Liquid crystal projector

Abstract

To suppress coloring in a liquid crystal projector.SOLUTION: In a liquid crystal projector 1, when an optical responsiveness of a liquid crystal panel 100G corresponding to G is better than the optical responsiveness of a liquid crystal panel 100R corresponding to R, a display control circuit 20 performs tr correction and tf correction of overdrive processing with respect to R, and performs only the tr correction and not the tf correction of overdrive processing with respect to G. The display control circuit 20 performs black float processing to R, G, and B.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a liquid crystal projector.

Background Art

[0002] In a liquid crystal projector, a liquid crystal panel is provided for each of the three primary colors, for example, for each of red (R), green (G), and blue (B). Primary color light is incident on the liquid crystal panel, and a modulated image is generated for each primary color. These modulated images are combined, and the combined image is projected and enlarged onto a screen or the like. In the liquid crystal panel used in the liquid crystal projector, a blurring phenomenon occurs due to insufficient optical responsiveness to electrical changes.

[0003] In order to reduce this blurring phenomenon, a technique (see Patent Document 1) is known in which gradation data supplied to the liquid crystal panel is determined according to the combination before and after the change in gradation data. Also known is a technique (see Patent Document 2) in which a drive voltage supplied to the liquid crystal panel is determined according to the combination of an input image signal one vertical period before processed according to the predicted value of the transmittance of the pixels of the liquid crystal panel and the input image signal of the current vertical period. When a LUT (look-up table) is used to determine the gradation data supplied to the liquid crystal panel based on before and after the transition of the gradation data, a technique is also known in which target gradation data is calculated by interpolation calculation in order to suppress the capacity of the LUT (see Patent Document 3).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in a liquid crystal projector, the optical responsiveness of the liquid crystal panel may vary for each color. If the optical responsiveness of the liquid crystal panel varies for each color, even when it is desired to display achromatic color in the synthesized image, the transmittance in the liquid crystal panel does not become the same, and there is a problem that it is not achromatic color but chromatic color, that is, it is visually recognized with color.

Means for Solving the Problem

[0006] To solve the above problems, a liquid crystal projector according to an aspect of the present disclosure processes first-color video data among video data specifying gradation levels of pixels and outputs it as a first data signal, and processes second-color video data different from the first color among the video data and outputs it as a second data signal. A display control circuit, a first liquid crystal panel having a first liquid crystal element to which a voltage corresponding to the first data signal is applied, and in the first liquid crystal element, the incident light of the first color is output as first output light at a ratio corresponding to the applied voltage, a second liquid crystal panel having a second liquid crystal element to which a voltage corresponding to the second data signal is applied, and in the second liquid crystal element, the incident light of the second color is output as second output light at a ratio corresponding to the applied voltage, and a combining unit that combines the first output light and the second output light and outputs them as combined light. The display control circuit corrects the first data signal when the voltage applied to the first liquid crystal element is less than a first threshold corresponding to the gradation level specified by the first-color video data, and increases the voltage applied to the first liquid crystal element to be higher than the voltage corresponding to the gradation level, and when the voltage applied to the second liquid crystal element is less than a second threshold corresponding to the gradation level specified by the second-color video data, corrects the second data signal and increases the voltage applied to the second liquid crystal element to be higher than the voltage corresponding to the gradation level. The display control circuit includes a gradation level conversion unit, and when the voltage applied to the first liquid crystal element decreases due to a change in the gradation level specified by the first-color video data, performs an overdrive process on the first liquid crystal element, and when the voltage applied to the second liquid crystal element decreases due to a change in the gradation level specified by the second-color video data, performs an overdrive process on the first liquid crystal element.

Brief Description of the Drawings

[0007]

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Embodiments for Carrying Out the Invention

[0008] Hereinafter, a liquid crystal projector will be described with reference to the drawings in the embodiments. Note that, in each figure, the dimensions and scales of each part are appropriately different from the actual ones. Also, since the following embodiments are preferred specific examples, various technically preferable limitations are imposed. Therefore, the scope of the present disclosure is not limited to these forms unless otherwise specified in the following description to particularly limit the present disclosure.

[0009] FIG. 1 is a diagram showing an optical configuration of a liquid crystal projector 1 according to an embodiment. As shown in the figure, the liquid crystal projector 1 includes liquid crystal panels 100R, 100G, and 100B. Further, inside the liquid crystal projector 1, a light source unit 2102 composed of a light source such as a halogen lamp is provided. The light emitted from this light source unit 2102 is separated into three primary colors of R, G, and B by three mirrors 2106 and two dichroic mirrors 2108 arranged inside. Among these, the light of R is incident on the liquid crystal panel 100R, the light of G is incident on the liquid crystal panel 100G, and the light of B is incident on the liquid crystal panel 100B. Note that the optical path of B is longer than those of other R and G. Therefore, the light of B is guided to the liquid crystal panel 100B through a relay lens system 2121 composed of an incident lens 2122, a relay lens 2123, and an exit lens 2124 in order to prevent loss in the optical path.

[0010] The liquid crystal panel 100R has a pixel circuit arranged in a matrix as will be described later. The transmittance of the light emitted from the liquid crystal element in the above pixel circuit is controlled based on a data signal corresponding to R. Therefore, in the liquid crystal panel 100R, the light emitted from the liquid crystal element functions as a pixel which is the minimum unit of an image. By such control, the liquid crystal panel 100R generates a transmitted image of R based on the data signal corresponding to R. Similarly, the liquid crystal panel 100G generates a transmitted image of G based on the data signal corresponding to G, and the liquid crystal panel 100B generates a transmitted image of B based on the data signal corresponding to B.

[0011] The transmitted images of each color respectively generated by the liquid crystal panels 100R, 100G, and 100B are incident on the dichroic prism 2112 from three directions. And in the dichroic prism 2112, the light of R and B is refracted by 90 degrees, while the light of G travels straight. Therefore, the dichroic prism 2112 functions as a combining unit that combines the images of each color. The combined light by the dichroic prism 2112 is incident on the projection lens 2114 via the shift device 230. The projection lens 2114 enlarges and projects the combined image via the shift device 230 onto the screen 2120. The shift device 230 shifts the emission direction from the dichroic prism 2112. Specifically, the shift device 230 can shift the image projected onto the screen 2120 in the left - right direction and the up - down direction with respect to the projection plane.

[0012] FIG. 2 is a block diagram showing the electrical configuration of the liquid crystal projector 1. As shown in the figure, the liquid crystal projector 1 includes a display control circuit 20, liquid crystal panels 100R, 100G, and 100B, and a shift device 230.

[0013] Video data Vid - in is supplied to the display control circuit 20 from a host device (not shown) or the like in synchronization with the synchronization signal Sync. The video data Vid - in is data indicating the image to be displayed on the liquid crystal projector 1, and specifies the gradation level of each pixel of the image in 8 bits for each of RGB, for example. The synchronization signal Sync includes a vertical synchronization signal indicating the start of vertical scanning in the video data Vid - in, a horizontal synchronization signal indicating the start of horizontal scanning, and a clock signal indicating the timing of one pixel of the video data.

[0014] For convenience of explanation, in order to distinguish the pixels whose gradation is specified in the video data Vid-in from the pixels in the composite image of the liquid crystal panels 100R, 100G, and 100B, the pixels whose gradation is specified in the video data Vid-in are referred to as video data pixels, and the pixels by the liquid crystal panels 100R, 100G, or 100B are referred to as panel pixels. Also, the position of the pixels projected onto the screen 2120 by combining the R panel pixels, G panel pixels, and B panel pixels, that is, the position of the panel pixels shifted by the shift device 230, is simply referred to as the projection position.

[0015] In the present embodiment, the color image projected onto the screen 2120 is expressed by superimposing the transmission images of the liquid crystal panels 100R, 100G, and 100B. Therefore, the pixels, which are the minimum units of the color image, can be divided into red panel pixels by the liquid crystal panel 100R, green panel pixels by the liquid crystal panel 100G, and blue panel pixels by the liquid crystal panel 100B. Strictly speaking, the red panel pixels, green panel pixels, and blue panel pixels should be referred to as sub-pixels, but in this description, they are referred to as panel pixels as described above.

[0016] For the liquid crystal panels 100R, 100G, and 100G, the color of the incident light, that is, the wavelength, is different, and structurally they are generally common. Therefore, for the liquid crystal panels 100R, 100G, and 100G, if there is no need to specify the color, they are described with the symbol 100. As will be described later, the liquid crystal panels 100R, 100G, and 100G may have different optical responses depending on the cell gap, the temperature of the liquid crystal layer, etc.

[0017] The display control circuit 20 includes a scan control circuit 21 and a video processing circuit 22. In the present embodiment, the pixel array of the image specified by the video data Vid-in is, for example, twice as large in the vertical direction and twice as large in the horizontal direction as the array of panel pixels in the liquid crystal panel 100. For this reason, in the present embodiment, in order to pseudo-increase the resolution, the projection direction is shifted by the shift device 230. Specifically, the period for displaying one frame of the image represented by the video data Vid is divided into four fields, and the projection position is shifted for each field. Due to such a shift, one panel pixel is visually recognized as if it is displaying the four pixels specified by the video data Vid-in.

[0018] Therefore, next, before the description of the scanning control circuit 21 and the video processing circuit 22, a method for expressing the four pixels specified by the video data Vid-in by one panel pixel in the liquid crystal panel 100 will be described.

[0019] FIG. 3 is a diagram for explaining the relationship between a frame and fields in the present embodiment. As shown in the figure, the frame F is the period for displaying one frame. In the present embodiment, the frame F is divided into four fields. For the sake of convenience in distinguishing the four fields in the frame F, symbols are assigned as f1, f2, f3, and f4 in the order of time. Note that when the frequency of the vertical synchronization signal included in the synchronization signal Sync is 60 Hz, the period length of the frame F is 16.7 milliseconds for one cycle. In this case, the period lengths of the fields f1 to f4 are each 4.17 milliseconds, which is 1 / 4 of the period length of one frame.

[0020] Next, the relationship between the video data pixel whose gradation level is specified by the video data Vid-in, the panel pixel by the liquid crystal panel 100, and the projection position by the shift device 230 will be described. Note that for the shift device 230, as described above, it shifts the projection direction from the dichroic prism 2112. For the sake of convenience, the shift amount will be described in terms of the size of the projection pixel on the screen 2120, that is, the panel pixel.

[0021] The left column in FIG. 4 is a diagram showing only a part of the video data pixels extracted. Also, the right column in the same figure is a diagram showing the array of panel pixels corresponding to the array of the video data pixels in the left column, extracted.

[0022] In the array of the left column in FIG. 4, for the purpose of distinguishing video data pixels, for convenience, as symbols, A1 to A6 are given in the first row, B1 to B6 are given in the second row, C1 to C6 are given in the third row, D1 to D6 are given in the fourth row, E1 to E6 are given in the fifth row, and F1 to F6 are given in the sixth row, respectively. Similarly, in the array of the right column in FIG. 4, for the purpose of distinguishing panel pixels, for convenience, as symbols, a1 to a3 are given in the first row, b1 to b3 are given in the second row, and c1 to c3 are given in the third row, respectively.

[0023] FIG. 5 is a diagram showing which of the video data pixels the panel pixels in the liquid crystal projector 1 display at which projection positions. Specifically, FIG. 5 is a diagram showing which of the video data pixels in the left column of FIG. 4 the nine panel pixels in the right column of FIG. 4 display at which projection positions in fields f1 to f4.

[0024] For the convenience of explanation, the projection position in field f1 of frame F is taken as the reference position. In field f1, the panel pixels a1 to a3, b1 to b3, and c1 to c3 display the video data pixels A1, A3, A5, C1, C3, C5, E1, E3, and E5 in order. In the next field f2, the shift device 230 shifts the projection position by 0.5 pixel of the panel pixels in the right direction in the figure from the projection position in field f1 indicated by the dashed line. Also, in field f2, the panel pixels a1 to a3, b1 to b3, and c1 to c3 display the video data pixels A2, A4, A6, C2, C4, C6, E2, E4, and E6 in order. In field f3, the shift device 230 shifts the projection position downward by 0.5 pixel of the panel pixels from the projection position in field f2 indicated by the dashed line. Also, in field f3, the panel pixels a1~a3, b1~b3, c1~c3 display the video data pixels B2, B4, B6, D2, D4, D6, F2, F4, and F6 in order. Then, in field f4, the shift device 230 shifts the projection position leftward by 0.5 pixel of the panel pixels from the projection position in field f3 indicated by the dashed line. Also, in field f4, the panel pixels a1~a3, b1~b3, c1~c3 display the video data pixels B1, B3, B5, D1, D3, D5, F1, F3, and F5 in order. After field f4, the shift device 230 shifts the projection position upward by 0.5 pixel of the panel pixels from the projection position in field f4 indicated by the dashed line and returns it to the position in field f1.

[0025] Returning to FIG. 2 for explanation again, the scan control circuit 21 generates a control signal Ctr for controlling the scanning of the liquid crystal panels 100R, 100G, and 100B for each field. Also, the scan control circuit 21 generates a control signal Lac for controlling the projection position by the shift device 230 for each field.

[0026] The video processing circuit 22, although details will be described later, temporarily stores the video data Vid-in, and reads out the video data corresponding to the panel pixels to be displayed in the field from the stored video data Vid-in. Further, the video processing circuit 22 processes the read video data by color, converts it to analog, and outputs it as data signals Vid_R, Vid_G, and Vid_B. Among these, the data signal Vid_R is a signal in which the R component of the video data Vid-in is processed, and is supplied to the liquid crystal panel 100R. Similarly, the data signal Vid_G is a signal in which the G component of the video data Vid-in is processed, and is supplied to the liquid crystal panel 100G. The data signal Vid_B is a signal in which the B component of the video data Vid-in is processed, and is supplied to the liquid crystal panel 100B.

[0027] Next, the liquid crystal panels 100R, 100G, and 100G will be generally described without specifying the color.

[0028] FIG. 6 is a diagram showing a main part of the liquid crystal panel 100, and FIG. 7 is a cross-sectional view taken along the line H-h in FIG. 6. As shown in these figures, the liquid crystal panel 100 includes an element substrate 100a provided with pixel electrodes 118 and a counter substrate 100b provided with common electrodes 108. The two are bonded to each other with a sealing material 90 including spacers (not shown) so that their electrode formation surfaces face each other while maintaining a constant gap, and liquid crystal 105 is encapsulated in this gap. Note that the length of the gap between the element substrate 100a and the counter substrate 100b is generally called a cell gap. In the figure, the cell gap is indicated by the symbol d.

[0029] As the element substrate 100a and the counter substrate 100b, substrates having light transmissibility such as glass and quartz are used respectively. As shown in FIG. 6, one side of the element substrate 100a protrudes from the counter substrate 100b. A plurality of terminals 106 are provided along this protruding region along the one side. One end of an FPC 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 various signals described above are supplied.

[0030] On the surface of the element substrate 100a facing the counter substrate 100b, the pixel electrodes 118 are formed by patterning a conductive layer having transparency such as ITO. Note that ITO is an abbreviation for Indium Tin Oxide. In addition, various elements other than electrodes are provided on the opposing surfaces of the element substrate 100a and the opposing substrate 100b, but are omitted in the figure.

[0031] FIG. 8 is a block diagram showing the electrical configuration of the liquid crystal panel 100. In the liquid crystal panel 100, a scanning line driving circuit 130 and a data line driving circuit 140 are provided at the periphery of the display area 10.

[0032] In the display area 10 of the liquid crystal panel 100, pixel circuits 110 are arranged in a matrix. Specifically, in the display area 10, a plurality of scanning lines 12 extend horizontally as shown in the figure, and a plurality of data lines 14 extend vertically as shown in the figure and are provided while maintaining electrical insulation from the scanning lines 12. Then, the pixel circuits 110 are arranged in a matrix corresponding to the intersections of the plurality of scanning lines 12 and the plurality of data lines 14.

[0033] When 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 in the vertical direction × n columns in the horizontal direction. Both m and n are integers of 2 or more. In the scanning lines 12 and the pixel circuits 110, in order to distinguish the rows of the matrix, they may be referred to as the 1st, 2nd, 3rd,..., (m - 1)th, and mth rows in order from the top in the figure. Similarly, in the data lines 14 and the pixel circuits 110, in order to distinguish the columns of the matrix, they may be referred to as the 1st, 2nd, 3rd,..., (n - 1)th, and nth columns in order from the left in the figure.

[0034] The scanning line driving circuit 130 sequentially selects the scanning lines 12 one by one in the order of, for example, the 1st, 2nd, 3rd,..., mth rows according to the control by the scanning control circuit 21, and sets the scanning signal to the selected scanning line 12 to the 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 the L level. The data line driving circuit 140 latches the data signals supplied from the video processing circuit 22 for one row according to the control by the scanning control circuit 21, and outputs them to the pixel circuits 110 located on the scanning line 12 via the data lines 14 during the period when the scanning signal to the scanning line 12 becomes the H level.

[0035] FIG. 9 is a diagram showing equivalent circuits of four pixel circuits 110 in a 2-row 2-column arrangement 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 the scanning line 12, its source node is connected to the data line 14, and its drain node is connected to a pixel electrode 118 that is substantially square in plan view.

[0036] A common electrode 108 is provided commonly for all pixel circuits so as to face the pixel electrode 118. A voltage LCcom is applied to the common electrode 108. Then, 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. Although a storage capacitor may be provided in parallel with the liquid crystal element 120, it is not important in this case and is thus omitted.

[0037] In the scanning line 12 at which the scanning signal becomes the H level, the transistor 116 of the pixel circuit 110 provided corresponding to the 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, so that the data signal supplied to the data line 14 reaches the pixel electrode 118 through the turned-on transistor 116. When the scanning line 12 becomes the L level, the transistor 116 is turned off, but the voltage of the data signal that has reached the pixel electrode 118 is held by the capacitance of the liquid crystal element 120.

[0038] As is well known, in the liquid crystal element 120, the alignment of liquid crystal molecules changes according to the electric field generated by the pixel electrode 118 and the common electrode 108. Therefore, the liquid crystal element 120 has a transmittance corresponding to the effective voltage value of the voltage difference between the voltage of the data signal and the voltage LCcom of the common electrode 108. In this embodiment, the liquid crystal element 120 is in a normally black mode in which the transmittance increases as the effective voltage value increases.

[0039] By executing the operation of supplying the data signal to the pixel electrode 118 of the liquid crystal element 120 in the order of the 1st, 2nd, 3rd,..., m-th rows, a voltage corresponding 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. By holding such a voltage, each liquid crystal element 120 has a target transmittance, and a transmissive image of the corresponding color is generated by the pixels arranged in m rows and n columns.

[0040] FIG. 10 is a diagram showing the temporal change of the selected scanning line 12 when the vertical axis represents the 1st row to the m-th row, which are the number of rows of the scanning line 12, and the horizontal axis represents the elapsed time. When the selection of the scanning line 12 is indicated by a thick black line, since the scanning line 12 is exclusively selected one row at a time, the selected scanning line 12 sequentially shifts from the 1st row to the m-th row as time elapses. In a certain field, when a certain scanning line 12 is selected, a data signal corresponding to the field and the panel pixel is supplied from a certain data line 14 to the pixel circuit 110 corresponding to the intersection of the scanning line 12 and the data line 14. Therefore, in the field, the liquid crystal element 120 of the pixel circuit 110 changes to a transmittance corresponding to the voltage of the data signal.

[0041] Incidentally, the optical responsiveness in the liquid crystal panels 100R, 100G, and 100B, specifically, the responsiveness of the transmittance to the voltage change applied to the liquid crystal element 120, may vary depending on various factors.

[0042] As an example of the cause, there is a difference in the cell gap d in the liquid crystal panels 100R, 100G, and 100B. Specifically, the smaller the cell gap d, the better the optical responsiveness. In the present embodiment, the cell gap d of the liquid crystal panel 100G is, for example, about 25% smaller than the cell gaps d of the liquid crystal panels 100R and 100B. For this reason, the optical responsiveness of the liquid crystal panels 100R and 100B is substantially the same and lower than that of the liquid crystal panel 100G. In other words, the optical responsiveness of the liquid crystal panel 100G is higher than that of the liquid crystal panels 100R and 100B.

[0043] In addition, as another example of the cause, there is a difference in the temperature of the liquid crystal panels 100R, 100G, and 100B, specifically, the temperature of the liquid crystal 105. When the temperature rises, the viscosity of the liquid crystal 105 decreases, so the optical responsiveness in the liquid crystal element 120 improves, that is, the response speed increases. Specifically, in the liquid crystal projector 1 shown in FIG. 1, the amount of incident light on the liquid crystal panel 100G is larger than the amount of incident light on the liquid crystal panels 100R and 100B. For this reason, the temperature of the liquid crystal panel 100G tends to be higher than the temperatures of the liquid crystal panels 100R and 100B.

[0044] On the other hand, in a hold-type display element such as the liquid crystal element 120, a blurring phenomenon is likely to occur when displaying a moving image. In order to reduce such a blurring phenomenon, in the present embodiment, the video processing circuit 22 executes an overdrive process. The overdrive process is a process for applying a voltage that is excessively swung in the changing direction instead of a voltage corresponding to the changed gradation level to the liquid crystal element of the panel pixel when the gradation level of the pixel specified by the video data changes from one value to another value to change the transmittance of the panel pixel.

[0045] For example, when the gradation level corresponding to a certain panel pixel increases from, for example, "50" to "100", the applied voltage of the liquid crystal element 120 of the panel pixel is changed as shown in FIG. 11 by overdrive processing. Specifically, when the gradation level changes, in the overdrive processing, instead of the voltage corresponding to "100" of the gradation level shown by the broken line, a voltage corresponding to, for example, "120" with an excessive swing in the increasing direction is applied to the liquid crystal element 120 of the panel pixel as shown by the solid line. Note that in FIGS. 12 to 14 hereinafter including FIG. 11, the voltage applied to the liquid crystal element 120 is shown in terms of the gradation level. Here, the voltage applied to the liquid crystal element 120 is the absolute value of the difference between the voltage of the data signal applied to the pixel electrode 118 and the voltage LCcom applied to the common electrode 108. Also, even when a voltage as shown in the figure is applied to the liquid crystal element 120, the transmittance cannot immediately follow the voltage change and change. The amount that swings excessively more than the gradation level after the change may be called the overdrive amount OD.

[0046] When increasing the gradation level in this way, that is, when increasing the applied voltage of the liquid crystal element 120 in the normally black mode, the overdrive processing is called tr correction. Also, when the gradation level corresponding to the panel pixel continues at "100", the voltage corresponding to "100" is applied to the liquid crystal element 120.

[0047] On the other hand, when the gradation level corresponding to a certain panel pixel decreases from, for example, "100" to "50", the applied voltage of the liquid crystal element 120 of the panel pixel is changed as shown in FIG. 12 by overdrive processing. Specifically, when the gradation level changes, in the overdrive processing, instead of the voltage corresponding to "50" of the gradation level shown by the broken line, a voltage corresponding to, for example, "25" with an excessive swing in the decreasing direction is applied to the liquid crystal element 120 of the panel pixel as shown by the solid line. When reducing the gradation level in this way, that is, when lowering the applied voltage of the liquid crystal element 120 in the normal black mode, the overdrive process is called tf correction.

[0048] The overdrive amount depends on the gradation level before the change and the gradation level after the change. Therefore, the overdrive amount is generally configured to be output by a look-up table (LUT) or calculation that takes the gradation level before the change and the gradation level after the change as arguments.

[0049] As described above, the optical responsivities of the liquid crystal panels 100R, 100G, and 100B are different. Specifically, the optical responsivity of the liquid crystal panel 100G is better than the optical response characteristics of the liquid crystal panels 100R and 100B. Therefore, when applying the same overdrive process for RGB, due to the difference in optical responsivity, different transmittances may result for RGB. Specifically, even when trying to change to the same gradation level for RGB, different transmittances will result for RGB due to the difference in optical responsivity, and there is a problem that a place that should be visually recognized as achromatic is visually recognized as being colored with only a specific color emphasized.

[0050] Such coloring may not be improved only by making the overdrive amount different for each of RGB. Therefore, in the present embodiment, first, for R and B, both tr correction when the gradation level increases and tf correction when the gradation level decreases in the overdrive process are executed, and for G, only tr correction in the overdrive process is executed and tf correction is not executed.

[0051] Regarding tr correction in the overdrive process, it is executed for all of RGB. However, when the gradation level increases from a state lower than a certain value, the optical responsivity tends to decrease. Specifically, the change from the dark state to the bright state tends to take a long time. Therefore, in the present embodiment, second, in addition to the overdrive process, a so-called black floating process is also executed. The black floating process is a process for applying a voltage of a slightly higher initial voltage (for example, 1V) to the liquid crystal element 120 of a panel pixel instead of applying a voltage of the lowest 0V when the gradation level of a certain panel pixel is, for example, the minimum "0". When the gradation level specified for a panel pixel is "0", especially when displaying a moving image, the next specified gradation level is likely to be other than "0". Therefore, according to the black floating process, even if the gradation level specified for a panel pixel in a certain field is "0", the gradation level is replaced with, for example, "10" corresponding to the initial voltage so that it can quickly respond to the changed gradation level.

[0052] More specifically, when the liquid crystal is, for example, of the VA type, when the applied voltage to the liquid crystal element 120 is 0V, the liquid crystal molecules are arranged substantially perpendicular to the substrate. In this alignment state, even if the gradation level changes and the applied voltage to the liquid crystal element 120 increases, the liquid crystal molecules are not easily tilted immediately in the direction of the alignment treatment applied to the substrate, so the optical responsiveness is poor. Therefore, when the gradation level is "0", an initial voltage is applied to the liquid crystal element 120 so that the liquid crystal molecules are not arranged perpendicular to the substrate but are slightly tilted with respect to the perpendicular direction of the substrate. According to this black floating process, the liquid crystal molecules follow the subsequent change in the gradation level and are more easily tilted, thus improving the optical responsiveness.

[0053] Note that even when the gradation level is "0", an initial voltage is applied to the liquid crystal element 120, and the transmittance does not become the lowest, resulting in a state where black floats. For this reason, it is called the black floating process in the sense of floating black. Also, the black floating process is executed when the gradation level is other than "0", specifically, when the gradation level is less than the threshold value. The threshold value of the black floating process may be different for each of R, G, and B, or may be the same.

[0054] Also, in the black floating process, when the voltage applied to the liquid crystal element 120 is less than the threshold value corresponding to the gradation level specified in the video data, that is, when the gradation level is less than the threshold value, the applied voltage of the liquid crystal element 120 is increased to be higher than the voltage corresponding to the gradation level. In other words, the black floating process can be said to be a process of correcting the data signal so as to increase the voltage applied to the liquid crystal element 120 to be higher than the voltage corresponding to the gradation level specified in the video data.

[0055] When the tf correction of the overdrive process and the black floating process are combined for R and B, specifically, when the gradation levels of the panel pixels are specified in the order of "50", "0", "0", the applied voltage of the liquid crystal element 120 is as follows. That is, in this case, as shown in FIG. 13, the applied voltage of the liquid crystal element 120 is, in order, the voltage corresponding to the gradation level "50", the voltage corresponding to the gradation level "0" by tf correction, and the voltage corresponding to the gradation level "10" by the black floating process. Note that the voltage corresponding to the gradation level "10" is the initial voltage described above. On the other hand, when the tf correction of the overdrive process is not executed for G and the black floating process is executed, and similarly when the gradation levels of the panel pixels are specified in the order of "50", "0", "0", the applied voltage of the liquid crystal element 120 is as follows. That is, in this case, as shown in FIG. 14, the applied voltage of the liquid crystal element 120 is, in order, the voltage corresponding to the gradation level "50", the voltage corresponding to the gradation level "10" corrected by the black floating process, and the voltage corresponding to the gradation level "10" corrected by the black floating process.

[0056] Note that when the gradation level "0" is replaced with the gradation level "10" corresponding to the initial voltage by the black floating process, when the next specified gradation level increases to "50", the gradation level before the change is not "0" but the replaced gradation level "10".

[0057] The video processing circuit 22 that performs different overdrive processes and black floating processes for R, B, and G will be described.

[0058] FIG. 15 is a block diagram showing the configuration of the video processing circuit 22. As shown in the figure, the video processing circuit 22 includes a frame memory 220, and processing circuits 230R, 230G, and 230B. The frame memory 220 is used to store the video data Vid-in and read out the video data corresponding to a field. Specifically, the video data Vid-in is stored in the frame memory 220 according to the control by the scan control circuit 21 (see FIG. 2). Then, from the frame memory 220, the video data Vid-in to be displayed on the panel pixels in a certain field is read out by the scan control circuit 21 in accordance with the scan timing.

[0059] Specifically, the following video data Vid-in is read out from the frame memory 220. For example, when the first scan line 12 in the field f1 is selected, among the video data pixels in the left column of FIG. 4, the video data Vid-in corresponding to the video data pixels A1, A3, A5,... is read out. When the second scan line 12 in the field f1 is selected, the video data Vid-in corresponding to the video data pixels C1, C3, C5,... is read out. Also, for example, when the first scan line 12 in the field f2 is selected, the video data Vid-in corresponding to the video data pixels A2, A4, A6,... is read out. When the second scan line 12 in the field f2 is selected, the video data Vid-in corresponding to the video data pixels C2, C4, C6,... is read out. In this way, the video data Vid-in to be displayed on the panel pixels is read out from the frame memory 220 in a certain field.

[0060] Of the video data Vid-in read from the frame memory 220, the R component is supplied to the processing circuit 230R as video data V_R(f). Similarly, of the video data Vid-in read from the frame memory 220, the G component is supplied to the processing circuit 230G as video data V_G(f), and the B component is supplied to the processing circuit 230B as video data V_B(f).

[0061] The processing circuit 230R includes a delay device 231, a LUT 232R, a multiplier 233, an adder 234, a DA converter 235, and a gradation level converter 239.

[0062] The gradation level converter 239 in the processing circuit 230R performs a black floating process on the video data V_R(f) and outputs the data after the black floating process as video data Vb_R(f). Specifically, if the gradation level specified for the panel pixel in the current field is less than the threshold value, the gradation level is replaced with the threshold value. For example, when the threshold value is set to "10", if the gradation level specified by the video data V_R(f) is from "0" to "9", the gradation level is replaced with "10" and output as video data Vb_R(f).

[0063] Here, the "10" of the gradation level is a value that makes the voltage applied to the liquid crystal element 120 the initial voltage of the black floating when it is converted to an analog by the DA converter 235. Also, if the gradation level specified for the panel pixel in the current field is greater than or equal to the threshold value, the gradation level converter 239 outputs the video data V_R(f) as it is without converting the gradation level specified by the video data V_R(f) as video data Vb_R(f).

[0064] The delay device 231 in the processing circuit 230R delays the video data Vb_R(f) for a period corresponding to one field and outputs it as video data Vb_R(f - 1). Note that the meaning of (f - 1) indicates one field before (f) and corresponds to the same panel pixel. Also, the reason for delaying the video data V_R(f) for a period corresponding to one field and outputting it as video data Vb_R(f - 1) is to obtain the change amount by comparing with the gradation level specified by the video data Vb_R(f) for a certain panel pixel.

[0065] The LUT 232R in the processing circuit 230R is a look-up table in which the overdrive amount with the gradation level of the current field and the gradation level of one field before as arguments is stored in advance for R. Note that in the LUT 232R for R, the overdrive amounts for both the case where the gradation level of the current field indicated by the video data Vb_R(f) increases from the gradation level of one field before and the case where it decreases are stored. From the LUT 232R, data Od_R corresponding to the gradation level indicated by the video data Vb_R(f) and the gradation level indicated by the video data Vb_R(f - 1) is output. Note that the data Od_R is a positive value when the gradation level increases, a negative value when the gradation level decreases, and zero when the gradation level does not change, when viewed in decimal values.

[0066] The multiplier 233 in the processing circuit 230R multiplies the data Od_R by the coefficient K_R and outputs the multiplication result as correction amount data Odv_R. Note that the coefficient K_R can be arbitrarily set in the range from "0" to "1" in decimal values, but when the liquid crystal response becomes slow due to the environmental temperature or the like, it may be set larger than "1". Here, for convenience of explanation, "1" is used as the initial value.

[0067] The adder 234 in the processing circuit 230R adds the data Odv_R to the video data Vb_R(f). Note that, as described above, the data Od_R and Odv_R can take negative values, so the actual operation content in the adder 234 includes not only addition but also subtraction. The DA converter 235 converts the addition result by the adder 234 into a data signal Vid_R of an analog voltage with the polarity specified by the scan control circuit 21.

[0068] In this way, the processing circuit 230R performs black levelling processing on the video data V_R(f) of the R component in the video data Vid-in, and executes overdrive processing for both the case where the gradation level specified for the panel pixel increases and the case where it decreases. Then, the processing circuit 230R converts the video data subjected to black levelling processing and overdrive processing into analog, and outputs the conversion result as a data signal Vid_R to the liquid crystal panel 100R.

[0069] The processing circuit 230B corresponding to B is the same as the processing circuit 230R. Specifically, the processing circuit 230B performs black levelling processing on the video data V_B(f) of the B component in the video data Vid-in, and executes overdrive processing for both the case where the gradation level specified for the panel pixel increases and the case where it decreases. Then, the processing circuit 230B converts the video data subjected to black levelling processing and overdrive processing into analog, and outputs the conversion result as a data signal Vid_B to the liquid crystal panel 100B.

[0070] The processing circuit 230G corresponding to G is different from the processing circuits 230R and 230B. Specifically, the processing circuit 230G is the same as the processing circuits 230R and 230B in that it performs black floating processing, overdrive processing, analog conversion on the video data V_G(f) of the G component in the video data Vid-in, and outputs the conversion result as a data signal Vid_G to the liquid crystal panel 100G. However, among the overdrive processes, only the tr correction is executed when the gradation level specified for the panel pixel increases, and the tf correction is not executed when the gradation level decreases. Specifically, the LUT232G in the processing circuit 230G stores only the overdrive amount when the gradation level of the current field increases from the gradation level of the previous field. Therefore, in the LUT232G, zero is output as the overdrive amount when the gradation level decreases or does not change.

[0071] Note that the coefficients K_R, K_G, and K_B are supplied so as to be changeable by, for example, the scanning control circuit 21. Similar to the coefficient K_R, the coefficients K_G and K_B can be arbitrarily set within the range from "0" to "1" in decimal values, but can also be set to be greater than "1". For the sake of convenience of explanation, "1" is used as the initial value. The overdrive amount may be obtained by calculation instead of conversion by the LUT232R, 232G, or 232B.

[0072] In this embodiment, among the overdrive processes, both tr correction and tf correction are executed for R and B, tr correction is executed for G without executing tf correction, and furthermore, black floating processing is executed for R, G, and B. The superiority of such a configuration will be described by taking the case of a certain display as an example.

[0073] FIG. 16 is a diagram showing an example of the display contents of the video data pixels A1, A2, B2, and B1 and the display contents of the panel pixels corresponding to the video data pixels A1, A2, and B2. In the figure, Pattern A is the case where the display contents of video data pixels A1, A2, B2, and B1 are white, black, white, and black in this order. In this case, the panel pixels repeat black and white for each field. Here, white means that the maximum value of the gradation level is specified for the video data, and the maximum value of the transmittance is specified for the panel pixels. Also, black here means that the minimum value of the gradation level is specified for the video data, and the minimum value of the transmittance is specified for the panel pixels.

[0074] Pattern B is the case where the display contents of video data pixels A1, A2, B2, and B1 are white, white, black, and black in this order. In this case, the panel pixels have white continuous in fields f1 and f2, and then black continuous in fields f3 and f4. Pattern C is the case where the display contents of video data pixels A1, A2, B2, and B1 are black, white, white, and white in this order. In this case, after the black in field f1, white is continuous in fields f2, f3, and f4 for the panel pixels. Pattern D is the case where the display contents of video data pixels A1, A2, B2, and B1 are white, black, black, and black in this order. In this case, after the white in field f1, black is continuous in fields f2, f3, and f4 for the panel pixels.

[0075] Figures 17 to 20 are diagrams showing how the transmittance of the panel pixels changes for each of R, G, and B when Patterns A, B, C, and D are used. Note that in Figures 17 to 20, the comparative example is the case where only tr correction is performed and tf correction and black floating processing are not performed. The characteristics of the transmittance in the comparative example are shown by a broken line. Also, in the embodiment, both tr correction and tf correction are performed for R and B, only tr correction is performed for G, and a configuration is adopted in which black floating processing is performed for R, G, and B. However, for B in Figures 17 to 20, as a reference example, the case where tr correction and black floating processing are performed and tf correction is not performed is shown. The characteristics of the transmittance in the embodiment and the reference example are shown by a solid line.

[0076] When displaying pattern A as shown in FIG. 17, for R, according to the comparative example, by tr correction, in fields f1 and f3, the applied voltage of liquid crystal element 120 is 2.6V, and in fields f2 and f4, it is 0.0V. In the embodiment, tr correction and black floating processing are executed, but for pattern A, it is the same as the comparative example. Therefore, when displaying pattern A for R, there is no difference between the comparative example and the embodiment. For G, according to the comparative example, by tr correction, in fields f1 and f3, the applied voltage of liquid crystal element 120 is 2.3V, and in fields f2 and f4, it is 0.0V. In the embodiment, by black floating processing, the rising characteristic of the transmittance is improved with a small overdrive amount. Specifically, when changing from black to white by tr correction, the applied voltage of liquid crystal element 120 is 2.3V in the comparative example, but in the embodiment, since the voltage before the change is replaced with 1.0V by black floating processing, it only needs to be 2.2V, which is lower than that in the comparative example. For this reason, in the embodiment, the rising characteristic of the transmittance in fields f1 and f3 is improved compared to the comparative example, approaching the characteristic of R in the embodiment. Note that the actual transmittance is visually recognized as the integral value of the above transmittance characteristics. For B, according to the comparative example, by tr correction, in fields f1 and f3, the applied voltage of liquid crystal element 120 is 2.3V, and in fields f2 and f4, it is 0.0V. In the embodiment, by black floating processing, the rising characteristic of the transmittance is improved with a small overdrive amount. Specifically, when changing from black to white by tr correction, the applied voltage of liquid crystal element 120 is 2.3V in the comparative example, but in the embodiment, since the voltage before the change is replaced with 1.0V by black floating processing, it only needs to be 2.2V, which is lower than that in the comparative example. However, in this reference example, tf correction is not executed, so there is room for improving the falling characteristic of the transmittance. In other words, if tf correction is executed as in the embodiment for B, it is considered that the falling characteristic of the transmittance will be improved and approach the characteristic of R.

[0077] When displaying pattern B as shown in FIG. 18, for R, according to the comparative example, by tr correction, in field f1, the applied voltage of liquid crystal element 120 is 2.6V, and in field f2, it is the voltage corresponding to white and is 2.2V without over-drive. Also, in fields f3 and f4, it becomes 0.0V. In the embodiment, for R, the applied voltage of liquid crystal element 120 is changed to 1.0V by black floating processing in field f4 compared to the comparative example. Therefore, in the embodiment, when changing from field f4 to field f1 compared to the comparative example, the rising characteristic of the transmittance is improved. For G, according to the comparative example, by tr correction, in field f1, the applied voltage of liquid crystal element 120 is 2.3V, and in field f2, it is the voltage corresponding to white and is 2.1V without over-drive. Also, in fields f3 and f4, it becomes 0.0V. In the embodiment, for G, without performing tf correction, by performing black floating processing, it is changed to 1.0V in fields f3 and 4 compared to the comparative example. In the embodiment, in field f1, by black floating processing, the rising characteristic of the transmittance is improved with a small over-drive amount. Specifically, when changing from black to white by tr correction, the applied voltage of liquid crystal element 120 is 2.3V in the comparative example, but in the embodiment, since the voltage before change is replaced with 1.0V by black floating processing, it only needs to be 2.2V, which is lower than the comparative example. Therefore, in the embodiment, when changing from field f4 to field f1 compared to the comparative example, the rising characteristic of the transmittance is improved and approaches the characteristic of R in the embodiment. For B, according to the comparative example, by tr correction, in field f1, the applied voltage of liquid crystal element 120 is 2.2V, and in field f2, it is the voltage corresponding to white and is 2.0V without over-drive. Also, in fields f3 and f4, it becomes 0.0V. In the reference example, by performing black floating processing, it is changed to 1.0V in fields f3 and 4. In the embodiment, in field f1, by black floating processing, the rising characteristic of the transmittance is improved with a small over-drive amount. However, in this reference example, since tf correction is not performed, there is room for improving the fall characteristic of the transmittance. In other words, for B, if tf correction is performed as in the embodiment, specifically, if the applied voltage of the liquid crystal element 120 is set to 0.0 V in the field f3, it is considered that the fall characteristic of the transmittance is improved and approaches the characteristic of R.

[0078] When displaying the pattern C as shown in FIG. 19, for R, according to the comparative example, in the field f1, the applied voltage of the liquid crystal element 120 is 0.0 V, and in the field f2, it becomes 2.6 V by tr correction. Further, in the fields f3 and f4, it becomes 2.2 V corresponding to white. In the embodiment, tr correction and black floating processing are performed, but for the pattern A, it is the same as the comparative example. Therefore, when displaying the pattern A for R, there is no difference between the comparative example and the embodiment. For G, according to the comparative example, in the field f1, the applied voltage of the liquid crystal element 120 is 0.0 V, and in the field f2, it becomes 2.3 V by tr correction. Further, in the fields f3 and f4, it becomes 2.1 V corresponding to white. In the embodiment, for G, tf correction is not performed, and by performing black floating processing, it is changed to 1.0 V in the field f1 with respect to the comparative example. Further, by this black floating processing, the rise characteristic of the transmittance is improved with a small overdrive amount. Specifically, when changing to white in the field f2, in the embodiment, it is sufficient to be 2.2 V, which is lower than the comparative example, due to the black floating processing. For this reason, in the embodiment, the rise characteristic of the transmittance in the field f2 is improved with respect to the comparative example and approaches the characteristic of R in the embodiment. For B, according to the comparative example, in the field f1, the applied voltage of the liquid crystal element 120 is 0.0 V, and in the field f2, it becomes 2.3 V by tr correction. Further, in the fields f3 and f4, it becomes 2.0 V corresponding to white. In the embodiment, by black floating processing, in the field f1, the applied voltage of the liquid crystal element 120 is 1.0 V, and in the field f2, it becomes 2.2 V by tr correction. Further, in the fields f3 and f4, it becomes 2.0 V corresponding to white. However, in this reference example, since tf correction is not performed, there is room for improving the fall characteristic of the transmittance. Specifically, if the applied voltage of the liquid crystal element 120 in the field f1 is set to 0.0 V, it is considered that the fall characteristic of the transmittance is improved and approaches the characteristic of R.

[0079] When displaying the pattern D as shown in FIG. 20, for R in the comparative example, due to tr correction, the applied voltage of the liquid crystal element 120 becomes 2.6 V in the field f1, 0.0 V in the field f2, and 0.0 V corresponding to black in the fields f3 and f4. For R in the embodiment, the applied voltage of the liquid crystal element 120 becomes 2.3 V in the field f1 due to tr correction, 0.0 V in the field f2 due to tf correction, and 1.0 V in the fields f3 and f4 due to the black floating process. The rise characteristic of the transmittance in the field f1 is improved by the black floating process in the field f4. When displaying the pattern D, for G in the comparative example, due to tr correction, the applied voltage of the liquid crystal element 120 becomes 2.3 V in the field f1 and 0.0 V corresponding to black in the fields f2, f3, and f4. For G in the embodiment, the applied voltage of the liquid crystal element 120 becomes 2.2 V in the field f1 due to tr correction, 1.0 V by the black floating process without performing tf correction in the field f2, and also 1.0 V in the fields f3 and f4. By the black floating process in the field f4, the rise characteristic of the transmittance in the field f1 is improved with a smaller overdrive amount than in the comparative example. For B in the comparative example, due to tr correction, the applied voltage of the liquid crystal element 120 becomes 2.3 V in the field f1 and 0.0 V corresponding to black in the fields f2, f3, and f4. For B in the reference example, the applied voltage of the liquid crystal element 120 becomes 2.2 V in the field f1 due to tr correction and 1.0 V by the black floating process in the fields f2, f3, and f4, similar to G. However, in this reference example, since tf correction is not performed, there is room for improving the fall characteristic of the transmittance in the field f2. In other words, for B, if tf correction is performed as in the embodiment, specifically, if the applied voltage of the liquid crystal element 120 in the field f2 is set to 0.0V, the fall characteristic of the transmittance is improved.

[0080] When displaying the patterns A, B, C, and D in this way, if tr correction and tf correction are performed not only for R but also for B, tr correction only is performed for G, and black floating processing is performed for R, G, and B, the transmittances of R, G, and B are likely to be made uniform, so it becomes easy to suppress coloration.

[0081] In the embodiment, the following modifications or applications are possible. In the embodiment, the liquid crystal panels 100R, 100G, and 100B are transmissive types, but they may be reflective types. When the liquid crystal panels 100R, 100G, and 100B are reflective types, the transmittance in the optical responsiveness may be read as reflectance. The liquid crystal element 120 is in the normally black mode, but it may be in the normally white mode. When the liquid crystal element 120 is in the normally white mode, a configuration may be adopted in which a data signal that decreases the applied voltage of the liquid crystal element 120 is output as the gradation level increases.

[0082] Even when the normally white mode is adopted, similar to the normally black mode, in the black floating process, when the voltage applied to the liquid crystal element 120 becomes less than the threshold value corresponding to the gradation level specified by the video data, the applied voltage of the liquid crystal element 120 is increased to be higher than the voltage corresponding to the gradation level. However, when the normally white mode is adopted, the black floating process is performed when the gradation level exceeds the threshold value.

[0083] Coloration occurs when the optical response characteristics of the liquid crystal panels 100R, 100G, and 100B are different even without shifting the projection position by the shift device 230. Therefore, this is effective even in a configuration without the shift device 230. Specifically, when the optical response characteristic of the liquid crystal panel 100G is better than those of the liquid crystal panels 100R and 100B, even in a configuration without the shift device 230 and without shifting the projection position, by performing tr correction and tf correction for R and B, performing only tr correction for G, and performing black floating processing for R, G, and B, the transmittances of R, G, and B are likely to be made uniform, so that coloration can be suppressed. Conversely, in a configuration where the shift device 230 divides a frame into a plurality of fields and shifts the projection position for each field, since the period of each field becomes short, the difference in optical response characteristics is likely to appear as coloration. Therefore, when creating a composite image using a plurality of liquid crystal panels 100, when there is a difference in optical response characteristics among the plurality of liquid crystal panels 100, it is preferable to perform tr correction and tf correction for the liquid crystal panel 100 of the color with low optical response characteristics, perform only tr correction for the liquid crystal panel 100 of the color with high optical response characteristics, and perform black floating processing for each color liquid crystal panel 100.

[0084] As described above, the optical response characteristic of the liquid crystal element 120 in the liquid crystal panel 100 changes depending on the temperature, and the optical response characteristic of the liquid crystal element 120 improves as the temperature increases. If the optical response characteristic is good, the overdrive amount can be small (in terms of absolute value). In the liquid crystal projector 1, depending on the usage situation, specifically, the temperature rises according to the elapsed time since the power was turned on, and the optical response characteristic may improve. In the embodiment, the overdrive amount can be adjusted by the multiplier 233 in FIG. 15. Specifically, it is possible to adjust the overdrive amount according to the temperature by gradually decreasing the coefficients K_R, K_G, and K_B from "1" according to the elapsed time since the power was turned on. The coefficients K_R, K_G, and K_B may have the same value, or may be supplied with independent values for each color.

[0085] In the embodiment, G is an example of the first color, R or B is an example of the second color, liquid crystal panel 100G is an example of the first liquid crystal panel, and liquid crystal panel 100R or liquid crystal panel 100B is an example of the second liquid crystal panel. Also, liquid crystal element 120 of pixel circuit 110 in liquid crystal panel 100G is an example of the first liquid crystal element, and liquid crystal element 120 of pixel circuit 110 in liquid crystal panel 100R or 100B is an example of the second liquid crystal element. Data signal Vid_G is an example of the first data signal, and data signal Vid_R or Vid_B is an example of the second data signal. tr correction is an example of the first correction, and tf correction is an example of the second correction. LUT232R and LUT232B are examples of the first LUT, and LUT232G is an example of the second LUT. When the voltage applied to liquid crystal element 120 of G is less than the threshold value and the black floating process is executed, the threshold value is an example of the first threshold value. Also, when the voltage applied to liquid crystal element 120 of R or B is less than the threshold value and the black floating process is executed, the threshold value is an example of the second threshold value. Video data pixel A1 is an example of the first pixel, and video data pixel A2 is an example of the second pixel. Dichroic prism 2112 is an example of the combining unit. Among the projection positions by shift device 230, the projection position in field f1 is an example of the first position, and the projection position in field f2 is an example of the second position.

Explanation of Reference Numerals

[0086] 1... Liquid crystal projector, 20... Display control circuit, 21... Scanning control circuit, 22... Video processing circuit, 100R, 100G, 100B... Liquid crystal panels, 110... Pixel circuit, 120... Liquid crystal element.

Claims

1. A display control circuit that processes video data of a first color among video data specifying pixel gray levels, outputs it as a first data signal, and processes video data of a second color different from the first color among the video data and outputs it as a second data signal; A first liquid crystal panel having a first liquid crystal element to which a voltage corresponding to the first data signal is applied, and in the first liquid crystal element, incident light of the first color is emitted as first emitted light at a ratio corresponding to the applied voltage; A second liquid crystal panel having a second liquid crystal element to which a voltage corresponding to the second data signal is applied, and in the second liquid crystal element, incident light of the second color is emitted as second emitted light at a ratio corresponding to the applied voltage; A combining unit that combines the first emitted light and the second emitted light and emits it as combined light; A shift device that shifts the projection position of the combined light by the combining unit from a first position to a second position; Comprising: The shift device is: Among a first field and a second field included in one frame, when the first emitted light is emitted from the first liquid crystal element based on the video data of the first color among the video data specifying the gray level of the first pixel to be displayed in the first field, and the second emitted light is emitted from the second liquid crystal element based on the video data of the second color, the shift device sets the projection position to the first position; Among the video data specifying the gray level of the second pixel to be displayed in the second field, when the first emitted light is emitted from the first liquid crystal element based on the video data of the first color, and the second emitted light is emitted from the second liquid crystal element based on the video data of the second color, the shift device sets the projection position to the second position; The display control circuit is: When the gray level specified by the video data of the first color is less than a first threshold value, the gray level specified by the video data of the first color is replaced with the first threshold value, and when the gray level specified by the video data of the second color is less than a second threshold value, a gray level converter that replaces the gray level specified by the video data of the second color with the second threshold value. When the gradation level specified by the video data of the first color to be displayed in the first field changes in a direction in which the gradation level specified by the video data of the first color to be displayed in the second field decreases, a voltage corresponding to the gradation level specified by the video data of the first color to be displayed in the second field is applied to the first liquid crystal element. When the gradation level specified by the video data of the second color to be displayed in the first field changes in a direction in which the gradation level specified by the video data of the second color to be displayed in the second field decreases, the gradation level specified by the video data of the second color to be displayed in the second field is corrected so that the amount of decrease is larger than the difference between the gradation level specified by the video data of the second color to be displayed in the first field and the gradation level specified by the video data of the second color to be displayed in the second field, and a voltage corresponding to the corrected gradation level specified by the video data of the second color to be displayed in the second field is applied to the second liquid crystal element. Liquid crystal projector.

2. The display control circuit: When the gradation level specified by the video data of the first color to be displayed in the first field changes in a direction in which the gradation level specified by the video data of the first color to be displayed in the second field increases, the gradation level specified by the video data of the first color to be displayed in the second field is corrected so that the amount of increase is larger than the difference between the gradation level specified by the video data of the first color to be displayed in the first field and the gradation level specified by the video data of the first color to be displayed in the second field, and a voltage corresponding to the corrected gradation level specified by the video data of the first color to be displayed in the second field is applied to the first liquid crystal element. When the gradation level specified by the video data of the second color to be displayed in the first field changes in a direction in which the gradation level specified by the video data of the second color to be displayed in the second field increases, the difference between the gradation level specified by the video data of the second color to be displayed in the first field and the gradation level specified by the video data of the second color to be displayed in the second field is used to correct the gradation level specified by the video data of the second color to be displayed in the second field so that the increase amount is larger than the difference, and a voltage corresponding to the gradation level specified by the video data of the second color to be displayed in the corrected second field is applied to the second liquid crystal element. The liquid crystal projector according to claim 1.

3. The display control circuit is a first LUT storing an increase amount of the gradation level specified by the video data of the first color to be displayed in the second field when the gradation level specified by the video data of the first color to be displayed in the first field changes in a direction in which the gradation level specified by the video data of the first color to be displayed in the second field increases, and a second LUT storing an increase amount when the gradation level specified by the video data of the second color to be displayed in the first field changes in a direction in which the gradation level specified by the video data of the second color to be displayed in the second field increases and a decrease amount when the gradation level specified by the video data of the second color to be displayed in the first field changes in a direction in which the gradation level specified by the video data of the second color to be displayed in the second field decreases, Based on the first LUT, perform correction when the gradation level specified by the video data of the first color to be displayed in the first field changes in a direction in which the gradation level specified by the video data of the first color to be displayed in the second field increases, Based on the second LUT, perform correction when the gradation level specified by the video data of the second color to be displayed in the first field changes in a direction in which the gradation level specified by the video data of the second color to be displayed in the second field increases and when the gradation level specified by the video data of the second color to be displayed in the first field changes in a direction in which the gradation level specified by the video data of the second color to be displayed in the second field decreases. The liquid crystal projector according to claim 2.

4. The responsiveness of the transmittance with respect to the voltage change applied to the second liquid crystal element is lower than the responsiveness of the transmittance with respect to the voltage change applied to the first liquid crystal element. The liquid crystal projector according to any one of claims 1 to 3.

5. When the gradation level designated by the video data of the first color to be displayed in the first field changes in a direction in which the gradation level designated by the video data of the first color to be displayed in the second field increases, the correction amount is smaller than the correction amount when the gradation level designated by the video data of the second color to be displayed in the first field changes in a direction in which the gradation level designated by the video data of the second color to be displayed in the second field increases. The liquid crystal projector according to any one of claims 2 to 4.

6. The correction amount when the gradation level designated by the video data of the first color to be displayed in the first field changes in a direction in which the gradation level designated by the video data of the first color to be displayed in the second field increases, and the correction amount when the gradation level designated by the video data of the second color to be displayed in the first field changes in a direction in which the gradation level designated by the video data of the second color to be displayed in the second field increases, and the correction amount when the gradation level designated by the video data of the second color to be displayed in the first field changes in a direction in which the gradation level designated by the video data of the second color to be displayed in the second field decreases are changeable. The liquid crystal projector according to any one of claims 2 to 5.

Images