JP2004021025A - Image display device and method of driving image display device - Google Patents

Abstract

In a display device including an image shift element, a shift in timing between display timing in the image display element and image shift in the image shift element is reduced.
A display device according to the present invention includes an image display element having a plurality of pixels arranged therein, in which images to be displayed are sequentially written based on an input signal, and an image display element disposed on a light emitting side of the image display element. And an image shift element 3 for optically shifting an image displayed on the image display element 2. Since the image writing period to the image display element in one vertical period is shorter than the effective image display period in one vertical period of the original signal of the input signal, the operation of the image shift element 3 is divided in a plane. Even if not. can do.
[Selection diagram] FIG.

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image display device including an image shift element, and more particularly, to an image display device such as a head-mounted display (hereinafter, referred to as “HMD”) or a projection display device (projector).
[0002]
[Prior art]
The liquid crystal display device includes a pair of substrates and a liquid crystal layer sandwiched between the substrates. The substrate has a plurality of pixel electrodes regularly arranged in rows and columns (matrix), and a driving voltage corresponding to an image signal is applied to each of the pixel electrodes. The application of this voltage changes the optical characteristics (light transmittance and reflectance) of the liquid crystal layer for each pixel, so that images and characters can be displayed.
[0003]
Methods for applying an independent drive voltage to each pixel electrode on the substrate include a "simple matrix method" and an "active matrix method".
[0004]
In the case of the active matrix system, switching elements corresponding to each pixel electrode are arranged on a substrate. A substrate on which such switching elements are arranged is called an active matrix substrate. A switching element on the active matrix substrate functions to switch between an electrically conductive state and a non-conductive state between a corresponding pixel electrode and a signal wiring. As such a switching element, a metal-insulator-metal (MIM) element, a thin film transistor (TFT), or the like is suitably used.
[0005]
The switching element is required to exhibit as high an electrical resistance as possible when in a non-conductive state. However, when strong light enters the non-conductive switching element, the electric resistance of the switching element decreases and a leak current is generated, so that the charge stored in the pixel electrode is discharged. Occurs. In addition, an appropriate level of drive voltage is not applied to the pixel electrode, so that the original display operation is not performed. Even in a black state, light leaks and the contrast ratio decreases.
[0006]
In the case where the liquid crystal display element is a transmission type, a light-blocking layer called a black matrix (BM) is provided on an active matrix substrate or on a counter substrate facing the active matrix substrate with a liquid crystal layer interposed therebetween in order to solve the above problem. Be placed. The presence of the black matrix reduces the area ratio (opening ratio) of the pixel opening. In order to achieve high definition by reducing the occupied area of the black matrix, the switching elements and wirings may be miniaturized. However, miniaturization of the switching elements and wirings causes a decrease in driving force and an increase in wiring resistance. Will be. Also, it is difficult to miniaturize the switching elements and wirings due to restrictions on manufacturing technology.
[0007]
U.S. Pat. No. 4,984,091 discloses a technique for optically moving a display image by a pixel pitch for the purpose of achieving higher definition using a non-display area on a black matrix. According to this technique, an image corresponding to the moved pixel position is displayed in synchronization with the movement of the pixel. As a result, the apparent number of pixels increases, so that even when a display element with a low resolution is used, a display similar to that when a high-definition display panel is used can be performed.
[0008]
U.S. Patent No. 6,0643 discloses a method in which red, green, and blue (hereinafter, referred to as "RGB") pixels are sequentially shifted optically by a shift element, and the shifted pixels are superimposed and displayed. are doing. In this method, RGB pixels are displayed in a time-division manner in a region corresponding to one pixel. As a result, the apparent resolution can be tripled without reducing the pixel pitch on the display panel.
[0009]
U.S. Pat. No. 6,0643 discloses an image shift element which combines a liquid crystal element and a birefringent element as means for optically shifting an image. The birefringent element is formed of a material whose light refraction direction changes depending on the polarization direction of incident light. If the polarization direction of the light incident on the birefringent element is changed by the liquid crystal element, the optical axis of the light emitted from the birefringent element can be shifted.
[0010]
FIG. 1 shows a known image shift element. The image shift element includes a liquid crystal element 10 and a birefringent element 12 that are arranged in series along the light propagation direction. The liquid crystal element 10 changes the polarization state between a state in which an incident electric field vector vibration plane of linearly polarized light (hereinafter, referred to as a “polarization plane”) is rotated by 90 ° and a state in which the plane is transmitted without being rotated. Switching. The birefringent element 12 can shift the light beam according to the direction of the plane of polarization of the linearly polarized light that has entered.
[0011]
In the example shown in FIG. 1, the electric field vector direction (polarization direction) of light incident on the liquid crystal element 10 is parallel to the paper. Since the liquid crystal element 10 uses a TN mode liquid crystal (TN liquid crystal) having a positive refractive index anisotropy Δε, when no voltage is applied to the liquid crystal layer of the liquid crystal element 10 (when the voltage is OFF), Molecules are twisted by 90 °, and their optical rotation rotates the plane of polarization of incident light by 90 °. On the other hand, when a voltage higher than a predetermined level is applied to the liquid crystal layer of the liquid crystal element 10 (when the voltage is ON), the direction of the major axis of the liquid crystal molecules is aligned with the direction of the electric field, so that the incident light The light is emitted while the polarization plane is parallel to the paper. The illustrated birefringent element 12 allows light having a polarization plane parallel to the paper surface to pass through as it is, but can shift light perpendicular to the paper surface.
[0012]
The liquid crystal element 10 in the image shift element as shown in FIG. 1 emits the first linearly polarized light according to the magnitude of the applied voltage and the second linearly polarized light having a plane of polarization perpendicular to the first linearly polarized light. It is required to appropriately and quickly switch the state between the state of emitting polarized light and the state of emitting polarized light.
[0013]
A projection type image display device using such an image shift element is disclosed in Japanese Patent Application Laid-Open No. 4-63332.
[0014]
Japanese Patent Application Laid-Open No. 8-194207 discloses that the image shift element is divided into a plurality of regions along the vertical scanning direction of the image display element, so that the image display timing of the image display element and the image shift element A technique for reducing the deviation from the shift timing is disclosed.
[0015]
With reference to FIG. 2, an operation when the image shift element is divided into three areas A to C and driven sequentially will be described. In FIG. 2, the liquid crystal element and the birefringent element are integrally described as "image shift element 3 '" without distinction.
[0016]
The image display element has a display area in which a plurality of pixels are regularly arranged, and each row of pixels corresponds to a horizontal scanning line. Image writing is performed in units of scanning lines from the top to the bottom of the display area. After the corresponding image data is written on the k-th horizontal scanning line from the top (k is a positive integer), the corresponding image data is written on the (k + 1) -th horizontal scanning line. The interval from the start of writing the image data to the k-th horizontal scanning line to the start of writing the image data to the (k + 1) -th horizontal scanning line is called "one horizontal scanning period (1H)". Since there is a blanking period (horizontal blanking period) in which image data is not written in one horizontal scanning period, a period in which image data is actually written to each horizontal scanning line is referred to as “horizontal image writing”. This is referred to as a “period” and is distinguished from “one horizontal scanning period (1H)”.
[0017]
When the writing of the image data to the bottom horizontal scanning line in the display area is completed, the writing of the next image data is started. A period from the start of writing the image data forming the m-th (m is a positive integer) screen to the start of writing the image data forming the (m + 1) -th screen is referred to as a “vertical scanning period (1 V)”. Is done. Since there is a blanking period (vertical blanking period) in which image data is not written in one vertical scanning period, a period in which image data forming one screen is written is referred to as a “vertical image writing period”. And is distinguished from the vertical scanning period.
[0018]
The three areas A to C of the image shift element 3 'are driven not at the same time but at different timings. Specifically, a transparent electrode provided on a liquid crystal element (not shown in FIG. 2) in the image shift element 3 'is divided into three regions, and different voltages are applied to three regions of the liquid crystal layer in the liquid crystal element. Can be applied independently. The timing of driving each area of the liquid crystal layer is a point in time when half of the writing of the image to the area corresponding to each of the three areas A to C of the liquid crystal element is completed in the display section of the image display element. That is, assuming that one vertical image writing period is n seconds, image writing to the uppermost area when the screen is divided into three is performed only during a period from the start of the vertical image writing period until n / 3 seconds have elapsed. Be executed. The image writing in the middle area is executed only for a period of elapsed time of n / 3 to 2n / 3 seconds. Image writing to the bottom area is executed only during the period of elapsed time of 2n / 3 to n seconds. Accordingly, the point in time when image writing to each area is half completed is the point in time when the elapsed time in the vertical image writing period is n / 6 seconds, 3n / 6 seconds, and 5n / 6 seconds, respectively. Then, the image is shifted by the image shift element 3 '.
[0019]
As is apparent from the above, the difference between the timing at which the pixel data is written to each horizontal scanning line and the timing of the image shift is n / 6 seconds at the maximum. On the other hand, when the liquid crystal element of the image shift element is not divided into three regions, the difference between the timing of writing pixel data on each horizontal scanning line and the timing of image shift is n / 2 seconds at the maximum. become. As described above, by dividing the region to be shifted into a plurality of parts, the timing shift is reduced, and the display quality is improved.
[0020]
[Problems to be solved by the invention]
However, when an image is shifted for each of a plurality of divided areas along the vertical direction of the image display element 2, the following problem occurs.
[0021]
As shown in FIG. 3, the light emitted from the image display element 2 is not perfectly parallel light, but enters the image shift element 3 'with a certain spread angle. Further, since a glass substrate or a polarizing plate is interposed between the actual image display element 2 and the image shift element 3 ', a certain distance is required between them. For this reason, the light emitted from the display area of the image display element 2 corresponding to the boundary of the divided area in the image shift element 3 ′ is incident on two areas of the image shift element 3 ′, and the light incident on each area is Each shifts at a different timing. Therefore, light emitted from the same pixel is displayed at two different positions. In other words, since the image (pixels in one row) corresponding to one horizontal scanning line is shifted twice within one vertical period at different timings, a double image is formed for a certain period, and the image quality is degraded. Become.
[0022]
In the example of FIG. 3, light emitted from a certain scanning line of the image display element 2 is incident on the areas B and C of the image shift element 3 ′. It is assumed that light emitted from this scanning line originally enters the area B and should be shifted by the area B. Further, it is assumed that the light incident on the area B is shifted at time t2 and the light incident on the area C is shifted at time t3. Therefore, light incident on both the region B and the region C is displayed at two positions for a time determined by t3−t2, and a double image is generated.
[0023]
In order to reduce such a problem as much as possible, it is only necessary to make light hard to enter the two regions. For this reason, it is preferable that the image shift element 3 ′ is as close as possible to the emission surface of the image display element 2. However, as described above, since the glass substrate and the polarizing plate exist between the image display element 2 and the image shift element 3 ′, the distance between the image display element 2 and the image shift element 3 ′ should be reduced to a certain value or less. Can not.
[0024]
In the case of a three-panel type liquid crystal projector using three image display elements, as shown in FIG. 4, the liquid crystal projector is positioned adjacent to three display elements of R (red light), G (green light), and B (blue light). It is necessary to arrange the image shift elements one by one. That is, three image shift elements are required, which increases the cost. The apparatus shown in FIG. 4 includes an image display element 2 and an image shift element 3 ′ arranged on respective optical paths of R (red light), G (green light), and B (blue light). Are transmitted by the light combining prism, and then projected on a screen (not shown) by the projection lens 6.
[0025]
The present invention has been made in view of the above circumstances, and a main object of the present invention is to provide an image display device that can perform bright, high-resolution, and uniform display.
[0026]
[Means for Solving the Problems]
The image display device of the present invention has a plurality of pixels arranged, an image display element in which an image to be displayed is written by sequential scanning based on an input signal, and is disposed on a light emission side of the image display element, An image shift element for optically shifting an image displayed on the image display element, wherein an image writing period to the image display element within one vertical period is equal to an original signal of the input signal. Is shorter than the image writing period in one vertical period.
[0027]
In a preferred embodiment, the image shift element simultaneously shifts the entire image displayed on the image display element.
[0028]
In a preferred embodiment, a signal conversion circuit is provided for receiving an original signal of the input signal and generating an input signal in which an image writing period within one vertical period of the original signal is reduced to half or less.
[0029]
In a preferred embodiment, the image writing period is set to be 1/3 or less of an effective image display period of the original signal.
[0030]
In a preferred embodiment, a vertical blanking period of the input signal is set longer than a vertical blanking period of the original signal.
[0031]
In a preferred embodiment, one horizontal period of the input signal is shorter than one horizontal period of the original signal.
[0032]
In a preferred embodiment, a horizontal blanking period of the input signal is shorter than a horizontal blanking period of the original signal.
[0033]
In a preferred embodiment, a memory unit for storing data of an image displayed on the image display element is provided, and when the data is written to the memory unit and / or the data is read, the image is stored for a predetermined period. The period for writing an image to the display device is adjusted.
[0034]
In a preferred embodiment, the image shift by the image shift element is performed in synchronization with a point in time when about half of the image writing to the image display element is performed.
[0035]
In a preferred embodiment, light from a light source is separated into red, green, and blue light, and a color separation optical system that irradiates one image display element with the light is provided on a light incident side of the image display element. Light control means for condensing the red, green, and blue lights separated by the separation means on corresponding pixel regions in the image display element, and projection means for projecting light emitted from the image shift element, It has.
[0036]
In a preferred embodiment, a color separation optical system that separates light from a light source into red, green, and blue light; a color combining unit that combines the red, green, and blue light; Projecting means for projecting outgoing light, wherein the image display element is arranged so as to cross each of the red, green, and blue optical paths, and the image shift element is provided with the color synthesizing means and the projecting means. And is located between.
[0037]
A method of driving an image display device according to the present invention includes an image display element having a plurality of pixels arranged, an image to be displayed is sequentially written based on an input signal, and an image display element disposed on a light emitting side of the image display element. An image shift element for optically shifting an image displayed on the image display element, the method comprising: receiving an original signal of the input signal; and Generating, based on the original signal, an input signal in which an image writing period to a display element is shorter than an effective image display period within one vertical period of the original signal; and forming an image based on the input signal. Writing to the display element.
[0038]
BEST MODE FOR CARRYING OUT THE INVENTION
An image display device according to the present invention includes an image display element in which an image to be displayed (image data) is written by sequential scanning based on an input signal, and an image shift element that optically shifts an image displayed on the image display element. The image writing period (effective image display period) to the image display element in one vertical period is shorter than the image writing period (effective image display period) in one vertical period of the original signal of the input signal. It is characterized by points.
[0039]
When the image writing period to the image display element is shortened, the period from the image writing start point to the writing end point (= effective image display period) is shortened. Therefore, even when the screen batch type image shift is performed. In addition, it is possible to reduce the maximum deviation amount between the timing of image writing and the timing of image shift.
[0040]
Hereinafter, preferred embodiments of the image display device according to the present invention will be described.
[0041]
(Embodiment 1)
First, a basic configuration of a first embodiment of the image display device according to the present invention will be described with reference to FIGS.
[0042]
The image display device shown in FIG. 5 includes a backlight 1, an image display element 2, an image shift element 3, and an observation optical system 4. The image display element 2 of the present embodiment is a transmissive liquid crystal display panel, and the backlight 1 is a light source that illuminates the image display element 2. The image display element 2 can receive a drive signal and a signal such as a video signal from the drive circuit and display an image having contents corresponding to the video signal and the like. Before and after the image display element 2, a polarizing plate (not shown) that regulates the polarization of light entering and exiting the image display element 2 is arranged in a crossed Nicols state. The “image” in the present specification broadly includes a two-dimensional array of information, and may be not only an image or a video but also text or other data (information).
[0043]
The observation optical system 4 is an optical system for optically enlarging an image displayed on the image display element 2. An observer can observe an image displayed on the image display device 2 via the image shift element 3 and the observation optical system 4.
[0044]
In the present embodiment, the image display element 2 is configured using a transmissive liquid crystal display panel required for the backlight 1, but a reflective liquid crystal display may be used as long as the element can display an image. Further, a self-luminous display element such as an organic EL element or a plasma display panel (PDP) can be used.
[0045]
The operation of the image shift element 3 is controlled by a drive circuit (not shown) for the image shift element. This drive circuit supplies a drive signal synchronized with the image display of the liquid crystal image display element 2 to the image shift element 3. The drive circuit for the image shift element has a voltage application unit for individually applying a plurality of levels (High / Low) of voltages to a plurality of liquid crystal elements included in the image shift element 3.
[0046]
FIG. 6 shows a configuration example of the image shift element 3 of the present embodiment. Although the illustrated image shift element 3 has two optical path shift units, that is, the first shift unit 150 and the second shift unit 200, it may have only one optical path shift unit. . In this embodiment, since the image shift element 3 in which the two shift units are arranged in series as described above is provided, an image can be wobbled between three different positions on the same straight line. In addition, if a configuration in which the shift direction of the first shift unit 150 is made orthogonal to the shift direction of the second shift unit 200 is adopted, as shown in FIG. 18, position A → position B → position C → position D → position It is also possible to realize an image shift that circulates with A.
[0047]
The first shift unit 150 is manufactured using the liquid crystal element 10 and the birefringent element 12, and the second shift unit 200 is manufactured using the liquid crystal element 11 and the birefringent element 12. Each of the liquid crystal elements 10 and 11 includes a liquid crystal layer, a pair of transparent electrodes (not shown) sandwiching a light incident surface and a light emitting surface of the liquid crystal layer, and a pair of transparent substrates sandwiching these. The liquid crystal element 10 and the birefringent element 12 may be integrated by an adhesive or the like, and the first shift unit 150 may be configured to function as one component. The same applies to the second shift unit 200. Further, the first shift unit 150 and the second shift unit 200 may be integrated.
[0048]
The liquid crystal elements 10 and 11 according to the present embodiment are manufactured using TN mode liquid crystal, and rotate the polarization plane of the incident light by about 90 ° according to the applied voltage High / Low (first state). ) And a state (a second state) of emitting the incident light without substantially rotating the polarization plane of the incident light. The type of liquid crystal that can be used for the above-described liquid crystal element is not limited to a TN liquid crystal, and for example, an OCB mode or ECB mode liquid crystal, a ferroelectric liquid crystal, or the like can be used. The “linearly polarized light” in the present specification does not need to be completely linearly polarized light in the entire range included in the visible light band, and may be substantially linearly polarized light within a predetermined wavelength range.
[0049]
The liquid crystal elements 10 and 11 typically include a pair of transparent substrates, a liquid crystal layer located between the transparent substrates, and a transparent electrode (transparent conductive film) for applying a voltage to the liquid crystal layer. Each of the liquid crystal elements 10 and 11 used in this embodiment has an electrode structure for applying a voltage having a substantially uniform distribution in the plane. In order to provide a uniform voltage distribution to the liquid crystal layer, it is preferable that each of the liquid crystal elements 10 and 11 has a pair of electrodes sandwiching each liquid crystal layer. However, even with the electrode patterns divided in the plane, if the same level of voltage is applied to each electrode pattern at the same time, substantially the same effect as in the case of having uniform electrodes can be obtained. In the present embodiment, as shown in FIG. 2, image shift is performed on the entire screen without separately performing image shift for each of the divided areas. Therefore, in the present embodiment, the problem described with reference to FIG. 3 does not inherently occur.
[0050]
Each birefringent element 12 in the image shift element 3 is an element manufactured from a uniaxial crystal material (for example, quartz). The material used for the birefringent element 12 may be any material as long as it is a uniaxial crystal. For example, lithium niobate, calcite, mica, rutile (TiO ₂ ), Chile saltpeter (NaNO ₃ ) Can be used. However, when it is necessary to reduce the total weight of the display device like the HMD, it is preferable to use lithium niobate or rutile having a relatively large refractive index anisotropy (Δn). If the material has a large Δn, the thickness of the birefringent element 120 required to obtain a required image shift amount can be reduced, which is suitable for miniaturization and weight reduction.
[0051]
By periodically changing the level of the voltage applied to each of the liquid crystal layers of the liquid crystal elements 10 and 11, the polarization direction of the incident light can be switched in a direction perpendicular or horizontal to the main section of the birefringent element 12. In the main cross section of the birefringent element 12, the incident light can be shifted. As a result, the image displayed on the image display element 2 can be shifted in a direction perpendicular to the incident optical axis.
[0052]
In the present embodiment, the images of fields 1 to 3 shown on the right side of FIG. 7 are sequentially displayed on the image display element 2, and the displayed images of fields 1 to 3 are shifted as shown in FIG. Note that the number of fields constituting one frame is not limited to three.
[0053]
First, the configuration of the fields 1 to 3 will be described in detail with reference to FIG.
[0054]
The left part of FIG. 7 shows the contents of the R, G, and B signals that constitute a certain frame, and the right part of FIG. 7 is created based on the R, G, and B signals. The contents of fields 1 to 3 are shown. According to the present embodiment, in the first third period (first field period) of a certain frame, the image of field 1 is displayed on the projection surface on the projection surface. Then, in the next third period (second field period), the image of field 2 is displayed, and in the last third period (third field period), the image of field 3 is displayed. Is done. In the present embodiment, these three field images are shifted up and down as shown in FIG. 8 and are synthesized with a time lag. As a result, the three images shown in the left part of FIG. The superimposed image (original image) is recognized. In this specification, a plurality of images (sub-frame images) displayed within one frame period are expressed by the same term as "field" used in interlace driving.
[0055]
Next, taking the field 1 as an example, the data configuration of the field image will be described in detail. First, as shown in FIG. 7, the data for the first-row pixel area in the field 1 is formed from data on the first-row pixels (R1) of the R signal. The data for the second row pixel area in the field 1 is formed from data relating to the second row pixels (G2) of the G signal. The data for the third row pixel area of the field 1 is formed from data on the third row pixels (B3) of the B signal. The data for the fourth-row pixel area in the field 1 is formed from data on the fourth-row pixels (R4) of the R signal. Hereinafter, the data of the field 1 is configured in the same procedure.
[0056]
The data of fields 2 and 3 are also configured in the same manner as in the case of field 1. For example, in the case of field 2, the data for the 0th row pixel area is formed from the data for the first row pixels (B1) of the B signal, and the data for the 1st row pixel area of the field 2 is the second signal of the R signal. It is formed from data on the row pixel (R2). The data for the second row pixel area in the field 2 is formed from the data for the third row pixel (G3) of the G signal, and the data for the third row pixel area in the field 2 is the fourth row pixel (B) of the B signal. B4).
[0057]
In this manner, by combining the R, G, and B signals in a preset order, data of each field displayed in a time-division manner is generated. As a result, each of the field data includes information on all the colors of R, G, and B, but each of R, G, and B is spatially one-third of the entire area. They only have information about More specifically, in the case of field 1, the information of R is only related to the pixels in the first, fourth, seventh, tenth,... Rows of the frame image to be formed, as is apparent from FIG. The R information for the pixels in the other rows of the frame image is assigned to fields 2 and 3.
[0058]
In the present embodiment, information of the same color is always displayed in each pixel area of the image display element 2. However, it is possible to synthesize a frame image by shifting and projecting an image between fields. it can.
[0059]
In the present embodiment, the signals of fields 1 to 3 created in this way are referred to as original signals.
[0060]
Next, an example of a system configuration of the image display device according to the present embodiment will be described with reference to FIG.
[0061]
As shown in FIG. 9, the present system mainly includes a video signal processing circuit 100, an illumination optical system (light source or the like) 102, a display element (liquid crystal display panel) 2, an image shift element 3, and an image shift element control circuit 108. , And the observation optical system 4.
[0062]
The illumination optical system 102, the image display element 2, the image shift element 3, and the observation optical system 4 correspond to the backlight 1, the image display element 2, the image shift element 3, and the observation optical system 4 in FIG. The detailed description thereof is omitted here. In the following, the relationship between the components will be described with a focus on the video signal processing circuit 100 and the image shift element control circuit 108.
[0063]
The video signal processing circuit 100 according to the present embodiment includes an input signal selection circuit 120, a video demodulation circuit 122, a Y / C separation circuit 124, a frame rate conversion circuit 126, a frame transmission circuit 128, a system control circuit 132, and a frame memory circuit. 134. The input signal selection circuit 120 can receive a plurality of types of video signals, and performs processing according to the types of the video signals. The video signal includes a signal (RGB signal) separated into R, G, and B, a signal (Y / C signal) separated into a luminance signal Y and color difference signals BY and RY, and a color difference signal including a color carrier. There is a composite video signal (composite signal) obtained by frequency-multiplexing the color signal C and the luminance signal Y modulated by.
[0064]
The Y / C signal is demodulated by the video demodulation circuit 122 via the input signal selection circuit 120. The composite signal passes through an input signal selection circuit 120, is separated into a luminance signal Y and a chrominance signal by a Y / C separation circuit 124, is sent to a video demodulation circuit 122, and is demodulated. The video demodulation circuit 122 outputs RGB signals demodulated from the video signal.
[0065]
The RGB signals input to the input signal selection circuit 120 and the RGB signals output from the video demodulation circuit 122 are sent to a frame rate conversion circuit 126. The frame rate conversion circuit 128 converts the frame rate of the input video signal into a frame rate suitable for the operation of the present system.
[0066]
The frame transmission circuit 128 has a function of shortening a period of writing an image to the image display element (vertical image writing period) in one vertical period (= 1 field period) than a vertical image writing period in one vertical period of the original signal. are doing. In the present embodiment, the frame transmission circuit 128 changes the vertical image writing to の of the original signal. The signal output from the frame transmission circuit 128 is input to the image display element 2 after being input to the frame memory.
[0067]
The original signal before the vertical image writing period is shortened by the frame transmission circuit 128 has the waveforms shown in FIGS. 10A and 10B. The waveform of the signal output from the frame transmission circuit 128 is as follows. It has the waveforms shown in FIGS. 11 (a) and 11 (b). As can be seen from a comparison between the two, the length of one field remains the same, but the vertical image writing period c is reduced from 5.29 msec to 1.76 msec. In the examples shown in FIGS. 11A and 11B, the vertical back porch period b and the vertical front porch period d are made longer than the original signal, and one horizontal period (1H) is made shorter than the original signal. Thus, the vertical image writing period c is shortened. In this embodiment, in order to secure a sufficient horizontal image writing period c ′ while shortening one horizontal period (1H), a horizontal blanking period (= horizontal synchronization period a ′ + horizontal back porch period b ′ + The horizontal front porch period d ') is shortened. The specific numerical values shown in FIGS. 10 and 11 are only examples.
[0068]
The signal (input signal) whose vertical image writing period c has been shortened by the frame transmission circuit 128 is input to the frame memory circuit 134. The frame memory circuit 134 has a plurality of frame memories for storing input signals. Each frame memory has a function of storing input signals for one vertical period (one field period). The function of the frame memory circuit 134 will be described with reference to FIGS.
[0069]
As shown in FIG. 12, the frame memory circuit 134 includes frame memories A and B and switches A and B. The switches A and B are alternately connected to the frame memories A and B. Specifically, since the signal (control signal) shown in FIG. 13 is input to the switches A and B, the vertical image writing period is shortened by the frame rate conversion circuit 128 during the first vertical period (V). The input signal is input to the frame memory A via the switch A. During the next one vertical period, this input signal is input to the frame memory B via the switch A, during which the frame memory A is connected to the image display device 2 via the switch B. As a result, the signal stored in the frame memory A is sent to the image display element 2, and a display image is formed based on the signal.
[0070]
In the next one vertical period, the input signal sent from the frame rate conversion circuit 128 is input to the frame memory A via the switch A, during which the frame memory B is connected to the image display element 2 via the switch B. Is connected to A signal stored in the frame memory B is sent to the image display element 2, and a display image is formed based on the signal.
[0071]
By such a switching operation by the switches A and B, each frame memory alternately performs an operation of storing a signal for one frame and an operation of outputting a signal. The number and combination of the frame memories in the frame memory circuit 134 are not limited to the example shown in FIG. In the present embodiment, the input signal after shortening the vertical image writing period is written in the frame memory, but the present invention is not limited to this. When writing to or reading from the frame memory, the vertical image writing period may be shortened.
[0072]
The system control circuit 132 controls operations of the input signal selection circuit 120, the frame rate conversion circuit 126, the frame transmission circuit 128, the frame memory circuit 134, the image shift element control circuit 108, and the like.
[0073]
The image shift element control circuit 108 controls the operation of the image shift element 3 based on the signal output from the system control circuit 132 so as to synchronize with the display of the fields 1 to 3.
[0074]
In the present embodiment, the effective image display period (image writing period) in each vertical period is shortened by increasing the vertical blanking time. In addition, it is preferable that the vertical blanking time be lengthened and the horizontal blanking period be shortened, since the horizontal image writing period can be sufficiently ensured.
[0075]
In the present embodiment, the three field signals read from the frame memory circuit 134 are sequentially written to the image display element 2 and displayed. By synchronizing the display timing with the image shift element as shown in FIG. 8, an R, G, and B image can be displayed by one pixel.
[0076]
At this time, as shown in FIG. 14, the switching timing of the image shift element shifts the image of the entire screen when the image writing to the image display element 2 is performed about half of the screen. As described above, assuming that one vertical image writing period is n seconds, an image shift by the image shift element 3 is executed when n / 2 seconds elapse from the start of the image vertical image writing period. Here, the time from the writing of the image data to the scanning line at the upper end of the screen to the execution of the image shift is n / 2 seconds. The time until data is written is also n / 2 seconds. Accordingly, the maximum shift generated between the timing of writing the image data and the timing of the image shift is n / 2 seconds. In the present embodiment, since the vertical image writing period n is shorter than the original signal, it is reduced to 1/3. That is, while the vertical image writing period of the original signal is 5.29 ms, the vertical image writing period of the input signal after the frame shift is 1.76 ms. For this reason, the shift in timing indicated by n / 2 seconds is reduced to 1/3 as compared with the conventional example in which no frame shift is performed.
[0077]
As in the present embodiment, if the image shift by the image shift element is performed in synchronization with the time when the image writing to the image display element is performed about half, the timing shift can be made substantially equal between the upper and lower sides of the screen, and as a result, It becomes easy to reduce the maximum value of the deviation.
[0078]
In the present embodiment, an input signal in which the vertical image writing period of the original signal is shortened to 1/3 is generated and used for image display, but the present invention is not limited to this. If the vertical image writing period in the original signal is reduced to half or less of the vertical image writing period, the effect of the present invention can be sufficiently obtained. However, in order to further reduce the timing shift, the vertical image writing period in the original signal is made shorter than 1/3. Is preferred.
[0079]
Since a response delay occurs in the liquid crystal element used for the image shift element 3, it is preferable to adjust the shift timing by the image shift element in consideration of the response speed of the liquid crystal layer employed. This makes it possible to balance the timing shift between the upper and lower parts of the screen.
[0080]
According to the present embodiment, the amount of timing shift generated between the image displayed on the image display element 2 and the image shift element 3 is one-third that of the conventional method (a method in which the image shift element is not divided). Thus, a high-resolution image that can hardly be visually recognized can be obtained. In addition, generation of a double image due to light straddling a divided region which occurs when the image shift element is divided does not occur in principle.
[0081]
Although the present embodiment has a system for observing a virtual image of an image displayed on an image display device by an eyepiece such as an HMD, the present invention is not limited to this. It can be applied to the case of directly observing an image. Further, as shown in FIGS. 15 and 16, one micro lens (light) is provided for three pixels corresponding to R, G, and B of the image display element 2. The present invention can also be applied to a projection type image display device associated with the control means). The projection type image display device shown in FIGS. 15 and 16 is a single-panel type, in which R is separated by a dichroic mirror (color separation optical system) by a microlens array 2a provided on the light incident side of one liquid crystal panel. , G, and B light can be applied to corresponding pixel regions in one image display device 2 respectively. According to such an image display device, a full-color projection image can be formed using one image display element 2.
[0082]
The present invention is also applicable to a system that simply projects a liquid crystal display device having R, G, and B color filters.
[0083]
In the present embodiment, the pixels are shifted so that the R, G, and B pixels are superimposed. However, the pixels may be shifted between the pixels for the purpose of enhancing the definition. It may be shifted in any oblique direction.
[0084]
(Embodiment 2)
FIG. 17 shows a main part of another embodiment of the display device according to the present invention. The display device of the present embodiment is a three-panel projection type including three image display elements (liquid crystal display elements) 2. In this embodiment, each image display element 2 modulates red light, blue light, or green light in accordance with an image signal. Light emitted from each image display element 2 is synthesized by a color synthesis prism 5, then shifted by an image shift element 3, and projected by a projection lens 6.
[0085]
Although the basic configuration of the image shift element 3 is the same as that used in the first embodiment, in the present embodiment, the pixels of the three image display elements 2 are moved from position A to position B to position as shown in FIG. Shift in the order of C → position D →. The shift position is between pixels.
[0086]
In the present embodiment, the pixel shift timing is performed in the same manner as in the first embodiment. In the present embodiment, as in the first embodiment, the field signal for each shift position is generated by the frame rate conversion circuit, and the vertical and horizontal blanking periods are adjusted by the frame transmission circuit, whereby the original signal is adjusted. The effective image display period in one field of (field signal) is reduced to 1/3.
[0087]
According to the present embodiment, it is necessary to arrange three image shift elements 3 on the light emission side of each display element 2. In addition, the timing shift that occurs between the display of the image displayed on the image display element 2 and the image shift by the image shift element 3 is 1/3 of the conventional method (a method in which the image shift element is not divided), and It is possible to realize a high-resolution image at which the timing shift between the upper and lower parts of the screen is hardly visually recognized, at a lower cost.
[0088]
In the present embodiment, the pixels of the image display element 2 are shifted in the order of position A → position B → position C → position D, but the order of image shift is not limited to this, and the shift direction is also up and down. , Left, right and oblique directions.
[0089]
【The invention's effect】
By reducing the length of the vertical image writing period occupying one vertical period of the signal input to the image display element to be shorter than the length of the effective image display period occupying one vertical period of the original signal, the display timing of the image display element and the image Since the shift in timing from the image shift in the shift element can be reduced, display quality is improved. According to the present invention, even if the image shift element is not divided in a plane, the same timing shift reduction effect as in the case of division can be obtained.
[0090]
If the image shift element is not divided in the plane, the image shift element can be arranged at a position distant from the image display element. For example, when the present invention is applied to a three-panel liquid crystal projector, one image shift element is required. Since the image shift can be performed by using the apparatus, the manufacturing cost of the apparatus can be reduced.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a configuration of a shift element including a liquid crystal element and a birefringent element.
FIG. 2 is a perspective view for explaining an operation of an image shift element in which a region for shifting an image is divided into three regions A to C, and the three regions A to C are sequentially driven.
FIG. 3 is a cross-sectional view illustrating a problem of the image shift element of FIG. 2;
FIG. 4 is a diagram showing a main configuration of a projection-type image display device including three image shift elements shown in FIG. 2;
FIG. 5 is a schematic diagram showing a schematic configuration of a first embodiment of a display device according to the present invention.
FIG. 6 is a configuration diagram of a shift element used in the embodiment.
FIG. 7 is a diagram illustrating a configuration example of a field employed in an embodiment of the present invention.
FIG. 8 is a cross-sectional view showing a shift of a field in the embodiment of the present invention.
FIG. 9 is a diagram illustrating a configuration example of a system according to the present embodiment.
FIG. 10A is a waveform diagram showing one field of an original signal, and FIG. 10B is a waveform diagram showing one horizontal period of the original signal.
FIG. 11A is a waveform diagram showing one field of a signal in which the effective image writing period has been shortened by the frame transmission circuit, and FIG. 11B is a waveform diagram showing one horizontal period of the signal.
FIG. 12 is a diagram illustrating a configuration example of a frame memory circuit used in an embodiment of the present invention.
FIG. 13 is a waveform diagram showing signals input to switches A and B of the frame memory circuit.
FIG. 14 is a perspective view showing a relationship between a shift timing by a shift element used in the embodiment and an image writing timing of an image display device.
FIG. 15 is a diagram showing still another configuration example of the display device according to the present invention.
FIG. 16 is a sectional view showing a liquid crystal display element used in the device of FIG.
FIG. 17 is a view showing another embodiment of the display device according to the present invention.
FIG. 18 is a plan view showing a pixel arrangement before and after a shift by an image shift element used in the display device according to the present invention.
[Explanation of symbols]
1 Backlight
2 Image display device (liquid crystal display panel or liquid crystal device)
3 Image shift element
4 Observation optical system
10 Liquid crystal element
11 Liquid crystal element
12 Birefringent element
120 Input signal selection circuit
122 Video demodulation circuit
124 Y / C separation circuit
126 Frame rate conversion circuit
128 frame transmission circuit
132 System control circuit
134 frame memory circuit
150 First shift unit
200 Second shift unit

Claims (12)

An image display element having a plurality of pixels arranged, and an image to be displayed is written by sequential scanning based on an input signal,
An image shift element that is arranged on a light emission side of the image display element and optically shifts an image displayed on the image display element;
An image display device comprising:
An image display device wherein an image writing period to the image display element in one vertical period is shorter than an image writing period in one vertical period of the original signal of the input signal. The image display device according to claim 1, wherein the image shift element simultaneously shifts an entire image displayed on the image display element. 3. The image display device according to claim 1, further comprising a signal conversion circuit that receives an original signal of the input signal and generates an input signal in which an image writing period within one vertical period of the original signal is reduced to half or less. . 4. The image display device according to claim 1, wherein the shortened image writing period is set to be equal to or less than １ ／ of the image writing period of the original signal. 5. The image display device according to claim 1, wherein a vertical blanking period of the input signal is set longer than a vertical blanking period of the original signal. The image display device according to claim 1, wherein one horizontal period of the input signal is shorter than one horizontal period of the original signal. The image display device according to claim 6, wherein a horizontal blanking period of the input signal is shorter than a horizontal blanking period of the original signal. A memory unit that stores data of an image displayed on the image display element,
The image display device according to claim 1, wherein an image writing period to the image display device is adjusted when writing data to the memory unit and / or when reading data. 9. The image display device according to claim 1, wherein the image shift by the image shift element is performed in synchronization with a point in time when writing of image data to the image display element is performed about half. A color separation optical system that separates light from a light source into red, green, and blue light and irradiates one image display element;
Light control means provided on the light incident side of the image display element, for condensing red, green, and blue light separated by the color separation means, respectively, into a corresponding pixel region in the image display element,
Projecting means for projecting light emitted from the image shift element,
The image display device according to any one of claims 1 to 9, further comprising: A color separation optical system that separates light from the light source into red, green, and blue light;
A color synthesizing unit that synthesizes the red, green, and blue light;
Projecting means for projecting light emitted from the color synthesizing means,
With
The image display element is arranged to cross each of the red, green, and blue optical paths,
The image display device according to claim 1, wherein the image shift element is arranged between the color synthesizing unit and the projecting unit. An image display element having a plurality of pixels arranged, and an image to be displayed is sequentially written based on an input signal,
An image shift element that is arranged on a light emission side of the image display element and optically shifts an image displayed on the image display element;
A method for driving an image display device comprising:
Receiving an original signal of the input signal;
Generating, based on the original signal, an input signal in which an image writing period to the image display element in one vertical period is shorter than an effective image display period in one vertical period of the original signal;
Writing an image to the image display element based on the input signal;
A method for driving an image display device, comprising:

Images