JP6701147B2 - Liquid crystal driving device, image display device, liquid crystal driving method, and liquid crystal driving program - Google Patents

Description

  The present invention relates to a liquid crystal driving device that drives a liquid crystal element by a digital driving method.

  The liquid crystal element includes a transmissive liquid crystal element such as a TN (Twisted Nematic) element and a reflective liquid crystal element such as a VAN (Vertical Alignment Nematic) element. Driving methods of these liquid crystal elements include an analog driving method in which the voltage applied to the liquid crystal layer is changed according to the gradation to control the brightness, and a voltage applied to the liquid crystal layer by binarizing the voltage. There is a digital drive system in which brightness is controlled by changing time. In this digital driving method, one frame period is divided into a plurality of subfield periods on the time axis, and application (ON) and non-application (OFF) of a predetermined voltage to a pixel are controlled for each subfield to control the pixel. There is a sub-field drive system that displays gradation.

  Here, a general subfield driving method will be described. FIG. 11 shows an example in which one frame period is divided into a plurality of subfield periods (bit length). The numerical value described on each subfield shows the time weight within one frame period of the subfield. Here, as an example, a case of expressing 64 gradations is shown. Further, in the description here, the period having the time weight of 1+2+4+8+16 is referred to as an A subfield period, and the subfield period having the time weight of 32 is referred to as a B subfield period. Further, the subfield period in which the predetermined voltage is turned on is referred to as an on period, and the subfield period in which the predetermined voltage is turned off is referred to as an off period.

  FIG. 12 shows all gradation data corresponding to the subfield division example shown in FIG. The vertical axis represents gradation and the horizontal axis represents one frame period. In addition, a white subfield period in the drawing indicates an on period in which a pixel is in a white display state, and a black subfield period indicates an off period in which a pixel is in a black display state. According to this gradation data, two pixels adjacent to each other (hereinafter referred to as adjacent pixels) in the liquid crystal element are displayed two gradations adjacent to each other (hereinafter referred to as adjacent gradations), for example, 32 gradations and 33 gradations. In this case, the A sub-field period is an on period for 32 gradations and an off period for 33 gradations. Further, the B sub-field period is an off period for 32 gradations and an on period for 33 gradations.

  In this manner, when the ON period and the OFF period overlap in time in the adjacent pixel, that is, when a predetermined voltage is applied to one of the adjacent pixels and not applied to the other in the same period, so-called disclination occurs. When it occurs, the brightness of the pixel on the ON period side decreases. The upper part of FIG. 15A shows an image of brightness reduction due to disclination when a gradation image in the horizontal direction is projected. When there is no disclination, smooth gradation is expressed, but in an adjacent gradation in which the ON period and the OFF period of adjacent pixels are long, the brightness decreases due to the influence of the disclination and a dark line appears.

  In Patent Document 1, a common (uniform) correction amount is added to gradation data of all pixels for each frame, and the correction amount is periodically changed to observe image quality deterioration due to disclination. A method for making it difficult for a person to visually recognize is disclosed.

JP, 2013-050681, A

  However, the method disclosed in Patent Document 1 may impair the gradation. For example, there is a case where the correction amount is set to be subtracted in the next frame by the same amount as the correction amount added to the gradation data of all pixels in the first frame. In this case, in the pixel displaying the halftone, the same brightness as the correction amount added in the first frame is subtracted in the next frame, so that the original brightness can be expressed by the average of the two frames, and the gradation Is kept. However, for a pixel displaying a gradation lower than the correction amount, if the same amount of the correction added in the first frame is subtracted in the next frame, the subtraction cannot be performed because the gradation is less than the minimum gradation, and thus the subtraction cannot be performed in two frames. On average, the brightness is higher than the original gradation. On the other hand, in a pixel displaying a high gradation, if the correction amount is added in the first frame, it exceeds the maximum gradation, and therefore the addition cannot be performed, and the average of two frames reduces the brightness from the original gradation. To do.

  The present invention provides a liquid crystal driving device or the like that suppresses deterioration of image quality due to disclination while suppressing deterioration of brightness and gradation.

A liquid crystal driving device according to one aspect of the present invention is a liquid crystal driving device that drives a liquid crystal element having a plurality of pixels, and a grayscale value of a first pixel having a grayscale value less than a predetermined threshold value in an input frame. Is converted into a gradation value obtained by multiplying the gradation value of the first pixel by a first gain larger than 1, and a second pixel having a gradation value of a predetermined threshold value or more in the input frame The gradation value is converted into the maximum gradation value that can be set in the first subframe to generate the first subframe, and the gradation value of the first pixel of the input frame is set to 0 for the gradation value of the first pixel. It is a gradation value obtained by multiplying a second gain that is larger and smaller than 1, and is converted into a gradation value that increases in accordance with an increase in the gradation value of the input frame, and the gradation of the second pixel of the input frame. The gradation value is a gradation value obtained by subtracting the maximum gradation value from the value obtained by multiplying the gradation value of the second pixel by a third gain larger than 1, and is a gradation value according to the increase of the gradation value of the input frame. The liquid crystal is generated in each of the plurality of subfield periods included in one frame period based on the generating unit that generates the second subframe by converting the increasing grayscale value and the grayscale value of each pixel of each subframe. A driving unit configured to control the application of the first voltage and the application of a second voltage lower than the first voltage to the corresponding pixel of the element to form a gradation in the pixel, and the driving unit generates the gradation. In the first subframe and the second subframe, the average of the grayscale values of the pixels corresponding to the first pixel of the input frame is equal to the grayscale value of the first pixel, and the first subframe and the second subframe , The average of the grayscale values of the pixels corresponding to the second pixel of the input frame is equal to the grayscale value of the second pixel , and the driving means drives the liquid crystal element based on the first subframe , and drives the second subframe. It is characterized in that the driving of the liquid crystal element based on the frame is alternately executed.

  An image display device having the above liquid crystal drive device and liquid crystal element also constitutes another aspect of the present invention.

A liquid crystal driving method according to another aspect of the present invention is a liquid crystal driving method for driving a liquid crystal element having a plurality of pixels, wherein the first pixel has a grayscale value less than a predetermined threshold value in an input frame. Is converted into a gradation value obtained by multiplying the gradation value of the first pixel by a first gain larger than 1, and the gradation value of the input frame is equal to or larger than a predetermined threshold value. The gradation value of the second pixel is converted into the maximum gradation value that can be set in the first sub-frame to generate the first sub-frame, and the gradation value of the first pixel of the input frame is converted into the gradation value of the first pixel. The tone value is a tone value obtained by multiplying the tone value by a second gain that is greater than 0 and less than 1, and is converted into a tone value that increases in accordance with an increase in the tone value of the input frame, and The gradation value of two pixels is a gradation value obtained by subtracting the maximum gradation value from the value obtained by multiplying the gradation value of the second pixel by a third gain larger than 1, and is the gradation value of the input frame. A step of generating a second sub-frame by converting to a gradation value that increases in accordance with the increase, and a plurality of sub-field periods included in one frame period based on the gradation value of each pixel of each sub-frame Controlling the application of the first voltage to the corresponding pixel of the liquid crystal element and the application of the second voltage lower than the first voltage to form a gradation in the pixel. The average of the grayscale values of the pixels corresponding to the first pixel of the input frame in each of the first subframe and the second subframe generated by is equal to the grayscale value of the first pixel, In the step of forming an average gradation value of pixels corresponding to the second pixel of the input frame in each of the two sub-frames is equal to the gradation value of the second pixel , driving of the liquid crystal element based on the first sub-frame is performed. , and executes the driving of the liquid crystal element based on the second sub-frame, alternately.

  A liquid crystal drive program, which is a computer program that causes a computer to execute the processing according to the liquid crystal drive method, also constitutes another aspect of the present invention.

  According to the present invention, it is possible to suppress deterioration of image quality due to disclination, while suppressing deterioration of brightness and gradation.

FIG. 1 is a diagram showing an optical configuration of a liquid crystal projector that is Embodiment 1 of the present invention. 3 is a cross-sectional view of a liquid crystal element used in the projector of Embodiment 1. FIG. FIG. 6 is a diagram showing a plurality of subfield periods within one frame period according to the first embodiment. FIG. 6 is a diagram showing grayscale data in an A subfield period in the first embodiment. FIG. 3 is a diagram showing all gradation data in Example 1. FIG. 3 is a diagram showing pixel lines in the first embodiment. FIG. 6 is a diagram showing a response characteristic of the liquid crystal when switching from all-white display to monochrome display in the first embodiment. FIG. 6 is a diagram showing a response characteristic of brightness when switching from all-white display to monochrome display in the first embodiment. FIG. 6 is a diagram showing a response characteristic of the liquid crystal when the all black display is switched to the monochrome display in the first embodiment. FIG. 6 is a diagram illustrating a response characteristic of brightness when switching from full black to black and white display in the first embodiment. The figure which shows the several subfield period in 1 frame period in the prior art. The figure which shows the conventional all gradation data. The figure which shows all the gradation data of patent document 1. 3 is a block diagram showing the configuration of a control circuit in Embodiment 1. FIG. FIG. 6 is a diagram showing how the first and second gains and the disclination dark line appear in Example 1; FIG. 6 is a diagram showing a comparative example with respect to the first embodiment. FIG. 6 is a diagram showing a modification of the first embodiment. 6 is a block diagram showing the configuration of a control circuit in Embodiment 3. FIG. The figure which shows the 1st and 2nd gain in Example 2 and a comparative example. FIG. 11 is a diagram showing gains applied to 1st, 2nd, 3rd, and 4th subframes in the third embodiment. FIG. 8 is a diagram illustrating a problem to be solved by the second embodiment. FIG. 10 is a diagram showing how the first and second gains and the disclination dark line appear in Example 2; FIG. 16 is a diagram showing how the first and second gains and the disclination dark line appear in Example 4; FIG. 10 is a diagram illustrating an effect unique to the fourth embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an optical configuration of a liquid crystal projector as an image display device that is Embodiment 1 of the present invention. In this embodiment, a projector will be described as an example of an image display device using a liquid crystal element, but the image display device also includes an image display device using a liquid crystal element other than the projector, such as a direct-view monitor.

  The control circuit 303 corresponds to a liquid crystal driving device. The control circuit 303 includes a video input unit (image acquisition means) 303a for acquiring an input video signal (input image) from an external device (not shown), and a floor described later according to the gradation of the input video signal (input gradation). A drive circuit section 303b for generating a pixel drive signal corresponding to the tonal data. Pixel drive signals are generated for each of red, green and blue colors, and the pixel drive signals for the respective colors are input to the red liquid crystal element 3R, the green liquid crystal element 3G and the blue liquid crystal element 3B. As a result, the red liquid crystal element 3R, the green liquid crystal element 3G, and the blue liquid crystal element 3B are driven independently of each other. The red liquid crystal element 3R, the green liquid crystal element 3G, and the blue liquid crystal element 3B are vertical alignment mode reflective liquid crystal elements.

  The illumination optical system 301 makes white light from a light source (such as a discharge lamp) incident on the dichroic mirror 305 with its polarization direction aligned. The dichroic mirror 305 reflects magenta light and transmits green light. The magenta light reflected by the dichroic mirror 305 is incident on the blue cross color polarizer 311, and a half-wave retardation is given only to the blue light, whereby blue light and red light whose polarization directions are orthogonal to each other are generated. .. The blue light and the red light are incident on the polarization beam splitter 310, and the blue light is transmitted through the polarization separation film of the polarization beam splitter 310 and guided to the blue liquid crystal element 3B. The red color component is reflected by the polarization separation film and guided to the red liquid crystal element 3R.

  On the other hand, the green light transmitted through the dichroic mirror 305 passes through the dummy glass 306 for correcting the optical path length, enters the polarization beam splitter 307, is reflected by the polarization separation film, and is guided to the green liquid crystal element 3G. ..

  Each liquid crystal element (3R, 3G, 3B) modulates and reflects the incident light according to the modulation state of each pixel. The red light modulated by the red liquid crystal element 3R passes through the polarization separation film of the polarization beam splitter 310 and enters the red cross color polarizer 312, where half wavelength retardation is given. Then, this red light enters the polarization beam splitter 308, is reflected by the polarization separation film, and travels to the projection optical system 304.

  The blue light modulated by the blue liquid crystal element 3B is reflected by the polarization separation film of the polarization beam splitter 310, passes through the red cross color polarizer 312 as it is, enters the polarization beam splitter 308, and enters the polarization separation film. Is reflected by and goes to the projection optical system 304. The green light modulated by the green liquid crystal element 3G passes through the polarization separation film of the polarization beam splitter 307, passes through the dummy glass 309 for correcting the optical path length, enters the polarization beam splitter 308, and splits the polarization. It passes through the film and goes to a projection optical system 304 having a projection lens. In this way, the color-synthesized red light, green light, and blue light are incident on the projection optical system 304. Then, the combined color light is enlarged and projected by the projection optical system 304 onto a projection surface 313 such as a screen.

  In this embodiment, the case of using a reflective liquid crystal element will be described, but a transmissive liquid crystal element may be used.

  FIG. 2 shows a sectional structure of the reflective liquid crystal element (3R, 3G, 3B). Reference numeral 101 is an AR coat film, 102 is a glass substrate, 103 is a common electrode, 104 is an alignment film, 105 is a liquid crystal layer, 106 is an alignment film, 107 is a pixel electrode, and 108 is a Si substrate.

  The control circuit 303 shown in FIG. 1 drives each pixel by the subfield driving method described above. That is, one frame period is divided into a plurality of sub-field periods on the time axis, and on/off (non-application) of a predetermined voltage to a pixel is controlled for each sub-field period according to grayscale data. A gradation is formed (displayed) on the pixel. The one frame period is a period in which one frame image is displayed on the liquid crystal element. In this embodiment, the liquid crystal element is driven at 120 Hz, and one frame period is 8.33 ms.

  Note that no voltage may be applied during the off period, but the off period is a period for expressing pixels in black, and the voltage does not necessarily have to be zero for design reasons or the like. That is, turning on and off of the predetermined voltage can be rephrased as application of the first voltage (predetermined voltage) and application of the second voltage lower than the first voltage.

  The setting of the subfield period and the grayscale data in the control circuit 303 will be described below. The control circuit 303 may be configured by a computer, and the following subfield period settings and ON/OFF of a predetermined voltage for each subfield period may be controlled according to a liquid crystal drive program as a computer program.

  FIG. 3 shows division of one frame period into a plurality of subfield periods (bit length) in this embodiment. The numerical value described on each subfield shows the time weight within one frame period of the subfield. In this embodiment, 96 gradations are expressed. In the description here, the period of time weighting 1+2+4+8 is referred to as the A subfield period (first period), and the bit indicating the gradation represented in binary in the A subfield period is referred to as the lower bit. In addition, the 10 subfield periods with the time weight of 8 are collectively referred to as a B subfield period (second period), and the bit indicating the grayscale represented in binary in the B subfield period is referred to as an upper bit. The time weight 1 corresponds to 0.087 ms, and the time weight 8 corresponds to 0.69 ms.

  Further, the subfield period in which the predetermined voltage is turned on (the first voltage is applied) is called an on period, and the subfield period in which the predetermined voltage is turned off (the second voltage is applied) is called an off period.

  FIG. 4 shows grayscale data in the A subfield period shown in FIG. The vertical axis represents gradation and the horizontal axis represents one frame period. In the A subfield period, 16 gradations are expressed. The white sub-field period in the figure shows the ON period in which the above-mentioned predetermined voltage is applied so that the pixel is in the white display state, and the black sub-field period is in which the predetermined voltage is turned off so that the pixel is in the black display state. Indicates the off period.

  FIG. 5 shows grayscale data in the A and B subfield periods (lower and upper bits) in this embodiment. This gradation data is gradation data for expressing 96 gradations as all gradations. In this gradation data, an A subfield period (lower bit) is arranged at the time center of one frame period, and before and after that, a B subfield period (upper bit) is divided into 1SF to 5SF and 6SF to 10SF. It is arranged. That is, the B subfield period is divided into two, and each B subfield period includes two or more subfield periods.

  According to the grayscale data, when displaying adjacent grayscales of two grayscales adjacent to each other, that is, two grayscales adjacent to each other in the liquid crystal element, for example, 48 grayscales and 49 grayscales, The field period is an on period for 48 gradations and an off period for 49 gradations. Further, in 48 gradations, 1SF, 4SF, 5SF, 6SF, 7SF, and 10SF of the B subfield period are OFF periods, and 2SF, 3SF, 8SF, and 9SF are ON periods. On the other hand, in 49 gradations, 1SF, 5SF, 6SF, and 10SF of the B subfield period are off periods, and 2SF, 3SF, 4SF, 7SF, 8SF, and 9SF are on periods. Then, when such an adjacent gradation is displayed on the adjacent pixel, an ON/OFF adjacent period in which the ON period and the OFF period overlap in the adjacent pixel occurs. Specifically, when displaying 48 gradations and 49 gradations in the adjacent pixels, 4SF and 7SF of the B subfield period are ON/OFF adjacent periods.

  Here, the grayscale data of this embodiment is compared with the conventional (patent document 1) grayscale data shown in FIG. In the grayscale data of FIG. 13, one B subfield period continues after the A subframe period, but in the grayscale data of this embodiment shown in FIG. 5, the B subfield period is divided before and after the A subframe period. Are arranged. For example, paying attention to the 48th gray scale and the 49th gray scale, in FIG. 13, 5SF and 6SF of the B subfield period are ON/OFF adjacent periods, and 16 ON/OFF adjacent periods continue as time weights. .. This is the same for the other adjacent gradations of 16 and 17 gradations, 32 and 33 gradations, 64 and 65 gradations, 80 and 81 gradations, and the like. On the other hand, in the present embodiment shown in FIG. 5, in any of the above-mentioned adjacent gray scales, the ON/OFF adjacent period continues in the B sub-field period as a time weighting of 1 sub-field. It is a period (=0.69 ms). Then, a plurality of (two) ON/OFF adjacent periods, which are the one subfield period, exist apart from each other with the A subframe period interposed therebetween.

  Next, an effect obtained by disposing the on/off adjacent periods in a distributed manner as in the present embodiment will be described.

  First, when the pixels arranged in a matrix as shown in FIG. 6 are switched from the all-white display state to the black-and-white display state in which white and black are alternately displayed for each pixel line, and when the all-black display state is changed to black-and-white. The response characteristics of the liquid crystal when switching to the display state will be described. The 4×4 pixels shown in FIG. 6 are arranged in a matrix with a pixel pitch of 8 μm. In the all white display state, both the pixels of the A pixel line and the pixels of the B pixel line in FIG. 6 display white. In the monochrome display state, the pixels of the A pixel line are switched from the white display state to the black display state, and the pixels of the B pixel line are maintained in the white display state.

  FIG. 7 shows the response characteristics of the liquid crystal. The horizontal axis indicates the position of the pixel, and the vertical axis indicates the brightness (where white is 1) of each pixel. A horizontal axis of 0 to 8 μm indicates pixels of the A pixel line shown in FIG. 6, and 8 μm to 16 μm indicates pixels of the B pixel line. The plurality of curves show the brightness for each elapsed time (0.3 ms, 0.6 ms, 1.0 ms, 1.3 ms) when the switching time point from the all white display state to the monochrome display state is 0 ms.

  As described above, the pixels of the A pixel line are switched from the white display state to the black display state, but the pixels of the A pixel line are relatively uniformly bright without being affected by the disclination due to the relationship of the direction of the pretilt angle in the liquid crystal. It changes (it gets darker). On the other hand, in the pixels of the B pixel line, disclination does not occur in the all white display state. However, the brightness curve gradually becomes distorted with the passage of time after the black and white display state due to the influence of disclination, and becomes dark (a dark line appears) particularly in the vicinity of 12 μm to 16 μm.

  Generally, the gamma curve (gamma characteristic) that determines the driving gray level of a liquid crystal element with respect to the input gray level shows the response characteristics when the same gray level is displayed on the entire liquid crystal element where disclination does not occur and that gray level is changed. Created as a premise. Therefore, when the liquid crystal element is driven using such a gamma curve, disclination occurs in a black and white display state, and brightness lower than the original brightness corresponding to the gamma curve can be obtained.

  FIG. 8 shows a change in brightness depending on the presence or absence of disclination when the liquid crystal element is switched from the all white display state to the monochrome display state. The horizontal axis represents the elapsed time from the switching time point, and the vertical axis represents the change in the integrated value of the total brightness of the pixels of the A and B pixel lines (hereinafter, simply referred to as brightness). The brightness is shown as a ratio when the all-white display state is 1. When disclination occurs (“with disclination”), the brightness of the pixel on the A pixel line changes with a characteristic close to the response characteristic shown in the vicinity of 1 to 6 μm in FIG. The brightness of the pixel is 100% over the entire area, and white is displayed. Then, with the passage of time thereafter, the amount of decrease in brightness when the disclination occurs is larger than the amount of decrease in brightness when the disclination does not occur (“no disclination”). It will become.

  On the other hand, when switching from the all black display state to the black and white display, both the pixels of the A pixel line and the pixels of the B pixel line shown in FIG. 6 are changed from the black display state to the B pixel while the pixels of the A pixel line are kept in the black display state. The pixels on the line are displayed in white. FIG. 9 shows the response characteristic of the liquid crystal at this time. The horizontal axis indicates the position of the pixel, and the vertical axis indicates the brightness (where white is 1) of each pixel. A horizontal axis of 0 to 8 μm indicates pixels of the A pixel line shown in FIG. 6, and 8 μm to 16 μm indicates pixels of the B pixel line. A plurality of curves show the brightness for each elapsed time (0.3 ms, 0.6 ms, 1.0 ms, 1.3 ms) when the switching time point from the all black display state to the monochrome display state is 0 ms.

  As described above, the pixels of the B pixel line are switched from the black display state to the white display state. However, the pixels of the B pixel line are gradually affected by the disclination after the white display state and are gradually changed over time. The brightness curve becomes distorted. Then, it becomes dark (a dark line appears) particularly near 12 μm to 16 μm. Also, the distorted shape of the brightness curve becomes more prominent over time.

  As described above, in general, the gamma curve (gamma characteristic) that determines the driving gradation of the liquid crystal element with respect to the input gradation changes while the same gradation is displayed on the entire surface of the liquid crystal element where disclination does not occur. It is created on the premise of the response characteristic in the case of making it. Therefore, when the liquid crystal element is driven using such a gamma curve, disclination occurs in a black and white display state, and brightness lower than the original brightness corresponding to the gamma curve can be obtained.

  FIG. 10 shows a change in brightness depending on the presence or absence of disclination when the liquid crystal element is switched from the all black display state to the monochrome display state. The horizontal axis indicates the elapsed time from the switching time point, and the vertical axis indicates the integrated value of the total brightness of the pixels of the A and B pixel lines (hereinafter, simply referred to as brightness, the ratio when the all-white display state is 1). ) Is shown. As for the brightness when no disclination occurs (“no disclination”), the pixels of the A pixel line are always in the black display state, and the pixels of the B pixel line are switched from the black display state to the white display state. It shows the change in brightness as it goes. On the other hand, when disclination occurs (“with disclination”), it indicates a change in the integrated value of the sum of the brightness of the pixels of the A pixel line and the pixel of the B pixel line shown in FIG. ..

In FIG. 10, when the disclination occurs, the amount of increase in brightness with time is smaller than when the disclination does not occur. That is, the longer the disclination occurs after switching from the all-black display state to the black-and-white display state, the darker it becomes compared to the case where no disclination occurs.
Next, a case where 48 gradations are displayed on the pixels of the A pixel line and 49 gradations are displayed on the pixels of the B pixel line by the conventional gradation data shown in FIG. 13 will be described. When this gradation data is used, the period in which disclination occurs is in the B subfield period in which the pixels in the A pixel line are in the black display state and the pixels in the B pixel line are in the white display state, which is the disclination occurrence display state. 5SF and 6SF. In 4SF before 5SF, both the pixels of the A pixel line and the pixels of the B pixel line are in a white display state, and the disclination does not occur.

  The response characteristics of the liquid crystal from 5SF to 6SF are characteristics corresponding to "with disclination" in FIG. In 4SF, 100% brightness is output because it is in the all-white display state, and disclination occurs during 1.39ms from the start of 5SF to the end of 6SF. This corresponds to 0 ms in 8 and the end of 6 SF corresponds to 1.39 ms. At this time, the brightness is lowered to 0.27 as compared with 0.5 when the disclination does not occur. As described above, when the gamma characteristic created on the premise that the entire surface has the same gradation is used as a reference, the ratio becomes 54% (=0.27/0.5) from 5SF to 6SF where disclination occurs.

  On the other hand, in the present embodiment, 48 gradations are displayed on the pixels of the A pixel line (second pixel) and 49 gradations are displayed on the pixels of the B pixel line (first pixel) by the gradation data shown in FIG. The case of displaying will be described. When this gradation data is used, the period in which disclination occurs is 4SF and 7SF in the B subfield period in which the pixels in the A pixel line and the pixels in the B pixel line are in the disclination occurrence display state. In 3SF before 4SF, both the pixels of the A pixel line and the pixels of the B pixel line are in the white display state, and the disclination does not occur.

  The response characteristic of the liquid crystal in 4SF is a characteristic corresponding to "with disclination" in FIG. In 3SF, 100% brightness is output because of the all-white display state, and disclination occurs during 0.69 ms of 4SF. Therefore, the start of 4SF corresponds to 0 ms in FIG. The end time corresponds to 0.69 ms. At this time, the brightness drops only to 0.65, compared to 0.7 when no disclination occurs.

  Further, the response characteristic of the liquid crystal in 7SF, which is the subfield period in which another disclination occurs, is a characteristic corresponding to "with disclination" in FIG. In 6SF, the brightness is 0% because it is in the all black display state, and since disclination occurs during 0.69ms of 7SF, the start of 7SF corresponds to 0ms in FIG. 10, and the end of 7SF. Corresponds to 0.69 ms. At this time, the brightness only drops to 0.18, compared with 0.25 when no disclination occurs.

  The sum of brightness when disclination does not occur in 4SF and 7SF is 0.95 (=0.70+0.25), whereas the sum of brightness when disclination occurs is It becomes 0.83 (=0.65+0.18). If the gamma characteristic created on the premise that the entire surface has the same gray level is used as a reference, the ratio of the disclination occurrence display state becomes only 87% (=0.83/0.95). That is, according to this embodiment, it is possible to suppress a decrease in brightness.

  Next, the case of displaying other adjacent gradations will be described. First, the case where 16 gradations are displayed on the pixels of the A pixel line and 17 gradations are displayed on the pixels of the B pixel line shown in FIG. 6 using the conventional gradation data shown in FIG. When this gradation data is used, the period in which disclination occurs is in the B subfield period in which the pixels in the A pixel line are in the black display state and the pixels in the B pixel line are in the white display state, which is the disclination occurrence display state. 1SF and 2SF.

  The response characteristics of the liquid crystal from 1SF to 2SF are characteristics corresponding to “with disclination” in FIG. Disclination occurs during 1.39 ms from the start of 1SF to the end of 2SF. Therefore, the start time of 1SF corresponds to 0 ms in FIG. 10, and the end time of 2SF corresponds to 1.39 ms. At this time, the brightness is lowered to 0.27 as compared with 0.5 when the disclination does not occur. As described in the first embodiment, when the gamma characteristic created on the premise of the same gray level on the entire surface is used as a reference, a ratio of 54% (=0.27/0.5) from 1SF to 2SF in which disclination occurs. Becomes dark.

  On the other hand, in the present embodiment, 16 gradations are displayed on the pixels of the A pixel line (second pixel) and 17 gradations are displayed on the pixels of the B pixel line (first pixel) by the gradation data shown in FIG. The case of displaying will be described. When this gradation data is used, the period in which disclination occurs is 3SF and 8SF in the B subfield period in which the pixels in the A pixel line and the pixels in the B pixel line are in the disclination occurrence display state. In 2SF before 3SF, both the pixels of the A pixel line and the pixels of the B pixel line are in the black display state, and the disclination does not occur. The response characteristic of the liquid crystal in 3SF is a characteristic corresponding to "with disclination" in FIG. In 2SF, the brightness is 0% due to the all black display state, and disclination occurs during 0.69 ms of 3SF, so the start of 3SF corresponds to 0 ms in FIG. 10, and the end of 3SF. Corresponds to 0.69 ms. At this time, the brightness only drops to 0.18, compared with 0.25 when no disclination occurs.

  In addition, the response characteristic of the liquid crystal in the subfield period 8SF in which another disclination occurs is also a characteristic corresponding to “with disclination” in FIG. In 7SF, the brightness is 0% due to the all black display state, and since disclination occurs during 0.69ms of 8SF, the start of 8SF corresponds to 0ms in FIG. 10 and the end of 8SF. Corresponds to 0.69 ms. At this time, the brightness only drops to 0.18, compared with 0.25 when no disclination occurs.

  Then, the sum of brightness when disclination does not occur in 3SF and 8SF is 0.50 (=0.25+0.25), whereas the sum of brightness when disclination occurs is It becomes 0.36 (=0.18+0.18). If the gamma characteristic created on the assumption that the entire surface has the same gradation is used as a reference, the ratio of darkness is 72% (=0.36/0.50) in the disclination occurrence display state. That is, according to this embodiment, it is possible to suppress a decrease in brightness.

  As described above, according to the present exemplary embodiment, a plurality of on/off adjacent periods that are in a disclination occurrence display state when displaying adjacent grayscales are provided (distributed) from each other within one frame period to provide one The continuous on/off adjacent period is shortened. That is, the disclination occurrence display state in the adjacent pixel is shifted to another display state before the brightness decrease due to the disclination becomes large. As a result, it is possible to suppress a decrease in brightness caused by disclination so that dark lines are not noticeable, and it is possible to display an image with good image quality.

  The liquid crystal element driving method described above (hereinafter referred to as the first driving method) can suppress the occurrence of disclination. However, in order to make the dark line due to the disclination more inconspicuous, the following driving method (hereinafter referred to as the second driving method) is also used in this embodiment.

  FIG. 14 shows the internal configuration of the control circuit 303. The input unit 303a takes in an input video signal via a receiver IC (not shown) such as DVI or HDMI (registered trademark). The input unit 303a down-converts or up-converts the input video signal by the scaling function and outputs the input image data in a predetermined image format. The input image data is composed of a plurality of continuous input frame image data, and includes a vertical synchronizing signal and a horizontal synchronizing signal.

  The input unit 303a and the drive circuit unit 303b are connected to the CPU 200 via the register bus 199.

  The drive circuit unit 303b sequentially receives the input frame image data from the input unit 303a, and receives a plurality of pixels (hereinafter, referred to as liquid crystal pixels) of the liquid crystal element 3 (three liquid crystal elements 3R, 3G, and 3B shown in FIG. 1). Drive each. That is, a pixel drive signal for displaying a gradation on each liquid crystal pixel is generated. The drive circuit unit 303b includes an image generation unit 410 and a panel drive unit 420. The image generation unit 410 corresponds to image data generation means, and the panel drive unit 420 corresponds to drive means.

  The image generation unit 410 includes a double speed conversion unit 411, an image memory 412, a brightness linear conversion unit 413, a first gain application unit 414, a second gain application unit 415, and an output switching unit 419.

  The double speed conversion unit 411 writes each input frame image data in the image memory 412 and generates a plurality of sub-frame image data for the input frame image data. Specifically, when converting to double speed, the double speed conversion unit 411 uses a double data width at the time of writing to the image memory 412 or doubles the speed at the time of writing to the image memory 412. The sub-frame image data is generated by reading at the speed of. For example, when the frequency of the vertical synchronizing signal of the input frame image data is 60 Hz, the double speed conversion unit 411 generates two sub-frame image data in a cycle corresponding to 120 Hz. All of the plurality of sub-frame image data generated by the double speed conversion unit 411 is the same image data as the input frame image data. That is, the input frame image data and the plurality of sub-frame image data generated by the double speed conversion unit 411 have the same gradation value at the same pixel position between them.

  In the present embodiment, the double speed conversion unit 411 is assumed to generate two sub-frame image data, the sub-frame image data generated earlier is called 1st sub-frame image data, and the sub-frame image data generated later is called. It is called 2nd sub-frame image data. Further, the double speed conversion unit 411 generates a field signal for identifying whether the generated sub-frame image data is the 1st sub-frame image data or the 2nd sub-frame image data, and outputs the field signal to the output switching unit 419.

  The brightness linear conversion unit 413 linearly increases the driving gradation of the liquid crystal pixel with respect to the increase of the gradation value (that is, the input gradation value) of each sub-frame image data input from the double speed conversion unit 411. The gradation value conversion for the input gradation value is performed. In the following description, the relationship in which the driving gradation of the liquid crystal pixels increases linearly (proportionally) with respect to the increase in the input gradation value is called the luminance linear relationship. Then, the brightness linear conversion unit 413 outputs the input gradation value after the gradation value conversion of the 1st sub-frame image data to the first gain application unit 414, and the input floor after the gradation value conversion of the 2nd sub-frame image data. The key value is output to the second gain application unit 415.

  The first gain applying unit 414 applies (multiplies) a first gain, which will be described later, to the input gradation value after the gradation value conversion of the 1st sub-frame image data to obtain a first gradation value. The 1st output gradation value is calculated. Then, the first gain application unit 414 outputs the 1st sub-frame image data having the 1st output gradation value to the output switching unit 419. Further, the second gain application unit 415 applies a second gain, which will be described later, to the input gradation value after the gradation value conversion of the 2nd sub-frame image data, so that the second gradation value 2nd is obtained. Calculate the output gradation value. Then, the second gain application unit 415 outputs the 2nd sub-frame image data having the 2nd output gradation value to the output switching unit 419.

The first and second gain application sections 414 and 415 in the present embodiment set the area of the input gradation value less than the predetermined gradation value as the low gradation area, and the input gradation value of the predetermined gradation value or more. A region (that is, a predetermined region) is a high gradation region. Then, the first and second gain application units 414 and 415 set different gains for the low gradation region and the high gradation region for each of the first and second gains. The above calculations performed by the first and second gain application sections 414 and 415 are collectively referred to as gain calculations in the following description, and will be described in detail later.

  The output switching unit 419 synchronizes with the vertical synchronizing signal of each sub-frame image data, and according to the field signal from the double speed converting unit 411, the first and second gain applying units 414 and 415 input 1st and 2nd. Sub-frame image data is alternately switched and output. As a result, the 1st sub-frame image data after the gain calculation and the 2nd sub-frame image data after the gain calculation are alternately input to the panel driving section 420.

  The panel driving unit 420 includes a VT gamma conversion unit 421 and a PWM conversion unit 422. The VT gamma conversion unit 421 uses the 1st and 2nd output grayscale values of the 1st and 2nd sub-frame image data so that necessary optical characteristics can be obtained according to the grayscale characteristics that vary depending on the response characteristics of the liquid crystal in the liquid crystal element 3. Gamma correction is performed on.

  The PWM conversion unit 422 drives the liquid crystal element 3 by the above-described subfield driving method based on the gamma-corrected 1st and 2nd subframe image data (1st and 2nd output grayscale values) from the VT gamma conversion unit 421. To output a PWM signal for.

  Next, the gain calculation performed by the first and second gain application units 414 and 415 will be specifically described with reference to FIGS. Here, the case where each of the reflective liquid crystal elements 3G, 3R, and 3B has 96 pixels in the horizontal direction will be described. 15A to 15C, the first and second gains applied to the input tone value by the first and second gain application units 414 and 415 and the gradation image projected on the projection surface ( It shows the relationship with the appearance of image quality deterioration due to disclination in the projected image). The image quality deterioration due to disclination is shown as a dark line (black line).

  FIG. 15A shows the relationship between the input gradation value and the output gradation value when the gain calculation is not performed, that is, when 1.0 times (100%) as the reference gain is applied to the input gradation value. Show. At this time, in the projected image, there are five dark lines (which are simply referred to as disclinations in the figure, hereinafter referred to as disclination dark lines) generated by the disclinations.

  As shown in FIG. 15B, the first gain applying unit 414 sets the first gain higher than the target gain as the reference gain shown in FIG. 15A to the input gradation value of the 1st sub-frame image data. Apply. The first gain is higher than the target gain and has a different slope depending on the area of the input gradation value. Specifically, the first gain is 1.1 times (110%) gain when the input gradation value is a low input gradation value included in the low gradation region from 1 to 87. Further, the first gain is the maximum gradation that can be set in the sub-frame image data when the input gradation value is a high input gradation value included in the high gradation region of 88 to 96. The gain is a value (saturation gradation value). In other words, the first gain for the high gradation region can set the 1st output gradation value for the high input gradation value in the 1st sub-frame image data while the increase rate for the increase of the high input gradation value is 0%. It is a gain that gives a maximum gradation value.

On the other hand, as shown in FIG. 15C, the second gain application unit 415 applies the second gain, which is lower than the target gain as the reference gain, to the input gradation value of the 1st sub-frame image data. The second gain is a gain that is lower than the target gain and has a different slope depending on the region of the input gradation value as described above. Specifically, the second gain is a gain that is 1.0 times (100%) the average of the first gain, and with respect to the input gradation value of the low gradation region from 1 to 87. Is 0.9 times (90%). Further, with respect to the input gradation value in the high gradation region from 88 to 96, the gain is 1.0 times (100%) on average with the first gain that gives the saturated gradation value.
The output switching unit 419 alternates between the gain-calculated 1st sub-frame image data output from the first gain application unit 414 and the gain-calculated 2nd sub-frame image data output from the second gain application unit 415. Output to the gamma conversion unit 421. Thereby, on each liquid crystal element and the projection surface, the 1st sub-frame image which is the image corresponding to the 1st sub-frame image data after the gain calculation and the 2nd sub-frame which is the image corresponding to the 2nd sub-frame image data after the gain calculation are performed. The images and are displayed sequentially (alternately). The brightness of these two sub-frame images is averaged so that the brightness and gradation are not reduced as compared with the projection image (frame image) projected without gain calculation, and the disclination dark line It is possible to display a projection image that is difficult for an observer to see.

  It is assumed that the input gradation value is X, the output gradation value from the first gain application unit 414 is Y1, and the output gradation value from the second gain application unit 415 is Y2. The maximum output gradation value is Ymax, and the gain applied to the low gradation region in the first gain application unit 414 is A (1<A≦2). At this time, the gain applied by the first gain application unit 414 and the second gain application unit 415 to the input gradation value of each subframe image data is expressed as follows.

When X<Ymax/A, Y1=AX (1)
When X≧Ymax/A, Y1=Ymax (2)
When X<Ymax/A, Y2=(2-A)X (3)
When X≧Ymax/A, Y2=2X−Ymax (4)
The reason why the disclination dark line is hard to be visually recognized by using the above gain will be described.

  When the gain calculation is not performed, the output grayscale values 64 and 65 are displayed on the adjacent liquid crystal pixels whose horizontal coordinates (that is, the input grayscale values) H are 64 and 65, as shown in FIG. At this time, for the above-mentioned reason, the disclination dark line is generated at the position of the adjacent liquid crystal pixels at the horizontal coordinates H=64 and 65.

  On the other hand, when the first gain shown in FIG. 15B is applied to the input grayscale values 64 and 65, the output grayscale values are obtained at the positions of the adjacent liquid crystal pixels whose horizontal coordinates H are 58 and 59. 64 and 65 are displayed. Then, a disclination dark line is generated at the positions of the adjacent liquid crystal pixels at the horizontal coordinates H=58 and 59.

  On the other hand, when the second gain shown in FIG. 15C is applied to the input gradation values 64 and 65, the output gradation values 64 and 65 are located at the positions of the adjacent liquid crystal pixels whose horizontal coordinates H are 71 and 72. Is displayed. Then, a disclination dark line is generated at the positions of the adjacent liquid crystal pixels at the horizontal coordinates H=71 and 72.

  By alternately projecting (displaying) the 1st subframe image and the 2nd subframe image after the gain calculation obtained in this way, the generation position of the disclination dark line changes on the projection surface. Therefore, the disclination dark line visually recognized by the observer has a density of about 1/2, and it is possible to make the disclination dark line less visible as shown in FIG.

  Further, as shown in FIG. 15B, all the 87 to 96 gradations (high input gradation values) of the high gradation region in the 1st sub-frame image data are converted into the same saturated gradation value. Therefore, the disclination dark line does not occur in the high gradation area of the 1st sub-frame image. On the other hand, a disclination dark line may occur in the high gradation region of the 2nd sub-frame image, but a disclination dark line does not occur in the high gradation region of the 1st sub-frame image. Therefore, the disclination dark line does not occur continuously at the same position (pixel) in the continuous 1st and 2nd sub-frame images. Therefore, the darkness of the disclination dark line is about 1/2 the density in any area in the projected image, and the darkness of the disclination dark line can be made difficult to be visually recognized.

  Furthermore, the first gain and the second gain are gains which are 100% on average for each input gradation value, that is, gains corresponding to the reference gain shown in FIG. 15A. It is set. This means that the brightness is reduced by the gain calculation using the second gain by the amount of increase in the brightness calculated by the gain calculation using the first gain. Therefore, with respect to all the input gradation values of the input frame image data, it is possible to express the brightness and the gradation property equivalent to the brightness and the gradation property of the projected image displayed without performing the gain calculation.

  In addition, when displaying the 1st sub-frame image including the high gradation region converted into the saturated gradation value by the gain calculation, since the liquid crystal pixel displaying the saturated gradation value does not cause disclination, the saturation is saturated. It is desirable that the width of the high gradation area converted into the gradation value is large. However, if the low gradation region of 50% or less of the maximum gradation value that can be input is converted into the saturated gradation value, the gradation property in the average between the 1st and 2nd sub-frame images cannot be maintained.

  For example, FIG. 16A shows a first gain for converting an input gradation value of 50% or more of the maximum gradation value into a saturated gradation value. The second gain with respect to the first gain is calculated as shown in FIG. In order to maintain the gradation in the average between the 1st and 2nd sub-frame images, it is necessary to set the second gain so as to correct the input gradation value in the low gradation region to the negative output gradation value. .. However, since it is not possible to express a negative output grayscale value in practice, the first and second gains as shown in FIG. 16C are set, so that between the 1st and 2nd sub-frame images. The gradation property in the average of is decreased. Therefore, it is desirable to set the first gain so that a gradation value lower than 50% of the maximum gradation value that can be set in the sub-frame image data is not converted into a saturation gradation value.

  In order to make the average luminance of the two sub-frame images displayed after gain calculation equal to the luminance of the projected image displayed without gain calculation, the input gradation value is set to the driving gradation of the liquid crystal pixel. On the other hand, it is desirable to perform gain calculation after conversion so as to have a luminance linear relationship. However, if the difference between the average brightness of the two sub-frame images displayed after gain calculation and the brightness of the projection image displayed without gain calculation is within the allowable range, the brightness linear conversion unit 413 is omitted. The gain calculation may be performed without performing the conversion into the luminance linear relationship. By omitting the brightness linear conversion unit 413, it is possible to simplify the processing, promote downsizing of the circuit, and reduce heat generation from the circuit.

  Further, in order to obtain the effect of making the disclination dark line less visible, it is not always necessary to use the first and second gains having the shapes shown in FIGS. 15B and 15C. For example, as shown in FIG. 17A, the slopes of the first and second gains may be changed smoothly. In particular, when it is difficult to obtain a smooth gradation due to a calculation error due to the omission of the brightness linear conversion unit 413, as shown in FIG. 17A, the first gain with a smooth change in inclination is set. By doing so, a smoother gradation can be obtained. Also, in the same case, as shown in FIG. 17B, the gain applied to the high gradation region of the first gain may be a gain that does not convert the high gradation region into a saturated gradation value. In other words, the first gain for the high gradation region may be a gain for generating the 1st output gradation value whose increase rate with respect to the increase of the high input gradation value is less than 100%.

  However, since the disclination dark line may occur in the high gradation region by not converting the high gradation region into the saturated gradation value, the slope of the gain with respect to the high gradation region can be minimized as much as possible. It is desirable to keep the inclination small.

In the present embodiment, the gradation values less than the predetermined gradation value are set as the low gradation area, the gradation values equal to or more than the predetermined gradation value are set as the high gradation area, and each of the first and second gains is the low gradation area. The case where the gains are different in the high gradation region and in the high gradation region has been described. However, gains other than this may be set. For example, the image generation unit 410 holds a plurality of look-up tables (LUTs) as a first data table and a second data table showing the first output gradation value and the second output gradation value with respect to the input gradation value, respectively. You may. In this case, the double speed conversion unit 411 can generate a plurality of subframe image data having different gains by changing the LUT to be referred to for each generated subframe image data.

  Further, the LUT may be composed of data of output gradation values for all input gradations, but since a large storage capacity is required, the LUT only has data of output gradation values for typical input gradation values. Alternatively, the gradation value conversion may be performed on another input gradation value by interpolation processing.

Furthermore, the first and second gains may be changed for each input frame image data.
According to the present embodiment, it is possible to prevent the deterioration of image quality due to disclination from being visually recognized by moving the disclination dark line for each sub-frame image while suppressing deterioration of the brightness and gradation of the projected image.

  Next, a second embodiment of the present invention will be described. In this embodiment, the same components as those in the first embodiment are designated by the same reference numerals.

  The configuration of the drive circuit unit 303b in this embodiment is the same as that in the first embodiment, but the operations of the first gain application unit 414 and the second gain application unit 415 are different from those in the first embodiment. Specifically, the first and second gain application units 414 and 415 in the present embodiment perform the first gain calculation for the input grayscale value equal to or lower than the predetermined first grayscale threshold, and The second gain calculation is performed for the input grayscale value that is larger than the grayscale threshold value of 1 and is equal to or smaller than the predetermined second grayscale threshold value. Further, the first and second gain application units 414 and 415 perform the third gain calculation for the input gradation value larger than the predetermined third gradation threshold value. That is, in the present embodiment, each of the first and second gain application units 414 and 415 can set two changing points of the first gain and the second gain applied to the input gradation value. The advantages of adopting such a configuration will be described below.

  In the first embodiment, the appearance of the disclination dark line when displaying a gradation image in which the gradation value increases by 1 for each pixel in the horizontal direction has been described as an example. That is, the gradation difference between adjacent liquid crystal pixels was 1. If the gradation difference between adjacent liquid crystal pixels is small, the difference between the first and second gains applied to the input gradation values of the 1st and 2nd sub-frame image data (hereinafter referred to as the gain swing width) is small. Also, the location of the disclination dark line changes. However, the position of the disclination dark line is less likely to change as the difference in gradation value between adjacent liquid crystal pixels increases.

  For example, FIGS. 21A to 21C show an example of displaying a gradation image in which the gradation value in the horizontal direction increases by 6 for each pixel. Similar to FIG. 15A of the first embodiment, FIG. 21A applies no gain calculation, that is, applies 1.0 times (100%) as a reference gain to the input gradation value. The relationship between the input gradation value and the output gradation value at this time is shown. At this time, there are seven disclination dark lines in the projected image.

  21B and 21C are horizontal position of the disclination dark line when the first and second gains similar to those of FIGS. 15B and 15C of the first embodiment are set, respectively. (Horizontal coordinate) is shown. In this case, since the gain swing width is small with respect to the gradation difference between the adjacent liquid crystal pixels in which the disclination dark line is generated, the change in the output gradation value due to the gain calculation is small, and the position of the disclination dark line is small. Is hard to change. As a result, as shown in FIG. 21D, the observer may visually recognize the disclination dark line.

  On the other hand, in this embodiment, the gain swing width is made larger than that in the first embodiment. 22A and 22B show the first and second gains when A in the equation (1) described in Example 1 is set to 1.4 and the appearance of the disclination dark line in the projected image when these are applied. It is shown in d) and (e). In this case, the gain swing width is sufficiently large with respect to the gradation difference between the adjacent liquid crystal pixels in which the disclination dark line is generated. Therefore, the change in the gradation value due to the gain calculation also becomes large, and the position of the disclination dark line changes for each sub-frame image. As a result, as shown in FIG. 22G, the disclination dark line can be made hard to be visually recognized.

  Since various gradation values may be adjacent in the actual input frame image data, increase the difference in gain swing width to increase the combination of gradation values that can make the disclination dark line less visible. You can

  For the reason described above, a case where the gain swing width in the first embodiment is temporarily increased will be described. Specifically, in the first embodiment, a case will be described in which the gain swing width is set large as shown in FIG. 19A to make the disclination dark line generated near the input gradation value X1 less visible. .. In this case, for the reason described above, it is effective to apply a larger gain to the input gradation value X1 in order to make the disclination dark line less visible. An example in which a larger gain is applied to the input gradation value X1 is shown in FIG. The gain swing width at the input gradation value X1 is sufficiently larger than that in FIG.

  On the other hand, focusing on the vicinity of the input gradation value X2 on the higher gradation side than the input gradation value X1, the gain swing width is considerably larger than that in FIG. As described above, when the gain swing width is too large, the difference in brightness between the 1st and 2nd sub-frame image data output from the output switching unit 419 becomes large. May be visible.

  Therefore, the first and second gain application units 414 and 415 in the present embodiment set the first and second gains each having two change points, as shown in FIG. 19C. Focusing on the vicinity of the input gradation value X1, since a sufficiently large gain swing width is secured as in FIG. 19B, the disclination dark line can be made difficult to be visually recognized. Further, in the vicinity of the input gradation value X2 on the high gradation side, the gain swing width is set to be equal to that of FIG. 19A, and therefore the difference in brightness between the 1st and 2nd sub-frame image data does not become large, The visual recognition of flicker can be suppressed.

  As described above, in the present embodiment, the change points of the first and second gains are increased to two points (or more points may be set), so that visual recognition of flicker is suppressed and the low gradation side is reduced. The disclination dark line can be made less visible.

  Next, a third embodiment of the present invention will be described. In this embodiment, the same components as those in the first embodiment are designated by the same reference numerals.

  FIG. 18 shows the internal structure of the drive circuit unit 303b in this embodiment. The first embodiment is different from the first embodiment in that a third gain applying unit 416 and a fourth gain applying unit 417 are added between the luminance linear conversion unit 413 and the output switching unit 419. The basic operation of the third gain applying section 416 and the fourth gain applying section 417 is the same as that of the first gain applying section 414. Hereinafter, parts of this embodiment different from the first embodiment will be described.

  In the first embodiment, the double speed conversion unit 411 doubles the frequency of the vertical synchronization signal of the input frame image data to generate the 1st and 2nd sub-frame image data. In this case, for example, if the frequency of the vertical synchronizing signal of the input frame image data is 24 Hz, the frequency of the vertical synchronizing signal of each sub-frame image data becomes as low as 48 Hz, and flicker may be visually recognized. Therefore, it is preferable to set the frequency of the vertical synchronizing signal of each sub-frame image data to a high frequency (for example, about 90 Hz or more) so that the flicker is not visually recognized.

  Therefore, in this embodiment, the double speed conversion unit 411 generates a plurality of sub-frame image data so that the frequency of the vertical synchronizing signal of each sub-frame image data is equal to or higher than a predetermined frequency. The CPU 200 may determine the number of sub-frame image data generated by the double speed conversion unit 411 based on the frequency of the vertical synchronizing signal measured by the input unit 303a, or the double speed changing unit 411 may perform vertical synchronization of the input frame image data. The frequency of the signal may be measured and determined.

As a specific example, when the frequency of the vertical synchronizing signal of each input frame image data is 24 Hz, the double speed conversion unit 411 according to the present embodiment calculates from the input frame image data four sub-frame images at a cycle corresponding to 96 Hz. Generate data. Of the four pieces of sub-frame image data, those that are first generated are referred to as 1st sub-frame image data, 2nd sub-frame image data, 3rd sub-frame image data and 4th sub-frame image data.
Further, the double speed conversion unit 411 generates a field signal for identifying which subframe of the generated subframe image data is the 1st, 2nd, 3rd and 4th subframe image data and outputs the field signal to the output switching unit 419. To do.

  Similar to the first embodiment, the first and second gain application units 414 and 415 respectively set the first gain and the second gain with respect to the input gradation values of the 1st sub-frame image data and the 2nd sub-frame image data. Perform the applicable gain processing. Then, the 1st and 2nd sub-frame image data after the gain processing is output to the output switching unit 419. The third gain application unit 416 performs a gain process of applying a third gain to the input tone value of the 3rd sub-frame image data (third sub-frame image data), and obtains the 3rd output tone value after the gain process. The 3rd sub-frame image data included therein is output to the output switching unit 419. The fourth gain application unit 417 performs gain processing for applying a fourth gain to the input gradation value of the 4th sub-frame image data (fourth sub-frame image data), and obtains the 4th output gradation value after the gain processing. The 4th sub-frame image data included therein is output to the output switching unit 419.

  The output switching unit 419 is synchronized with the vertical synchronization signal of each sub-frame image data, and is output from the first to fourth gain application units 414 to 417 in accordance with the field signal from the double speed conversion unit 411. Subframe image data is sequentially switched and output. As a result, the 1st to 4th sub-frame image data after the gain calculation is sequentially input to the panel drive unit 420.

  20A to 20G, the first to fourth gains applied by the first to fourth gain application units 414 to 417 in the present embodiment and the projection image visually recognized by the observer are shown. The disclination dark line is shown. Similar to FIG. 15A of the first embodiment, FIG. 20A applies no gain calculation, that is, applies 1.0 times (100%) as the reference gain to the input gradation value. The relationship between the input gradation value and the output gradation value at this time is shown. At this time, there are seven disclination dark lines in the projected image.

  20B and 20C respectively show the first and second gains applied by the first and second gain applying units 414 and 415, respectively. These first and second gains are the same as the first and second gains shown in FIGS. 15B and 15C of the first embodiment.

  When these first and second gains are applied to the 3rd and 4th subframe image data, respectively, the first gain is applied to the 1st and 3rd subframe image data, and the second gain is applied to the 2nd and 4th subframe image data. Will be applied. In this case, the disclination dark line occurs at the same position in at least two sub-frame images among the four sub-frame images projected (displayed). Therefore, the darkness of the disclination dark line visually recognized by the observer is about ½ of that in the case where the gain calculation is not performed, and it is possible to make the disclination dark line less visible.

  However, in the present embodiment, by using gains different from the first and second gains as the third and fourth gains, respectively, the disclination dark line is made more difficult to be visually recognized as described below.

  20D and 20E show the third gain and the fourth gain, respectively. The high gradation region and the low gradation region set by the third and fourth gain applying units 416 and 417 are different from the high gradation region and the low gradation region in the first and second gain applying units 414 and 415. Specifically, the third and fourth gain application units 416 and 417 set the low gradation region as the region having the input gradation values of 1 to 67, and the high gradation region as the region of the input gradation values of 68 to 96. To do. Then, gains having different inclinations are set in the high gradation region and the low gradation region.

  The third and fourth gains are set so that the average of these third and fourth gains is 1 (100%). Further, unlike the first gain, the third gain is set to a gain that does not convert the input gradation value in the high gradation region of the 3rd sub-frame image data into the saturated gradation value. The reason will be described below.

  If the high gradation area of the 3rd sub-frame image data is converted to a saturation gradation value, the slope of the fourth gain applied to the high gradation area of the 4th sub-frame image data is 100% on average with the third gain. Therefore, it must be 2.0 times (200%). On the other hand, the slope of the second gain applied in the high gradation area of the 2nd sub-frame image data is also 2.0 times (200%). As a result, disclination dark lines occur at the same positions in the displayed 2nd and 4th sub-frame images. When the disclination dark line occurs at the same position in two sub-frame images among the four sub-frame images in this way, the density of the disclination dark line visually recognized by the observer does not become lower than about 1/2. In order to further enhance the effect of making the disclination dark line less visible, it is desirable that the slopes of the gains applied to the 1st to 4th sub-frame image data are all different.

  As shown in FIG. 20D, by setting the third gain to a gain that does not convert the high gradation region of the 3rd sub-frame image data into a saturated gradation value, if the slopes of the first to fourth gains are all different. Can be made. As a result, the generation positions of the disclination dark lines in the displayed 1st to 4th sub-frame images are different from each other, and the darkness of the disclination dark lines visually recognized by the observer is about 1/4. Therefore, the effect of making the disclination dark line difficult to be visually recognized can be further enhanced.

  As described above, in this embodiment, four sub-frame image data are generated from the input frame image data. Even in this case, the disclination dark line can be made difficult to be visually recognized by moving the disclination dark line for each sub-frame image while suppressing deterioration of the brightness and gradation of the projected image.

  Here, flicker may be visually recognized depending on the order of outputting the 1st to 4th sub-frame image data after the gain calculation from the output switching unit 419.

  The 1st and 3rd sub-frame images displayed after application of the first and third gains exceeding 100% are defined as bright sub-frame images. In addition, the 2nd and 4th sub-frame images displayed after the application of the second and fourth gains below 100% are dark sub-frame images. At this time, if the images are displayed in the order of bright sub-frame image→bright sub-frame image→dark sub-frame image→dark sub-frame image, flicker may be visually recognized. Therefore, it is desirable that the output switching section 419 alternately output the subframe image data corresponding to each of the bright subframe image and the dark subframe image. In other words, it is desirable not to continuously output the sub-frame image data corresponding to the bright sub-frame image or continuously output the sub-frame image data corresponding to the dark sub-frame image.

That is, in this embodiment, it is desirable that the output switching unit 419 output the 1st to 4th sub-frame image data in any of the following orders.
"1st (bright) -> 2nd (dark) -> 3rd (bright) -> 4th (dark)"
"1st (bright) -> 4th (dark) -> 3rd (bright) -> 2nd (dark)"
“2nd (dark) → 3rd (bright) → 4th (dark) → 1st (bright)”
"2nd (dark) → 1st (bright) → 4th (dark) → 3rd (bright)"
"3rd (bright) → 4th (dark) → 1st (bright) → 2nd (dark)"
"3rd (bright) -> 2nd (dark) -> 1st (bright) -> 4th (dark)"
"4th (dark) -> 1st (bright) -> 2nd (dark) -> 3rd (bright)"
"4th (dark) → 3rd (bright) → 1st (bright) → 2nd (dark)"
Although the double speed conversion unit 411 generates an even number of sub-frame image data for the input frame image data in the first to third embodiments, an odd number of sub-frame image data may be generated. In this case, a gain (reference gain) of 1 time (100%) is applied to one of the odd-numbered sub-frame image data to be generated, and the other sub-frame image data will be described in the first to third embodiments. A similar effect can be obtained by applying a gain different from the above-mentioned 1×.

  Specifically, when the double speed conversion unit 411 generates five pieces of sub-frame image data for the input frame image data, a gain of one time (100%) is applied to one of the five pieces of sub-frame image data. To do. Then, a gain different from 1 is applied to the other four sub-frame image data as in the third embodiment.

  Further, since the output switching unit 419 switches the output of these sub-frame image data at a speed that is not visually recognized by the observer, the observer can average the five displayed sub-frame images even if the output order is changed. One will observe the projected image with brightness. Therefore, the gradation of the projected image can be maintained.

  The sub-frame image data to which the above-described gain of 1 time (100%) is applied may be output in any order. However, it is desirable to output the bright sub-frame images in a non-continuous order.

  In this way, even when an odd number of sub-frame image data is generated, the disclination is performed while suppressing a decrease in the brightness and gradation of the projected image, as in the case of generating an even number of sub-frame image data. The dark line is moved for each sub-frame image. As a result, it is possible to make it difficult for the image quality deterioration due to disclination to be visually recognized.

  Next, a fourth embodiment of the present invention will be described. In this embodiment, the same components as those in the first embodiment are designated by the same reference numerals. The method of determining the parameters applied to the first and second gain applying sections 414 and 415 is the same as that in the first embodiment, but in this embodiment, first, the dark subframe is output, and then the bright subframe is output. Is different from the first embodiment. Here, the dark subframe is a subframe to which a gain lower than 100% is applied, and the bright subframe is a subframe to which a gain higher than 100% is applied.

  By outputting the dark sub-frame first and then outputting the bright sub-frame as in the present embodiment, the dark line due to the disclination can be made more difficult to be visually recognized. The reason will be described below.

  As described in the first embodiment, the disclination takes a time of the order of several milliseconds due to the transient response. On the other hand, there is also a transient response in the time from the occurrence of disclination until the dark line due to the disclination is no longer visible (called relaxation time). In order to reduce the disclination, it is necessary to maintain a time period in which no discnation occurs, that is, white display in both adjacent liquid crystal pixels or black display in both adjacent liquid crystal pixels for a certain period of time. In the present embodiment, it is assumed that the reflection type liquid crystal elements 3G, 3R, 3B are used in which the relaxation time is longer than the generation time until disclination occurs and the darkness becomes visible as a dark line. As described above, when a liquid crystal element having a long relaxation time is used, the dark line due to disclination can be more difficult to be visually recognized by displaying the first sub-frame as the dark sub-frame first.

  The reason why it is desirable to display the dark subframe first will be described below with reference to FIG. In this embodiment, the PWM conversion unit 422 is assumed to drive the liquid crystal elements 3G, 3R, 3B by the PWM of FIG. 5 as in the first embodiment. FIG. 23A shows a projected image when the gain calculation is not performed. Further, the first and second gains applied to the input gradation value by the first and second gain application units 414 and 415 in the present embodiment and the discrepancies in the gradation image (projection image) projected on the projection surface. 23(b) and 23(c) show the relationship with the appearance of the image quality deterioration due to the nation. Further, FIG. 23D shows a state of the disclination dark line visually recognized by the observer.

  23B and 23C, the description will be given focusing on the projection image area whose horizontal coordinate H is 87 to 96. For the sake of explanation, this area is called the area of interest. The region of interest is a region in which when the gradation image of FIG. 23A is input, the saturated gradation value is output by calculation using the 2nd sub-frame applied gain of the present embodiment. In the attention area of the 1st sub-frame, as shown in FIG. 23B, disclination occurs between the adjacent liquid crystal pixels at the horizontal coordinates H of 88 and 89. On the other hand, in the region of interest of the 2nd sub-frame, the saturation gradation value is output, and thus disclination does not occur.

  If the first sub-frame is a bright sub-frame and the second sub-frame is a dark sub-frame, a sufficient disclination relaxation period cannot be secured depending on the gradation value of the frame image input next. There is. On the other hand, by setting the first sub-frame as the dark sub-frame and the second sub-frame as the bright sub-frame as in the present embodiment, at least in the region where the gray scale of the high gray scale region is input, that is, in the region of interest in the present embodiment. Even if disclination occurs in the 1st subframe, the white display period continues between the adjacent quadrant pixels in the 2nd subframe for one subframe period. Therefore, it is possible to surely secure the time for the disclination to relax, and it is possible to make the dark line due to the disclination difficult to be visually recognized.

  With reference to FIG. 24, the reason why the time for disclination relaxation can be reliably ensured will be described in more detail. The squares in FIG. 24 represent pixels, and the numbers in the squares represent the gradation values in each pixel. As shown in FIG. 24A, when the input images A and B having a size of 1×10 columns are continuously input from the input unit 303a, the 1st subframe is a bright subframe and the 2nd subframe is a dark subframe. The image output from the output switching unit 419 in this case is shown in FIG. An image output from the output switching unit 419 when the 1st subframe is the dark subframe and the 2nd subframe is the bright subframe is shown in FIG.

  Note that the hatched pixels in FIGS. 23B and 23C indicate that there is a period in which white display and black display are different between adjacent liquid crystal pixels in PWM in one subframe period. In addition, pixels not hatched in FIGS. 23B and 23C indicate that there is no period in which white display and black display are different between adjacent liquid crystal pixels in PWM in one subframe period. In other words, it is possible to reduce the disclination in the pixels not hatched in FIGS. 23(b) and 23(c).

  FIG. 23B shows an output image when the 1st subframe is a bright subframe and the 2nd subframe is a dark subframe. In this case, the second sub-frame image for the input image A is a dark sub-frame, and disclination occurs between the adjacent liquid crystal pixels that output the grayscale values 80 and 82 at the horizontal coordinates 2 and 3. In the subsequent sub-frames, the pixels of the horizontal coordinates 2 and 3 are indicated by hatching, which means that in the PWM of one sub-frame period, there is a period in which white display and black display are different between adjacent pixels. .. Therefore, it indicates that the disclination that occurred is difficult to alleviate.

  As shown in FIG. 23C, when the 1st sub-frame is the dark sub-frame and the 2nd sub-frame is the bright sub-frame, the 1st sub-frame image for the input image A becomes the dark sub-frame, and the horizontal coordinates 2, 3 Disclination occurs between the adjacent liquid crystal pixels outputting the gray scale values 80 and 82. In the next sub-frame, the 2nd sub-frame image for the input image A, all pixels including the pixels of the horizontal coordinates 2 and 3 are not hatched, and white display is performed between adjacent liquid crystal pixels in the PWM of one sub-frame period. This means that black display is a pixel in which different periods do not exist. Therefore, as compared with FIG. 23B, even when a liquid crystal element in which a sufficient time for relaxing the generated disclination is secured and the relaxation time for the disclination is long is used, The dark line can be made more difficult to be visually recognized.

  Therefore, according to the present embodiment, it is possible to reduce the deterioration of the image quality due to the disclination by moving the disclination dark line for each sub-frame image while suppressing the deterioration of the brightness and gradation of the projected image. it can. Further, as an effect peculiar to this embodiment, by outputting the dark sub-frame and the light sub-frame in this order, the disclination relaxation time can be surely secured in the high gradation area. Can be made less visible.

Needless to say, the shape of the gain curve in FIG. 23 is an example, and the shapes described in other embodiments such as FIGS. 16, 17, and 19 may be used, or shapes other than the illustrated shapes may be used.
(Other embodiments)
Note that the present invention supplies a program that implements one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read the program. It can also be realized by executing processing. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  The embodiments described above are merely representative examples, and various modifications and changes can be made to the embodiments when implementing the present invention.

303 Control Circuits 3G, 3R, 3B Reflective Liquid Crystal Element 410 Image Generation Unit 411 Double Speed Circuit 412 Image Memory 414 First Gain Applying Unit 415 Second Gain Applying Unit 416 Third Gain Applying Unit 417 Fourth Gain Applying Unit 419 Output Switching Unit 420 panel drive

Claims (9)

A liquid crystal drive device for driving a liquid crystal element having a plurality of pixels,
The gradation value of the first pixel having the gradation value less than the predetermined threshold value in the input frame is converted into the gradation value obtained by multiplying the gradation value of the first pixel by the first gain larger than 1. And converting the gradation value of the second pixel having a gradation value equal to or higher than the predetermined threshold value in the input frame into the maximum gradation value that can be set in the first sub-frame, and setting the first sub-frame. Generate,
The gradation value of the first pixel of the input frame is a gradation value obtained by multiplying the gradation value of the first pixel by a second gain larger than 0 and smaller than 1, A value obtained by converting the gradation value of the second pixel of the input frame into a gradation value that increases in accordance with an increase in the value and multiplying the gradation value of the second pixel by a third gain larger than 1. Generating means for generating a second sub-frame by converting into a gradation value obtained by subtracting the maximum gradation value from, and increasing in accordance with an increase in the gradation value of the input frame .
Based on the gradation value of each pixel of each sub-frame, in each of the plurality of sub-field periods included in one frame period, the first voltage applied to the corresponding pixel of the liquid crystal element and the first voltage lower than the first voltage are applied. A driving unit that controls the application of two voltages to form gradation in the pixel,
The average of the gradation values of the pixels corresponding to the first pixel of the input frame in each of the first sub-frame and the second sub-frame generated by the generation means is equal to the gradation value of the first pixel. , The average of the gradation values of the pixels corresponding to the second pixels of the input frame in each of the first sub-frame and the second sub-frame is equal to the gradation value of the second pixel ,
It said drive means, a liquid crystal driving device which is characterized by performing the driving of the liquid crystal element based on the first sub-frame, and driving of the liquid crystal element based on the second sub-frame, alternately. An input gradation value less than a predetermined threshold value is associated with a gradation value obtained by multiplying the input gradation value by a first gain larger than 1, and an input gradation value greater than or equal to the predetermined threshold value is set as a maximum gradation value. The associated first data table is associated with a value obtained by multiplying the input gradation value less than the predetermined threshold value by a second gain that is greater than 0 and smaller than 1, and is equal to or greater than the predetermined threshold value. Storage means for storing a second data table in which the input grayscale value is associated with a grayscale value obtained by multiplying the input grayscale value by a third gain larger than 1.
Generating a first subframe by converting the gradation value of the input frame using the first data table, the second sub-frame by converting the gradation value of the input frame using the second data table Generating means for generating,
Based on the gradation value of each pixel of each sub-frame, in each of the plurality of sub-field periods included in one frame period, the first voltage applied to the corresponding pixel of the liquid crystal element and the first voltage lower than the first voltage are applied. Drive means for controlling the application of two voltages to form gradation in the pixel;
Equipped with
The average of the gradation values of the pixels corresponding to the first pixel of the input frame in each of the first subframe and the second subframe generated by the generation means is the gradation value of the first pixel. And an average of gradation values of pixels corresponding to the second pixel of the input frame in each of the first subframe and the second subframe is equal to a gradation value of the second pixel ,
It said drive means, a liquid crystal driving device which is characterized by performing the driving of the liquid crystal element based on the first sub-frame, and driving of the liquid crystal element based on the second sub-frame, alternately.   The liquid crystal drive device according to claim 1, wherein the second gain is a value obtained by subtracting the first gain from 2, and the third gain is 2.   4. The liquid crystal according to claim 1, wherein the predetermined threshold value is a gradation value that is 50% or more of a maximum gradation value that the gradation value of the input frame can take. Drive.   5. The driving unit drives the plurality of pixels based on the second sub-frame, and then drives the plurality of pixels based on the first sub-frame. Item 3. A liquid crystal drive device according to item. A light source for inputting light to the liquid crystal element,
A projection lens for projecting the light modulated by the liquid crystal element onto a projection surface;
The liquid crystal drive device according to claim 1, further comprising: Liquid crystal element,
A liquid crystal drive device according to any one of claims 1 to 6,
An image display device comprising: A liquid crystal driving method for driving a liquid crystal element having a plurality of pixels,
The gradation value of the first pixel having the gradation value less than the predetermined threshold value in the input frame is converted into the gradation value obtained by multiplying the gradation value of the first pixel by the first gain larger than 1. And converting the gradation value of the second pixel having a gradation value equal to or higher than the predetermined threshold value in the input frame into the maximum gradation value that can be set in the first sub-frame, and setting the first sub-frame. Generate,
The gradation value of the first pixel of the input frame is a gradation value obtained by multiplying the gradation value of the first pixel by a second gain larger than 0 and smaller than 1, A value obtained by converting the gradation value of the second pixel in the input frame to a gradation value that increases in accordance with an increase in the value and multiplying the gradation value of the second pixel by a third gain larger than 1. To a gradation value that is obtained by subtracting the maximum gradation value from, and that increases in accordance with an increase in the gradation value of the input frame to generate the second sub-frame .
Based on the grayscale value of each pixel of each sub-frame, in each of a plurality of sub-field periods included in one frame period, application of a first voltage to a corresponding pixel of the liquid crystal element and a first voltage lower than the first voltage are applied. Controlling the application of two voltages to form gradation in the pixel,
Floor average of the first pixel of the gray scale values of pixels corresponding to the first pixel of the input frame in each of the second sub-frame to have been generated the first subframe by the step of pre-SL generated Equal to the tone value, and the average of the tone values of the pixels corresponding to the second pixel of the input frame in each of the first subframe and the second subframe is equal to the tone value of the second pixel. ,
In step of the formed liquid crystal driving method characterized by performing the driving of the liquid crystal element based on the first sub-frame, and driving of the liquid crystal element based on the second sub-frame, alternately. A computer that controls the driving of a liquid crystal element having a plurality of pixels
The gradation value of the first pixel having the gradation value less than the predetermined threshold value in the input frame is converted into the gradation value obtained by multiplying the gradation value of the first pixel by the first gain larger than 1. And converting the gradation value of the second pixel having a gradation value equal to or higher than the predetermined threshold value in the input frame into the maximum gradation value that can be set in the first sub-frame, and setting the first sub-frame. Generate,
The gradation value of the first pixel of the input frame is a gradation value obtained by multiplying the gradation value of the first pixel by a second gain larger than 0 and smaller than 1, A value obtained by converting the gradation value of the second pixel in the input frame to a gradation value that increases in accordance with an increase in the value and multiplying the gradation value of the second pixel by a third gain larger than 1. A gradation value that is obtained by subtracting the maximum gradation value from, and that is converted into a gradation value that increases in accordance with an increase in the gradation value of the input frame to generate the second sub-frame ;
Based on the gradation value of each pixel of each sub-frame, in each of the plurality of sub-field periods included in one frame period, the first voltage applied to the corresponding pixel of the liquid crystal element and the first voltage lower than the first voltage are applied. A computer program for controlling the application of two voltages to execute processing for forming gradation in the pixel,
The average of the gradation values of the pixels corresponding to the first pixel of the input frame in each of the first sub-frame and the second sub-frame generated by the generating process is the gradation of the first pixel. An average of gradation values of pixels corresponding to the second pixel of the input frame in each of the first sub-frame and the second sub-frame is equal to a gradation value of the second pixel ,
In the process for the formation, on the computer, a liquid crystal drive, characterized in that to execute the driving of the liquid crystal element based on the first sub-frame, and driving of the liquid crystal element based on the second sub-frame, the alternate program.