Projection type display device

Abstract

To prevent a reduction in display quality when a specific display pattern appears.SOLUTION: A projection type display device includes: a liquid crystal panel that has panel pixels; an optical path shift element that shifts projection pixels projected from the panel pixels for every n unit periods from a first unit period to the n-th (n is an integer of 2 or more) unit period included in one frame period; and a display control circuit that controls the liquid crystal panel and the optical path shift element. In a unit period f1-1 in four unit periods in an odd-numbered frame period and a unit period f2-1 in four unit periods in an even-numbered frame period, the display control circuit supplies the same data signals to the liquid crystal panel, and controls the projection pixels at the same positions. The display control circuit controls the optical path shift element so that the positions of the projection pixels from a unit period f1-2 to a unit period f1-4 in the odd-numbered frame period, and the positions of the projection pixels from a unit period f2-2 to a unit period f2-4 in the even-numbered frame period, become different from each other.SELECTED DRAWING: Figure 11

Description

Technical Field

[0001] The present invention relates to a projection display device.

Background Art

[0002] In a projection display device that projects image light created by a liquid crystal panel or the like onto a screen or the like, a technique for pseudo-enhancing the resolution by an optical path shift element is known. Specifically, in a projection display device, the projection position of one panel pixel in a liquid crystal panel is shifted for each of a plurality of unit periods in one frame period to represent a plurality of pixel data in video data (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the above technique has a problem that when a specific display pattern appears as a still image in an image specified by video data, the display quality deteriorates. In view of such circumstances, an aspect of the present disclosure aims to provide a technique for suppressing a decrease in display quality even when a specific display pattern appears in an image specified by video data.

Means for Solving the Problems

[0005] To solve the above problems, a projection display device according to one aspect of the present disclosure includes a liquid crystal panel having panel pixels, an optical path shift element that shifts the position of projection pixels projected from the panel pixels every n unit periods, from the first unit period to the nth (where n is an integer of 2 or more) unit periods included in one frame period, and a display control circuit that controls the liquid crystal panel and the optical path shift element, wherein the display control circuit supplies data signals corresponding to pixel data constituting video data to the panel pixels every unit period, and shifts the position of the projection pixels to the optical path shift element every unit period The system controls the optical path shift element so that the positions of the projected pixels are the same, and the optical path shift element is controlled so that the positions of the projected pixels from the second unit period to the nth unit period in the first frame period and the positions of the projected pixels from the second unit period to the nth unit period in the second frame period are different. [Brief explanation of the drawing]

[0006] [Figure 1] This is a diagram showing a projection-type display device according to an embodiment. [Figure 2] This is a block diagram showing the configuration of a projection display device. [Figure 3] This is a perspective view showing the configuration of a liquid crystal panel in a projection display device. [Figure 4] This is a cross-sectional view showing the structure of a liquid crystal panel. [Figure 5] This block diagram shows the electrical configuration of an LCD panel. [Figure 6] This diagram shows the configuration of the pixel circuit in a liquid crystal panel. [Figure 7] This figure shows the frame duration and unit duration in a projection-type display device. [Figure 8] This figure shows the operation of the optical path shift element in the embodiment. [Figure 9] This diagram shows the relationship between the arrangement of image pixels and the arrangement of panel pixels. [Figure 10] This figure shows the correspondence between video pixels and panel pixels during each frame period in the embodiment. [Figure 11] This diagram shows the order of pixel data supplied to the panel pixels in the embodiment. [Figure 12] This figure shows the relationship between video pixels, panel pixels, and projection position during odd-numbered frame periods in the embodiment. [Figure 13] This figure shows the relationship between video pixels, panel pixels, and projection position during even-numbered frame periods in the embodiment. [Figure 14] This figure shows a specific pattern in video data. [Figure 15] This figure shows the change in panel pixels when displaying a specific pattern in the embodiment. [Figure 16] This figure shows the projection images in the first comparative example and the embodiment. [Modes for carrying out the invention]

[0007] The electro-optical apparatus of the embodiment will be described below with reference to the drawings. Note that the dimensions and scale of each part in each drawing have been appropriately changed from the actual ones. Furthermore, the embodiments described below are preferred examples and are subject to various technically preferred limitations, but the scope of this disclosure is not limited to these forms unless otherwise stated in the following description.

[0008] Figure 1 shows the optical configuration of a projection-type display device 1 according to an embodiment. As shown in the figure, the projection-type display device 1 includes liquid crystal panels 100R, 100G, and 100B. Inside the projection-type display device 1, there is a lamp unit 2102 consisting of a white light source such as a halogen lamp. The projected light emitted from this lamp unit 2102 is separated into three primary colors, red (R), green (G), and blue (B), by three mirrors 2106 and two dichroic mirrors 2108 arranged inside. Of these, the R light is incident on the liquid crystal panel 100R, the G light on the liquid crystal panel 100G, and the B light on the liquid crystal panel 100B. Furthermore, since the optical path B is longer than the optical paths R and G, it is necessary to prevent losses in the optical path B. For this reason, the optical path B is provided with a relay lens system 2121 consisting of an incident lens 2122, a relay lens 2123, and an exit lens 2124.

[0009] The liquid crystal panel 100R has multiple pixel circuits. Each of the multiple pixel circuits includes a liquid crystal element. The liquid crystal elements of the liquid crystal panel 100R are driven based on a data signal corresponding to R, as described later, so that their transmittance corresponds to the voltage of the data signal. Therefore, in the liquid crystal panel 100R, a transmitted image of R is generated by individually controlling the transmittance of the liquid crystal elements. Similarly, in the liquid crystal panel 100G, a transmitted image of G is generated based on the data signal corresponding to G, and in the liquid crystal panel 100B, a transmitted image of B is generated based on the data signal corresponding to B.

[0010] The transmitted images of each color, generated by the liquid crystal panels 100R, 100G, and 100B respectively, are incident on the dichroic prism 2112 from three directions. In the dichroic prism 2112, the R and B light is refracted at 90 degrees, while the G light travels in a straight line. Therefore, the dichroic prism 2112 synthesizes the images of each color. The synthesized image from the dichroic prism 2112 is incident on the projection lens 2114 via the optical path shift element 230. The projection lens 2114 enlarges and projects the composite image through the optical path shift element 230 onto the screen Scr.

[0011] The optical path shift element 230 shifts the composite image emitted from the dichroic prism 2112. Specifically, the optical path shift element 230 shifts the image projected onto the screen Scr in the left - right direction or / and the downward direction with respect to the projection plane.

[0012] Note that the transmitted images by the liquid crystal panels 100R and 100B are projected after being reflected by the dichroic prism 2112, while the transmitted image by the liquid crystal panel 100G is projected straight. Therefore, each transmitted image by the liquid crystal panels 100R and 100B has a left - right reversed relationship with respect to the transmitted image of the liquid crystal panel 100G. For convenience of explanation, when viewing the projection plane of the screen Scr from the projection type display device 1, the left - right direction is taken as the X - axis, and the up - down direction is taken as the Y - axis. Among the left - right directions along the X - axis, the right direction is the X - direction, and the left direction is the opposite direction of the X - direction. Also, among the up - down directions along the Y - axis, the downward direction is the Y - direction, and the upward direction is the opposite direction of the Y - direction. The projection direction of the projection type display device 1 is the Z - direction. Note that in the embodiment, the Y - axis is an example of the first axis, and the X - axis is an example of the second axis.

[0013] FIG. 2 is a block diagram showing the electrical configuration of the projection type display device 1. As shown in the figure, the projection type display device 1 includes a display control circuit 20, the above - mentioned liquid crystal panels 100R, 100G, and 100B, and the optical path shift element 230.

[0014] Video data Vid - in is supplied from a host device or the like (not shown) in synchronization with the synchronization signal Sync. The video data Vid - in specifies the gradation level of pixels in the image to be displayed, for example, 8 bits for each of RGB.

[0015] Furthermore, the pixels of the image specified in the video data Vid-in are referred to as video pixels, the data of the video pixels is referred to as pixel data, and the pixels of the composite image formed by the liquid crystal panels 100R, 100G, and 100B are referred to as panel pixels. In addition, the position of the panel pixels that are shifted by the optical path shift element 230 and projected onto the screen Scr is referred to as the projection position. In the composite image of the liquid crystal panels 100R, 100G, and 100B, the panel pixels are arranged in a matrix in both the vertical and horizontal directions. In this embodiment, the arrangement of image pixels for which the gradation level is specified in the image data Vid-in is twice as large in the vertical direction and twice as large in the horizontal direction compared to the arrangement of panel pixels composited by the liquid crystal panels 100R, 100G, or 100B.

[0016] In this embodiment, the color image projected onto the screen Scr is represented by combining the transmitted images of the liquid crystal panels 100R, 100G, and 100B. Therefore, the smallest unit of the color image, the pixel, can be divided into red subpixels from liquid crystal panel 100R, green subpixels from liquid crystal panel 100G, and blue subpixels from liquid crystal panel 100B. However, in cases where it is not necessary to specify the color of the subpixels in liquid crystal panels 100R, 100G, and 100B, or when only brightness and darkness are relevant, it is not necessary to explicitly refer to them as subpixels. Therefore, in this description, the display unit in liquid crystal panels 100R, 100G, and 100B will also be referred to as a panel pixel.

[0017] The Sync synchronization signal includes a vertical synchronization signal that instructs the start of vertical scanning of the video data Vid-in, a horizontal synchronization signal that instructs the start of horizontal scanning, and a clock signal that indicates the timing of one video pixel in the video data Vid-in.

[0018] The display control circuit 20 includes a processing circuit 22, and conversion circuits 23R, 23G, and 23B. The processing circuit 22 stores video data Vid-in from the higher-level device for one or more frame periods, then reads the pixel data of the video pixels corresponding to the projection position by the optical path shift element 230, and outputs it separately for the RGB components. Of the pixel data V output from the processing circuit 22, the R component is denoted as pixel data Vad_R, the G component as pixel data Vad_G, and the B component as pixel data Vad_B.

[0019] In the projection-type display device 1, the projection position changes for each unit period obtained by dividing one frame period into four parts. However, in the eight unit periods of two consecutive frame periods, it is possible to have eight projection positions. However, in this embodiment, the projection positions in the eight unit periods are set to seven, as will be described later. Each unit period is the period during which the user will see a composite image created by the liquid crystal panels 100R, 100G, and 100B, which is an image with the resolution of the image for one frame period specified in the video data Vid-in reduced to 1 / 4.

[0020] The processing circuit 22 controls the projection position of the optical path shift element 230 in each unit period. Specifically, the processing circuit 22 controls the shift of the optical path shift element 230 along the X-axis with the control signal P_x, and controls the shift along the Y-axis with the control signal P_y. Details regarding the projection position for each unit period, and which video pixels are represented by the video data Vid-id specified for each projection position, will be described later. Furthermore, the processing circuit 22 generates control signals Ctr for controlling the liquid crystal panels 100R, 100G, and 100B at unit intervals.

[0021] The conversion circuit 23R converts pixel data Vad_R into an analog voltage data signal Vid_R and supplies it to the liquid crystal panel 100R. The conversion circuit 23G converts pixel data Vad_G into an analog voltage data signal Vid_G and supplies it to the liquid crystal panel 100G. The conversion circuit 23B converts pixel data Vad_B into an analog voltage data signal Vid_B and supplies it to the liquid crystal panel 100B.

[0022] Next, we will describe the liquid crystal panels 100R, 100G, and 100B. The only difference between the liquid crystal panels 100R, 100G, and 100B is the color of the incident light, i.e., the wavelength; structurally, they are the same. Therefore, we will refer to the liquid crystal panels 100R, 100G, and 100B as "100" and describe them generally without specifying the color.

[0023] Figure 3 shows the main parts of the liquid crystal panel 100, and Figure 4 is a cross-sectional view taken along the Hh line in Figure 3. As shown in these figures, in the liquid crystal panel 100, an element substrate 100a on which pixel electrodes 118 are provided and a counter substrate 100b on which common electrodes 108 are provided are bonded together with a sealing material 90 so that their electrode-forming surfaces face each other while maintaining a certain gap, and liquid crystal 105 is sealed in this gap.

[0024] The element substrate 100a and the opposing substrate 100b are made of light-transmitting substrates such as glass or quartz, respectively. As shown in Figure 3, one side of the element substrate 100a extends beyond the opposing substrate 100b. Multiple terminals 106 are provided along the transverse direction in the figure in this extended region. One end of an FPC (Flexible Printed Circuits) substrate, not shown, is connected to these multiple terminals 106. The other end of the FPC substrate is connected to the display control circuit 20, to which the various signals mentioned above are supplied.

[0025] On the element substrate 100a, the pixel electrode 118 is formed on the surface facing the opposing substrate 100b by patterning a transparent conductive layer, such as ITO (Indium Tin Oxide). Furthermore, various elements other than electrodes are provided on the opposing surfaces of the element substrate 100a and the opposing substrate 100b, but these are omitted in the figure.

[0026] Figure 5 is a block diagram showing the electrical configuration of the liquid crystal panel 100. The liquid crystal panel 100 is provided with a scan line drive circuit 130 and a data line drive circuit 140 around the periphery of the display area 10.

[0027] In the display area 10 of the liquid crystal panel 100, pixel circuits 110 are arranged in a matrix. More specifically, in the display area 10, multiple scan lines 12 are provided extending horizontally in the figure, and multiple data lines 14 are provided extending vertically, maintaining electrical isolation from the scan lines 12. The pixel circuits 110 are then arranged in a matrix corresponding to the intersections of the multiple scan lines 12 and the multiple data lines 14.

[0028] If the number of scan lines 12 is m and the number of data lines 14 is n, the pixel circuits 110 are arranged in a matrix with m rows and n columns. Both m and n are integers greater than or equal to 2. In the scan lines 12 and pixel circuits 110, the rows of the matrix are sometimes referred to as 1, 2, 3, ..., (m-1), and m rows from top to bottom in the diagram. Similarly, in the data lines 14 and pixel circuits 110, the columns of the matrix are sometimes referred to as 1, 2, 3, ..., (n-1), and n columns from left to right in the diagram.

[0029] The scan line driving circuit 130 selects scan lines 12 one by one in the order of, for example, the 1st, 2nd, 3rd, ..., mth row, according to the control of the display control circuit 200, and sets the scan signal to the selected scan line 12 to the H level. The scan line driving circuit 130 also sets the scan signal to the scan lines 12 other than the selected scan line 12 to the L level. The data line driving circuit 140 latches one line of data signals supplied from the corresponding color circuit among the processing circuits 220R, 220G, or 220B, and outputs to the pixel circuit 110 located on the scan line 12 via the data line 14 during the period when the scan signal to the scan line 12 is at a high level.

[0030] Figure 6 shows the equivalent circuits of the pixel circuits 110, consisting of four pixels arranged in two vertical rows and two horizontal columns, corresponding to the intersections of two adjacent scan lines 12 and two adjacent data lines 14. As shown in the figure, the pixel circuit 110 includes a transistor 116 and a liquid crystal element 120. The transistor 116 is, for example, an n-channel thin-film transistor. In the pixel circuit 110, the gate node of the transistor 116 is connected to the scan line 12, its source node is connected to the data line 14, and its drain node is connected to a pixel electrode 118 which is square in shape in plan view.

[0031] A common electrode 108 is provided for all pixels, facing the pixel electrode 118. A voltage LCcom is applied to the common electrode 108. Then, as described above, liquid crystal 105 is sandwiched between the pixel electrode 118 and the common electrode 108. Therefore, for each pixel circuit 110, a liquid crystal element 120 is formed, with the liquid crystal 105 sandwiched between the pixel electrode 118 and the common electrode 108. Furthermore, a storage capacitor 109 is provided in parallel with the liquid crystal element 120. One end of the storage capacitor 109 is connected to the pixel electrode 118, and the other end is connected to the capacitance line 107. A voltage constant over time, for example, the same voltage LCcom as the voltage applied to the common electrode 108, is applied to the capacitance line 107. The pixel circuit 110 is arranged in a matrix shape across the horizontal direction, which is the direction in which the scan lines 12 extend, and the vertical direction, which is the direction in which the data lines 14 extend. Therefore, the pixel electrodes 118 included in the pixel circuit 110 are also arranged across both the vertical and horizontal directions.

[0032] When the scanning signal reaches the H level on scan line 12, the transistor 116 of the pixel circuit 110, which is provided in conjunction with that scan line 12, turns on. When transistor 116 turns on, the data line 14 and the pixel electrode 118 are electrically connected, so the data signal supplied to the data line 14 reaches the pixel electrode 118 via the turned-on transistor 116. When scan line 12 reaches the L level, transistor 116 turns off, but the voltage of the data signal that reached the pixel electrode 118 is maintained by the capacitive and storage capacitance 109 of the liquid crystal element 120.

[0033] As is well known, in the liquid crystal element 120, the orientation of the liquid crystal molecules changes in response to the electric field generated by the pixel electrode 118 and the common electrode 108. Therefore, the transmittance of the liquid crystal element 120 corresponds to the effective value of the applied voltage. Furthermore, the region that functions as a pixel in the liquid crystal element 120, that is, the region whose transmittance corresponds to the effective value of the voltage, is the region where the pixel electrode 118 and the common electrode 108 overlap when the element substrate 100a and the opposing substrate 100b are viewed in plan view. Since the pixel electrode 118 is square in plan view, the shape of the pixel in the liquid crystal panel 100 is also square. Furthermore, in this embodiment, it is assumed that the normally black mode is in which the transmittance increases as the voltage applied to the liquid crystal element 120 increases.

[0034] The operation of supplying data signals to the pixel electrodes 118 of the liquid crystal element 120 is performed in the order of rows 1, 2, 3, ..., m within a single unit period. As a result, a voltage corresponding to the data signal is maintained in each of the liquid crystal elements 120 of the pixel circuit 110 arranged in m rows and n columns, so that each liquid crystal element 120 reaches the desired transmittance, and a transmitted image of the corresponding color is generated by the liquid crystal elements 120 arranged in m rows and n columns. In this way, the transmission image is generated for each RGB channel, and the resulting color image, created by combining the RGB channels, is projected onto the screen (Scr). The pixel data Vad_R, Vad_G, and Vad_B of the video pixels output from the processing circuit 22 in response to one unit period are the pixel data of the video pixels corresponding to that unit period. Therefore, in that unit period, a composite color image corresponding to the projection position is projected at that projection position.

[0035] As described above, the arrangement of video pixels in the video data Vid-in is twice as large vertically and twice as large horizontally compared to the m rows and n columns of the panel pixels in the liquid crystal panels 100R, 100G, and 100B, resulting in 2m rows and 2n columns. In other words, the arrangement of panel pixels is half the size in the vertical direction and half the size in the horizontal direction compared to the arrangement of video pixels. Therefore, in this embodiment, by shifting one panel pixel at a total of four locations (2 vertical x 2 horizontal) over a single frame period, one panel pixel is made to appear as if it represents four video pixels specified in the video data Vid-in.

[0036] However, in a configuration where a single panel pixel is simply shifted to four locations within one frame period to represent image pixels, the display quality may deteriorate, as will be described later. Therefore, in this embodiment, the projection position of a single panel pixel is shifted every eight unit periods of two frames to represent image pixels, and furthermore, the direction in which the projection position is shifted every unit period in odd-numbered frame periods is opposite to the direction in which the projection position is shifted every unit period in even-numbered frame periods.

[0037] Figure 7 is a diagram illustrating the relationship between frames and unit periods in this embodiment. As shown in the figure, in this embodiment, a 2-frame (2F) period is divided into an preceding odd-frame period and a succeeding even-frame period.

[0038] Odd-numbered frame periods are divided into four unit periods. For convenience, the four unit periods in odd-numbered frame periods are assigned the codes f1-1, f1-2, f1-3, and f1-4 in chronological order. Similarly, even-numbered frame periods are divided into four unit periods. For convenience, the four unit periods in even-numbered frame periods are assigned the codes f2-1, f2-2, f2-3, and f2-4 in chronological order.

[0039] Note that "4," the number of unit periods included in odd-numbered and even-numbered frame periods, is an example of an integer n greater than or equal to 2. Also, odd-numbered frame periods are an example of the first frame period, and even-numbered frame periods are an example of the second frame period. Unit periods f1-1 and f2-1 are examples of the first unit period, unit periods f1-2 and f2-2 are examples of the second unit period, unit periods f1-3 and f2-3 are examples of the third unit period, and unit periods f1-4 and f2-4 are examples of the fourth unit period.

[0040] A frame period is the period during which one frame of the image, indicated by the video data Vid-in from the host device, is supplied. If the frequency of the vertical synchronization signal included in the synchronization signal Sync is 60Hz, then one period is 16.7 milliseconds. In this case, the length of each unit period is 4.17 milliseconds, which is 1 / 4 the length of a frame period.

[0041] Figure 8 shows an example of the waveforms of the control signals P_x and P_y supplied to the optical path shift element 230. The optical path shift element 230 shifts the image projected onto the screen Scr in the X and Y axes relative to the projection surface. For convenience, the amount of this shift will be explained by converting it to the size of the pixels projected onto the screen Scr, i.e., the size of the panel pixels.

[0042] The control signals P_x and P_y take on one of three levels—+A, 0, or -A—except during the trailing period in the unit periods f1-1 to f1-4 and f2-1 to f2-4. The levels of the control signals P_x and P_y change during the trailing period, which corresponds to the vertical scan retrace period. Note that the level of the control signal P_x or P_y may remain constant across two consecutive unit periods.

[0043] For the sake of explanation, the reference position is defined as the projection position during a unit period f1-1 in an odd-numbered frame period, excluding the trailing period, i.e., the projection position during the period when the levels of the control signals P_x and P_y are 0. The optical path shift element 230 shifts the projection position by half the width of a panel pixel in the X direction from the reference position if the level of the control signal P_x is +A, and shifts the projection position by half the width of a panel pixel in the opposite direction in the X direction from the reference position if the level of the control signal P_x is -A. The optical path shift element 230 shifts the projection position by half the width of a panel pixel in the Y direction from the reference position if the level of the control signal P_y is +A, and shifts the projection position by half the width of a panel pixel in the opposite direction in the Y direction from the reference position if the level of the control signal P_y is -A.

[0044] Therefore, for example, if the level of the control signal P_x is +A, the optical path shift element 230 shifts the projection position from the reference position by half the panel pixel width in both the X and Y directions.

[0045] In Figure 8, the arrows shown at the end of each unit period indicate the direction in which the projection position shifts when the levels of the control signals P_x and P_y change or remain constant during that end period. Furthermore, the shift in projection position caused by the optical path shift element 230 may not be in accordance with the levels of the control signals P_x and P_y, and may be accompanied by a time delay.

[0046] Next, we will explain which image pixels of the video data Vid-in are represented by the panel pixels of the liquid crystal panel 100 during odd-numbered and even-numbered frame periods. Furthermore, for a panel pixel to represent a certain image pixel means that the panel pixel reaches a state where it has the transmittance specified by the pixel data corresponding to that image pixel.

[0047] The left column in Figure 9 shows a portion of the video image shown in the video data Vid-in, in order to illustrate the arrangement of video pixels. The right column in the same figure shows the arrangement of panel pixels, corresponding to the arrangement of video pixels in the left column.

[0048] In the left column of Figure 9, the codes A11, B11, A21, B21, A31, and B31 are assigned to the first row for convenience in order to distinguish the video pixels of the video data Vid-in. Similarly, codes are assigned to the 2nd to 5th rows as shown in the figure. In the right column of Figure 9, for convenience, the panel pixels are assigned codes p11, p21, and p31 in the first row, and p12, p22, and p32 in the second row, respectively, in order to distinguish them.

[0049] Figure 10 shows the image pixels represented by a panel pixel during odd-numbered and even-numbered frame periods. In the figure, the thick black borders surrounding the four image pixels arranged in 2 rows and 2 columns indicate the group of image pixels represented by a single panel pixel. The four image pixels represented by a single panel pixel differ between odd-numbered and even-numbered frame periods. Specifically, in this embodiment, the 2x2 image pixels represented by a given panel pixel during an even-numbered frame period are shifted by one image pixel to the right and one image pixel downwards compared to the 2x2 image pixels represented by the same panel pixel during an odd-numbered frame period.

[0050] Figure 11 focuses particularly on panel pixel p11 and shows the order of image pixels represented by panel pixel p11 during odd-numbered frame periods and even-numbered frame periods. As shown in the figure, panel pixel p11 represents image pixels C11, B11, A11, and D11 in order during the unit period f1-1 to 1-4 of the odd-numbered frame period, and represents image pixels C11, D21, A22, and B12 in order during the unit period f2-1 to 2-4 of the even-numbered frame period. In other words, the arrangement of image pixels B11, A11, and D11 represented by panel pixel p11 during odd-numbered frame periods and the arrangement of image pixels B11, A11, and D11 represented by panel pixel p11 during even-numbered frame periods are rotationally symmetric (twice symmetric) around image pixel C11, meaning they overlap when rotated 180 degrees.

[0051] Figures 12 and 13 show which image pixels are represented by which projection position in the projection-type display device 1 according to the embodiment. Specifically, Figure 12 shows which projection positions the six panel pixels in Figure 9 use to represent the image pixels in the left column of Figure 9 in the unit periods f1-1 to f1-4 of the odd-numbered frame period. Figure 13 shows which projection positions the six panel pixels use to represent the image pixels in the unit periods f2-1 to f2-4 of the even-numbered frame period.

[0052] For convenience, the projection position in the unit period f1-1 of the odd-numbered frame period is used as the reference position. As shown in Figure 12, in the unit period f1-1 of the odd-numbered frame period, panel pixels p11, p21, p31, p12, p22, and p32 represent the hatched video pixels C11, C21, C31, C12, C22, and C32, respectively.

[0053] During the trailing period (vertical retrace period) of unit period f1-1, the optical path shift element 230 shifts the projection position by 0.5 pixels of panel pixels upward (opposite direction to the Y direction) in the figure from the reference position in unit period f1-1, shown by the dashed line. In the next unit period f1-2, panel pixels p11, p21, p31, p12, p22, and p32 represent the hatched image pixels B11, B21, B31, B12, B22, and B32, respectively. During the trailing period of unit period f1-2, the optical path shift element 230 shifts the projection position by 0.5 pixels of panel pixels to the left (opposite direction to the X direction) in the figure from the projection position in unit period f1-2, which is shown by the dashed line. In the next unit period f1-3, panel pixels p11, p21, p31, p12, p22, and p32 represent the hatched image pixels A11, A21, A31, A12, A22, and A32, respectively. During the trailing period of unit period f1-3, the optical path shift element 230 shifts the projection position by 0.5 pixels of panel pixels downward (Y direction) in the figure from the projection position in unit period f1-3, which is shown by the dashed line. In the next unit period f1-4, panel pixels p11, p21, p31, p12, p22, and p32 represent the hatched image pixels D11, D21, D31, D12, D22, and D32, respectively.

[0054] During the trailing period of unit period f1-4, the optical path shift element 230 shifts the projection position from the projection position in unit period f1-4 (shown by the dashed line) to the right (X direction) by 0.5 pixels of the panel pixels in the figure, returning it to the reference position. In the first unit period f2-1 of an even-numbered frame period, panel pixels p11, p21, p31, p12, p22, and p32 represent the hatched image pixels C11, C21, C31, C12, C22, and C32, respectively. That is, the image pixel represented by a given panel pixel in unit period 1-1 is the same as the image pixel represented by the same panel pixel in unit period 2-1. During the trailing period of unit period f2-1, the optical path shift element 230 shifts the projection position by 0.5 pixels of panel pixels to the right (X direction) in the figure from the reference position in unit period f2-1, which is shown by the dashed line. In the next unit period f2-2, panel pixels p11, p21, p31, p12, p22, and p32 represent the hatched image pixels D21, D31, D41, D22, D32, and D42, respectively. During the trailing period of unit period f2-2, the optical path shift element 230 shifts the projection position by 0.5 pixels of panel pixels downward (Y direction) in the figure from the projection position in unit period f2-2, which is shown by the dashed line. In unit period f2-3, panel pixels p11, p21, p31, p12, p22, and p32 represent the hatched image pixels A22, A32, A42, A23, A33, and A42, respectively. During the trailing period of unit period f2-3, the optical path shift element 230 shifts the projection position by 0.5 pixels of panel pixels to the left (opposite direction to the X direction) in the figure from the projection position in unit period f2-3, which is shown by the dashed line. In the next unit period f2-4, panel pixels p11, p21, p31, p12, p22, and p32 represent the hatched image pixels B12, B22, B32, B13, B23, and B33, respectively. During the trailing period of the unit period f2-4, the optical path shift element 230 shifts the projection position from the projection position shown by the dashed line upwards (opposite direction to the Y direction) by 0.5 pixels of the panel pixels in the figure, returning it to the reference position.

[0055] Thus, in this embodiment, the optical path shift element 230 is controlled so that each projection position corresponding to the unit periods f1-2 to 1-4 in odd-numbered frame periods is different from each projection position corresponding to the unit periods f2-2 to 2-4 in even-numbered frame periods. Specifically, the projection position corresponding to unit period f1-2 is different from the projection position corresponding to unit period f2-2, the projection position corresponding to unit period f1-3 is different from the projection position corresponding to unit period f2-3, and the projection position corresponding to unit period f1-4 is different from the projection position corresponding to unit period f2-4.

[0056] Next, we will explain how, in this embodiment, a decrease in display quality is suppressed even when a specific pattern appears in the video image specified by the video data Vid-in.

[0057] Figure 14 shows a specific pattern that appears in the video image specified by the video data Vid-in. As shown in this figure, the specific pattern is a still image, for example, a pattern in which a white video pixel is used as the background and black video pixels are used to form diagonal lines at a 45-degree angle. In the case of still images, the image pixels will be the same for odd-numbered and even-numbered frame periods. Furthermore, a white image pixel refers to an image pixel to which the highest (or near-highest) gradation level is specified for each of the three primary colors: red, green, and blue. A black image pixel refers to an image pixel to which the lowest (or near-lowest) gradation level is specified for each of the three primary colors: red, green, and blue.

[0058] Figure 15 shows which image pixels are represented by which projection position in the unit periods f1-1 to f1-4 of odd-numbered frames and f2-1 to f2-4 of even-numbered frames, when the image pixels have a specific pattern. Note that in Figure 15, compared to Figure 9, one row of panel pixels has been added in the Y direction for explanatory purposes. Also, in Figure 15, the thick dashed line indicates the panel pixel p22 that represents the black image pixel C22 in unit periods f1-1 and 2-1. The representation of which image pixel and projection position the panel pixel p22 represents in the unit periods f1-1 to f1-4 for odd-numbered frames and f2-1 to f2-4 for even-numbered frames has already been explained in Figures 12 and 13.

[0059] In Figure 15, the reason why panel pixel p22 is represented in gray (hatched) during unit periods f1-2 and f2-2 is as follows: Generally, when the response of liquid crystal elements in liquid crystal panels 100R, 100G, and 100B is slow, the transition from black to white does not occur immediately, but rather passes through gray, which is between white and black. Therefore, panel pixels transitioning from black to white are visible as gray during the unit period in which they change from black.

[0060] Before discussing how the degradation of display quality is suppressed in the embodiment, let's describe a comparative example. In the embodiment, the frame period is distinguished into odd-numbered frame periods and even-numbered frame periods, and the 2x2 image pixels represented by a single panel pixel differ between odd-numbered and even-numbered frame periods. In the comparative example, the frame period is not distinguished between odd-numbered and even-numbered frame periods. Therefore, in the comparative example, a single frame period is divided into four unit periods, and in each of these four unit periods, one panel pixel represents 2x2 image pixels. In other words, the comparative example is a configuration in which only either odd-numbered or even-numbered frame periods are used, not both, in the embodiment. Here, for convenience, only odd-numbered frame periods are used as the comparative example. In the comparative example, for example, panel pixel p22 represents image pixel C22 in unit period f1-1, image pixel B22 in unit period f1-2, image pixel A22 in unit period f1-3, and image pixel D22 in unit period f1-4.

[0061] The upper section of Figure 16 is a simplified diagram showing how the specific pattern shown in Figure 14 appears to the user when projected onto a screen (Scr) using the comparative example. In the comparative example, the operation of odd-numbered frame periods from unit period f1-1 to f1-4 in Figure 15 is repeated. When this operation is repeated, as shown in the upper section of Figure 16, on the screen (Scr), the projection pixels that should be perceived as diagonal 45-degree lines are affected by the gray projection pixels (transition pixels) that appear when transitioning from black to white, resulting in an uneven distribution of bright and dark areas, and appearing as a distorted shape. In contrast, as shown in the lower section of Figure 16, in this embodiment, the effect of the transition pixels on the projection pixels that should be perceived as diagonal 45-degree lines is evenly distributed, making it less likely to appear as a distorted shape. Therefore, in this embodiment, the deterioration of display quality can be suppressed when displaying a specific pattern.

[0062] <Variations or applications> In the embodiments described above, various modifications or applications are possible as follows.

[0063] In this embodiment, the frame duration is divided into four unit durations. Specifically, "4" is used as an example to represent n, the number of unit durations contained within one frame duration. However, n is not limited to "4"; it can be "2" or greater.

[0064] In the embodiments, a specific pattern was described using a still image with a white background and black image pixels forming a diagonal 45-degree line, specifically a line pointing upwards to the right. However, the same principle applies to lines pointing upwards to the left, where the degradation of display quality can be suppressed. Similarly, the same principle applies to diagonal 45-degree lines with a black background and white image pixels forming a diagonal line.

[0065] In the embodiments, the period during which the levels of the control signals P_x and P_y supplied to the optical path shift element 230 change is set to the trailing period, which corresponds to the vertical scanning period in the unit periods f1-1 to f1-4 and f2-1 to f2-4. However, as described above, the shift of the projection position by the optical path shift element 230 may not be in line with the levels of the control signals P_x and P_y, and may be accompanied by a time delay. In such cases, for example, the change in the levels of the control signals P_x and P_y may be started in anticipation of the time delay, so that the image formed by the liquid crystal panel 100 in a unit period is shifted to the projection position corresponding to that unit period.

[0066] <Note> From the forms exemplified above, the following aspects can be understood, for example.

[0067] A projection display device according to one embodiment (embodiment 1) includes a liquid crystal panel having panel pixels, an optical path shift element that shifts the position of projection pixels projected from the panel pixels every n unit periods, from the first unit period to the nth (where n is an integer of 2 or more) unit periods included in one frame period, and a display control circuit that controls the liquid crystal panel and the optical path shift element, wherein the display control circuit supplies data signals corresponding to pixel data constituting video data to the panel pixels every unit period, and controls the optical path shift element to shift the position of the projection pixels every unit period. The optical path shift element is controlled such that the positions of the projected pixels are the same, and the positions of the projected pixels are the same, and the optical path shift element is controlled such that the positions of the projected pixels from the second unit period to the nth unit period in the first frame period and the positions of the projected pixels from the second unit period to the nth unit period in the second frame period are different. According to Embodiment 1, even if a specific display pattern appears in the image specified by the video data, a decrease in display quality can be suppressed.

[0068] In a specific embodiment of Embodiment 1 (Embodiment 2), the pixel data constituting the video data is arranged along the first axis and the second axis, and the optical path shift element shifts the projected pixels in the direction along the first axis or the direction along the second axis for each unit period. According to embodiment 2, the direction in which the optical path shift element shifts the projection pixels is along the first axis or the second axis, so that the amount of shift of the projection pixels in each unit period can be made uniform.

[0069] In a specific embodiment of Embodiment 2 (Embodiment 3), n is 4, and the optical path shift element shifts the position of the projection pixel in one direction along the first axis from the first unit period to the second unit period, in one direction along the second axis from the second unit period to the third unit period, in the other direction along the first axis from the third unit period to the fourth unit period, and in the other direction along the second axis from the fourth unit period to the first unit period of the second frame period. According to Embodiment 3, since there are four positions for the projected pixels during the first frame period, the resolution of the projected image visible to the user is effectively increased to four times the resolution of the liquid crystal panel. In Embodiment 4, if the four positions of the projected pixels during the first frame period are shifted counterclockwise, for example, then the four positions of the projected pixels will be shifted counterclockwise during the second frame period. Furthermore, "one direction along the axis" refers to one of two directions along that axis, and "the other direction along the axis" refers to the other of two directions along that axis.

[0070] In a specific embodiment of Embodiment 1, 2, or 3 (Embodiment 4), the array of pixel data corresponding to the first unit period to the nth unit period of the first frame period and the array of pixel data corresponding to the first unit period to the nth unit period of the second frame period are rotationally symmetric with respect to the pixel data corresponding to the first unit period of the first frame period and the first unit period of the second frame period. [Explanation of Symbols]

[0071] 1... Projection-type display device, 100R, 100G, 100B... Liquid crystal panel, 110... Pixel circuit, 118... Pixel electrode, 120... Liquid crystal element, 200... Display control circuit, 220R, 220R, 220G... Processing circuit, 230... Optical path shift element.

Claims

1. A liquid crystal panel having panel pixels, An optical path shift element that shifts the position of the projection pixel projected from the panel pixel every n unit periods, from the first unit period to the nth (where n is an integer greater than or equal to 2 and is even) unit period, which are included in one frame period. A display control circuit that controls the liquid crystal panel and the optical path shift element, Includes, The aforementioned display control circuit is A data signal corresponding to the pixel data constituting the video data is supplied to the panel pixels at each unit period. With respect to the optical path shift element, the shift of the position of the projection pixel is controlled for each unit period. In the first unit period of the n unit periods in the first frame period, and in the first unit period of the n unit periods in the second frame period following the first frame period, data signals corresponding to the same pixel data are supplied to the liquid crystal panel, and the position of the projected pixels is controlled to be the same. The positions of the projection pixels from the second unit period to the nth unit period in the first frame period, The optical path shift element is controlled so that the position of each projection pixel from the second unit period to the nth unit period in the second frame period is different from that of the optical path shift element. A projection-type display device characterized by the following features.

2. The pixel data constituting the aforementioned video data is Arranged along the first and second axes, The optical path shifting element is For each unit period, the projection pixel is, Shift in the direction along the first axis or in the direction along the second axis The projection display device according to feature 1.

3. The above n is 4, The optical path shifting element is The position of the aforementioned projection pixel is During the aforementioned first frame period, From the first unit period to the second unit period, it shifts in one direction along the first axis, From the second unit period to the third unit period, it shifts in one direction along the second axis, During the third unit period to the fourth unit period, it shifts in the other direction along the first axis, From the fourth unit period to the first unit period of the second frame period, it shifts in the other direction along the second axis. The projection display device according to feature 2.

4. The array of pixel data corresponding to the first unit period to the nth unit period of the first frame period and the array of pixel data corresponding to the first unit period to the nth unit period of the second frame period are: The pixel data corresponding to the first unit period of the first frame period and the first unit period of the second frame period are rotationally symmetrical with respect to the pixel data. The projection display device according to claim 1, 2, or 3.

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