JP5772091B2 - Pixel shift display device, pixel shift display method, and projection display device including pixel shift display device - Google Patents

Description

The present invention relates to a pixel shift display device for displaying a high-definition image, a pixel shift display method, and a projection display device including the pixel shift display device.

  As one of methods for displaying a high-definition image, a pixel shift display method is known. In this method, each time an image is updated, the image on the projection surface (display surface) is alternately shifted by a predetermined distance and displayed, so that the number of pixels constituting one image is larger than that. High definition video can be obtained visually.

  However, when this method is applied to a liquid crystal display element, since the response characteristics of the liquid crystal display element are insufficient, so-called crosstalk occurs in which the image before update and the image after update overlap at the image update timing. . For example, when a 60 Hz video signal is displayed with a pixel shift, since the liquid crystal drive is 120 Hz, the pixel display period is about 8.4 ms, and two different images alternately shifted by a predetermined distance are about 8.4 ms each. It is necessary to display in time sequence. On the other hand, the rise time and fall time, which are indicators of the response characteristics of the liquid crystal display element, are about 4 ms in the case of nematic liquid crystal. That is, there is a possibility that crosstalk will occur for a period of 4 ms in the display period of 8.4 ms. As a result, a phenomenon occurs in which each pixel of the image that is not shifted and each pixel of the shifted image appear to be connected to each other, resulting in a decrease in separation characteristics between images and deterioration in resolution, which is the original purpose of pixel shifting. It becomes an obstacle to fine display.

  With respect to such a problem, Japanese Patent Laying-Open No. 2005-57457 (Patent Document 1) proposes a technique for suppressing crosstalk. In this method, crosstalk is eliminated by controlling the illumination light to be blocked during the image update period. In this control, a mechanical shutter is used as a light shielding means for the light output from the optical integrator.

JP 2005-57457 A

  In the configuration of Patent Document 1 using a mechanical shutter, it is necessary to secure a wide space in consideration of thermal measures in the display device, which inevitably increases the size of the device and increases the manufacturing cost.

  In view of such a problem, the present invention is a pixel-shifted display device, a pixel-shifted display method, and a projection-type display device including a pixel-shifted display device that can reduce manufacturing costs and have a simple structure that does not visually recognize the influence of crosstalk. For the purpose of provision.

A first aspect of the present invention is a pixel-shifted display device, in which a liquid crystal display element that emits light by polarization-modulating light according to the intensity of a display image, and the liquid crystal according to the start of switching of the display image A first polarization conversion element that changes the polarization direction of light from the display element by 90 ° around the optical axis, and an optical path at the time of emission of light from the first polarization conversion element according to the polarization direction The birefringence element to be shifted and the polarization direction of the light from the birefringence element in 90 ° increments around the optical axis from the polarization direction set by the first polarization conversion element in response to completion of switching of the display image The polarization direction of the second polarization conversion element to be changed and the light from the second polarization conversion element is one of the two polarization directions that can be set by the first polarization conversion element. A polarizing element that emits only light in a direction, and the polarizing element And a projection optical system for enlarging and projecting light from the child toward the projection surface.

  The incident surface of the polarizing element is preferably inclined with respect to the traveling direction of the light from the second polarization conversion element so that the light reflected from the incident surface does not enter the incident surface again. .

  The polarizing element is preferably a wire grid.

According to a second aspect of the present invention, light is polarization-modulated and emitted according to the intensity of the display image, and as the first polarization direction rotation, the polarization direction of the light according to the start of switching of the display image Is changed by 90 ° around the optical axis, the optical path of the light is shifted according to the polarization direction using a birefringence element, and the polarization direction of the light with the shifted optical path is the first direction. A pixel-shifted display method of emitting only light in one of the two polarization directions that can be set by rotating the polarization direction of the image, and enlarging and projecting the emitted light toward the projection plane, As the polarization direction rotation, in accordance with the completion of switching of the display image, the polarization direction of the light whose optical path is shifted is changed by 90 ° around the optical axis from the polarization direction set by the first polarization direction rotation. It is characterized by making it.

  According to a third aspect of the present invention, there is provided a projection display device including the pixel shift display device according to the first aspect.

  According to the present invention, every time the display image is updated, the projection of the image onto the projection surface is stopped, so that the projection surface is a so-called black display. Therefore, it is possible to provide a high-definition video without making the viewer visually recognize the influence of crosstalk at the time of update on the video. In addition, since the pixel shift display device has a simple configuration, a projection display device using the pixel shift display device can be provided at low cost.

It is a schematic block diagram of the projection type display apparatus carrying the pixel shift display apparatus which concerns on one Embodiment of this invention. It is a schematic block diagram of the pixel shift display apparatus which concerns on one Embodiment of this invention. It is a schematic diagram for demonstrating operation | movement of the pixel shift display apparatus which concerns on one Embodiment of this invention. 5 is a timing chart showing the operation of the pixel shift display device according to the embodiment of the present invention in time series. It is a modification of the pixel shift display apparatus which concerns on one Embodiment of this invention. It is a figure which shows the optical path of the unnecessary light in the pixel shift display apparatus which concerns on one Embodiment of this invention.

  A pixel shift display device according to an embodiment of the present invention will be described with reference to the drawings. The pixel-shifted display device of this embodiment is mounted on a projection display device 30 such as a projector shown in FIG.

  FIG. 1 is a schematic configuration diagram of a projection display device 30 equipped with a pixel shift display device 1 of the present embodiment. In this example of the projection display device 30, the pixel-shifted display device 1 is light of a color synthesis prism (cross dichroic prism) 18 that emits three light beams of red, green, and blue incident from individual optical paths into one optical path. Provided on the exit side.

  As shown in FIG. 1, the projection display device 30 includes a light source 11, an integrator 12 and a polarization beam combiner 13 provided on the side where light from the light source 11 travels.

  As the light source 11, a high-pressure mercury lamp, a metal halide lamp, or the like is used. The white light emitted from the light source 11 is reflected by the reflector 11a having a straight or rotating paraboloid and is incident on the integrator 12 as substantially parallel light.

  The integrator 12 includes a first integrator 12a and a second integrator 12b, and spatially equalizes the intensity of incident white light. The polarization combining element 13 is an optical element composed of a plurality of polarization beam splitters and retardation plates arranged in parallel in a strip shape and formed in a flat plate shape, and the polarization direction of randomly polarized incident light is constant. The light is emitted with the same polarization direction. In the present embodiment, the polarization beam combiner 13 converts incident random polarized light into P waves. As another form, the polarization beam combiner 13 may align incident light into S waves, and then convert the S waves into P waves using a rotator (not shown) or the like.

  The projection display device 30 further includes a cross-type dichroic mirror 14. The cross-type dichroic mirror 14 separates the white light from the polarization combining element 13 into light B containing a blue component and light Y containing a yellow component, and each emits them to different optical paths.

  The blue light B that has passed through the cross-type dichroic mirror 14 is reflected by the dichroic mirror 15 and enters a wire grid 16 as a polarization beam splitter (PBS). The dichroic mirror 15 may be a known mirror formed of an aluminum vapor deposition film or the like. The wire grid 16 transmits the P wave and reflects the S wave. Since the light B from the cross-type dichroic mirror 14 is a P wave, it passes through the wire grid 16 and enters the blue liquid crystal display element 17. The blue liquid crystal display element 17 reflects the incident light toward the wire grid 16 while modulating the polarization component (that is, the P wave component) of the incident light B into an S wave according to the intensity of the blue component of the display image. To do. In the reflected light from the blue liquid crystal display element 17, only the S wave component is reflected by the wire grid 16 and enters the color synthesis prism 18.

  On the other hand, the yellow light Y that has passed through the cross-type dichroic mirror 14 passes through the dichroic mirror 19 and further enters the dichroic mirror 20. The dichroic mirror 19 may be a known mirror formed of an aluminum vapor deposition film or the like.

  In the dichroic mirror 20, yellow light Y is separated into green light G and red light R, green light G is reflected, and red light R is transmitted. As shown in FIG. 1, the wire grid 21 and the green liquid crystal display element 22 as PBS, the wire grid 23 and the red liquid crystal display element 24 as PBS are installed on the optical paths of the light G and the light R thereafter. These functions are the same as those of the wire grid 16 and the blue liquid crystal display element 17 used for the light B. Therefore, for the green light G, only the S wave component obtained by the polarization modulation by the green liquid crystal display element 22 is incident on the color combining prism 18, and for the red light R, the polarization by the red liquid crystal display element 24 is performed. Only the S wave component obtained by the modulation enters the color synthesis prism 18.

  The selection and arrangement of each optical element up to the color synthesis prism 18 are not limited to those shown in FIG. 1 and can be changed as appropriate. Further, the liquid crystal display elements 17, 22, and 24 are not limited to the reflection type, and may be a transmission type.

  The color synthesizing prism 18 synthesizes light B, G, and R incident from the side surfaces and the back surface, and emits the light from the front surface. The light emitted from the color synthesis prism 18 enters the projection lens 7 as the projection optical system via the pixel shift unit 2 of the pixel shift display device 1. The projection lens 7 projects the incident illumination light onto a screen (not shown), forms an image, and displays an image.

  FIG. 2 is a schematic configuration diagram of the pixel shift display device 1. The pixel shift display device 1 includes the liquid crystal display elements 17, 22, and 24 described above, a pixel shift unit 2 that is an assembly of optical elements, a polarization control driver 8, and a shutter control driver 9.

  The pixel shifting unit 2 includes a half-wave plate 31, a polarization angle rotation element (first polarization conversion element) 3, a birefringence element 4 provided after the polarization angle rotation element 3, and a birefringence element 4. A shutter element (second polarization conversion element) 5 provided in the rear stage and a polarizer (polarizing plate) 6 provided in the rear stage of the shutter element 5 are provided. Each optical element 3, 4, 5, 6 may be configured as a laminated structure, or may be configured to be supported by a member formed of transparent glass or the like. Light from the color synthesis prism 18 enters from the polarization angle rotation element 3, exits from the polarization element 6, and enters the projection lens 7 as a projection optical system.

  The half-wave plate 31 uses the optical axis (fast axis or slow axis) T of the half-wave plate 31 as incident light (S wave) in order to rotate the polarization direction of the incident S wave light by 45 °. ) With respect to the direction of polarization of light (i.e., the optical axis). As shown in FIG. 3, the light emitted from the half-wave plate 31 is polarized at 45 ° to the right with respect to the polarization direction of the incident light as viewed from the traveling direction of the light.

  The polarization angle rotating element 3 converts the polarized light in the right 45 ° direction into the polarized light in the left 45 ° direction by rotating the polarization angle (polarization direction) of the incident light by 90 ° around the optical axis. For the convenience of the following description, the right 45 ° direction polarization is referred to as an R wave, and the left 45 ° direction polarization is referred to as an L wave. This conversion is performed based on the output voltage (output signal) of the polarization control driver 8 every time the display image on the liquid crystal display elements 17, 22, 24 is updated. In this embodiment, a transmissive liquid crystal panel composed of, for example, nematic liquid crystal is used as an optical element having such an optical rotation function.

  The birefringent element 4 is an optical element formed of a substance (for example, quartz) that generates birefringence, and shifts the optical path at the time of emission according to the polarization directions of the incident R wave and L wave. The birefringent element 4 is also an optical low pass filter (OLPF). When the pixel pitch of the liquid crystal display elements 17, 22, and 24 is G, the birefringent element 4 of the present embodiment has an optical path shift amount of about (√2 / 2) G between the R wave and the L wave. Is formed.

  The shutter element 5 has the same configuration as that of the polarization angle rotation element 3, and by rotating the polarization angle of incident light by 90 ° around its optical axis in accordance with the voltage applied by the shutter control driver 9, an R wave is generated. Convert to L wave (or L wave to R wave).

  The polarizer 6 selects and emits only the light in one polarization direction out of the two polarization directions set by the polarization angle rotation element 3, and discards the light in the other polarization direction. The polarizing element 6 may be either a transmission type or a reflection type. The polarizing element 6 of the present embodiment is, for example, a wire grid, and is disposed so as to allow only the R wave to pass and block the L wave.

  The projection lens 5 magnifies and projects the light from the polarizer 6 toward the projection plane 28. The projection lens 5 may be configured using a known lens. Therefore, detailed description is omitted.

  The operation of the pixel shift display device 1 of the present embodiment will be described.

  FIG. 3 is a schematic diagram for explaining the operation of the pixel shift display device 1, and FIG. 4 is a timing chart showing this operation in time series.

  In the present embodiment, from one frame image (referred to as an original image) or from a plurality of frames before and after an original image, an image in which pixel shifting is not performed and an image in which pixel shifting is performed within the display period of one original image. Are generated (hereinafter referred to as sub-frame images). Moreover, it is good also as a structure which is not produced | generated by a projection type display apparatus and these subframe images are supplied to a projection type display apparatus from the outside. For example, as shown in FIG. 4, display of the original image A is assigned during a period from time t0 to time t4, and display of the original image B is assigned from time t4 to time t8. Therefore, in this example, within the period of the original image A, the sub-frame image A (1) that is not subjected to pixel shifting is first projected on the projection plane, and then the sub-frame image A (2) that is subjected to pixel shifting is then displayed. Projected. Thereafter, within the display period of the original image B, the subframe image B (1) without pixel shift is projected, and then the subframe image B (2) with pixel shift is projected. Thereafter, such update / display of the sub-frame image is repeated.

  This series of image display will be described in detail. First, it is assumed that the projection of the sub-frame image A (1) on the projection plane 28 is started at time t0. The image display light 27 is originally light that has been polarization-modulated by the liquid crystal display element 17 (22, 24) and reflected from the wire grid 16 (21, 23). Therefore, this light is polarized into S waves, and is incident on the polarization angle rotation element 3 at a right angle of 45 ° at the exit of the half-wave plate 31 as shown in FIG.

  At time t0, the output of the polarization control driver 8 is in a voltage low state (off). Therefore, the polarization angle rotation element 3 does not rotate the polarization direction of the image display light 27, passes through the polarization angle rotation element 3 as it is, and enters the birefringence element 4. In the birefringent element 4, refraction corresponding to this polarization state (that is, R wave) occurs. The image display light 27 is refracted by the birefringent element 4, and further advances straight and enters the shutter element 5.

  At time t0, the output of the shutter control driver 9 is in a voltage high state (on). Accordingly, the polarization direction of the shutter element 5 is also rotated, and the R-wave image display light 27 is transmitted through the shutter element 5 and becomes L-wave. In other words, the shutter element 5 converts R-wave light into L-wave (this is referred to as RL conversion for convenience). The image display light 27 transmitted through the shutter element 5 then enters the polarizer 6. As described above, since the polarizer 6 of the present embodiment is arranged so as to transmit the R wave, the image display light 27 cannot pass through the polarizer 6. As a result, the sub-frame image A (1) is not projected on the projection plane 28. Due to the response characteristics of the liquid crystal display elements 17, 22, and 24, at the time when the sub-frame image A (1) rises, the trajectory overlap (crosstalk) of pixels at the same position on both images is changed from time t0 to time t1. The image is not displayed during this period.

  At time t1, the output of the shutter control driver 9 is set to a voltage low state (off). The R-wave image display light 27 remains as the R wave even if it passes through the shutter element 5. (This is called RR conversion for convenience). The image display light 27 transmitted through the shutter element 5 then enters the polarizer 6. As described above, since the polarizer 6 of the present embodiment is arranged so as to transmit the R wave, the image display light 27 can pass through the polarizer 6.

  Next, consider the display of the subframe image A (2). In the present embodiment, the sub-frame image A (2) is projected onto the projection plane after pixel shifting. Therefore, ideally, the image display light 27 of the sub-frame image A (2) is converted into an L wave at time t2, and the optical path is shifted by about (√2 / 2) G in the birefringent element 4, and then What is necessary is just to convert the image display light 27 into R wave again. However, due to the response characteristics of the liquid crystal display elements 17, 22, and 24, the locus overlap (crosstalk) of pixels at the same position on both images occurs at the time when the subframe image A (2) rises. Therefore, during the period in which the crosstalk is occurring, the projection onto the projection surface 28 is stopped, and this crosstalk is visually excluded.

  Specifically, the following processing is performed. At time t2 when the liquid crystal display elements 17, 22, and 24 start displaying the sub-frame image A (2), the output of the polarization control driver 8 is set to the voltage high state (on). Accordingly, the polarization direction of the image display light 27 rotates in the polarization angle rotation element 3 and enters the birefringence element 4. In the birefringent element 4, refraction corresponding to this polarization state (that is, L wave) occurs. The image display light 27 is refracted by the birefringent element 4, the optical path is shifted by about (√2 / 2) G, and further advances straight and enters the shutter element 5.

  The output of the shutter control driver 9 is left in the voltage low state (off). Then, the shutter element 5 maintains the polarization direction (L wave) of the image display light 27 as it is (referred to as LL conversion for convenience). Since the image display light 27, which is an L wave, is blocked from traveling by the polarizer 6, as a result, the projection of the sub-frame image A (2) onto the projection plane 28 is stopped.

  Thereafter, when the time when the crosstalk disappears (that is, the display image on the liquid crystal display elements 17, 22, and 24 is completely switched from the subframe image A (1) to the subframe image A (2)) is t3, At t3, the shutter control driver 9 is switched from the voltage low state (off) to the voltage high state (on). Therefore, the shutter element 5 performs a rotation operation in the polarization direction (this is referred to as LR conversion for convenience). The image display light 27 that has become an R wave can pass through the polarizing element 6. As a result, the sub-frame image A (2) is projected onto the projection plane 28 in a state where the pixel shift by the birefringence element 4 is performed.

  When switching from the subframe image A (2) to the subframe image B (1), the same operation as the operation from the time t0 to the time t1 is performed. That is, assuming that the time when the liquid crystal display elements 17, 22, and 24 start displaying the sub-frame image A (2) is t4 and the time when the crosstalk disappears is t5, the shutter control driver is used during the period from time t4 to time t5. 9 is kept in the voltage high state (on), and at time t5, the output of the shutter control driver 9 is switched from the voltage high state (on) to the voltage low state (off). During the period from time t4 to time t5, the light transmitted through the shutter element 5 remains as an L wave and is blocked by the polarizer 6. Next, since the rotation operation from the L wave to the R wave is started at time t <b> 5, the R wave image display light 27 passes through the shutter element 5 as it is and is not blocked by the polarizer 6. As a result, the projection of the sub-frame image A (2) onto the projection plane 28 is started. That is, the state of the polarization angle rotating element 3 and the shutter element 5 in the period from time t4 to time t5 is the same as the state in the period from time t0 to time t1.

  In the period from time t6 to time t8, the same operation as in the period from time t2 to t4 is repeated.

  With the above operation, when the projection of the sub-frame image is switched, the projection is temporarily stopped. Accordingly, it is possible for the viewer to display a high-definition pixel-shifted image without visually recognizing the crosstalk of the image generated during this time.

  Note that the polarizing element 6 of the above-described pixel shift display device 1 is preferably arranged so as to be inclined by a predetermined angle θ with respect to the traveling direction of light from the shutter element 5 as shown in FIG.

  When the incident surface of the polarizing element 6 is arranged perpendicularly to the light traveling direction, unnecessary light (P wave) reflected by the incident surface travels backward through the optical path so far, and thus enters the polarizing element 6. There is a possibility of repeated re-incidence. In this case, since the unnecessary light has an S wave component by the polarization angle rotating element 3 or the like, a ghost image is generated when the light of this component passes through the polarizing element 6.

  Therefore, the light reflected by the incident surface of the polarizing element 6 is inclined at an angle θ with respect to the traveling direction of the light from the shutter element 5 so that it does not enter the incident surface again. As a result, as shown in FIGS. 6A to 6C, the unnecessary light 29 of each color of blue, green, and red is prevented from re-incident on the polarizing element 6, and the generation of a ghost image is suppressed.

  In this case, it is more preferable to use a wire grid as the polarizing element 6. In general, the wire grid has a low dependence on the polarization characteristic with respect to the incident angle of light, and it is easy to maintain the blocking characteristic of the P wave even if it is tilted. Furthermore, heat generation caused by absorption of unnecessary light can be suppressed as compared with an absorption type polarizing element.

  Note that the inclination angle θ of the polarizing element 6 is appropriately changed depending on the arrangement of the optical system in the image display apparatus on which the pixel shifting unit 2 is mounted, and the optical system of the image display apparatus applied to this embodiment is shown in each drawing. Not limited to those.

  As described above, according to the pixel-shifted display device and the pixel-shifted display method of this embodiment, the projection of the image onto the projection plane is stopped every time the display image is updated, so that the projection plane is a so-called black display. Therefore, it is possible to provide a high-definition video without causing the viewer to visually recognize the influence of crosstalk when updating the image. Further, as described above, the pixel-shifted display device according to the present embodiment has a simple configuration and can be provided at a low cost.

  Furthermore, when the polarizing element is tilted in the pixel shifting unit, it is possible to suppress the re-incident reflected light from entering the polarizing element, so it is possible to suppress the ghost image and improve the reliability of pixel display. is there.

DESCRIPTION OF SYMBOLS 1 ... Pixel shift display apparatus, 2 ... Pixel shift unit, 3 ... Polarization angle rotation element (1st polarization conversion element), 4 ... Birefringence element, 5 ... Shutter element (2nd polarization conversion element), 6 ... Polarization , 7 ... projection lens (projection optical system), 8 ... polarization control driver, 9 ... shutter control driver, 11 ... light source, 12 ... integrator, 13 ... polarization combining element, 14 ... cross dichroic mirror, 15, 19, 20 ... Dichroic mirror, 18 ... Color synthesis prism, 16, 21, 23 ... Wire grid, 17, 22, 24 ... Liquid crystal display element, 29 ... Unnecessary light, 30 ... Projection type display device, 31 ... 1/2 wavelength plate

Claims (5)

A liquid crystal display element that emits light after polarization modulation according to the intensity of the display image;
A first polarization conversion element that changes a polarization direction of light from the liquid crystal display element by 90 ° around its optical axis in response to the start of switching of the display image;
A birefringent element that shifts an optical path at the time of emission of light from the first polarization conversion element according to the polarization direction;
Second polarization that changes the polarization direction of light from the birefringent element by 90 ° around the optical axis from the polarization direction set by the first polarization conversion element in response to completion of switching of the display image. A conversion element;
A polarization element that emits only light in one of the two polarization directions that can be set by the first polarization conversion element with respect to the light from the second polarization conversion element; ,
A pixel shift display device comprising: a projection optical system that enlarges and projects light from the polarizing element toward a projection plane.   The incident surface of the polarizing element is inclined with respect to the traveling direction of the light from the second polarization conversion element so that light reflected from the incident surface does not enter the incident surface again. The pixel shift display device according to claim 1. The pixel shifting display device according to claim 1, wherein the polarizing element is a wire grid. Depending on the intensity of the display image, the light is polarized and emitted, and as the first polarization direction rotation, the polarization direction of the light is 90 ° around its optical axis in response to the start of switching of the display image. Change
Using a birefringent element, the optical path of the light is shifted according to the polarization direction,
With respect to the light whose optical path is shifted, the polarization direction of the light is emitted only in one of the two polarization directions that can be set by rotating the first polarization direction.
A pixel shifted display method for enlarging and projecting the emitted light toward a projection plane,
As the second polarization direction rotation, the polarization direction of the light whose optical path is shifted in response to the completion of switching of the display image is changed from the polarization direction set by the first polarization direction rotation around the optical axis. A pixel-shifted display method characterized by changing in degrees.   A projection display device comprising the pixel-shifted display device according to any one of claims 1 to 3.

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