Projection type display device

Abstract

To suppress deterioration of display quality due to an alignment defect when a projection position is shifted by an optical path shift element.SOLUTION: A projection type display device comprises: a liquid crystal panel that has panel pixels; an optical path shift element that shifts a projection position of a projection pixel for each four unit period, for example; and a display control circuit that controls the liquid crystal panel and the optical path shift element. The display control circuit supplies a data signal corresponding to a gradation level designated by video pixel data constituting video data to the panel pixel for each unit period, and controls the projection position for each unit period for the optical path shift element, and the optical path shift element shifts it to a target projection position after passing through the target projection position being a target for each unit period.SELECTED DRAWING: Figure 9

Description

[Technical Field]

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

[0002] In liquid crystal projectors that use liquid crystal panels, a technique is known in which the projection positions of panel pixels projected onto a screen or the like are shifted using an optical path shift element in order to artificially increase the resolution (see, for example, Patent Document 1). More specifically, this technique divides one frame period into multiple unit periods, and shifts the projection position so that it is different for each unit period. This technique allows the user to perceive as if more pixels are being projected than the number of panel pixels in the liquid crystal panel. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-39995 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, as liquid crystal panels have become smaller and higher definition, the gaps between pixel electrodes have become narrower. This causes poor alignment of the liquid crystal due to the electric field generated between adjacent pixel electrodes, which is visible as a display defect. When the projection position is shifted by the light path shift element, display defects due to such poor orientation are visually stretched in the shift direction, resulting in a significant degradation in display quality. [Means for solving the problem]

[0005] In order to solve the above problem, a projection display device according to one embodiment of the present disclosure includes a liquid crystal panel having panel pixels; a light path shift element that shifts an optical path of the projection light so as to change a projection position of the projection pixel displayed by the projection light projected from the panel pixels for each of k unit periods from a first unit period to a kth unit period (k is an integer of 2 or more) included in one frame period; and a display control circuit that controls the liquid crystal panel and the light path shift element, wherein the display control circuit supplies a data signal corresponding to a gradation level specified by video pixel data that constitutes video data to the panel pixels for each unit period, and controls the projection position for each unit period with respect to the light path shift element, and the light path shift element shifts the projection position to a target projection position after passing the target projection position for each unit period. [Brief explanation of the drawings]

[0006] [Figure 1] 1 is a diagram showing a projection display device according to a first embodiment. [Figure 2] FIG. 1 is a block diagram showing a configuration of a projection display device. [Figure 3] FIG. 1 is a perspective view showing a configuration of a liquid crystal panel in a projection display device. [Figure 4] FIG. 2 is a cross-sectional view showing the structure of a liquid crystal panel. [Figure 5] FIG. 2 is a block diagram showing the electrical configuration of a liquid crystal panel. [Figure 6] FIG. 2 is a diagram showing the configuration of a pixel circuit in a liquid crystal panel. [Figure 7] FIG. 1 is a diagram showing the relationship between one frame period and a unit period in a projection display device. [Figure 8] FIG. 2 is a diagram showing video pixels represented by one panel pixel in one frame period. [Figure 9] FIG. 4 is a diagram showing a locus of a projection position by a light path shift element in the first embodiment. [Figure 10] 10A and 10B are diagrams illustrating loci of projection positions by a light path shift element in a comparative example. [Figure 11]FIG. 10 is a diagram showing control details for a light path shift element and a light source unit in one frame period. [Figure 12] FIG. 1 is a diagram showing the relationship between image pixels, panel pixels, and projection positions in one frame period in a projection display device. [Figure 13] FIG. 2 is a diagram showing an example of an arrangement of video pixels. [Figure 14] FIG. 10 is a diagram illustrating a state in which a domain occurs. [Figure 15] FIG. 10 is a diagram showing an example of a display by panel pixels that is actually viewed. [Figure 16] FIG. 10 is a diagram for explaining a visually recognized display in a comparative example. [Figure 17] FIG. 2 is a diagram for explaining a visually recognized display in the first embodiment. [Figure 18] FIG. 10 is a diagram showing a locus of a projection position by a light path shift element in the second embodiment. [Figure 19] FIG. 11 is a diagram showing a locus of projection positions by a light path shift element in the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0007] Projection display devices according to embodiments will be described below with reference to the drawings. In each drawing, the dimensions and scale of each part are appropriately different from those of the actual device. The embodiments described below are preferred examples, and therefore various technically preferable limitations are applied. However, the scope of the present disclosure is not limited to these embodiments unless otherwise specified in the following description to the effect that the present disclosure is limited.

[0008] FIG. 1 is a diagram showing the optical configuration of a projection display device 1 according to an embodiment. As shown in the figure, the projection display device 1 includes liquid crystal panels 100R, 100G, and 100B. A light source unit 2102 consisting of a white light source such as a laser is provided inside the projection display device 1. Projection light emitted from the light source 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 enters the liquid crystal panel 100R, the G light enters the liquid crystal panel 100G, and the B light enters the liquid crystal panel 100B. Since the optical path of B is longer than the optical paths of R and G, it is necessary to prevent loss in the optical path of B. For this reason, a relay lens system 2121 consisting of an input lens 2122, a relay lens 2123, and an output lens 2124 is provided in the optical path of B.

[0009] The liquid crystal panel 100R has a plurality of pixel circuits, as will be described later. Each of the plurality of 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, and exhibit a transmittance according to the voltage of the data signal. Therefore, an R transmission image is generated in the liquid crystal panel 100R by individually controlling the transmittance of the liquid crystal elements based on the data signal corresponding to R. Similarly, a G transmission image is generated in the liquid crystal panel 100G based on the data signal corresponding to G, and a B transmission image is generated in the liquid crystal panel 100B 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 are incident on the dichroic prism 2112 from three directions. In the dichroic prism 2112, the R and B light are refracted at 90 degrees, while the G light travels straight. Therefore, the dichroic prism 2112 combines the images of each color. The combined image by 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 a screen Scr, which is a projection surface.

[0011] The light path shift element 230 shifts the light path of the light (projected light) emitted from the dichroic prism 2112. In detail, the light path shift element 230 shifts the position of the projected composite image in the left-right direction and / or the up-down direction relative to the projection surface.

[0012] The transmitted images by the liquid crystal panels 100R and 100B are projected after being reflected by the dichroic prism 2112, whereas the transmitted image by the liquid crystal panel 100G is projected in a straight line. Therefore, the transmitted images by the liquid crystal panels 100R and 100B are left-right inverted relative to the transmitted image by the liquid crystal panel 100G.

[0013] 2 is a block diagram showing the electrical configuration of the projection display device 1. As shown in the figure, the projection display device 1 includes a display control circuit 20, liquid crystal panels 100R, 100G, and 100B, a light path shift element 230, and a light source unit 2102.

[0014] Video data Vid_in is supplied from a host device or other higher-level device (not shown) in synchronization with a synchronization signal Sync. The video data Vid_in specifies the gradation levels of the pixels that make up one frame period of video, for example, by 8 bits for each RGB.

[0015] Note that the pixels of an image specified by the video data Vid_in are referred to as video pixels, and the data specifying the gradation levels of the video pixels are referred to as video pixel data, but in some cases, no distinction is made between video pixels and video pixel data. Furthermore, the pixels of an image before or after composition by the liquid crystal panels 100R, 100G, or 100B are referred to as panel pixels. The panel pixels that are shifted by the light path shift element 230 and projected onto the screen Scr are referred to as projected pixels, and the positions where the panel pixels are projected are referred to as projection positions. In the liquid crystal panels 100R, 100G, and 100B, the panel pixels are arranged in a matrix in a plan view. In the embodiment, the arrangement of the video pixels specified by the video data Vid_in is, for example, twice as large vertically and twice as large horizontally as the arrangement of the panel pixels of the liquid crystal panels 100R, 100G, or 100B.

[0016] In this embodiment, a color image projected onto the screen Scr is expressed by combining the transmitted images of the liquid crystal panels 100R, 100G, and 100B. Therefore, the smallest unit of a color image can be divided into a red subpixel of the liquid crystal panel 100R, a green subpixel of the liquid crystal panel 100G, and a blue subpixel of the liquid crystal panel 100B. However, when it is not necessary to specify the color of the subpixels of the liquid crystal panels 100R, 100G, and 100B, or when only brightness is an issue, there is no need to refer to them as subpixels. Therefore, in this description, the display units of the liquid crystal panels 100R, 100G, and 100B will also be referred to as panel pixels.

[0017] The synchronization signal Sync 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 21, and conversion circuits 22R, 22G, and 22B. The processing circuit 21 controls the conversion circuits 22R, 22G, 22G, the liquid crystal panels 100R, 100G, 100B, the light path shift element 230, and the light source unit 2102 in each unit period f1 to f4, which will be described later, based on the synchronization signal Sync. The light path shift element 230 shifts the projection position in accordance with the control signals P_x and P_y output from the processing circuit 21. The light source unit 2102 changes the intensity of the emitted light in accordance with a control signal Lgt output from the processing circuit 21.

[0019] Of the video data Vid_in supplied from the higher-level device, the R component is represented as video data Va_R, the G component is represented as video data Va_G, and the B component is represented as video data Va_B. The conversion circuit 22R temporarily stores the video data Va_R supplied from the higher-level device in an internal buffer for one or more frame periods, then reads out the video data corresponding to the unit period, converts it into an analog voltage data signal Vid_R, and supplies it to the liquid crystal panel 100R. Conversion circuits 22G and 22B differ from conversion circuit 22R only in the color components of the video data to be converted, but otherwise share the same components as conversion circuit 22R. That is, conversion circuit 22G converts video data Va_G corresponding to a unit period into an analog voltage data signal Vid_G and supplies it to liquid crystal panel 100G, while conversion circuit 22B converts video data Va_B corresponding to a unit period into an analog voltage data signal Vid_G and supplies it to liquid crystal panel 100B.

[0020] Next, liquid crystal panels 100R, 100G, and 100B will be described. Liquid crystal panels 100R, 100G, and 100B have a common structure, with the only difference being the color, or wavelength, of the light incident on them. Therefore, liquid crystal panels 100R, 100G, and 100B will be generally described as liquid crystal panel 100, without specifying the color.

[0021] FIG. 3 is a perspective view showing the liquid crystal panel 100, and FIG. 4 is a cross-sectional view taken along line Hh in FIG. As shown in these figures, in the liquid crystal panel 100, an element substrate 100a on which a pixel electrode 118 is provided and an opposing substrate 100b on which a common electrode 108 is provided are bonded together with a sealing material 90 so that the electrode forming surfaces face each other while maintaining a certain gap, and liquid crystal 105 is sealed in this gap.

[0022] The element substrate 100a and the counter substrate 100b are each made of a light-transmitting substrate such as glass or quartz. As shown in FIG. 3, one side of the element substrate 100a extends beyond the counter substrate 100b. A plurality of terminals 106 are provided in this extending area along the horizontal direction in the figure. One end of an FPC (Flexible Printed Circuits) substrate (not shown) is connected to the plurality of terminals 106. The other end of the FPC substrate is connected to the display control circuit 20, and the various signals described above are supplied.

[0023] On the surface of the element substrate 100a facing the counter substrate 100b, pixel electrodes 118 are formed by patterning a transparent conductive layer made of, for example, ITO (Indium Tin Oxide). Although not shown, a microlens is provided for each panel pixel on the counter substrate 100b (or element substrate 100a) to efficiently send a large amount of light to the openings that become the panel pixels. With this configuration, light that would have been repelled by the light-shielding portion is sent to the openings of the microlens, thereby improving the light utilization efficiency.

[0024] 5 is a block diagram showing the electrical configuration of the liquid crystal panel 100. The liquid crystal panel 100 has a scanning line driving circuit 130 and a data line driving circuit 140 provided on the periphery of the display area 10.

[0025] In the display region 10 of the liquid crystal panel 100, pixel circuits 110 are arranged in a matrix. More specifically, in the display region 10, a plurality of scanning lines 12 are provided extending horizontally in the drawing, and a plurality of data lines 14 are provided extending vertically and electrically insulated from the scanning lines 12. The pixel circuits 110 are provided in a matrix corresponding to the intersections of the plurality of scanning lines 12 and the plurality of data lines 14.

[0026] If the number of scanning lines 12 is m and the number of data lines 14 is n, the pixel circuits 110 are arranged in a matrix of m rows and n columns. Both m and n are integers greater than or equal to 2. To distinguish between the rows of the matrix in the scanning lines 12 and the pixel circuits 110, they may be referred to as 1, 2, 3, ..., (m-1), m rows from top to bottom in the drawings. Similarly, to distinguish between the columns of the matrix in the data lines 14 and the pixel circuits 110, they may be referred to as 1, 2, 3, ..., (n-1), n columns from left to right in the drawings.

[0027] The scanning line driving circuit 130 selects the scanning lines 12 one by one in the order of, for example, the 1st, 2nd, 3rd, ..., mth rows in accordance with the control of the display control circuit 20, and sets the scanning signal to the selected scanning line 12 to H level. Note that the scanning line driving circuit 130 sets the scanning signals to the scanning lines 12 other than the selected scanning line 12 to L level. The data line driving circuit 140 latches the data signals supplied from the corresponding color circuit among the conversion circuits 22R, 22G, or 22B for one row, and outputs them via the data line 14 to the pixel circuit 110 located on that scanning line 12 during the period when the scanning signal to that scanning line 12 is at H level.

[0028] FIG. 6 is a diagram showing an equivalent circuit of four pixel circuits 110 arranged in two rows and two columns corresponding to the intersections of two adjacent scanning 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 a scan line 12, the source node is connected to a data line 14, and the drain node is connected to a pixel electrode 118 that has a square shape in a plan view.

[0029] A common electrode 108 is provided in common to all pixels so as to face the pixel electrode 118. A voltage LCcom is applied to the common electrode 108. As described above, the 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 in which the liquid crystal 105 is sandwiched between the pixel electrode 118 and the common electrode 108. Furthermore, a storage capacitor 109 is provided in parallel to the liquid crystal element 120. One end of the storage capacitor 109 is connected to a pixel electrode 118, and the other end is connected to a capacitance line 107. A time-constant voltage, for example, a voltage LCcom that is the same as the voltage applied to the common electrode 108, is applied to the capacitance line 107. The pixel circuits 110 are arranged in a matrix in the horizontal direction, which is the extension direction of the scanning lines 12, and in the vertical direction, which is the extension direction of the data lines 14, and therefore the pixel electrodes 118 included in the pixel circuits 110 are also arranged in both the vertical and horizontal directions.

[0030] When the scanning signal for a scanning line 12 becomes high, the transistor 116 of the pixel circuit 110 provided corresponding to that scanning line 12 is turned on. When the transistor 116 is turned on, the data line 14 and the pixel electrode 118 are electrically connected, and the data signal supplied to the data line 14 reaches the pixel electrode 118 via the transistor 116 that is turned on. When the scanning line 12 becomes low, the transistor 116 is turned off, but the voltage of the data signal that reaches the pixel electrode 118 is held by the capacitance of the liquid crystal element 120 and the storage capacitor 109.

[0031] 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 liquid crystal element 120 has a transmittance that corresponds to the effective value of the applied voltage. In addition, the region of the liquid crystal element 120 that functions as a panel pixel, i.e., the region that exhibits transmittance according to the effective value of the voltage, is the region where the pixel electrode 118 overlaps with the common electrode 108 when the element substrate 100a and the counter substrate 100b are viewed in a plan view. Since the pixel electrode 118 has a square shape in a plan view, the shape of the pixel formed by the liquid crystal panel 100 is also square. In addition, in this embodiment, the liquid crystal 105 is of a VA (Vertical Alignment) type, and is in a normally black mode in which the transmittance is lowest when the voltage applied to the liquid crystal element 120 is zero, and the transmittance increases as the applied voltage increases.

[0032] An operation of supplying a data signal to the pixel electrodes 118 of the liquid crystal elements 120 is executed for each horizontal scanning period in the order of the 1st, 2nd, 3rd, ..., mth rows during the effective vertical scanning period of unit periods f1 to f4. As a result, a voltage according to the data signal is held in each of the liquid crystal elements 120 of the pixel circuits 110 arranged in m rows and n columns, each liquid crystal element 120 has the target 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, a transmission image is generated for each of the R, G, and B colors, and a color image obtained by combining the R, G, and B colors is projected onto the screen Scr. The data signals Vid_R, Vid_G, and Vid_B output in a unit period correspond to the RGB components of the video data corresponding to that unit period, so that a composite image of a color corresponding to the projection position is projected at that projection position in that unit period.

[0033] 7 is a diagram showing the relationship between a frame period and a unit period in the projection display device 1 according to the embodiment. As shown in the figure, in this embodiment, one frame (1F) period is divided into four unit periods. For convenience of distinguishing the four unit periods, symbols f1, f2, f3, and f4 are assigned in chronological order. One frame period is the period during which one frame of an image represented by video data Vid_in is supplied from a higher-level device, and is 16.7 milliseconds, or one cycle, when the frequency of the vertical synchronization signal included in the synchronization signal Sync is 60 Hz. In this case, the length of each unit period is 4.17 milliseconds, which is 1 / 4 of the length of one frame period.

[0034] In this embodiment, the projection position is changed for each unit period f1 to f4, and at each projection position, the user is made to view an image in which the image resolution specified by the video data Vid_in is reduced to 1 / 4. In other words, the user is made to view a pseudo image having four times the resolution of the composite image produced by the liquid crystal panels 100R, 100G, and 100B.

[0035] The unit period f1 is divided into an effective vertical scanning period f1a and a vertical blanking period f1b. The effective vertical scanning period f1a is a period during which the scanning lines 12 from the first row to the mth row are horizontally scanned in sequence, and the vertical blanking period f1b is a preparation period for moving from the final mth row to the first row for horizontal scanning, and is the unit period f1 minus the effective vertical scanning period f1a. Similarly, the unit period f2 is divided into an effective vertical scanning period f2a and a vertical blanking period f2b, the unit period f3 is divided into an effective vertical scanning period f3a and a vertical blanking period f3b, and the unit period f4 is divided into an effective vertical scanning period f4a and a vertical blanking period f4b.

[0036] FIG. 8 is a diagram showing the correspondence between video pixels and panel pixels. In the figure, the left column shows a portion of the arrangement of video pixels indicated by the video data Vid_in, and the right column shows a portion of the panel pixels that corresponds to the arrangement of the video pixels in the left column.

[0037] It should be noted that the video pixels in the left column and the panel pixels in the right column are given symbols to distinguish them from one another. More specifically, video pixel codes and panel pixel codes having the same last two digits correspond to each other. For example, video pixels A11, B11, C11, and D11 correspond to panel pixel p11. Furthermore, the first digits A, B, C, and D in the symbols of video pixels indicate that the corresponding panel pixels are represented in unit periods f1, f2, f3, and f4, respectively. For example, video pixel D11 is represented by panel pixel p11 in unit period f4. In other words, panel pixel p11 represents video pixels A11, B11, C11, and D11, respectively, in unit periods f1, f2, f3, and f4, as indicated by the arrows. A certain video pixel is "expressed" by a panel pixel means that the liquid crystal element 120 of the panel pixel has a transmittance corresponding to the gray level (video pixel data) of the video pixel.

[0038] 9 is a diagram showing the locus of the projection position shifted by the light path shift element 230 in the first embodiment. For convenience, the position Ps1a, which is the projection position in the effective vertical scanning period f1a of the unit period f1, is used as the reference. In this embodiment, the projection position remains at the reference position Ps1a during the effective vertical scanning period f1a, and starts to shift upward with the start of the vertical blanking period f1b, reaching a position Ps1b that is one panel pixel away from position Ps1a. After this, the projection position reverses downward from position Ps1b and shifts to position Ps2a that is 0.5 panel pixels away from position Ps1b by the start of the effective vertical scanning period f2a. The projection position remains at position Ps2a during effective vertical scanning period f2a, and begins to shift rightward with the start of vertical blanking period f2b, reaching position Ps2b, which is one panel pixel away from position Ps2a.The projection position then inverts leftward from position Ps2b and shifts to position Ps3a, which is 0.5 panel pixels away from position Ps2b, by the start of effective vertical scanning period f3a. The projection position remains at position Ps3a during effective vertical scanning period f3a, and begins to shift downward with the start of vertical blanking period f3b, reaching position Ps3b, which is one panel pixel away from position Ps3a.The projection position then reverses upward from position Ps3b and shifts to position Ps4a, which is 0.5 panel pixels away from position Ps3b, by the start of effective vertical scanning period f4a. The projection position remains at position Ps4a during the effective vertical scanning period f4a, and begins to shift leftward with the start of vertical blanking period f4b, reaching position Ps4b, which is one panel pixel away from position Ps4a.The projection position then reverses rightward from position Ps4b and returns to position Ps1a, which is 0.5 panel pixels away from position Ps4b, by the start of effective vertical scanning period f1a.

[0039] 10 is a diagram showing the trajectory of the projection position shifted by the light path shift element 230 in a comparative example to the first embodiment. In the comparative example, the projection position remains at a reference position Ps1a during the effective vertical scanning period f1a, and shifts to a position Ps2a by the start of the effective vertical scanning period f2a. The projection position remains at position Ps2a during the effective vertical scanning period f2a, shifts to a position Ps3a by the start of the effective vertical scanning period f3a, and similarly progresses thereafter, returning to position Ps1a by the start of the effective vertical scanning period f1a. That is, in the comparative example, the projection position shifts directly from position Ps1a to position Ps2a between the end of effective vertical scanning period f1a and the start of effective vertical scanning period f2a, and does not follow an unnecessary path such as position Ps1b. In other words, in the first embodiment, compared to the comparative example, for example, between the end of the effective vertical scanning period f1a and the start of the effective vertical scanning period f2a, the projection position moves from position Ps1a, passes through position Ps2a, reaches position Ps1b, and then returns to position Ps2a, resulting in an overshoot.

[0040] The positions Ps1a, Ps2a, Ps3a, and Ps4a are target projection positions in the effective vertical scanning periods f1a, f2a, f3a, and f4a, respectively.

[0041] FIG. 11 is a diagram showing an example of waveforms of the control signals P_x, P_y and Lgt for drawing the locus of the projection position shown in FIG. The light path shift element 230 shifts the projection position left / right and / or up / down relative to the projection surface. Specifically, the light path shift element 230 shifts the projection position rightward by a distance corresponding to the amount of increase in the level of the control signal P_x, and shifts the projection position leftward by a distance corresponding to the amount of decrease in the level of the control signal P_x. The light path shift element 230 also shifts the projection position upward by a distance corresponding to the amount of increase in the level of the control signal P_y, and shifts the projection position downward by a distance corresponding to the amount of decrease in the level of the control signal P_y. When the levels of the control signals P_x and P_y are both 0, the light path shift element 230 determines that the projection position is at a reference position Ps1a, and when the levels of the control signals P_x and P_y change by A, the shift distance of the projection position is 0.5 panel pixels. For example, if the level of the control signal P_x is 0 and the level of the control signal P_y is +2A, the light path shift element 230 shifts the projection position from the reference position Ps1a upward to a position Ps1b that is one panel pixel away.

[0042] The light source unit 2102 sets the intensity of the emitted light relatively high when the level of the control signal Lgt is high, and sets the intensity of the emitted light relatively low when the level of the control signal Lgt is low. Specifically, when the level of the control signal Lgt is 1.0c, which is the standard, the light source unit 2102 sets the intensity of the emitted light higher than the standard when the level of the control signal Lgt is 1.2c.

[0043] FIG. 12 is a diagram showing the relationship between video pixels, panel pixels, and projection positions in one frame period. During the effective vertical scanning period f1a of the unit period f1, the projection position is the reference position Ps1a. Panel pixels p11, p12, p13, p21, p22, and p23 represent the hatched image pixels A11, A12, A13, A21, A22, and A23 in order at position Ps1a. After this, the projection position shifts to position Ps2a via position Ps1b during the vertical blanking period f1b. During the effective vertical scanning period f2a of the unit period f2, panel pixels p11, p12, p13, p21, p22, and p23 represent the hatched video pixels B11, B12, B13, B21, B22, and B23 in order at position Ps2a. Thereafter, the projection position shifts to position Ps3a via position Ps2b during the vertical blanking period f2b.

[0044] During the effective vertical scanning period f3a of the unit period f3, panel pixels p11, p12, p13, p21, p22, and p23 represent the hatched video pixels C11, C12, C13, C21, C22, and C23 in order at position Ps3a. Thereafter, the projection position shifts to position Ps4a via position Ps3b during the vertical blanking period f3b. During the effective vertical scanning period f4a of the unit period f4, panel pixels p11, p12, p13, p21, p22, and p23 represent hatched image pixels D11, D12, D13, D21, D22, and D23 in order at position Ps4a. Thereafter, the projection position returns to position Ps1a via position Ps4b during the vertical blanking period f4b.

[0045] In the liquid crystal panel 100, the transmittance of the panel pixels is determined by the magnitude of the voltage difference between the pixel electrode 118 and the common electrode 108, i.e., the tilt angle of the liquid crystal molecules aligned according to the magnitude of the electric field (vertical electric field) perpendicular to the substrate surface. However, when a dark panel pixel with low transmittance and a bright panel pixel with high transmittance are adjacent to each other, the voltage difference between the pixel electrodes 118 becomes large, and an electric field (horizontal electric field) is generated in the direction along the substrate surface in the area including the boundary between the two pixels in a planar view.

[0046] As a result, the alignment of liquid crystal molecules, which should be determined only by the vertical electric field, is disrupted by the influence of the horizontal electric field, resulting in alignment defects, or so-called domains. Generally, the greater the voltage difference between pixel electrodes 118, i.e., the greater the difference in gray level, the greater the degree of alignment defects near the boundary between two adjacent panel pixels.

[0047] In a normally black mode, regions where the alignment of liquid crystal molecules is disturbed will experience a decrease in transmittance, resulting in a darker image. However, because dark panel pixels are originally dark, a disturbance in the alignment of liquid crystal molecules is unlikely to be perceived as a degradation in display quality. In other words, alignment defects caused by adjacent bright and dark panel pixels occur in both the dark and bright panel pixels across the boundary, but the degradation in display quality due to alignment defects is perceived as a local decrease in transmittance in the bright panel pixels. Such alignment defects will be explained using a specific example.

[0048] FIG. 13 is a diagram showing an example of an arrangement of image pixels where alignment defects are easily noticeable, and FIG. 14 is a diagram showing the relationship between panel pixels that represent such image pixels and projection positions. 13 shows an example in which black video pixels having the lowest gradation level and white video pixels having the highest gradation level are arranged adjacent to each other. In more detail, the black area is made up of video pixels B11, C11, B12, C12, B13, C13, A11, D11, A12, D12, A13, and D13, and the white area is made up of video pixels B21, C21, B22, C22, B23, C23, A21, D21, A22, D22, A23, and D23.

[0049] When panel pixels represent such video pixels, in each unit period f1 to f4, panel pixels p11, p12, and p13 become dark panel pixels, and panel pixels p21, p22, and p23 become bright pixels, as shown in Fig. 14. Therefore, alignment defects occur in the region Dm on either side of the boundary, that is, in both the dark panel pixels and the bright panel pixels. However, the degradation of display quality due to poor alignment is not noticeable in the dark panel pixels, but is visible in the bright panel pixels p21, p22, and p23, as shown by the hatching in the figure. The width of the hatched area, i.e., the length perpendicular to the boundary between the bright panel pixel and the dark panel pixel, varies depending on the magnitude of the horizontal electric field, the duration of the horizontal electric field, etc., but for convenience in the figure it is shown as 0.5 panel pixels.

[0050] 14 indicate an absolute coordinate system in the vertical direction when the projection positions of the panel pixels are shifted by the light path shift element 230, with intervals of 0.5 panel pixels. For example, when the reference position is Ps1a during the effective vertical scanning period f1a, the upper sides of panel pixels p11, p12, and p13 are located at coordinate L2. Note that the absolute coordinate system is a coordinate system on the projection surface that is unrelated to the shift of the projection position.

[0051] Figure 15 shows the actual display state of the panel pixels. This display state shows the state in which white image pixels with the highest gradation level are displayed. For the sake of explanation, the projection position is fixed in this display state. As described above, the liquid crystal panel 100 is provided with a microlens for each panel pixel to improve light utilization efficiency. Therefore, the brightness of the projected panel pixels is not uniform, and in fact, as shown in the left column of Fig. 15, it is brighter near the center and becomes darker as it moves from the center to the outside. Note that the frame Px indicates the outer edge of the panel pixels in the liquid crystal panel 100. For ease of explanation, the right column of FIG. 14 shows the brightness of the panel pixels in a white display state expressed as line density, and the denser the line density, the darker the state.

[0052] In the comparative example, the projection position is configured not to overshoot, and therefore, in the comparative example, the projection position shifts in the following order: position Ps1a in unit period f1, position Ps2a in unit period f2, position Ps3a in unit period f3, and position Ps4a in unit period f4, as shown in Fig. 10 .

[0053] 14, among the region Dm where poor alignment occurs, the hatched region, i.e., the region where display quality deteriorates, is located as follows: In detail, the hatched region is located in the region of coordinates L4 to L5 in unit period f1, in the region of coordinates L3 to L4 in unit period f2, in the region of coordinates L3 to L4 in unit period f3, and in the region of coordinates L4 to L5 in unit period f4. In other words, in the region of coordinates L4 to L5, the display quality deteriorates in two unit periods, and since the region is a bright panel pixel in the remaining two unit periods, the deterioration in display quality is relatively easy to see. In the area of coordinates L3 to L4, the display quality deteriorates in two unit periods, but the panel pixels are dark in the remaining two unit periods. Therefore, even if the display quality deteriorates, it is buried in the dark panel pixels and is relatively hard to see as a deterioration in display quality.

[0054] This is shown in Figure 16. In detail, area K is an area where black video pixels result in dark panel pixels. Area Dma is an area where alignment defects occur, but the degradation of display quality is less noticeable due to the dark panel pixels. Area Dmb is an area where the degradation of display quality due to alignment defects is more noticeable.

[0055] In contrast to this comparative example, in the first embodiment, the projection positions in the effective vertical scanning periods f1a, f2a, f3a, and f4a are the same as those in the comparative example, but the projection positions in the vertical blanking periods f1b, f2b, f3b, and f4b shift along an overshoot trajectory. 14, the hatched area of the alignment defect-causing region Dm, where display quality is reduced, remains in the region of coordinates L4 to L5, particularly during the effective vertical scanning period f1a, but is pushed higher in the figure than the region of coordinates L4 to L5 due to trajectory overshoot during the vertical blanking period f1b. Therefore, the period during which the hatched area remains in the region of coordinates L4 to L5 is shorter than in the comparative example due to the overshoot, and the hatched area appears visually brighter than in the comparative example.

[0056] This is expressed in Fig. 17. In detail, the area K is the same as in the comparative example, but the areas Dma and Dmb are pushed upward in the figure compared to the comparative example.

[0057] In the first embodiment, the intensity of light emitted from the light source unit 2102 in vertical blanking periods f1b, f2b, f3b, and f4b is higher than the intensity of light emitted in effective vertical scanning periods f1a, f2a, f3a, and f4a. This brightens the display to compensate for the phenomenon of darkening due to poor alignment, making it possible to make the degradation of display quality less noticeable.

[0058] In this example, the case where black video pixels are arranged on the upper side and white video pixels are arranged on the lower side has been described as an example. Conversely, even when black video pixels are arranged on the lower side and white video pixels are arranged on the upper side, the degradation of display quality caused by poor alignment can be suppressed by overshooting during the vertical blanking period f3b. Furthermore, even when black video pixels are arranged on the right side and white video pixels are arranged on the left side, degradation of display quality due to poor alignment can be suppressed by overshooting during vertical blanking period f2b. Conversely, even when black video pixels are arranged on the left side and white video pixels are arranged on the right side, degradation of display quality due to poor alignment can be suppressed by overshooting during vertical blanking period f4b.

[0059] In the first embodiment, for example, in the shift from projection position Ps1a in an effective vertical scanning period f1a of unit period f1 to projection position Ps2a in an effective vertical scanning period f2a of the next unit period f2, the position Ps1b is the longest distance from position Ps1a, and this longest distance is equivalent to one panel pixel. However, the present invention is not limited to this, and the longest distance may be longer than one panel pixel.

[0060] In the first embodiment, the direction in which the projection position overshoots is, for example, only upward beyond the reference position Ps1a when shifting to the position Ps2a, but this is not limited to this. Therefore, a second and third embodiment will be described in which the locus of the overshooting projection position is changed.

[0061] FIG. 18 is a diagram showing the locus of the projection position in the second embodiment. In the second embodiment, the projection position remains at the reference position Ps1a during the effective vertical scanning period f1a, starts to shift upward with the start of the vertical blanking period f1b, passes through positions Ps2a, Ps1ba, Ps1bb, and Ps1bc, and returns to position Ps2a by the start of the effective vertical scanning period f2a. In detail, the projection position starts to shift upward with the start of the vertical blanking period f1b, turns left at position Ps2a, turns upward at position Ps1ba, turns right at position Ps1bb, turns downward at position Ps1bc, and returns to position Ps2a. The distance from position Ps2a to position Ps1ba, the distance from position Ps1ba to position Ps1bb, the distance from position Ps1bb to position Ps1bc, and the distance from position Ps1bc to position Ps2a are each, for example, 0.5 panel pixels.

[0062] Similarly, the projection position remains at position Ps2a during the effective vertical scanning period f2a, begins to shift to the right with the start of the vertical blanking period f2b, passes through positions Ps3a, Ps2ba, Ps2bb, and Ps2bc, and returns to position Ps3a by the start of the effective vertical scanning period f3a. The projection position remains at position Ps3a during the effective vertical scanning period f3a, and begins to shift downward with the start of the vertical blanking period f3b, passing through positions Ps4a, Ps3ba, Ps3bb, and Ps3bc, before returning to position Ps4a by the start of the effective vertical scanning period f4a. The projection position remains at position Ps4a during the effective vertical scanning period f4a, starts to shift leftward with the start of vertical blanking period f4b, passes through positions Ps1a, Ps4ba, Ps4bb, and Ps4bc, and returns to position Ps1a by the start of the effective vertical scanning period f1a.

[0063] In the first embodiment, the degradation of display quality due to poor alignment that occurs when black video pixels are arranged on the upper side and white video pixels are arranged on the lower side is reduced by an upward overshoot caused by the vertical blanking period f1b. In contrast, in the second embodiment, the degradation of display quality due to poor alignment that occurs when black video pixels are arranged on the upper side and white video pixels are arranged on the lower side is reduced by upward overshoot during vertical blanking periods f1b, f2b, f3b, and f4b. Conversely, the degradation of display quality due to poor alignment that occurs when black video pixels are arranged on the lower side and white video pixels are arranged on the upper side is reduced by the downward overshoot in the vertical blanking periods f1b, f2b, f3b, and f4b. In addition, the degradation of display quality due to poor alignment that occurs when black video pixels are arranged on the right and white video pixels are arranged on the left is reduced by the rightward overshoot during vertical blanking periods f1b, f2b, f3b, and f4b. Conversely, the degradation of display quality due to poor alignment that occurs when black video pixels are arranged on the left and white video pixels are arranged on the right is reduced by the leftward overshoot during vertical blanking periods f1b, f2b, f3b, and f4b.

[0064] In this way, in the second embodiment, degradation of display quality when black and white video pixels are arranged vertically or horizontally is reduced by each of the vertical blanking periods f1b, f2b, f3b, and f4b. Therefore, according to the second embodiment, degradation of display quality can be reduced more effectively than in the first embodiment.

[0065] In the second embodiment, the trajectories of the overshoots are all clockwise with respect to positions Ps1a, Ps2a, Ps3a, and Ps4a, but they may also be counterclockwise. When the trajectory of the overshoot is counterclockwise, for example, if the overshoot occurs in vertical blanking interval f1b, the projection position starts shifting upward from position Ps1a with the start of vertical blanking interval f1b, passes through positions Ps2a, Ps3a, Ps2ba, and Ps1bc, and returns to position P2a by the start of effective vertical scanning interval f2a.

[0066] FIG. 19 is a diagram showing the locus of the projection position in the third embodiment. In the third embodiment, the projection position remains at position Ps1a during effective vertical scanning period f1a, starts shifting upward with the start of vertical blanking period f1b, passes through position Ps2a, passes through Ps1bc, Ps1bb, and Ps1ba, and returns to position Ps2a by the start of effective vertical scanning period f2a. In detail, the projection position starts shifting upward with the start of vertical blanking period f1b, goes straight without turning at position Ps2a, turns left at position Ps1bc, turns downward at position Ps1bb, turns right at position Ps1ba, and returns to position Ps2a.

[0067] That is, in the third embodiment, the projection position in the overshoot passes through the position of the effective vertical scanning period of the next unit period, and then returns to the position of the effective vertical scanning period of the next unit period in the opposite direction to that in the second embodiment. Therefore, according to the third embodiment, it is possible to suppress the degradation of display quality as in the second embodiment, compared to the first embodiment. Furthermore, in the third embodiment, the projection position in the overshoot does not turn at positions Ps1a, Ps2a, Ps3a, and Ps4a but goes straight ahead, compared to the second embodiment. In other words, in the third embodiment, the projection position turns less times than in the second embodiment, and therefore high-speed response is not required of the light path shift element 230, and therefore cost reduction can be expected.

[0068] In the third embodiment, the trajectories of the overshoot are all counterclockwise with respect to positions Ps1a, Ps2a, Ps3a, and Ps4a, but they may also be clockwise. When the trajectory of the overshoot is clockwise, for example, if the overshoot occurs in vertical blanking interval f1b, the projection position starts shifting upward from position Ps1a with the start of vertical blanking interval f1b, passes through position Ps2a, passes through positions Ps1bc, Ps2ba, and Ps3a, and returns to position P2a by the start of effective vertical scanning interval f2a.

[0069] The first to third embodiments (hereinafter referred to as "embodiments, etc.") described above can be modified or applied in various ways as follows.

[0070] In the embodiment, the liquid crystal panel 100 is of a transmissive type, but it may be of a reflective type.

[0071] In the embodiment and the like, one frame period is divided into four unit periods. That is, the number k of unit periods included in one frame period is set to "4." The value of k is not limited to 4. Specifically, one frame period may be made up of two unit periods, or may be made up of three or five or more unit periods.

[0072] In the embodiments and the like, the period during which the locus of the projection position by the light path shift element 230 overshoots is not limited to the vertical blanking period. For example, the period during which the locus of the projection position overshoots may start midway through the effective vertical scanning period and overlap part of the rear end of the effective vertical scanning period, or may end midway through the effective vertical scanning period and overlap part of the front end of the effective vertical scanning period.

[0073] The period during which the amount of light emitted from the light source unit 2102 is increased from the standard amount is preferably configured to match the period during which the projection position is overshot.

[0074] From the above-described exemplary embodiments, the following aspects can be understood, for example.

[0075] A projection display device according to one aspect 1 includes a liquid crystal panel having panel pixels, a light path shift element that shifts the projection position of a projection pixel projected from the panel pixel for every k unit periods from a first unit period to a kth unit period (k is an integer equal to or greater than 2) included in one frame period, and a display control circuit that controls the liquid crystal panel and the light path shift element, wherein the display control circuit supplies a data signal corresponding to a gradation level specified by video pixel data that constitutes video data to the panel pixel for every unit period, and controls the projection position for the light path shift element for every unit period, and the light path shift element shifts the projection position to a target projection position after passing the target projection position for every unit period. According to the projection display device of the first aspect, degradation of display quality caused by poor alignment becomes less noticeable.

[0076] In a projection display device according to a specific aspect 2 of aspect 1, in a shift from a previous target projection position in a unit period preceding a unit period to a target projection position in the unit period, the maximum distance from the previous target projection position is one or more panel pixels.

[0077] In a projection display device according to a specific aspect 3 of aspect 2, the optical path shift element shifts the projection position from the previous target projection position to an opposite position based on the one target projection position, and then returns the projection position to the one target projection position.

[0078] In a projection display device according to a specific aspect 4 of aspect 1, the optical path shift element turns the projection position from the previous target projection position to the one target projection position, and then returns the projection position to the one target projection position in a clockwise or counterclockwise direction as viewed on the projection surface.

[0079] In a projection display device according to a specific aspect 5 of aspect 1, the optical path shift element moves the projection position from the previous target projection position straight to the one target projection position, and then returns the projection position to the one target projection position in a clockwise or counterclockwise direction as viewed on the projection surface. [Explanation of symbols]

[0080] 1...projection type display device, 100R, 100G, 100B...liquid crystal panel, 110...pixel circuit, 118...pixel electrode, 120...liquid crystal element, 20...display control circuit, 21...processing circuit, 22R, 22G, 22B...conversion circuit, 230...light path shift element, 2102...light source unit.

Claims

1. a liquid crystal panel having panel pixels; a light path shift element that shifts an optical path of the projection light so as to change a projection position of a projection pixel displayed by the projection light projected from the panel pixel for each of k unit periods from a first unit period to a k-th unit period (k is an integer of 2 or more) included in one frame period; a display control circuit that controls the liquid crystal panel and the light path shift element; Including, The display control circuit includes: supplying a data signal corresponding to a gradation level designated by video pixel data constituting video data to the panel pixel for each unit period; controlling the projection position of the light path shift element for each unit period; The optical path shift element shifts the light to a target projection position after passing the target projection position for each unit period. A projection display device characterized by:

2. a maximum distance from a previous target projection position in a unit period preceding a certain unit period to a certain target projection position in the certain unit period is one or more panel pixels; 2. The projection display device according to claim 1.

3. The light path shift element is shifting the projection position from the immediately preceding target projection position to an opposite position based on the one target projection position, and then returning the projection position to the one target projection position; 3. The projection display device according to claim 2.

4. The light path shift element is The projection position is turned from the immediately preceding target projection position to the one target projection position, and then returned to the one target projection position in a clockwise or counterclockwise direction as viewed on the projection surface.

2. The projection display device according to claim 1.

5. The light path shift element is The projection position is moved from the immediately preceding target projection position to the one target projection position, and then returned to the one target projection position in a clockwise or counterclockwise direction as viewed on the projection surface.

2. The projection display device according to claim 1.

Images