JP2018185377A - Liquid crystal drive device, image display device, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal drive device with which it is possible to alleviate a reduction in picture quality due to disclination.SOLUTION: Provided is a liquid crystal drive device (303) for driving a liquid crystal element (3), comprising: image data generation means (411, 412, 413) for generating first frame image data and second frame image data for each of successively inputted input frame image data; and drive means (415) for controlling the application of a first voltage and the application of a second voltage lower than the first voltage to pixels of the liquid crystal element (3) sequentially in each of a plurality of sub-frame periods included in one frame period on the basis of each of the first frame image data and the second frame image data and thereby causing grayscale to be formed in the pixels. The image data generation means adds a value that corresponds to the grayscale of the input frame image to at least one of the first frame image data and the second frame image data.SELECTED DRAWING: Figure 11

Description

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

  Examples of the liquid crystal element include 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. The driving method of these liquid crystal elements includes an analog driving method in which brightness is controlled by changing a voltage applied to the liquid crystal layer according to the gradation, and voltage application by binarizing the voltage applied to the liquid crystal layer. There is a digital drive system that controls brightness by changing time. In this digital driving method, one frame period is divided into a plurality of subframe periods on the time axis, and a predetermined voltage is applied (on) and non-applied (off) to the pixel for each subframe, thereby controlling the pixel. There is a sub-frame driving method for displaying gradation.

  Here, a general subframe driving method will be described. FIG. 20 shows an example in which one frame period is divided into a plurality of subframe periods (bit length). The numerical value described on each subframe indicates a time weight within one frame period of the subframe. Here, as an example, a case where 64 gradations are expressed is shown. In the description here, the period of time weight 1 + 2 + 4 + 8 + 16 is referred to as an A subframe period, and the subframe period of time weight 32 is referred to as a B subframe period. Further, the subframe period in which the predetermined voltage is turned on is referred to as an on period, and the subframe period in which the predetermined voltage is turned off is referred to as an off period.

  FIG. 21A shows all gradation data corresponding to the subframe division example shown in FIG. In FIG. 21A, the vertical axis represents gradation and the horizontal axis represents one frame period. In the drawing, the white subframe period indicates an on period in which the pixels are in a white display state, and the black subframe period indicates an off period in which the pixels are in a black display state. According to the gradation data, two gradations (hereinafter referred to as adjacent gradations) adjacent to two adjacent pixels (hereinafter referred to as adjacent pixels) on the liquid crystal element, for example, 32 gradations and 33 gradations are displayed. In this case, the A subframe period is an on period for 32 gradations and an off period for 33 gradations. The B subframe period is an off period for 32 gradations and an on period for 33 gradations.

  In this way, when an on-period and an off-period overlap in time in an 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. Occurring and the brightness of the pixels on the on-period side decreases. FIG. 21B is an image of a decrease in brightness due to disclination. In FIG. 21B, the vertical direction indicates the gradation, and the shading indicates the display brightness. When there is no disclination, smooth shading is expressed, but in adjacent gradations (32 gradations and 33 gradations in this case) where the on period and the off period overlap in adjacent pixels, due to the influence of disclination The brightness decreases and dark lines appear.

  Patent Document 1 discloses a drive circuit that generates a plurality of divided subframe periods by dividing one or a plurality of long subframe periods into a period equal to a period of a short subframe. Further, in the driving circuit of Patent Document 1, when the phase of each bit of the gradation data corresponding to the adjacent pixel is different, the gradation is maintained and the bit array of the gradation data corresponding to one pixel is maintained. On the other hand, correction is performed so as to approach the bit array of gradation data corresponding to the other pixel. As a result, compared to a case where a long subframe period is not divided, a subframe period in which an ON period and an OFF period overlap in adjacent pixels (hereinafter referred to as an ON / OFF adjacent period) can be shortened.

  Japanese Patent Application Laid-Open No. 2004-228561 adds a correction value common to all pixels to signal data corresponding to all pixels for each frame, and drives to reduce disclination by periodically changing the correction values. A method is disclosed.

JP2013-050681A JP2013-050679A

  However, in the method disclosed in Patent Document 1, since the shortest time of the on / off adjacent period in the adjacent pixel is long, a decrease in brightness due to disclination cannot be ignored. Moreover, since the ON / OFF adjacent period in the adjacent pixel is long, the amount of decrease in brightness due to disclination increases according to the response speed of the liquid crystal molecules.

  FIG. 22 shows all gradation data disclosed in Patent Document 1. The A subframe period corresponds to a time weight of 1 + 2 + 4 + 8, and the B subframe period is divided into a plurality of divided subframe periods 1SF (SF is a subframe) to 10SF corresponding to a time weight of 8, respectively. One divided subframe period is 0.69 ms. In this gradation data, the shortest time of the on / off adjacent period in the adjacent pixel is 1.39 ms corresponding to two divided subframe periods. Therefore, a decrease in brightness (that is, a dark line) due to disclination is conspicuous.

  Further, in the method disclosed in Patent Document 2, correction values common to all pixels are added. Therefore, if a large correction is performed, there is a possibility that an adverse effect at a low gradation such as flicker may occur.

  Therefore, the present invention provides a liquid crystal driving device, an image display device, and a program that can reduce a decrease in image quality due to disclination and reduce flicker.

  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, and includes first frame image data and second frame for each of input frame image data that are continuously input. Based on the image data generation means for generating image data, and each of the first frame image data and the second frame image data, the liquid crystal in each of a plurality of subframe periods included in one frame period in sequence. Drive means for controlling the application of the first voltage to the pixel of the element and the application of the second voltage lower than the first voltage to form a gradation in the pixel, and the image data generation means , For at least one of the first frame image data and the second frame image data, a value corresponding to the gradation of the input frame image is set. Calculated to.

  An image display device as another aspect of the present invention includes a liquid crystal element and the liquid crystal driving device.

  According to another aspect of the present invention, there is provided a program for causing a computer to drive a liquid crystal element, wherein the first frame image data and the second frame are input to each of continuously input frame image data. A pixel of the liquid crystal element is sequentially generated in each of a plurality of subframe periods included in one frame period based on a step of generating image data and each of the first frame image data and the second frame image data Controlling the application of the first voltage to the pixel and the application of the second voltage lower than the first voltage to form a gradation in the pixel, and the first frame image data And generating the second frame image data includes the first frame image data and the second frame image data. To at least one of the frame image data, comprising the step of adding a value corresponding to the gradation of the input frame image.

  Other objects and features of the present invention are illustrated in the following examples.

  According to the present invention, it is possible to provide a liquid crystal driving device, an image display device, and a program capable of reducing a decrease in image quality due to disclination and reducing flicker.

1 is a diagram illustrating an optical configuration of a liquid crystal projector in Embodiment 1. FIG. 3 is a cross-sectional view of a liquid crystal element used for the projector in Embodiment 1. FIG. FIG. 6 is a diagram illustrating a plurality of subframe periods within one frame period in the first embodiment. FIG. 6 is a diagram illustrating gradation data in an A subframe period in the first embodiment. It is a figure which shows all the gradation data in Example 1. FIG. 6 is a diagram illustrating pixel lines in Embodiment 1. FIG. FIG. 6 is a diagram illustrating response characteristics of liquid crystal when switching from all white display to black and white display in the first embodiment. It is a figure which shows the response characteristic of the brightness when it switches from the all-white display in Example 1 to a monochrome display. FIG. 6 is a diagram illustrating response characteristics of liquid crystal when switching from full black display to black and white display in the first embodiment. It is a figure showing the response characteristic of the brightness when it switches from black to black and white display in Example 1. 3 is a block diagram illustrating a configuration of a liquid crystal driver in Embodiment 1. FIG. FIG. 3 is a block diagram illustrating a detailed configuration of a correction circuit according to the first exemplary embodiment. It is a figure which shows the offset amount regarding the input data in Example 1. FIG. 4 is a diagram illustrating frame images sequentially displayed on a liquid crystal element in Example 1. FIG. 6 is another diagram showing frame images sequentially displayed on the liquid crystal element in Example 1. FIG. It is another figure which shows the offset amount regarding the input data in Example 1. FIG. It is another figure which shows the offset amount regarding the input data in Example 1. FIG. 6 is a block diagram illustrating a configuration of a liquid crystal driver in Embodiment 2. FIG. FIG. 6 is a block diagram illustrating a detailed configuration of a VT gamma circuit according to a second embodiment. The figure which shows the several sub-frame period in 1 frame period in the past. It is a figure which shows the disclination at the time of driving the liquid crystal element according to the conventional all gradation data and this gradation data. It is a figure which shows all the gradation data of patent document 1. FIG.

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

  FIG. 1 shows an optical configuration of a liquid crystal projector as an image display apparatus 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. However, the image display device includes an image display device using a liquid crystal element other than the projector, such as a direct-view monitor.

  The liquid crystal driver 303 corresponds to a liquid crystal driving device. The liquid crystal driver 303 includes a video input unit (image acquisition unit) 303a and a drive circuit unit (drive unit) 303b. The video input unit 303a acquires an input video signal (input image) from an external device (not shown). The drive circuit unit 303b generates a pixel drive signal corresponding to gradation data to be described later in accordance with the gradation (input data gradation) of the input video signal. The pixel drive signal is generated for each color of red, green, and blue, and the pixel drive signal for each color is 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 liquid crystal element 3R for red, the liquid crystal element 3G for green, and the liquid crystal element 3B for blue are vertical alignment mode reflective liquid crystal elements (liquid crystal panels).

  The illumination optical system 301 causes white light from a light source (discharge lamp or the like) to enter the dichroic mirror 305 with the 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, where half-wave retardation is given only to the blue light, thereby generating blue light and red light whose polarization directions are orthogonal to each other. . Blue light and red light enter the polarization beam splitter 310, and the blue light passes through the polarization separation film of the polarization beam splitter 310 and is 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 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-wave retardation is given. Then, the red light enters the polarization beam splitter 308, is reflected by the polarization separation film, and travels toward 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 is reflected by the polarization separation film. Then, it 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 the polarization separation thereof. The light passes through the film and travels toward the projection optical system 304. Thus, red light, green light, and blue light that have been color-combined enter the projection optical system 304. Then, the color light after color synthesis is enlarged and projected onto a projection surface 313 such as a screen by the projection optical system 304.

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

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

  The liquid crystal driver 303 shown in FIG. 1 drives each pixel by the above-described subframe driving method. That is, one frame period is divided into a plurality of subframe periods on the time axis, and on (applied) and off (non-applied) of a predetermined voltage for the pixel is controlled for each subframe period according to the gradation data. A gradation is formed (displayed) on the pixel. One frame period is a period during 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 set to 8.33 ms. The turning on and off of the predetermined voltage can be paraphrased as application of a first voltage (predetermined voltage) and application of a second voltage lower than the first voltage.

  Hereinafter, the setting of the subframe period and the gradation data in the liquid crystal driver 303 will be described. The liquid crystal driver 303 may be configured by a computer, and the setting of the following subframe period and on / off of a predetermined voltage for each subframe period may be controlled according to a program (liquid crystal driving program).

  FIG. 3 shows the division of one frame period into a plurality of subframe periods (bit lengths) in this embodiment. The numerical value described on each subframe indicates a time weight within one frame period of the subframe. In this embodiment, 96 gradations are expressed. In the description here, the period having the time weight of 1 + 2 + 4 + 8 is referred to as the A subframe period (first period), and the bit indicating the gradation expressed in the A subframe period is referred to as the lower bit. In addition, 10 subframe periods with a time weight of 8 are collectively referred to as a B subframe period (second period), and a bit indicating a gradation expressed in binary in the B subframe 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, a subframe period in which the predetermined voltage is turned on (a first voltage is applied) is referred to as an on period, and a subframe period in which the predetermined voltage is turned off (a second voltage is applied) is referred to as an off period.

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

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

  According to this gradation data, when displaying adjacent gradations that are two gradations adjacent to each other, for example, 48 gradations and 49 gradations, to adjacent pixels that are two adjacent pixels in the liquid crystal element, the A sub The frame period is an on period for 48 gradations and an off period for 49 gradations. In the 48 gradations, 1SF, 4SF, 5SF, 6SF, 7SF, and 10SF in the B subframe period are off periods, and 2SF, 3SF, 8SF, and 9SF are on periods. On the other hand, for 49 gradations, 1SF, 5SF, 6SF, and 10SF in the B subframe period are off periods, and 2SF, 3SF, 4SF, 7SF, 8SF, and 9SF are on periods. When such an adjacent gradation is displayed on an adjacent pixel, an ON / OFF adjacent period in which the ON period and the OFF period overlap is generated in the adjacent pixel. Specifically, when 48 gradations and 49 gradations are displayed on adjacent pixels, 4SF and 7SF in the B subframe period are on / off adjacent periods.

  Here, the gradation data of the present embodiment is compared with the conventional gradation data shown in FIG. In the grayscale data in FIG. 22, the B subframe period continues as one unit after the A subframe period. However, in the grayscale data of this embodiment shown in FIG. 5, the B subframe period is divided before and after the A subframe period. Are arranged. For example, paying attention to 48 and 49 gradations, in FIG. 22, 5SF and 6SF in the B subframe 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, ie, 16 gradation and 17 gradation, 32 gradation and 33 gradation, 64 gradation and 65 gradation, 80 gradation and 81 gradation, and the like. On the other hand, in this embodiment shown in FIG. 5, in any of the above adjacent gradations, the ON / OFF adjacent period continues in the B subframe period as one time subframe of 8 as a time weight. The period is (= 0.69 ms). A plurality (two) of ON / OFF adjacent periods, which are one subframe period, are separated from each other across the A subframe period.

  Next, the effect obtained by distributing the ON / OFF adjacent periods in a distributed manner as in this embodiment will be described.

  First, as shown in FIG. 6, when the pixels arranged in a matrix form are switched from the all-white display state to the monochrome display state in which white and black are alternately displayed for each pixel line, and from the all-black display state to the monochrome display state. 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 at each pixel (however, the ratio when white is 1). 0 to 8 μm on the horizontal axis represents pixels of the A pixel line shown in FIG. 6, and 8 to 16 μm represents pixels of the B pixel line. The plurality of curves indicate the brightness for each elapsed time (0.3 ms, 0.6 ms, 1.0 ms, 1.3 ms) when the switching point from the all white display state to the black and white display state is set to 0 ms.

  As described above, the pixels of the A pixel line are switched from the white display state to the black display state. However, the pixels of the A pixel line are relatively uniformly bright without being affected by disclination because of the pretilt angle direction in the liquid crystal. Changes (darkens). 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 as time passes under the influence of disclination after the black-and-white display state is reached, and darkens in the vicinity of 12 μm to 16 μm (dark lines appear).

  In general, the gamma curve (gamma characteristic) that determines the drive gradation of the liquid crystal element relative to the input data gradation is the response characteristic when the gradation is changed while displaying the same gradation on the entire surface of the liquid crystal element where no disclination occurs. It is created on the assumption. For this reason, when a liquid crystal element is driven using such a gamma curve, disclination occurs in a monochrome display state, and it is possible to obtain a brightness lower than the original brightness corresponding to the gamma curve.

  FIG. 8 shows changes 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 black and white display state. The horizontal axis represents the elapsed time from the switching point, and the vertical axis represents the change in the integrated value of the total brightness (hereinafter simply referred to as brightness) of the pixels of the A and B pixel lines. 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 of 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 pixels is in a state where white is displayed with 100% brightness. As the time elapses thereafter, the amount of decrease in brightness when disclination occurs is larger than the amount of decrease in brightness when no disclination occurs (“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 pixel of the A pixel line and the pixel 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 line pixels are set to the white display state. FIG. 9 shows the response characteristics of the liquid crystal at this time. The horizontal axis indicates the position of the pixel, and the vertical axis indicates the brightness at each pixel (however, the ratio when white is 1). 0 to 8 μm on the horizontal axis represents pixels of the A pixel line shown in FIG. 6, and 8 to 16 μm represents pixels of the B pixel line. The plurality of curves indicate the brightness for each elapsed time (0.3 ms, 0.6 ms, 1.0 ms, 1.3 ms) when the switching time from the all black display state to the black and white display state is set to 0 ms.

  As described above, the pixels of the B pixel line are switched from the black display state to the white display state, but the pixels of the B pixel line are gradually affected with the disclination after the white display state and gradually. The brightness curve becomes distorted. And it becomes dark especially in the vicinity of 12 μm to 16 μm (dark lines appear). Also, the irregular shape of the brightness curve becomes more prominent with the passage of 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 data gradation displays the same gradation while displaying the same gradation on the entire surface of the liquid crystal element where no disclination occurs. Created on the premise of response characteristics when changed. For this reason, when a liquid crystal element is driven using such a gamma curve, disclination occurs in a monochrome display state, and it is possible to obtain a brightness lower than the original brightness corresponding to the gamma curve.

  FIG. 10 shows changes 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 black and white display state. The abscissa represents the elapsed time from the switching point, and the ordinate represents the integrated value of the total brightness of the pixels of the A and B pixel lines (hereinafter simply referred to as brightness and the ratio when the all white display state is 1). ). As for the brightness when disclination does not occur (“no disclination”), the pixels in the A pixel line are always in the black display state, and the pixels in the B pixel line are switched from the black display state to the white display state. It shows the change in brightness as you go. 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 B pixel line shown in FIG. .

  In FIG. 10, when disclination occurs, the amount of increase in brightness over time is smaller than when 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 the disclination does not occur.

  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 using the conventional gradation data shown in FIG. When this gradation data is used, the period in which the disclination occurs is a B subframe period in which the A pixel line pixel is in the black display state and the B pixel line pixel is in the white display state. 5SF and 6SF. 4SF before 5SF is a period in which both the pixels of the A pixel line and the B pixel line pixels are in the white display state, and no disclination occurs.

  The response characteristics of the liquid crystal from 5SF to 6SF are characteristics corresponding to “with disclination” in FIG. Since 4SF is in an all-white display state, 100% brightness is output, and disclination occurs during 1.39 ms from the start of 5SF to the end of 6SF. 8 corresponds to 0 ms, and the end of 6SF corresponds to 1.39 ms. At this time, the brightness decreases to 0.27 from 0.5 when no disclination occurs. As described above, on the basis of the gamma characteristic created on the premise of the same gradation on the entire surface, the ratio becomes as dark as 54% (= 0.27 / 0.5) from 5SF to 6SF at which disclination occurs.

  On the other hand, in this embodiment, 48 gradations are displayed on the pixel (second pixel) of the A pixel line by the gradation data shown in FIG. 5, and 49 gradations are displayed on the pixel (first pixel) of the B pixel line. A case of displaying is described. The period in which the disclination occurs when using this gradation data is 4SF and 7SF in the B subframe period in which the pixels of the A pixel line and the pixels of the B pixel line are in the disclination occurrence display state. 3SF before 4SF is a period in which both the pixels of the A pixel line and the pixels of the B pixel line are in the white display state and no disclination occurs.

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

  Further, the response characteristic of the liquid crystal at 7SF, which is a sub-frame period in which another disclination occurs, is a characteristic corresponding to “with disclination” in FIG. In 6SF, since the display is all black, the brightness is 0%, and disclination occurs during 0.69 ms of 7SF. Therefore, the start time of 7SF corresponds to 0 ms in FIG. 10 and the end time of 7SF is reached. Corresponds to 0.69 ms. At this time, the brightness decreases only to 0.18, compared to 0.25 when no disclination occurs.

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

  Next, a case where other adjacent gradations are displayed will be described. First, a case where 16 gradations are displayed on the pixels of the A pixel line shown in FIG. 6 and 17 gradations are displayed on the pixels of the B pixel line based on the conventional gradation data shown in FIG. 22 will be described. When this gradation data is used, the period in which the disclination occurs is a B subframe period in which the A pixel line pixel is in the black display state and the B pixel line pixel is in the white 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 decreases to 0.27 from 0.5 when no disclination occurs. As described in the first embodiment, on the basis of the gamma characteristic created on the premise of the same gradation on the entire surface, the ratio is 54% (= 0.27 / 0.5) from 1SF to 2SF where disclination occurs. It becomes darker.

  On the other hand, in the present embodiment, 16 gradations are displayed on the pixel (second pixel) of the A pixel line by the gradation data shown in FIG. 5, and 17 gradations are displayed on the pixel (first pixel) of the B pixel line. A case of displaying is described. The period in which the disclination occurs when using this gradation data is 3SF and 8SF in the B subframe 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 a black display state, and disclination does not occur. The response characteristic of the liquid crystal at 3SF is a characteristic corresponding to “with disclination” in FIG. Since 2SF is in an all black display state, the brightness is 0%, and disclination occurs during 0.69 ms of 3SF. Therefore, the start time of 3SF corresponds to 0 ms in FIG. 10 and the end of 3SF. Corresponds to 0.69 ms. At this time, the brightness decreases only to 0.18, compared to 0.25 when no disclination occurs.

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

  The sum of brightness when disclination does not occur between 3SF and 8SF is 0.50 (= 0.25 + 0.25), whereas the sum of brightness when disclination occurs is 0.36 (= 0.18 + 0.18). When the gamma characteristic created on the premise of the same gradation on the entire surface is used as a reference, in the disclination occurrence display state, the ratio becomes dark only up to 72% (= 0.36 / 0.50). That is, according to the present embodiment, it is possible to suppress a decrease in brightness.

  As described above, in this embodiment, a plurality of ON / OFF adjacent periods that are in a disclination display state when displaying adjacent gradations are provided apart (distributed) within one frame period. The continuous on / off adjacent period is shortened. That is, the display state of the disclination occurrence in the adjacent pixels 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 due to disclination so that the dark line is not noticeable, and an image with good image quality can be displayed.

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

  FIG. 11 is a block diagram showing an internal configuration of the liquid crystal driver 303. The scaler 400 corresponds to the video input unit 303a shown in FIG. 1, and takes in an input video signal via a receiver IC (not shown) such as DVI or HDMI (registered trademark). Scaler 400 down-converts or up-converts the input video signal by the scaling function and outputs input image data in a predetermined image format. The input image data is composed of a plurality of continuous input frame image data.

  The drive circuit unit 303b sequentially receives the input frame image data from the scaler 400, and drives each pixel of the liquid crystal element 3 (three liquid crystal elements 3R, 3G, and 3B shown in FIG. 1). A pixel drive signal for displaying gradation is generated. The drive circuit unit 303b includes a double speed circuit 411, a VT gamma circuit 412, a correction circuit 413, a color unevenness circuit 414, and a PWM circuit 415.

  The double speed circuit 411 writes each input frame image data to the DDR memory 420 and generates a plurality of frame image data for one input frame image data. In this embodiment, when the input frequency is 60 Hz, two frame image data are generated at a period corresponding to 120 Hz. In the following description, one of these two frame image data is called ODD (odd number) input frame data (first frame image data), and the other is EVEN (even number) input frame data (second frame image data). That's it. These ODD and EVEN input frame data are the same image data as the input frame image data. That is, the pixel data at the pixel positions corresponding to each other between the ODD and EVEN input frame data have the same gradation.

  The VT gamma circuit 412 has a predetermined optical characteristic for the ODD and EVEN output frame data output from the double speed circuit 411 so that necessary optical characteristics can be obtained according to the gradation characteristic that varies depending on the response characteristic of the liquid crystal element 3. Perform gamma correction according to the gamma table. The correction circuit 413 performs correction (offset addition) corresponding to the gradation on the output data (image data) from the VT gamma circuit 412 to generate corrected image data. In the present embodiment, the double speed circuit 411, the VT gamma circuit (gamma correction means) 412 and the correction circuit (addition means) 413 constitute an image data generation means.

  The color unevenness circuit 414 generates color unevenness that occurs in the optical system of the projector including the liquid crystal element (liquid crystal panel) 3 with respect to the ODD and EVEN output frame data (correction frame image data) after the offset addition from the correction circuit 413. to correct. The PWM circuit (driving means) 415 drives the liquid crystal element 3 by the sub-frame driving method described above based on the ODD and EVEN output frame data output from the color unevenness circuit 414.

  Next, the operation of the correction circuit 413 will be described in detail with reference to FIG. FIG. 12 is a detailed block diagram of the correction circuit 413. The correction circuit 413 includes a data detection circuit 416, an addition circuit 417, and an addition table 418. The data detection circuit 416 receives the output data from the VT gamma circuit 412 and detects the data gradation. The addition circuit 417 adds a value corresponding to the data output from the data detection circuit 416 to the data output from the data detection circuit 416 according to the addition table 418.

  FIG. 13 is an example of the addition table 418 (offset amount table according to input data). When the input data gradation (input frame image) to the data detection circuit 416 is 0 to 5, the addition value (offset amount) is shown. ) Is set to 0. When the input data gradation is in the range of 0 to 5, there is almost no phase difference (difference between the on period and the off period in adjacent pixels) with respect to the liquid crystal drive, and even if the addition value (offset amount) is 0, the disclination There is almost no impact. In the range of the input data gradation 6 to 12 near the input data gradation 8, the offset amount is 1. In the range of the input data gradations 13 to 27 in the vicinity of the input data gradation 16, the offset amount is set to 2. In the range of the input data gradations 28 to 58 near the input data gradation 32, the offset amount is set to 3. In the range of the input data gradation 59 to 95 near the input data gradation 64, the offset amount is set to 4.

  That is, in the vicinity of the power-of-two input data 8, 16, 32, 64 in which a phase difference in PWM liquid crystal driving is likely to occur, the offset amount is expressed as “exponent of power-of-two input data—predetermined first constant (main In the embodiment, the offset amount is changed according to the input data. For example, the offset amount is 3-2 = 1 in the vicinity of 8, and 4-2 = 2 in the vicinity of 16. Further, the range is “power exponent of power of 2−index of exponential input data of power −2 + predetermined second constant (1 in this embodiment)”. For example, 8 neighborhood is 8-3 + 1 = 6, 16 neighborhood is 16-4 + 1 = 13, 32 neighborhood is 32-5 + 1 = 28, 6-12 is the offset amount near 8, 13-27 is 16 neighborhood It becomes an offset. The adder circuit 417 receives the ODD and EVEN frame information from the double speed circuit 411, and adds the addition amount by the addition circuit 417 to the addition amount of the addition table 417 or subtracts (the offset amount is minus addition). Decide what to do. For example, when ODD is + added, EVEN is subtracted. On the other hand, in the case of + adding with EVEN, subtraction is performed with ODD. That is, when the first value is added to the first frame image data, the addition circuit 417 subtracts the first value from the second frame image data and adds the second value to the second frame image data. In this case, the second value is subtracted from the first frame image data. In this way, the input data is driven while applying a + and-offset for each frame to maintain the gradation.

  FIG. 14 is a diagram showing frame images sequentially displayed on the liquid crystal element 3, and shows a display state when the addition table shown in FIG. 13 is used. FIG. 14A shows a normal driving state, and when the input image data has a gradation as shown in FIG. 14A, disclination occurs every 8th power of 2 (here, 2 to the 3rd power). The figure to show. In FIG. 14A showing a normal driving state, disclination is performed at the same position in N ODD frames (1st frame) and N EVEN frames (2nd frame) every 8 gradations. generate. As shown in FIG. 14 (A), the discerned image makes the dark disclination visible.

  FIG. 14B shows the occurrence state of disclination of the double-speed ODD frame (1st) / EVEN frame (2nd) when the offset amount corresponding to the input data of FIG. 13 is added. Here, a display when the offset amount is added to the ODD frame (1st) is shown. For example, when the input image data gradation level at which disclination is likely to occur is 8, 1 is added. Therefore, the disclination occurrence position is displayed at the 9 position. When the input image data gradation is 16, 2 is added. Therefore, the disclination occurrence position is displayed at the 18th position. When the input image data gradation is 32, 3 is added. Therefore, the disclination occurrence position is displayed at position 35. Here, a display when the offset amount is added to the EVEN frame (2nd) is shown. For example, when the input image data gradation that is likely to cause disclination is 8, −1 is added. Therefore, the disclination occurrence position is displayed at the position 7. When the input image data gradation is 16, -2 is added. Therefore, the disclination occurrence position is displayed at 16 positions. When the input image data gradation is 32, -3 is added. Therefore, the disclination occurrence position is displayed at position 29.

  FIGS. 15A and 15B show examples of specific display images (frame images). FIG. 15C shows a display image that should be originally displayed. FIG. 15A shows a 1st frame and a 2nd frame when the liquid crystal element 3 is sequentially driven by the ODD and EVEN output frame data generated without applying the offset addition for each gradation by the correction circuit 413. In addition, an image visually recognized by the observer is shown on the leftmost side of the figure. Since the position of the dark line by the disclination in the 1st frame and the 2nd frame is the same, the dark line is conspicuous to some extent in the visually recognized image.

  On the other hand, FIG. 15B shows the 1st frame when the liquid crystal element 3 is sequentially driven by the ODD and EVEN output frame data generated by applying + offset to the ODD frame (1st) and −offset to the EVEN frame (2nd). And 2nd frame. The brightest gradation on the outside is 64 in the 1st frame and 58 in the 2nd frame. The position of the dark line due to disclination on the 1st frame and the position of the dark line on the 2nd frame are shifted from each other. For this reason, in the visual image shown on the leftmost side of the figure, the dark line is almost inconspicuous by averaging the 1st frame and the 2nd frame. In this embodiment, the offset amount is reduced at low gradations that are less affected by disclination and sensitive to flicker, and the offset amount is increased toward higher gradations that are affected more by disclination and less affected by flicker. I will do it.

  As shown in FIG. 17, the offset amount after the 92nd gradation without the disclination occurrence gradation may be set to zero. In the case of the table of FIG. 13, it is necessary to apply gain or the like so that the maximum value of the input gradation data is 91 and to set the offset to 95 in advance. That is, in the case of the table of FIG. 13, in the vicinity of the maximum gradation (for example, the input data gradation is 95), even if the offset amount 4 is added, it is 95, so that the offset addition cannot be performed. As a result, only subtraction is effective and the image becomes dark. On the other hand, by setting the offset amount near the maximum gradation to 0 as in the table of FIG. 17, it is possible to avoid the image near the maximum gradation from becoming dark. In this embodiment, the offset amount can be added up to a value 91 obtained by subtracting the offset amount 4 from the input data gradation 95 which is the maximum gradation, and the image does not become dark. The amount may be zero. In the table of FIG. 17, the gradation 95 can be maintained in the ODD frame (1st) when averaging the ODD frame (1st) and the EVEN frame (2nd) in the 92-95 gradation.

  Also, as shown in the table of FIG. 16, only the input gradation portion where the disclination is likely to occur only in the vicinity of the powers of 2, 16, 32, which is a power of 2, and the offset amount is changed according to the power. It may be a table. In other words, the image data generating means applies an offset amount (in accordance with the length of the subframe period in which voltages (first voltage or second voltage) are applied so as to be different from each other in order to form two adjacent gradations. (Addition value, subtraction value) is changed.

  As shown in FIG. 16, the offset amount is 4 when the input data gradation is around 64. This is because when the input data gradation is 63, it is expressed as 00111111 (bit), and when it is 64, it is expressed as 01000000 (bit), and the phase difference between 0 and 1 (bit fluctuation) is large. On the other hand, for example, when the input data gradation is near 72, the offset amount is 1. This is because when the input data gradation is 71, it is expressed as 1000111 (bit), and when it is 72, it is expressed as 10001000 (bit), and the phase difference between 0 and 1 is relatively small. The same applies to the case where the input data gradation is around 8, for example.

  Further preferably, the image data generation means determines a gradation range to which the addition value is applied (addition range of predetermined offset amount (horizontal length) in FIG. 16) according to the gradation of the frame image data. change. Preferably, the image data generation unit changes the gradation range according to the length of the subframe period in which a voltage is applied differently to form two adjacent gradations.

  As described above, in this embodiment, the image data generation unit adds a value corresponding to the gradation of the input frame image to at least one of the first frame image data and the second frame image data. More preferably, the gamma correction means (VT gamma circuit 412) performs gamma correction on each of the first frame image data and the second frame image data according to a predetermined gamma table. The adding means (correction circuit 413) adds a value corresponding to the gradation of the input frame image to at least one of the first frame image data and the second frame image data after the gamma correction.

  Next, Embodiment 2 of the present invention will be described with reference to FIGS. FIG. 18 is a block diagram showing the configuration of the liquid crystal driver 303 in this embodiment. FIG. 19 is a block diagram showing a detailed configuration of the VT gamma circuit 412 in this embodiment. The liquid crystal driver 303 of this embodiment is different from that of the first embodiment in that it has a VT gamma circuit 412a instead of the VT gamma circuit 412, and there is no correction circuit 413. Other basic configurations are the same as those of the first embodiment, and the same components as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and the description thereof is omitted.

  The VT gamma circuit 412a has a VT gamma_ODD and VT gamma_EVEN gamma table 419 as VT gamma tables. Further, the VT gamma circuit 412 has an addition table 418. According to the gradation of the gamma table 419 of VT gamma_ODD and VT gamma_EVEN, the addition value for each gradation of the addition table 418 is output for the output data from the double speed circuit 411. Is added. The addition table 418 is a table as illustrated in FIG. 13, FIG. 16, or FIG. 17 described in the first embodiment. Similarly to the first embodiment, the value of the addition table is + In the case of addition, subtraction (offset amount minus addition) is performed by EVEN.

  As described above, the data may be offset for each gradation so as to reduce the disclination of the liquid crystal with respect to the gamma table that adjusts the gradation according to the characteristics of the liquid crystal. Further, the offset value is added from the addition table 418. However, a gamma table in which the offset value is previously added to the gamma table 419 of VT gamma_ODD and VT gamma_EVEN for each gradation is generated and the offset is applied. May be. Note that the correction tables of the first and second embodiments are merely examples, and are not limited to these. In addition, the gradation such as the gradation after the gamma correction such as the input gradation is not limited, and the gradation such as the VT gamma correction or the color unevenness correction is a gradation extended from the input gradation. It may be corrected.

  As described above, in the present embodiment, the gamma correction unit (VT gamma circuit 412a) performs gamma correction on each of the first frame image data and the second frame image data according to the gamma table. The gamma correction means corrects the gamma table according to the gradation of the input frame image, thereby adjusting the gradation of the input frame image with respect to at least one of the first frame image data and the second frame image data. Add the corresponding values.

(Other examples)
The present invention supplies a program that realizes 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 and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  In each embodiment, the generation position of the disclination when driving the liquid crystal element is appropriately shifted for each gradation based on each of the first and second frame image data. For this reason, according to each embodiment, it is possible to provide a liquid crystal driving device, an image display device, and a program that can reduce a decrease in image quality due to disclination and reduce flicker.

  As mentioned above, although the preferable Example of this invention was described, this invention is not limited to these Examples, A various deformation | transformation and change are possible within the range of the summary.

  For example, the liquid crystal driving device of each embodiment displays all black frame image data (first low gradation) by displaying black on all pixels of the liquid crystal element 3 (forming all pixels to form a black gradation having the same gradation). Frame image data and second low gradation frame image data) can be generated. Thereby, what is called black insertion can be performed and the visibility of a moving image can be improved. At this time, the image data generating means generates the first frame image data for the first input frame image data among the input frame image data continuously input, and has a higher level than the first frame image data. First low gradation frame image data having a low tone is generated. The image data generation means generates second frame image data for the second input frame image data, and outputs second low gradation frame image data having a gradation lower than that of the second frame image data. Generate. The driving means (PWM circuit 415) is based on each of the first frame image data, the first low gradation frame image data, the second frame image data, and the second low gradation frame image data. The gradation is formed in the pixel. Specifically, the driving unit sequentially applies the first voltage to the pixels of the liquid crystal element and the first voltage in each of a plurality of subframe periods included in one frame period based on each image data. The gradation is formed in the pixel by controlling application of the low second voltage.

  In addition, when black is inserted, the first frame image data is the ODD frame and the second frame image data is the EVEN frame, and the processing described in the first embodiment is performed. It is possible to apply.

303 Liquid crystal driver (liquid crystal driving device)
411 double speed circuit (image data generating means)
412 VT gamma circuit (image data generating means)
413 Correction circuit (image data generation means)
415 PWM circuit (drive means)

Claims (13)

A liquid crystal driving device for driving a liquid crystal element,
Image data generating means for generating the first frame image data and the second frame image data for each of the input frame image data that are continuously input;
Based on each of the first frame image data and the second frame image data, sequentially applying a first voltage to the pixels of the liquid crystal element in each of a plurality of subframe periods included in one frame period; Drive means for controlling the application of a second voltage lower than the first voltage to form a gradation in the pixel;
The liquid crystal drive characterized in that the image data generation means adds a value corresponding to a gradation of the input frame image to at least one of the first frame image data and the second frame image data. apparatus. The image data generating means
Gamma correction means for performing gamma correction on each of the first frame image data and the second frame image data according to a predetermined gamma table;
Adding means for adding the value corresponding to the gradation of the input frame image to at least one of the first frame image data and the second frame image data after the gamma correction; The liquid crystal driving device according to claim 1, wherein the liquid crystal driving device is a liquid crystal driving device. The image data generation means includes gamma correction means for performing gamma correction on each of the first frame image data and the second frame image data according to a gamma table,
The gamma correction unit corrects the gamma table in accordance with the gradation of the input frame image, thereby correcting the input with respect to at least one of the first frame image data and the second frame image data. The liquid crystal driving device according to claim 1, wherein the value corresponding to the gradation of the frame image is added.   The image data generating means adds the value corresponding to the gradation of the input frame image to one of the first frame image data and the second frame image data. The liquid crystal drive device according to any one of claims 1 to 3. The image data generation means, as the value according to the gradation of the input frame image,
When the first value is added to the first frame image data, the first value is subtracted from the second frame image data;
4. The method according to claim 1, wherein when a second value is added to the second frame image data, the second value is subtracted from the first frame image data. 5. Liquid crystal drive device.   6. The liquid crystal driving device according to claim 1, wherein the image data generation unit changes an addition value as the value in accordance with the gradation of the input frame image.   The image data generation unit changes the addition value according to the length of the subframe period in which a voltage is applied differently to form two adjacent gradations. 7. A liquid crystal drive device according to 6.   The liquid crystal driving device according to claim 6, wherein the image data generation unit changes a gradation range to which the addition value is applied according to the gradation of the frame image data.   The image data generation unit changes the gradation range according to the length of the subframe period in which a voltage is applied differently to form two adjacent gradations. Item 9. A liquid crystal driving device according to Item 8. The image data generating means further includes a first low gradation frame image data having a gradation lower than that of the first frame image data, and a second having a gradation lower than that of the second frame image data. Generate low gradation frame image data,
The driving means is based on each of the first frame image data, the first low gradation frame image data, the second frame image data, and the second low gradation frame image data. Sequentially, in each of the plurality of sub-frame periods included in one frame period, the application of the first voltage and the application of the second voltage to the pixel of the liquid crystal element is controlled to the pixel. The liquid crystal driving device according to claim 1, wherein a tone is formed. A liquid crystal driving device for driving a liquid crystal element,
Image data generating means for generating the first frame image data and the second frame image data for each of the input frame image data that are continuously input;
Based on each of the first frame image data and the second frame image data, sequentially applying a first voltage to the pixels of the liquid crystal element in each of a plurality of subframe periods included in one frame period; Drive means for controlling the application of a second voltage lower than the first voltage to form a gradation in the pixel;
The image data generation means performs gamma correction on each of the first frame image data and the second frame image data according to a predetermined gamma table corrected according to the gradation of the input frame image data. A liquid crystal driving device characterized in that: A liquid crystal element;
An image display device comprising: the liquid crystal driving device according to claim 1. A program for causing a computer to drive a liquid crystal element,
Generating first frame image data and second frame image data for each of continuously inputted input frame image data;
Based on each of the first frame image data and the second frame image data, sequentially applying a first voltage to the pixels of the liquid crystal element in each of a plurality of subframe periods included in one frame period; Causing the computer to execute gradation of the pixel by controlling application of a second voltage lower than the first voltage; and
The step of generating the first frame image data and the second frame image data includes: gradation of the input frame image with respect to at least one of the first frame image data and the second frame image data. A program characterized by including a step of adding a value according to.