 4is a diagram showing an array of pixels on the projection plane (screen plane), of both first light modulating device301and second light modulating device302, after projection lights have been synthesized by the light path synthesizing section200. That is,FIG. 4shows the array of pixels on the projection plane (screen plane) obtained given that a beam shifting section400is not provided.

InFIG. 3and subsequent figures illustrating the array of pixels, the open area ratio of each pixel is reduced so that the pixels do not overlap one another. However, the open area ratio of each pixel may be increased so that, for example, inFIG. 4, pixels of the first LCD overlap pixels of the second LCD.

As shown inFIG. 2A, the first light modulating device301and the second light modulating device302are arranged offset from each other by half a pixel pitch in a horizontal direction. As shown inFIG. 4, the positional relationship between the first light modulating device301(first LCD) and the second light modulating device302(second LCD) is determined so that the projected pixels of the first light modulating device301is adjacent to the respective projected pixels of the second light modulating device302in the horizontal direction.

Projection lights (video image lights) synthesized by the light path synthesizing section200are incident on the beam shifting section400. The beam shifting section400is composed of a polarization rotatable liquid crystal panel410that can rotate a polarized light and a birefringence plate420.

The liquid crystal panel410is composed of a TN type liquid crystal panel. Rotation of the polarized light can be controlled by turning on and off voltage applied to the liquid crystal panel410. Specifically, if the voltage applied to the liquid crystal, panel410is off, the P-polarized light is rotated to become an S-polarized light. The S-polarized light is rotated to become a P-polarized light. If the voltage applied to the liquid crystal panel410is on, the P-polarized light passes through the liquid crystal panel410as it is without being rotated. Likewise, the S-polarized light passes through the liquid crystal panel410as it is without being rotated.

The birefringence plate420is a colorless transparent crystal plate having birefringence and may be a quartz plate, a lithium niobate plate, or the like. The birefringence plate420is configured so that its crystal axis normally lies at 45° with an incident plane. The birefringence plate420separates an incident light into an ordinary light (no) and an extraordinary light (ne) depending on the direction of polarization of the incident light. In the present embodiment, as shown inFIG. 1, the beam of the S-polarized light passes through the birefringence plate420without being shifted by the birefringence plate420. The beam of the P-polarized light is shifted by the birefringence plate420. The shift amount is half a pixel pitch as described later. The shift amount can be determined depending on the material and thickness of the birefringence plate420.

FIGS. 5A and 5Bare diagrams illustrating the action of the beam shifting section400.FIG. 5Ashows the case where the voltage applied to the liquid crystal panel410is off.FIG. 5Bshows the case where the voltage applied to the liquid crystal panel410is on. InFIGS. 5A and 5B, for convenience, the first light modulating device301and the second light modulating device302are drawn so as to be offset from each other in a vertical direction. Thus, beams from the first light modulating device301and second light modulating device302are drawn so as to be offset from each other in a vertical direction. However, the first light modulating device301and the second light modulating device302have an optically conjugate positional relationship. For example, the length of the optical path from the first light modulating device301to the polarization rotatable liquid crystal panel410is equal to that from the second light modulating device302to the polarization rotatable liquid crystal panel410. Furthermore, for convenience, the light path synthesizing section200is not shown.

FIGS. 6A and 6Bare diagrams showing an array of pixels on the projection plane (screen plane), of the first light modulating device (first LCD)301and second light modulating device (second LCD)302, after projection lights have passed through the beam shifting section400.FIG. 6Ashows the case where the voltage applied to the liquid crystal panel410is off.FIG. 6Bshows the case where the voltage applied to the liquid crystal panel410is on.

As shown inFIG. 5A, if the liquid crystal panel410is off, the P-polarized light from the first light modulating device301is rotated by the liquid crystal panel410to become an S-polarized light. The S-polarized light from the liquid crystal panel410passes through the birefringence plate420without being shifted. The S-polarized light from the second light modulating device302is rotated by the liquid crystal panel410to become a P-polarized light. The P-polarized light from the liquid crystal panel410is shifted in a vertical direction by the birefringence plate420. Accordingly, if the liquid crystal panel is off, then as shown inFIG. 6A, the pixel positions of the projection lights from the first light modulating device301are maintained. On the other hand, the pixel positions of the projection lights from the second light modulating device302are shifted by half a pixel pitch in the vertical direction. As a result, the pixel position (a) of the projection light from the first light modulating device301are offset from the pixel position (d) of the projection light from the second light modulating device302, by half a pixel pitch in both horizontal and vertical directions on the projection plane (screen plane), as shown inFIG. 6A.

As shown in5B, if the liquid crystal panel410is on, the P-polarized light from the first light modulating device301passes through the liquid crystal panel410without being rotated by the liquid crystal panel410. The P-polarized light is then shifted in the vertical direction by the birefringence plate420.

The S-polarized light from the second light modulating device302passes through the liquid crystal panel410without being rotated by the liquid crystal panel410and then passes through the birefringence plate420without being shifted by the birefringence plate420. Consequently, if the liquid crystal panel410is on, then as shown inFIG. 6B, the pixel positions of the projection lights from the first light modulating device301are shifted by half a pixel pitch in the vertical direction. On the other hand, the pixel positions of the projection lights from the second light modulating device302are maintained. As a result, the pixel position (b) of the projection light from the first light modulating device301are offset from the pixel position (c) of the projection light from the second light modulating device302, by half a pixel pitch in both horizontal and vertical directions on the projection plane (screen plane), as shown inFIG. 6B.

As is apparent from the above description, by turning on and off the liquid crystal panel410, it is possible to determine whether or not to shift the light incident on the beam shifting section400depending on the direction of polarization of the incident light. Accordingly, by temporally turning on and off the liquid crystal panel410synchronously with modulation timings for the first light modulating device301and second light modulating device302, it is possible to synthesize the display state shown inFIG. 6Aand the display state shown inFIG. 6Bin the direction of a time axis. As a result, a display state such as the one shown inFIG. 7can be realized by projecting an image on a screen520via a projection optical system510. Specifically, the pixels are shifted in the horizontal direction by a projection unit composed of the light path synthesizing section200, the first light modulating device301, and the second light modulating device302. The pixels are further shifted in the vertical direction by the beam shifting section400. It is therefore possible to realize the display state of a four-point pixel shift such as the one shown inFIG. 7.

FIG. 8is a block diagram showing a configuration for realizing a display of a four-point pixel shift such as the one shown inFIG. 7.

An input video signal is stored in a frame memory801. An image information generating circuit802extracts (samples) signal components from the video signal stored in the frame memory801, the signal components corresponding to pixel positions a, b, c, and d, shown inFIG. 7.

For a first field (the former half field of one frame), a timing signal from a timing signal generator803allows video signals for the pixel positions a and d to be supplied to a driving circuit804and a driving circuit805, respectively. Driving signals from the driving circuits804and805drive the first light modulating device301and the second modulating device302, respectively. On the basis of the timing signal from the timing signal generator803, a driving circuit806turns off the polarization rotatable liquid crystal panel410synchronously with a driving timing (display timing) for the first light modulating device301and second light modulating device302. As a result, in the first field, a display state such as the one shown inFIG. 6Ais obtained.

For a second field (the latter half field of one frame), a timing signal from the timing signal generator803allows video signals for the pixel positions b and c to be supplied to the driving circuit804and the driving circuit805, respectively. Driving signals from the driving circuits804and805drive the first light modulating device301and the second modulating device302, respectively. On the basis of the timing signal from the timing signal generator803, the driving circuit806turns on the polarization rotatable liquid crystal panel410synchronously with the driving timing (display timing) for the first light modulating device301and second light modulating device302. As a result, in the second field, a display state such as the one shown inFIG. 6Bis obtained.

In this manner, a display of a four-point pixel shift such as the one shown inFIG. 7is obtained. The screen520displays an image with pixels four times as many as the pixels of one light modulating device.

As described above, in the present embodiment, the pixels are shifted in the horizontal direction by the projection unit composed of the light path synthesizing section200, the first light modulating device301, and the second light modulating device302. The pixels are further shifted in the vertical direction by the beam shifting section400. That is, the pixels are shifted in the horizontal direction on the basis of the geometrical positional relationship between the first light modulating device301and the second light modulating device302. The pixels are further shifted in the vertical direction by the temporal switching of a beam shifting operation performed by the beam shifting section400. As a result, a display of a four-point pixel shift such as the one shown inFIG. 7is realized. Thus, by combining the pixel shift based on the geometrical positional relationship with the pixel shift based on the temporal switching operation, it is possible to obtain an image free from flickering without significantly reducing the light intensity. Therefore, the present embodiment provides images with an excellent display quality and a high resolution.

In the present embodiment, as shown inFIGS. 6A,6B, and7, the direction in which the pixels are arranged in the first field (seeFIG. 6A) crosses the direction in which the pixels are arranged in the second field (seeFIG. 6B). Thus, temporal and spatial deviations in the displayed image are small. Also in this connection, the display quality is improved.

In the above embodiment, colors are not referred to. However, each of the first light modulating device301and second light modulating device302can be constructed using a single plate liquid crystal panel having an array of pixels in three colors including R, G, and B. In this case, the pixel pitch corresponds to that of each color. Further, in the above embodiment, the projection unit shifts the pixels in the horizontal direction, while the beam shifting section400shifts the pixels in the vertical direction. However, the projection unit may shift the pixels in the vertical direction, while the beam shifting section400may shift the pixels in the horizontal direction. More-over, in the above embodiment, the projection optical system510is placed between the beam shifting section400and the screen520. However, the beam shifting section400may be placed between the projection optical system510and the screen520.

FIG. 9is a diagram schematically showing an image projection apparatus using a light modulating unit according to a second embodiment of the present invention. Components corresponding to those in the first embodiment are denoted by the same reference numerals, with their detailed description omitted.

In the above first embodiment, each of the light modulating devices301and302is a reflection type LCD. In the present embodiment, light modulating devices311and312are transmission type LCDs.

In the present embodiment, an illumination light from a light source110is incident on a PBS mirror131. The PBS mirror131separates the illumination light into a P-polarized light component and an S-polarized light component. The separated S-polarized light component is incident directly on a first light modulating device311. As in the case of the first embodiment, the first light modulating device311rotates the incident S-polarized light component in accordance with a video signal to supply a P-polarized light component to a light path synthesizing section200composed of a PBS prism. The P-polarized light component separated by the PBS mirror131is reflected by mirrors132and133and then impinges against a second light modulating device312. As in the case of the first embodiment, the second light modulating device312rotates the incident P-polarized light component in accordance with a video signal to supply an S-polarized light component to the light path synthesizing section200. The other basic operations are the same as those of the first embodiment.

In the present embodiment, as in the case of the first embodiment, the pixels are shifted in the horizontal direction on the basis of the relative positional relationship between the first light modulating device311and the second light modulating device312(a pixel shift by half a pixel pitch). The pixels are further shifted in the vertical direction by a beam shifting operation performed by the beam shifting section400(a pixel shift by half a pixel pitch). As a result, a four-point pixel shift can be realized as in the case of the first embodiment. Further, operations and effects similar to those of the first embodiment can be obtained.

FIG. 10is a diagram schematically showing an image projection apparatus using a light modulating unit according to a third embodiment of the present invention. Components corresponding to those in the first embodiment are denoted by the same reference numerals, with their detailed description omitted.

In the present embodiment, a color image is displayed using three projection units such as the one shown in the first embodiment.

An R (red) component of an illumination light from the light source110is reflected by a dichroic mirror141. The other color components are transmitted through the dichroic mirror141. The light transmitted through the dichroic mirror141is reflected by a dichroic mirror142and then impinges against a dichroic mirror143. The dichroic mirror143reflects a G (green) light and allows a B (blue) light to pass through. In the present embodiment, the three primary colors are generated using the white light source and the dichroic mirrors. However, an exclusive light source may be provided for each of R, G, and B. For example, three light sources may be used including an R color LED, a G color LED, and a B color LED.

The thus separated R, G, and B lights are incident on light path synthesizing sections (PBS prisms)200R,200G, and200B. The configuration of the light path synthesizing sections200R,200G, and200B is similar to that of the light path synthesizing section200, shown in the first embodiment. The polarization plane reflects an S-polarized light component and allows a P-polarized light component to pass through.

The light path synthesizing section200R is accompanied by a first light modulating device301R and a second light modulating device302R. The light path synthesizing section200G is accompanied by a first light modulating device301G and a second light modulating device302G. The light path synthesizing section200B is accompanied by a first light modulating device301B and a second light modulating device302B. The configuration and functions of these light modulating devices (reflection type LCDs) are the same as those of the light modulating devices shown in the first embodiment. Accordingly, as in the case of the first embodiment, the light path synthesizing section200R synthesizes a P-polarized light from the first light modulating device301R and an S-polarized light from the second light modulating device302R. The synthesized light is emitted by the light path synthesizing section200R. This also applies to the light path synthesizing section200G and light path synthesizing section200B.

The R, G, and B lights emitted by the light path synthesizing sections200R,200G, and200B are incident on a color synthesizing prism600. The color synthesizing prism600synthesizes the R, G, and B lights using the nature of the wavelength of each color. The color synthesizing prism is composed of a dichroic prism (X prism). Since both P-polarized light and S-polarized light are incident on the X prism, the difference between its characteristic for the P-polarized light and its characteristic for the S-polarized light (a difference in reflection characteristic and a difference in transmission characteristic) is desirably small. For example, the difference in reflectance between the P-polarized light and the S-polarized light is desirably at most 20%.

As in the case of the first embodiment, a projection light synthesized by the color synthesizing prism600reaches the screen520via the beam shifting section400and the projection optical system510. As a result, as in the case of the first embodiment, a four-point pixel shift can be realized. In this case, the light modulating devices are arranged so that the pixel positions for R, G, and B coincide with one another after a four-point pixel shift. In other words, the projection pixel positions for R, G, and B are superimposed on one another at each of the pixel positions (a), (b), (c), and (d) shown inFIG. 7.

In the present embodiment, as in the case of the first embodiment, the pixels are shifted in the horizontal direction on the basis of the relative positional relationship between the first light modulating devices301R,301G, and301B and the second light modulating devices302R,302G, and302B (a pixel shift by half a pixel pitch). The pixels are further shifted in the vertical direction by a beam shifting operation performed by the beam shifting section400(a pixel shift by half a pixel pitch). As a result, a four-point pixel shift can be realized as in the case of the first embodiment. Further, operations and effects similar to those of the first embodiment can be obtained.

FIG. 11is a diagram schematically showing an image projection apparatus using a light modulating unit according to a fourth embodiment of the present invention. Components corresponding to those in the first embodiment are denoted by the same reference numerals, with their detailed description omitted.

In the present embodiment, a color image is also displayed using a principle similar to that of a four-point pixel shift, shown in the first embodiment.

An illumination light from the light source110is incident on a PBS mirror151. The PBS mirror151then separates the light into a P-polarized light component and an S-polarized light component. The S-polarized light separated by the PBS mirror151is color-separated into an R light, a G light, and a B light by dichroic mirror152to156. The P-polarized light separated by the PBS mirror151is color-separated into an R light, a G light, and a B light by dichroic mirror157to161. The color-separated S-polarized light is supplied to a first light modulating section331. The color-separated P-polarized light is supplied to a second light modulating section332.

The first light modulating section331is composed of a first light modulating device341R for the R color, a first light modulating device341G for the G color, a first light modulating device341B for the B color, and a color synthesizing prism601. The basic configuration of the first light modulating devices341R,341G, and341B is similar to that of the light modulating device311, shown inFIG. 9. That is, any of the first light modulating devices341R,341G, and341B rotates an incident S-polarized light to obtain a P-polarized light. The basic configuration of the color synthesizing prism601is similar to the color synthesizing prism600, shown inFIG. 10. The color synthesizing prism601synthesizes an R, G, and B lights emitted by the first light modulating devices341R,341G, and341B, respectively, and emits a projection light of the P-polarized light.

The second light modulating section332is configured similarly to the first light modulating section331. The color synthesizing prism602synthesizes an R, G, and B lights emitted by the second light modulating devices342R,342G, and342B, respectively, and emits a projection light of the S-polarized light.

The light path synthesizing section200is supplied with the projection light of the P-polarized light color-synthesized by the color synthesizing prism601and the projection light of the S-polarized light color-synthesized by the color synthesizing prism602. As in the case of the first embodiment, the projection light emitted by the light path synthesizing section200reaches the screen520via the beam shifting section400and projection optical system510. As a result, a four-point pixel shift can be realized as in the case of the first embodiment. As also described in the third embodiment, the light modulating devices are of course arranged so that the pixel positions for R, G, and B coincide with one another after a four-point pixel shift.

In the present embodiment, as in the case of the first embodiment, the pixels are shifted in the horizontal direction on the basis of the relative positional relationship between the first light modulating devices341R,341G, and341B and the second light modulating devices342R,342G, and342B (a pixel shift by half a pixel pitch). The pixels are further shifted in the vertical direction by a beam shifting operation performed by the beam shifting section400(a pixel shift by half a pixel pitch). As a result, a four-point pixel shift can be realized as in the case of the first embodiment. Further, operations and effects similar to those of the first embodiment can be obtained.

FIG. 12is a diagram schematically showing an image projection apparatus using a light modulating unit according to a fifth embodiment of the present invention. Components corresponding to those in the first embodiment are denoted by the same reference numerals, with their detailed description omitted.

In the present embodiment, a color image is also displayed using a principle similar to that of a four-point pixel shift, shown in the first embodiment.

In the present embodiment, a first light modulating section361generates a three-primary-color image of a P-polarized light. A second light modulating section362generates a three-primary-color image of an S-polarized light.

The first light modulating section361is composed of a light modulating device block361a, an optical rotatory plate361b, a λ/2 plate (half-wave plate)361d, and a polarizing plate361c. The light modulating device block361ais an LCD unit of an RGB three-plate system. For a G light, the light modulating device block361aemits a projection light of a P-polarized light. For R and B lights, the light modulating device block361aemits a projection light of an S-polarized light. Of the G light (P-polarized light) and R and B lights (S-polarized lights) emitted by the light modulating device block361a, the optical rotatory plate361brotates only one light, the G light, to obtain an S-polarized light. Consequently, the optical rotatory plate361bemits an S-polarized light for all of the R, G, and B lights. Moreover, the S-polarized light from the optical rotatory light361bis rotated by the λ/2 plate361dto become a P-polarized light. The P-polarized light from the λ/2 plate361dis made by the polarization plate361cto be sharper. The sharper P-polarized light is then supplied to the light path synthesizing section200.

The second light modulating section362is composed of a light modulating device block362a, an optical rotatory plate362b, and a polarizing plate362c. The light modulating device block362ais an LCD unit of an RGB three-plate system. For a G light, the light modulating device block362aemits a projection light of a P-polarized light. For an R and B lights, the light modulating device block362aemits a projection light of an S-polarized light. Of the G light (P-polarized light) and R and B lights (S-polarized lights) emitted by the light modulating device block362a, the optical rotatory plate362brotates only the G light to obtain an S-polarized light. Consequently, the optical rotatory plate361bemits an S-polarized light for all of the R, G, and B lights. The S-polarized light from the optical rotatory plate361bis made by the polarization plate361cto be sharper. The sharper S-polarized light is then supplied to the light path synthesizing section200.

As is apparent from the above description, the basic configuration of the first light modulating section361is similar to that of the second light modulating section362. The first light modulating section361has the additional λ/2 plate361dto rotate an S-polarized light to obtain a P-polarized light. The P-polarized light is then supplied to the light path synthesizing section200.

The projection light synthesized by the light path synthesizing section200reaches the screen (not shown) via the beam shifting section400and projection optical system510as in the case of the first embodiment. As a result, a four-point pixel shift can be realized as in the case of the first embodiment. As already described, the light modulating devices are arranged so that the pixel positions for R, G, and B coincide with one another after a four-point pixel shift.

In the present embodiment, as in the case of the first embodiment, the pixels are shifted in the horizontal direction on the basis of the relative positional relationship between the light modulating devices included in the light modulating device block361aand the light modulating devices included in the light modulating device block362a(a pixel shift by half a pixel pitch). The pixels are further shifted in the vertical direction by a beam shifting operation performed by the beam shifting section400(a pixel shift by half a pixel pitch). As a result, a four-point pixel shift can be realized as in the case of the first embodiment. Further, operations and effects similar to those of the first embodiment can be obtained. Furthermore, in the present embodiment, the basic configuration of the first light modulating section361may be the same as that of the second light modulating section362except for the λ/2 plate361d.

FIG. 13is a diagram schematically showing an image projection apparatus using a light modulating unit according to a sixth embodiment of the present invention. Components corresponding to those in the first embodiment are denoted by the same reference numerals, with their detailed description omitted.

In the above embodiments, the light modulating devices are LCDs. However, in the present embodiment, the light modulating devices are DMDs (Digital Micromirror Devices).

An illumination light from the light source110reaches a PBS mirror171via an RGB color wheel170. The PBS mirror171then separates the light into a P-polarized light and an S-polarized light. The P-polarized light is spatially modulated by a first light modulating device371composed of a DMD. The modulated light is then supplied to the light path synthesizing section200via a mirror172. The S-polarized light is spatially modulated by a second light modulating device372composed of a DMD. The modulated light is then supplied to the light path synthesizing section200via a mirror173.

The projection light synthesized by the light path synthesizing section200reaches the screen520via the beam shifting section400and projection optical system510as in the case of the first embodiment. As a result, a four-point pixel shift can be realized as in the case of the first embodiment. As already described, the light modulating devices are arranged so that the pixel positions for R, G, and B coincide with one another after a four-point pixel shift.

In the present embodiment, as in the case of the first embodiment, the pixels are shifted in the horizontal direction on the basis of the relative positional relationship between the first light modulating device371and the second light modulating device372(a pixel shift by half a pixel pitch). The pixels are further shifted in the vertical direction by a beam shifting operation performed by the beam shifting section400(a pixel shift by half a pixel pitch). As a result, a four-point pixel shift can be realized as in the case of the first embodiment. Further, operations and effects similar to those of the first embodiment can be obtained.

The present embodiment determines whether or not the amount of input image information contained in an input video signal is larger than the amount of display image information that can be displayed by each light modulating unit. If the amount of input image information is larger than the amount of display image information (high resolution mode), an image of a relatively high resolution is displayed by a four-point pixel shift as already described. If the amount of input image information is smaller than the amount of display image information (low resolution mode), an image of a relatively low resolution is displayed.

For example, the description below assumes an HDTV (1,920×1,080 pixels) as a high resolution image and an SDTV (960×540 pixels) as a low resolution image. An HDTV-equivalent image can be displayed by using two LCDs for SDTV to carry out a four-point pixel shift.

If an SDTV image is inputted, a high resolution image equivalent to an HDTV image is not obtained even by carrying out a four-point pixel shift as in the case of the HDTV image. Instead, the four-point pixel shift for the SDTV image causes the image to flicker. It is contemplated that the beam shifting section400may not perform a shifting operation for SDTV images (the liquid crystal panel410is always kept off). However, this always results in an image display state such as the one shown inFIG. 6A. It is thus difficult to obtain a smooth display.

Thus, in the present embodiment, a voltage in a state midway between an on state and an off state is applied to the liquid crystal panel410for the SDTV image. Specifically, such a voltage as sets the polarization rotation angle of the liquid crystal panel410at about 45° is always applied to the liquid crystal panel410. With the polarization rotation angle thus set at 45°, the birefringence plate420separates the incident beam into an ordinary light (no) and an extraordinary light (ne) so that these lights have an almost equal quantity of light. Consequently, a pixel display state such as the one shown inFIG. 14can be realized by continuously applying a predetermined intermediate voltage to the liquid crystal panel410. That is, in each field, substantially the same image is displayed at the pixel positions a and b. Further, substantially the same image is displayed at the pixel positions c and d. In other words, an image is displayed which has undergone a spatial low pass filter action in the vertical direction.

FIG. 15is a flow chart showing an operation according to the present embodiment.

A resolution determining section (not shown) determines whether or not the amount of input image information contained in an input video signal is larger than the amount of display image information that can be displayed by each light modulating unit, that is, whether the number of pixels of the input video signal is larger or smaller than the number of pixels that can be displayed by each light modulating device (for example, 960×540 pixels). A high resolution mode is selected if the amount of input image information is larger than the amount of display image information. A low resolution mode is selected if the amount of input image information is smaller than the amount of display image information.

If a video signal of a high resolution (HDTV or the like) is inputted and the high resolution mode is selected, a four-pixel pixel shift is carried out as already described in the above embodiments. Specifically, the liquid crystal panel410is repeatedly turned on and off for each field to sequentially switch the liquid crystal panel410between the two states, that is, determine whether or not to rotate the direction of polarization of the projection light through 90°. Further, video signals are sampled at the pixel positions a, b, c, and d.

If a video signal of a low resolution (SDTV or the like) is inputted and the low resolution mode is selected, the liquid crystal panel410is maintained in a fixed state (half tone state) so as to rotate the direction of polarization of the projection light through 45°. Further, video signals are sampled at the pixel positions a and d (or b and c or a and c or b and d). Thus, a display such as the one shown inFIG. 14is obtained.

As described above, in the present embodiment, in the high resolution mode, by carrying out a four-point pixel shift as in the case of the first embodiment, it is possible to obtain operations and effects similar to those of the first embodiment. Further, in the present embodiment, different display methods are used in the high resolution mode and in the low resolution mode. This enables the appropriate display corresponding to each of the high and low resolution modes.

The present embodiment realizes a three dimensional image (3-D image) display using a technique similar to that described above in the first to sixth embodiments. The basic configuration of the present embodiment is similar to that of the first embodiment. In the description below, components corresponding to those in the first embodiment are denoted by the same reference numerals, with their detailed description omitted.

Some image projection apparatuses for 3-D image display are called polarization eyeglass systems. With the polarization eyeglass system, for example, an S-polarized light image is used as a left eye image (L image). A P-polarized light image is used as a right eye image (R image). A user observes a 3-D image with a pair of eyeglasses comprising a S-polarized light polarizing plate for the left eye and a P-polarized light polarizing plate for the right eye.

The pixel arrangement for obtaining a 3-D image may be similar to that described in the first embodiment and the like (seeFIGS. 4,6, and7). However, in the present embodiment, the pixel arrangement shown below is employed.

In the first embodiment, the first light modulating device301and the second light modulating device302are arranged offset from each other by half a pixel pitch only in the horizontal direction as shown inFIG. 4. However, in the present embodiment, as shown inFIG. 16, the first light modulating device301and the second light modulating device302are arranged offset from each other by half a pixel pitch not only in the horizontal direction but also in the vertical direction.FIG. 16is a diagram showing an array of pixels on the projection plane (screen plane), of both first light modulating device301and second light modulating device302, after projection lights have been synthesized by the light path synthesizing section, as shown inFIG. 4.

FIGS. 17A and 17Bare diagrams illustrating the action of a light modulating unit according to the present embodiment.FIG. 17Ashows the case where the voltage applied to the liquid crystal panel410is off.FIG. 17Bshows the case where the voltage applied to the liquid crystal panel410is on. For convenience, the light path synthesizing section is not shown.

FIGS. 18A and 18Bare diagrams showing the array of pixels on the projection plane (screen plane), of the first light modulating device (first LCD)301and second light modulating device (second LCD)302, after the projection lights have passed through a beam shifting section composed of the liquid crystal panel410and the birefringence plate420.FIG. 18Ashows the case where the voltage applied to the liquid crystal panel410is off.FIG. 18Bshows the case where the voltage applied to the liquid crystal panel410is on.

As described above, the first light modulating device301and the second light modulating device302are arranged offset from each other by half a pixel pitch not only in the horizontal direction but also in the vertical direction. Thus, the P-polarized light from the first light modulating device301and the S-polarized light from the second light modulating device302are already offset from each other by half a pixel pitch in the vertical direction before entering the liquid crystal panel410.

Accordingly, as shown inFIG. 17A, if the liquid crystal panel410is off, the projection light from the first light modulating device301and the projection light from the second light modulating device302have an equal height in the vertical direction after passing through the birefringence plate420. As a result, on the projection plane (screen plane), the pixel position (a) of the projection light from the first light modulating device301and the pixel position (d′) of the projection light from the second light modulating device302are offset from each other by half a pixel pitch in the horizontal direction but are not offset in the vertical direction, as shown inFIG. 18A.

Further, as shown inFIG. 17B, if the liquid crystal panel410is on, the projection light from the first light modulating device301and the projection light from the second light modulating device302are offset from each other by one pixel pitch in the vertical direction. As a result, on the projection plane (screen plane), the pixel position (b) of the projection light from the first light modulating device301and the pixel position (c′) of the projection light from the second light modulating device302are offset from each other by half a pixel pitch in the horizontal direction and by one pixel pitch in the vertical direction, as shown inFIG. 18B.

As already described, in the present embodiment, the S-polarized light image is used as an L image. The P-polarized light image is used as an R image. Accordingly, when the liquid crystal panel410is off, the S-polarized light image at the pixel position (a) corresponding to the first light modulating device301is displayed as an L image. The P-polarized light image at the pixel position (d′) corresponding to the second light modulating device302is displayed as an R image. When the liquid crystal panel410is on, the S-polarized light image at the pixel position (c′) corresponding to the second light modulating device302is displayed as an L image. The P-polarized light image at the pixel position (b) corresponding to the first light modulating device301is displayed as an R image.

FIG. 19is a diagram showing a pixel array state obtained by synthesizing the display state inFIG. 18Aand the display state inFIG. 18B. As shown inFIG. 19, a unit display area is composed of the pixel positions (a), (b), (c′), and (d′). InFIG. 19, there are no pixels adjacent to pixels around the periphery of a rectangular area E in the horizontal direction. Thus, the pixels may appear serrated or flickering around the periphery of the image, thus degrading the display quality. Therefore, the pixels outside the rectangular area E may be displayed as a black image.

FIG. 20is a table illustrating the temporal flow of the display state in the 3-D image projection apparatus according to the present embodiment.

As shown inFIG. 20, in the first field of each frame, the first light modulating device displays an L image (S-polarized light image) at the pixel position (a). The second light modulating device displays an R image (P-polarized light image) at the pixel position (d′). In the second field, the first light modulating device displays an R image (P-polarized light image) at the pixel position (b). The second light modulating device displays an L image (S-polarized light image) at the pixel position (c′).

Thus, in the present embodiment, 3-D images with an excellent display quality and a high resolution can be obtained by combining the pixel shift based on the geometrical positional relationship with the pixel shift based on the temporal switching operation as in the case of the first embodiment or the like. Further, since the pixel positions of the L and R images are reversed in the horizontal direction for each field, it is possible to obtain 3-D images with reduced temporal and spatial deviations in the displayed image as well as an excellent display quality.

As described above, according to the present invention, images with an excellent display quality and a high resolution can be obtained by combining the pixel shift based on the geometrical positional relationship with the pixel shift based on the temporal switching operation.