JP6316252B2 - Liquid crystal drive device, image display device, and liquid crystal drive 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.

  Liquid crystal elements include transmissive liquid crystal elements such as TN (Twisted Nematic) elements and reflective liquid crystal elements such as VAN (Vertical Alignment Nematic) elements. 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. 17 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. 18 shows all gradation data corresponding to the subframe division example shown in FIG. 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. 19 shows an image of brightness reduction due to disclination. The vertical direction indicates the gradation, and the shading indicates the brightness of the display. 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.

JP2013-050681A

  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. 20 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.

  The present invention provides a liquid crystal driving device and an image display device using the liquid crystal driving device, which can reduce the deterioration of image quality such as dark lines due to disclination.

A liquid crystal driving device according to one aspect of the present invention drives a liquid crystal element. The apparatus includes: image data generating means for generating first frame image data and second frame image data for each piece of input frame image data continuously input; and first and second frame image data. Based on each, sequentially controlling the application of the first voltage to the pixels of the liquid crystal element and the application of the second voltage lower than the first voltage in each of a plurality of subframe periods included in one frame period. And driving means for forming gradations in the pixel. The image data generating means generates the first frame image data by applying a first gain to the input frame image data, and the second different from the first gain for the input frame image data. The second frame image data is generated by applying a gain, and the difference between the first gain and the second gain is 20% or less of the higher one of the first and second gains. Features.

  Note that an image display device having the liquid crystal driving device and the liquid crystal element also constitutes another aspect of the present invention.

A liquid crystal drive program according to another aspect of the present invention is a computer program that causes a computer to drive a liquid crystal element based on an input image. The program causes a computer to generate first frame image data and second frame image data for each input frame image data that is continuously input, and to each of the first and second frame image data. And sequentially controlling the application of the first voltage to the pixels of the liquid crystal element and the application of the second voltage lower than the first voltage in each of a plurality of subframe periods included in one frame period. A gradation is formed on a pixel. In the step of generating image data, first frame image data is generated by applying a first gain to the input frame image data, and different from the first gain for the input frame image data. The second frame image data is generated by multiplying the gain of 2, and the difference between the first gain and the second gain is 20% or less of the higher one of the first and second gains. It is characterized by that.

  According to the present invention, it is possible to reduce deterioration in image quality due to disclination by shifting the occurrence position of disclination when driving the liquid crystal element based on each of the first and second frame image data. it can.

1 is a diagram illustrating an optical configuration of a liquid crystal projector that is Embodiment 1 of the present invention. FIG. FIG. 3 is a cross-sectional view of a liquid crystal element used in the projector according to the first embodiment. FIG. 3 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 according to the first embodiment. FIG. 4 is a diagram illustrating all gradation data in the first embodiment. FIG. 3 is a diagram showing pixel lines in Embodiment 1. 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. FIG. 6 is a diagram illustrating a response characteristic of brightness when switching from all white display to black and white display in the first embodiment. 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. The figure showing the response characteristic of the brightness at the time of switching from the whole black of Example 1 to monochrome display FIG. 3 is a block diagram illustrating a configuration of a liquid crystal driver according to the first embodiment. FIG. 6 is a diagram illustrating ODD and EVEN output frame data according to the first embodiment. The figure which shows the ODD and EVEN output frame data in Example 2 of this invention. FIG. 3 is a diagram illustrating frame images sequentially displayed on the liquid crystal element in the first embodiment. FIG. 6 is another diagram showing frame images sequentially displayed on the liquid crystal elements in the first embodiment. FIG. 10 is a diagram illustrating frame images sequentially displayed on the liquid crystal element in the second embodiment. The figure which shows the several sub-frame period in 1 frame period in the past. The figure which shows the conventional all gradation data. The figure which shows the disclination at the time of driving a liquid crystal element according to the gradation data of FIG. The figure which shows all the gradation data of patent document 1. FIG.

  Embodiments of the present invention will be described below 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 that acquires an input video signal (input image) from an external device (not shown), and a floor that will be described later according to the gradation (input gradation) of the input video signal. And a driving circuit unit (driving unit) 303b that generates a pixel driving signal corresponding to the tone data. 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 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 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, and enters the polarization beam splitter 308 to enter the polarization separation film. Is reflected toward 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 the first voltage (predetermined voltage) and application of the 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 liquid crystal driving program as a computer 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. Has been placed. 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 of FIG. 20, the B subframe period continues as a unit after the A subframe period, but 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 gradations and 49 gradations, in FIG. 20, 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 a liquid crystal element relative to the input gradation shows the response characteristics when changing the gradation while displaying the same gradation on the entire surface of the liquid crystal element where no disclination occurs. Created as a premise. 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, the gamma curve (gamma characteristic) that determines the drive gradation of the liquid crystal element relative to the input gradation generally changes the gradation while displaying the same gradation on the entire surface of the liquid crystal element where no disclination occurs. It is created on the assumption of the response characteristics when 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 horizontal axis represents elapsed time from the switching time point, and the vertical axis represents the integral value of the total brightness of the pixels of the A and B pixel line (hereinafter, simply referred to as brightness, a ratio of time taken as 1 a all white display state Show). 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 based on 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. 20 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 shows 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, 3B shown in FIG. 1). A pixel drive signal for displaying a tone is generated. The drive circuit unit 303b includes a double speed circuit 411, a gain circuit 412, a VTγ 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 frame 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 referred to as ODD (odd number) input frame data, and the other is referred to as EVEN (even number) input frame data. 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 gain circuit 412 multiplies the ODD input frame data and the EVEN input frame data from the double speed circuit 411 (multiplies the gain coefficient). As a result, ODD output frame data as first frame image data and EVEN output frame data as second frame image data are generated. The gain circuit 412 can make gains applied to ODD and EVEN input frame data different from each other. The double speed circuit 411 and the gain circuit 412 constitute image data generating means.

  The VTγ circuit 413 performs γ correction on the ODD and EVEN output frame data from the gain circuit 412 so that necessary optical characteristics can be obtained in accordance with gradation characteristics that change depending on the response characteristics of the liquid crystal of the liquid crystal element 3. .

  The color unevenness circuit 414 corrects color unevenness generated in the optical system of the projector including the liquid crystal panel 3 for the ODD and EVEN output frame data after the γ correction from the VTγ circuit 413.

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 from the color unevenness correction circuit 414 .

  Next, the operation of the gain circuit 412 will be specifically described. For example, a case where 48 gradations and 49 gradations adjacent to each other in the liquid crystal element 3 are displayed will be described. In each of the ODD and EVEN input frame data input to the gain circuit 412, pixel data of two adjacent pixel positions corresponding to the adjacent pixels (that is, adjacent pixel positions corresponding to each other between the ODD and EVEN input frame data) is 48. And 49 gradations. In the following description, the pixel data at the adjacent pixel position in each of the ODD and EVEN input / output frame data is referred to as adjacent pixel data.

  The gain circuit 412 multiplies the ODD and EVEN input frame data from the double speed circuit 411 with different gains to generate ODD and EVEN output frame data. FIG. 12A shows an example in which the ODD output frame data (1st) is generated by setting the first gain to be applied to the ODD input frame data to 1.0 (100%). In this example, the EVEN output frame data is generated by multiplying the second gain applied to the EVEN input frame data by 0.9 (90%). As a result, the gradation of adjacent pixel data in the ODD output frame data (1st) output from the gain circuit 412 is 48 and 49. On the other hand, the gradation of the adjacent pixel data in the EVEN output frame data (2nd) output from the gain circuit 412 is 43 and 44 (the decimal part is rounded off).

  The gain circuit 412 sums the first and second gains (100% + 90) applied to the ODD and EVEN input frame data generated by the double speed circuit 411 for each of the input frame image data that are continuously input. % = 190%) are the same.

  FIG. 14A shows a display image (projected image by the projector) when the liquid crystal element 3 is sequentially driven by the ODD output frame data and the EVEN output frame data generated without applying different gains by the gain circuit 412. Show. In the figure, a display image when the liquid crystal element 3 is driven by ODD output frame data is shown as a 1st frame, and a display image when the liquid crystal element 3 is driven by EVEN output frame data is shown as a 2nd frame. N is the frame number of the input frame image data. N: 1st and N: 2nd indicate the 1st frame and 2nd frame corresponding to the ODD output frame data and the EVEN output frame data generated for the input frame image data of N frames. FIG. 14C shows a display image that should be originally displayed.

  In FIG. 14A, both ODD and EVEN output frame data have 0 to 64 gradations from the upper end to the lower end. The rightmost side of the figure shows an image visually recognized by an observer who observes the 1st and 2nd frames continuously. In this case, the pixel data at all pixel positions corresponding to each other in the ODD and EVEN output frame data have the same gradation. For this reason, the 1st frame and the 2nd frame are the same image. As a result, in both the 1st and 2nd frames, dark lines due to disclination appear at positions such as 16-17 gradation, 32-33 gradation, and 48-49 gradation. In the figure, dark lines are shown dark for the sake of clarity, but since the liquid crystal element 3 is actually driven by the first driving method described above, only dark lines appear. However, the observer can visually recognize it as a dark line.

  FIG. 14B shows a 1st frame that is a display image when the liquid crystal element 3 is sequentially driven by the ODD output frame data and the EVEN output frame data generated by applying different gains by the gain circuit 412. 2nd frame is shown. The ODD output frame data has 0 to 64 gradations corresponding to a gain of 100% from the upper end to the lower end. On the other hand, the EVEN output frame data has 0 to 58 gradations corresponding to a gain of 90% from the upper end to the lower end. As a result, 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 different (shifted) from each other. For example, the position of the dark line (48-49 gradation position) a on the 1st frame is shifted from the position b of the dark line on the 2nd frame. Therefore, in the image visually recognized by the observer shown on the rightmost side of the figure, the dark line becomes approximately ½ dark by averaging the 1st frame and the 2nd frame. As a result, dark lines can be made less noticeable than when only the liquid crystal element 3 is driven by the first driving method.

FIGS. 15A and 15B show examples of specific display 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 ODD and EVEN output frame data generated without applying different gains by the gain circuit 412. Further, the rightmost side of the figure shows the image to be viewed by an observer. 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 a case where the liquid crystal element 3 is sequentially driven by ODD and EVEN output frame data generated by applying different gains (100% and 90%) by the gain circuit 412. 1st frame and 2nd frame are shown. 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 the second driving method described above, ODD and EVEN output frame data are generated so that pixel data at pixel positions corresponding to each other have different gradations, and the liquid crystal element 3 is formed by the ODD and EVEN output frame data. To drive. Thereby, the position of the dark line in the 1st and 2nd frames displayed can be shifted from each other, and the dark line can be made inconspicuous in the visually recognized image.

  Here, in the ODD and EVEN output frame data, the difference between the gradations of the pixel data at the pixel positions corresponding to each other is desirably 20% or less of the higher gradation among these gradations. . In other words, the difference between the first and second gains applied to each of the ODD and EVEN input frame data is desirably 20% or less of the higher one of the first and second gains. If the difference between gradations or the difference between the first and second gains exceeds 20%, the change in brightness between the 1st frame and the 2nd frame is noticeable as flicker, which is not preferable. The difference between the gradations is preferably 1% or more of the higher gradation among these gradations. In other words, the difference between the first and second gains is desirably 1% or more of the higher one of the first and second gains. If it is less than 1%, the positions of the dark lines in the 1st and 2nd frames are hardly shifted, and the effect of making the dark lines not sufficiently conspicuous cannot be obtained.

In the present embodiment, the case where two frame image data is generated at a period corresponding to 120 Hz with respect to input frame image data input at 60 Hz has been described. However, four frame images are generated at a period corresponding to 240 Hz. Data may be generated. In this case, two sets of ODD and EVEN input frame data are generated. For example, as shown in FIG 12 (B), ODD output frame by multiplying each of 100% and a gain of 90% gain for a pair in the ODD input frame data (1st) and EVEN input frame data (2nd) that generates the data (1st) and EVEN output frame data (2nd). Furthermore, ODD output frame data (3rd) and EVEN output frame data (3rd) and EVEN output frame data ( 3th) and EVEN input frame data (4th) are multiplied by 100% gain and 90% gain, respectively. 4th) that generates a. Thus, the same effect as in FIG. 1 4 (B) and FIG. 1 5 (B) is obtained.
In addition, when the first and second frame image data are generated at a period corresponding to 120 Hz, two first frame image data for two input frame image data in which the second frame image data is continuous are used. It may be intermediate image data generated by interpolation or the like. At this time, the second frame image data may include a region (region with motion) different from the first frame image data, and the first and second frame image data may not be the same image data. However, even in this case, if the pixel data at the corresponding pixel positions in the stationary region of the first and second frame image data have the same gradation, the second drive is performed for the region. The method can be applied.

  Next, a second embodiment of the present invention will be described. In the present embodiment, the same reference numerals as those in the first embodiment are assigned to components common to the first embodiment.

  In the first embodiment, as a second driving method, a gain of 100% is applied to ODD input frame data generated for all input frame image data that are continuously input, and EVEN input frame data is applied to EVEN input frame data. The case where a gain of 90% is applied has been described. In contrast, in this embodiment, the gain applied to the ODD and EVEN input frame data is changed for each input frame image data (for each frame).

FIG. 13A shows an example of gain that the gain circuit 412 applies to these ODD and EVEN input frame data when the ODD input frame data and the EVEN input frame data are generated at a period corresponding to 120 Hz. In this example, the gain circuit 412 multiplies the N-frame ODD input frame data (1st) by 100% gain (first gain ) to generate ODD output frame data (1st), and generates an EVEN input frame. for data (2nd) that generates an EVEN output frame data (2nd) over 90% of the gain (second gain). Thereby, when the gradation of the adjacent pixel data in the NDD ODD output frame data (1st) output from the gain circuit 412 is 48 and 49, the adjacent pixel data in the EVEN output frame data (2nd) The gradation is 43 and 44 (rounded off after the decimal point). This is the same for the N + 2 frame.

The gain circuit 412 multiplies the N + 1 frame ODD input frame data (1st) by a gain of 97.5% (first gain ) to generate ODD output frame data (1st), and the EVEN input frame that generates an EVEN output frame data (2nd) over 92.5% of the gain (second gain) for the data (2nd). Accordingly, the gradation of adjacent pixel data in the ODD output frame data (1st) output from the gain circuit 412 is 47 and 48, and the gradation of adjacent pixel data in the EVEN output frame data (2nd) is 44 and 45. It becomes. The same is true for N + 3 frames.

Also in this embodiment, the gain circuit 412 adds the first and second gains to be applied to the ODD and EVEN input frame data generated by the double speed circuit 411 for each of the input frame image data that are continuously input. Are the same as each other. That is,
Sum of first and second gains in N frame and N + 2 frame = 100% (1st) + 90% (2nd) = 190%
Sum of first and second gains in N + 1 frame and N + 3 frame = 97.5% (1st) + 92.5% (2nd) = 190%
Set each gain so that.

FIG. 16A shows a display image (projected image by the projector) when the liquid crystal element 3 is sequentially driven by the ODD and EVEN output frame data generated without applying different gains by the gain circuit 412. In the figure, a display image when the liquid crystal element 3 is driven by ODD output frame data is shown as a 1st frame, and a display image when the liquid crystal element 3 is driven by EVEN output frame data is shown as a 2nd frame. N is the frame number of the input frame image data, and N: 1st and N: 2nd are the 1st frame and 2nd frame corresponding to the ODD output frame data and EVEN output frame data generated for the N frame input frame image data. Indicates that FIG. 16C shows a display image that should be originally displayed.

In FIG. 16A, both ODD and EVEN output frame data have 0 to 64 gradations from the upper end to the lower end. The rightmost side of the figure shows an image visually recognized by an observer who observes the 1st and 2nd frames continuously. In this case, since the pixel data of all the pixel positions corresponding to each other between the ODD and EVEN output frame data have the same gradation, the 1st frame and the 2nd frame are the same image. As a result, in both the 1st and 2nd frames, dark lines due to disclination appear at positions such as 16-17 gradation, 32-33 gradation, and 48-49 gradation. In the figure, dark lines are shown dark for the sake of clarity, but since the liquid crystal element 3 is actually driven by the first driving method described above, only dark lines appear. However, the observer can visually recognize it as a dark line.

The FIG. 16 (B), the different gains from each other by the gain circuit 412 (100%, 90%, 97.5%, 92.5%) of the liquid crystal element 3 by ODD and EVEN output frame data generated are putting 1st and 2nd frames, which are display images when sequentially driven, are shown. In the N frame, the ODD output frame data has 0 to 64 gradations corresponding to a gain of 100% from the upper end to the lower end. On the other hand, the EVEN output frame data has 0 to 58 gradations corresponding to a gain of 90% from the upper end to the lower end. As a result, 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 different (shifted) from each other. For example, the position of the dark line (48-49 gradation position) a on the 1st frame and the position b of the dark line on the 2nd frame are shifted.

  Further, in the N + 1 frame, the ODD output frame data has 0 to 62 gradations corresponding to a gain of 97.5% from the upper end to the lower end. On the other hand, the EVEN output frame data has 0 to 59 gradations corresponding to a gain of 92.5% from the upper end to the lower end. As a result, 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 different (shifted) from each other. For example, the position of the dark line (48-49 gradation position) c on the 1st frame is shifted from the position d of the dark line on the 2nd frame. These positions c and d are also deviated from the positions a and b.

  Therefore, in the image visually recognized by the observer shown on the rightmost side of the figure, the dark line becomes approximately ¼ by averaging the 1st frame and the 2nd frame. As a result, dark lines can be made less noticeable than when the liquid crystal element 3 is only driven by the first driving method described above (and compared with the first embodiment).

In the present embodiment, the case where two frame image data is generated at a period corresponding to 120 Hz has been described, but four frame image data may be generated at a period corresponding to 240 Hz. In this case, two sets of ODD input frame data and EVEN input frame data are generated. For example, as shown in FIG. 13B, ODD output frame data (1st) and EVEN output frame data are obtained by multiplying the first set of ODD input frame data and EVEN input frame data by a gain of 100% and a gain of 90%, respectively. (2nd) is generated. Furthermore, ODD output frame data (3rd) and EVEN output frame data (4rt) are generated by multiplying the second set of ODD input frame data and EVEN input frame data by gain 97.5% and gain 92.5%, respectively. Is done. Thus, an example equivalent effects shown in FIG. 1 6 (B) is obtained.

Also in this embodiment, the difference between the gradations of the pixel data at the pixel positions corresponding to each other in the ODD and EVEN output frame data is 1% to 20% of the higher gradation of these gradations.
(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.

  Each embodiment described above is only a representative example, and various modifications and changes can be made to each embodiment in carrying out the present invention.

303 Liquid crystal drivers 3G, 3R, 3B Reflective liquid crystal elements 1SF to 10SF Subframe period 411 Double speed circuit 412 Gain circuit

Claims (7)

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 and second frame image data, the application of the first voltage to the pixels of the liquid crystal element in each of a plurality of subframe periods included in one frame period, and the first voltage Driving means for controlling the application of the low second voltage to form a gradation in the pixel;
The image data generating means generates a first frame image data by applying a first gain to the input frame image data, and a first gain different from the first gain for the input frame image data. The second frame image data is generated by multiplying the gain of 2, and the difference between the first gain and the second gain is 20% or less of the higher one of the first and second gains. A liquid crystal driving device characterized by the above. Difference between the first and second gain, the liquid crystal driving device according to claim 1, wherein said at higher gains 1% or more of. The image data generation means generates the first and second frame image data from each of the input frame image data continuously input so that the sum of the first and second gains is the same. the liquid crystal driving device according to claim 1 or 2, characterized in that. The subframe period in which the first voltage is applied to the pixel is an on period, and the subframe period in which the second voltage is applied is an off period. When the sub-frame period that is the on period for the first pixel and the off period for the second pixel among the two pixels is the on / off adjacent period,
The image data generation means is configured to turn on / off the first and second pixels when the liquid crystal element is driven based on one of the first and second frame image data. When the liquid crystal element is driven based on the other frame image data when the off-adjacent period occurs, the first / second adjacent period does not occur for the first and second pixels. liquid crystal driving device according to any one of claims 1, wherein a gain to give a difference between the second gain 3. The image data generating means includes a position where a disclination occurs in the liquid crystal element when the liquid crystal element is driven based on the first frame image data, and the liquid crystal based on the second frame image data. element is the different position of disclination occurs each other so when driven, any of claims 1 to 4, characterized in that to provide the difference between the second gain and the first gain A liquid crystal driving device according to claim 1. A liquid crystal element;
The image display apparatus characterized by having a liquid crystal driving device according to any one of claims 1 to 5. A computer program for causing a computer to drive a liquid crystal element,
In the computer,
Generating first frame image data and second frame image data for each of continuously input frame image data,
Based on each of the first and second frame image data, the application of the first voltage to the pixels of the liquid crystal element in each of a plurality of subframe periods included in one frame period, and the first voltage By controlling the application of a low second voltage, a gradation is formed in the pixel,
The step of generating the image data includes generating first frame image data by applying a first gain to the input frame image data, and what is the first gain for the input frame image data? A second frame image data is generated by applying a different second gain, and the difference between the first gain and the second gain is 20 of the higher one of the first and second gains . % Or less liquid crystal drive program.