JP2008299270A - Driving device for display device, and electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving device for display device displaying images of high display quality by reducing flicker and pattern noise and increasing the number of gradation when superposing two or more transmission type display panels. <P>SOLUTION: This driving device for display device superposing two or more transmission type display panels of n(m>n) bit gradation to which image data of m-bits is input, comprises a panel control means for outputting image data included in an input image source, to the two transmission type display panels as image data selecting a combination of gradation values to minimize the luminance difference between pixels composing a luminance pattern displayed through the at least two transmission type display panels out of the respective transmission type display panels. The number of gradation is thereby increased, and flicker and pattern noise can be reduced. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a drive device for a display device in which two or more transmissive display panels are stacked.

  In a display device having a large number of pixels arranged in a matrix, for example, the number of gradations of an input image signal is 1024 gradations (10-bit gradations), and the display device has up to 64 gradations (6-bit gradations) for each pixel. If there is only a display capability, it is necessary to perform image processing called multi-gradation that expresses many gradations with a small number of gradations so that the human eye can see a fine gradation difference of 1024 gradations. Become.

  The conventional multi-gradation method uses a pixel size of a display device to develop a two-dimensional space pattern with an arbitrary gradation value using a plurality of pixels as one group unit, and the area of the developed pattern. A dither method or error diffusion method that expresses a gradation with an average density, or a time integration effect of human vision, a plurality of display frames are set as one repetition period, and each pixel is arbitrarily set. A method by PWM (pulse width modulation) driving using a temporal ON / OFF pattern between gradations is generally known.

  However, the dither method or the error diffusion method has a drawback that a moire or a noise pattern can be seen by an image signal.

  Further, the PWM driving method has a drawback that flicker occurs because the display pattern is a blinking pattern.

  Therefore, as a technique for overcoming these drawbacks, for example, as disclosed in Patent Documents 1, 2, and 3, FRC (frame rate control) that compensates for noise and flicker by combining a spatial pattern and a temporal pattern is used. A method has been proposed.

  On the other hand, in recent liquid crystal TVs, color display is generally performed with a gradation number of 6 bits or more, and the screen is increased in size and the pixel size is increased. In such a situation, when FRC is used, the pattern itself such as the space pattern and the time pattern can be seen, or interference noise generated by the interference between the image and the pattern can be easily seen. There were drawbacks.

  In addition, in the liquid crystal, the applied voltage for alternating current changes alternately between positive polarity and negative polarity, but there is a slight luminance difference due to the difference in polarity, and this luminance difference and the pattern described above are There was a drawback that noise was generated by interference.

  Therefore, Patent Document 4 solves this problem by performing FRC that devised the space pattern and the time pattern.

As another multi-gradation method, the prior art document 5 has a structure in which two liquid crystal panels are overlapped to display a high gradation number equal to the product of the display gradation numbers of each panel.
JP 2-79092 (published March 19, 1990) JP 2-81091 (published March 22, 1990) JP 3-20780 (published January 29, 1991) JP2005-10520 (released on January 13, 2005) JP 5-88197 (published April 19, 1993) “Basics of Display” Kyoritsu Publishing December 2001 96-97

  However, in the multi-gradation using the FRC method as described in Patent Document 4, there is a pixel pattern when viewed in units of one frame, so interference noise occurs in a video pattern (killer pattern) that emphasizes the pattern. Resulting in. In addition, the moving image has a drawback in that image quality deteriorates due to generation of pattern-like noise and flicker in an image with gradation changes that overlap such that the patterns of the preceding and following frames are emphasized.

  Further, Patent Document 5 that discloses another multi-gradation method has the following problems.

  Since the gradation level of the liquid crystal is proportional to the transmittance, the gradation level when two liquid crystal panels are stacked is proportional to the transmittance obtained by multiplying the transmittance of the front panel and the transmittance of the rear panel. For example, when the transmittances of the front and rear panels are 1/2 and 1/3 and 1/3 and 1/2, respectively, the same transmittance is 1/6 as a result. That is, in order to express one gradation recognized on the display surface, there are a plurality of combinations of gradation levels input to the front and rear panels, and there is no one-to-one correspondence. As a result, even if two 256-level liquid crystal panels are overlapped and each controlled in gradation, it is possible to express up to a high gradation number equal to the product of the display gradation numbers of each panel, such as 256 * 256 = 65536 gradations. Can not.

  For example, in FIG. 7, for the sake of simplicity, when the gradation is assigned to two gradations of 0 and 1, and the transmittance of each gradation is assigned to 0 and 100%, the transmittance when the two panels are overlapped with each other is shown. It is the table | surface calculated | required by multiplying the transmittance | permeability of this panel. As can be seen from this table, when one transmittance value is counted as one gradation, it is not 2 * 2 = 4 gradations, and the number of gradations that can be expressed is smaller.

  Therefore, the technique disclosed in Patent Document 5 has a problem that the number of gradations does not increase as expected.

  The present invention has been made in view of the above problems, and its purpose is to reduce flicker and pattern noise and increase the number of gradations when two or more transmissive display panels are overlapped. Thus, an object of the present invention is to provide a drive device for a display device that can display an image with high display quality.

  In order to solve the above-described problem, a display device driving device according to the present invention is a display device in which m-bit video data is input and two or more transmissive display panels of n (m> n) bit gradation are stacked. To express the gradation of the input video data, the luminance pattern displayed through each of the transmissive display panels is formed, and the luminance between the pixels constituting the luminance pattern A panel control unit is provided that generates a combination of gradation values to be output to each transmissive panel so as to minimize the difference and outputs the combination to each transmissive display panel.

  According to the above configuration, the number of gradations can be increased by stacking two or more transmissive display panels as compared with a single transmissive display panel.

  In addition, in order to express the gradation of the input video data by the panel control means, a luminance pattern that is transmitted through each of the transmissive display panels is configured, and the luminance difference between the pixels constituting the luminance pattern is minimized. By generating a combination of gradation values to be output to each transmissive panel so as to be output to each transmissive display panel, flicker and noise caused by a luminance difference between pixels can be reduced. .

  The panel control means preferably controls the dither pattern of at least two of the transmissive display panels to be different from each other.

  According to the above configuration, all of the transmissive display devices are controlled by the panel control means so that at least two transmissive display panels among the transmissive display panels stacked two or more have different dither patterns. The number of gradations can be increased when the dither pattern of the panel is the same.

  In addition, by combining the dither patterns of at least two transmissive display panels as much as possible, a combination of gradation values that minimizes the luminance difference between the pixels constituting the luminance pattern displayed through the transmissive display panel. As a result, the display quality can be further improved.

  As a specific configuration of the panel control means, a distributor for distributing the video data included in the input video source signal to the number of transmissive display panels, and the number of video data distributed by the distributor are provided, A pattern generation circuit that generates a dither pattern of the video data output from the distributor and outputs the dither pattern to the corresponding transmissive display panel is included.

  Further, the specific configuration of the pattern generation circuit is provided for each color component of the video data included in the input video source signal, and the input video data is divided into gradations smaller than the number of gradation bits of the input video data. A data conversion unit for converting the output video data to the number of bits, a dither pattern generator for generating a dither pattern to be supplied to the data conversion unit, and timing control for timing the generation of the dither pattern in the dither pattern generator Part.

  The data converter separates the input video data of m-bit gradation into lower (mn) bits and outputs the data to the dither pattern generator; and the input video data of m-bit gradation A candidate generation unit that originally acquires and generates two n-bit gradation candidates from an LUT that incorporates two n-bit gradation candidates, and two n-bit gradation candidates supplied from the candidate generation unit, and selects n bits The dither pattern generator is based on lower order (mn) bit data supplied from the data separation unit and a timing signal from the timing control unit. 1-bit pattern data is generated and output to the selection unit, which selects two n-bit gradations from the 1-bit pattern from the dither pattern generator. It is preferable to select one of the candidates.

  With these configurations, the number of gradations can be increased as compared with a display device configured with a single transmissive display panel, and flicker and noise are significantly greater than when a conventional multi-gradation technology is applied. Therefore, the display quality can be made extremely high.

  Moreover, it is preferable that the drive device for the display device having the above-described structure is provided in an electronic device including the display device.

  In particular, flicker and noise become conspicuous when the size of each pixel increases due to the recent increase in the size of the display panel. Therefore, the present invention is suitable as a driving device for a large-sized display device.

  The display device drive device of the present invention is a drive device that receives m-bit video data and outputs it to a display device in which two or more transmissive display panels of n (m> n) bit gradation are stacked. In order to express the gradation of the input video data, a luminance pattern that is transmitted through each of the transmissive display panels is configured, and the luminance difference between pixels that configure the luminance pattern is minimized. Panel control means for generating a combination of gradation values to be output to the transmissive panel and outputting the combination to each transmissive display panel is provided. Thereby, by superposing two or more transmissive display panels, the number of gradations can be increased as compared with the case of one transmissive display panel, and the video data included in the input video source by the panel control means. Select a combination of gradation values so that the luminance difference between the pixels constituting the luminance pattern transmitted through at least two of the transmissive display panels is minimized. By outputting the processed video data to the at least two transmissive display panels, flicker and noise caused by the luminance difference between pixels can be reduced, so that the display quality can be very high. There is an effect that can be done.

  An embodiment of the present invention will be described as follows. Note that in this embodiment, a liquid crystal display device in which two transmissive liquid crystal panels are stacked is described as a transmissive display panel.

  The liquid crystal display device according to this embodiment will be described below.

  FIG. 3 is a schematic configuration diagram of the liquid crystal display device, and FIG. 4 is a schematic configuration cross-sectional view of the liquid crystal display device.

  In the liquid crystal display device according to the present embodiment, as shown in FIG. 3, a second liquid crystal panel is installed between the first liquid crystal panel and the backlight unit, and the first liquid crystal panel is formed by the second liquid crystal panel. The amount of light that illuminates the light is controlled to prevent light leakage of the liquid crystal panel in dark areas.

  As the second liquid crystal panel, a liquid crystal panel for monochrome display (without a color filter) is used. This is because the pixel shift due to parallax occurs. For example, when the red pixel of the second liquid crystal panel appears to overlap the blue pixel of the first liquid crystal panel when viewed from an oblique direction, the blue color filter is Because it does not pass red light, it will always be black. In addition, since there is no color filter, the light transmittance in the second liquid crystal panel is not impaired.

  The structure of the liquid crystal display device will be described in detail.

  As shown in FIG. 4, the liquid crystal display device includes a first liquid crystal panel and a second liquid crystal panel, and a polarizing plate A, a first liquid crystal panel, and a second liquid crystal panel are provided on the outermost surface side of the first liquid crystal panel. The polarizing plate B and the polarizing plate C are disposed on the backlight unit side of the second liquid crystal panel. The polarizing plates A and B and the polarizing plates B and C are arranged so that their polarization axes are orthogonal to each other. That is, the polarizing plates A and B and the polarizing plates B and C are arranged in crossed Nicols.

  Each of the first liquid crystal panel and the second liquid crystal panel is formed by enclosing liquid crystal between a pair of transparent substrates 1 and electrically changing the orientation of the liquid crystal to thereby make polarized light incident on the polarizing plate from the light source. Is provided with means for arbitrarily changing the state in which the light is rotated about 90 degrees, the state in which the polarization is not rotated, and the intermediate state thereof.

  The first and second liquid crystal panels have a function of displaying an image with a plurality of pixels. The display system having such a function includes a TN (TwistedNematic) system, a VA (Vertical Alignment) system, an IPS (InPlain Switching) system, an FFS system (Fringe Field Switching) system, or a combination of these methods. The VA method having the above is suitable and will be described here using the MVA (Multidomain Vertical Alignment) method. However, since the IPS method and the FFS method are also normally black methods, there are sufficient effects. The drive system uses active matrix drive by TFT (ThinFilmTransistor). Details of the MVA manufacturing method are disclosed in Japanese Published Patent Publication (JP-A-2001-83523).

  The first and second liquid crystal panels in the liquid crystal display device have the same structure, and both have a structure in which a liquid crystal layer is sandwiched between the counter substrate 10 and the active matrix substrate 11.

  However, in the liquid crystal display device according to the present embodiment, the color filter 2 (2a to 2c) is provided on the counter substrate 10 only in the first liquid crystal panel. As the liquid crystal, nematic liquid crystal having negative dielectric anisotropy is used.

  The counter substrate 10 of the first liquid crystal panel is obtained by forming a color filter 2, a black matrix 8, and a counter electrode 3 on a transparent substrate 1.

  On the other hand, the counter substrate 10 of the second liquid crystal panel is obtained by forming the black matrix 8 and the counter electrode 3 on the transparent substrate 1.

  The active matrix substrate 11 is obtained by forming the TFT 6, the signal wiring 5, the interlayer insulating film 7, and the pixel electrode 4 on the transparent substrate 1, and has the same configuration in both the first and second liquid crystal panels. It is.

  It is assumed that the pixel array of the liquid crystal panel has a resolution of horizontal (column) X pixels and vertical (row) Y lines. Since the first liquid crystal panel has a color filter formed on the panel, one pixel is composed of a total of 3 dots, one for each of RGB, and the second liquid crystal panel has no color filter, but corresponds to the first liquid crystal panel. One pixel is composed of a total of 3 dots.

  In addition, it is assumed that 1-dot gradation data of the first and second liquid crystal panels is composed of n bits.

  Here, a drive control system for the liquid crystal display device having the above-described configuration will be described.

  FIG. 1 is a schematic block diagram showing the drive control system.

  As shown in FIG. 1, the drive control system includes a panel control circuit 100 that generates a control signal for driving and controlling the first liquid crystal panel and the second liquid crystal panel from an input video source signal, and the panel control circuit 100. A first driver 200a that generates a drive signal for driving the first liquid crystal panel from the control signal generated by, and a second driver 200b that generates a drive signal for driving the second liquid crystal panel from the control signal. .

  Here, it is assumed that the input video source signal includes a video synchronization signal and video data, and the video data includes “m-bit gradation data”. The liquid crystal panel can display “n-bit gradation data”. In this case, m> n.

  The panel control circuit 100 distributes an input video source to two systems, and distributes a video synchronization signal and video data based on the video source signal to a subsequent circuit for each system, A first timing controller 102a that supplies a signal for driving a timing for driving the first liquid crystal panel based on the synchronization signal supplied from the distributor 101 to the first driver 200a, and is supplied from the distributor 101. A first spatiotemporal pattern generator for generating a spatiotemporal pattern for driving the first liquid crystal panel based on the video synchronizing signal and the video data (m-bit gradation data) to be supplied to the first driver 200a 103a and a signal for timing the drive for driving the second liquid crystal panel based on the synchronization signal supplied from the distributor 101. A space-time pattern for driving the second liquid crystal panel based on the second timing controller 102b supplied to the driver 200b and the synchronization signal and video data (m-bit gradation data) supplied from the distributor 101. A second spatiotemporal pattern generator 103b that generates and supplies the second driver 200b with the second spatiotemporal pattern generator 103b.

  The first driver 200a is connected to the first liquid crystal panel based on the timing signal supplied from the first timing controller 102a and the spatiotemporal pattern information supplied from the first spatiotemporal pattern generator 103a. A drive signal to be supplied is generated.

  In addition, the second driver 200b generates a second liquid crystal based on a timing signal supplied from the second timing controller 102b and the spatiotemporal pattern information supplied from the second spatiotemporal pattern generator 103b. A drive signal to be supplied to the panel is generated.

  That is, the panel control circuit 100 separates the input video signal into two systems through the distributor 101, and the video synchronization signal and the video data are respectively transmitted to the first timing controller 102a and the second timing controller 102b in the subsequent stage, and the first timing controller 102b. This is supplied to the spatiotemporal pattern generator 103a and the second spatiotemporal pattern generator 103b.

  The first timing controller 102a and the first spatiotemporal pattern generator 103a existing in the first system constitute a control circuit for the first liquid crystal panel and exist in the second system. The second timing controller 102b and the second spatiotemporal pattern generator 103b constitute a control circuit for the second liquid crystal panel.

  The first timing controller 102a and the second timing controller 102b generate signals for timing of sequentially lighting each pixel of each liquid crystal panel through the first driver 200a and the second driver 200b.

  The first spatio-temporal pattern generator 103a and the second spatio-temporal pattern generator 103b receive a video synchronization signal and video data (m-bit gray scale data), so that the number of gray scale bits can be reduced. A spatio-temporal pattern down to the number of gradations suitable for the number of key bits (n bits) is generated and output to the first driver 200a and the second driver 200b.

  The first driver 200a and the second driver 200b are circuits that generate drive signals that cause each pixel to display video data having a spatiotemporal pattern on each pixel at the timing of the timing controller.

  As a comparative example for the panel control circuit 100 shown in FIG. 1, FIG. 5 shows a schematic block diagram of the panel control circuit 1100 for a display device having a single liquid crystal panel configuration.

  In the panel control circuit 1100, each of the timing controller 1102 and the spatio-temporal pattern generator 1103 has one each, and outputs a signal from each circuit to the driver 1200 for driving the liquid crystal panel.

  Here, the difference in the configuration of the spatio-temporal pattern generator between the display device having one liquid crystal panel and the display device having two liquid crystal panels will be described below.

  First, a spatiotemporal pattern generator in a display device having a single liquid crystal panel configuration will be described.

  FIG. 6 is a diagram showing a circuit configuration of the spatiotemporal pattern generator 1103 shown in FIG.

  FIG. 6 shows an example in which the gradation bits of the input video data are converted to m bits (bits) and the gradation bits of the output video data are converted to n bits (bits). Any number of bits may be used as long as the number of gradation bits m> the number of gradation bits n of the output video data.

  As shown in FIG. 6, the spatio-temporal pattern generator 1103 converts input video data into output video data having a gradation bit number smaller than the gradation bit number of the input video data for each RGB. The data conversion unit 1300 (r, g, b), the RGB dither pattern generator 1400 that generates an RGB dither pattern to be supplied to the data conversion unit 1300, and the timing of the dither pattern generation in the RGB dither pattern generator 1400 The configuration includes a timing control unit 1500 for illustration.

  In the data conversion unit 1300, the data separation processing unit 1301 separates input video data of m-bit gradation into upper n bits and lower (mn) bits. The upper n bits are input to the addition processing unit 1302. The lower (mn) bits are input to the RGB dither pattern generator 1400. The input synchronization signal is input to the timing control unit 1500. At this time, the timing control unit 1500 outputs to the RGB dither pattern generator 1400 what row and column (y, x) the current pixel corresponds to and what frame (f) in the time pattern.

  The RGB dither pattern generator 1400 extracts a 1-bit pattern from the LUT containing the input information from the timing control unit 1500 and the lower (mn) bit data from the data separation processing unit 1301 as addresses, and performs addition processing. Output to the unit 1302.

  The addition processing unit 1302 adds the upper n bits and the 1-bit pattern and outputs the result to the overflow processing unit 1303.

  When the data added by the addition processing unit 1302 is input, the overflow processing unit 1303 performs processing so as not to exceed the maximum gradation of input bits, and outputs output video data (n bits).

  The above circuit operates in parallel independently for each of RGB.

Accordingly, each RGB video data is output to the output video data as a spatio-temporal pattern having a combination of gradation k and gradation (k + 1) ^where k <(2 ⁿ −1). The exception is when k = (2 ⁿ −1), and the gradation (k + 1) exceeds the range that can be expressed by the n-bit gradation, so that the gradation (k + 1) → gradation k is rounded by the overflow process. Cannot be expressed. However, according to Weber-Fechner's law, which is a generally known visual characteristic (non-patent document: “Basics of Display”, Kyoritsu Shuppan, published December 2001, P. 96-97), brightness sensation Q = αLogL (α is an arbitrary constant) Therefore, the higher the luminance, the more difficult it is to identify the gradation difference, so that fine gradation expression is not necessarily required and there is no problem in video expression.

  Next, a spatio-temporal pattern generator in a display device having two liquid crystal panels will be described.

  FIG. 2 is a diagram showing a circuit configuration of the first spatiotemporal pattern generator 103a and the second spatiotemporal pattern generator 103b shown in FIG. The first spatiotemporal pattern generator 103a and the second spatiotemporal pattern generator 103b have the same circuit configuration.

  In the data conversion unit 300 shown in FIG. 2, the addition processing unit 1302 and the overflow processing unit 1303 in the data conversion unit 1300 shown in FIG. 6 are eliminated, and a candidate generation unit 302 and a selection unit 303 are newly provided.

  Here, as in FIG. 6, an example in which the gradation bits of the input video data (video data output from the distributor 101) are converted to m bits (bits) and the gradation bits of the output video data are converted to n bits (bits). However, any number of bits may be used as long as the number of gradation bits of input video data is greater than the number of gradation bits of output video data.

  As in FIG. 6, the spatiotemporal pattern generator includes a data converter 300 for converting input video data into output video data having a gradation bit number smaller than the gradation bit number of the input video data; A configuration including an RGB dither pattern generator 400 that generates an RGB dither pattern to be supplied to the data converter 300, and a timing controller 500 for timing the generation of the dither pattern in the RGB dither pattern generator 400; It has become.

  In the data converter 300, the data separator 301 separates input video data of m-bit gradation into lower (mn) bits. Further, the input video data of m-bit gradation is also input to the candidate generation unit 302. The lower (mn) bits are input to the RGB dither pattern generator 400. The input synchronization signal is input to the timing control unit 500. At this time, the timing controller 500 outputs to the RGB dither pattern generator 400 what row and column (y, x) the current pixel corresponds to and what frame (f) in the time pattern.

  The RGB dither pattern generator 400 extracts a 1-bit pattern from a built-in LUT based on input information from the timing control unit 500 and lower (mn) bit data from the data separation processing unit 301, and selects a selection unit. It outputs to 303.

  The candidate generation unit 302 acquires and generates two n-bit gradation candidates from the built-in LUT based on the input m bits, and outputs them to the selection unit 303.

  The selection unit 303 selects one of the two n-bit gradation candidates from the 1-bit pattern from the RGB dither pattern generator 400 and outputs output video data (n bits).

  The above circuit operates in parallel independently for each of RGB.

Therefore, for each RGB video data, a spatio-temporal pattern that is a combination of gradation KU and gradation KB with k <(2 ⁿ −1) is output to the output image data, and the difference between gradations KU and KB is limited to 1. It can be set arbitrarily. The method of setting the combination of the gradation KU and the gradation KB and the arrangement of the space-time pattern of those gradations in the RGB dither pattern generator will be described later.

  The circuit described above generates a drive signal for displaying different dither patterns for the first liquid crystal panel and the second liquid crystal panel.

  In the liquid crystal display device having the above-described structure, the control circuit shown in FIG. 1 is used to enable multi-gradation display in which the number of gradations exceeds the display performance of the liquid crystal panel.

  In multi-gradation, when a spatial pattern and a temporal pattern are combined, the pattern is visible and interference noise occurs because the luminance and chromaticity differences between the pixels in the pattern are connected spatially and temporally. The cause is that it becomes a pattern and is recognized by the human eye.

  Therefore, if the luminance difference or chromaticity difference between the pixels is made as small as possible, the pattern becomes inconspicuous, and as a result, only the gradation feeling is recognized.

  Therefore, for example, as shown in FIG. 3, a display pattern for increasing the number of gradations is devised by using a structure in which two liquid crystal panels (first liquid crystal panel and second liquid crystal panel) are overlapped. Thus, a pattern with reduced luminance difference is formed.

  FIG. 7 shows the number of sets of transmittance when two two-tone liquid crystal panels are stacked.

  For simplicity, FIG. 7 shows the transmittance when two panels are overlapped when the transmittance of each gradation is assigned to 0 and 100% in two gradations of 0 and 1. It is the figure calculated | required by multiplying the transmittance | permeability of a panel. As can be seen from FIG. 7, if one transmittance value is counted as one gradation, it is not 2 * 2 = 4 gradations, and the number of gradations that can be expressed is smaller.

  FIG. 8 shows the number of sets of transmittance when two 16-gradation liquid crystal panels are stacked. As in the case shown in FIG. 7, there is no set of transmittances for 16 * 16 = 256 tones, but there are more than 16 tones that can be expressed by one liquid crystal panel.

  That is, in the case of a single panel, a pattern (spatio-temporal pattern) made up of a spatial pattern and a temporal pattern was created using 16 pixels of 16 gradations. By superimposing, the number of gradations that can be handled by one pixel is increased, and by using the increased number of gradations, more space-time patterns can be used, and the number of gradations that can be actually expressed can be increased. FIG. 9 is a 3D graph of the results shown in FIG.

  The γ curve representing the change in transmittance of the panel shown in FIG. 8 is 1.0 for both the front surface and the rear surface. The formula for calculating the transmittance T is given by:

T = (k / maximum gradation) ^ γ
Therefore, for example, the transmittance of gradation 3 in FIG. 8 is (3/15) ^ 1.0 = 20.0%. Further, if the front panel has gradation 3 and the rear panel has gradation 6, the respective transmittances are 20.0% and 40.0%. Since the brightness on the screen is multiplied by the transmittance of the two panels, 20.0% × 40.0% = 8%, and 8% × the brightness at which the backlight luminance is recognized. Actually, the brightness decreases due to other factors such as a color filter.

  A specific example showing the effect of intentionally increasing the number of gradations is shown below.

  FIG. 10A is a diagram illustrating a spatiotemporal pattern of one liquid crystal panel, and FIG. 10B is a graph illustrating a luminance difference in the pattern illustrated in FIG.

  FIG. 11A is a diagram showing a spatio-temporal pattern when two liquid crystal panels are overlapped, and FIG. 11B is a graph showing a luminance difference in the pattern shown in FIG. 11A.

  First, an example of a spatiotemporal pattern in one liquid crystal panel will be described.

  Here, when expressing a gradation as close as possible to a transmittance of 15%, for example, as shown in FIG. 10 (a), in the case of “one liquid crystal panel”, a level close to a transmittance of 15% is obtained from the table shown in FIG. Spatio-temporal pattern generator, ie, figure, in a display device composed of two gradations, tone 2 (transmittance 13.3%) and gradation 3 (transmittance 20.0%), that is, the above-mentioned one liquid crystal panel. If the expression described in the configuration shown in FIG. 6 is used, the luminance difference between the pixels of the spatiotemporal pattern can be minimized by forming the spatiotemporal pattern using the gradation k and the gradation (k + 1) (FIG. 10B). .

  That is, in the frame 1 in FIG. 10A, the 2 × 2 spatial pattern is composed of gradations 3, 2, 2, and 3, so that the transmittance is 20.0%, 13.3%, 13.3%, The combination is 20.0%, and the average transmittance A in the 2 × 2 spatial pattern in the frame 1 is 16.6%. That is, the brightness obtained by multiplying the average transmittance and the backlight luminance is spatially recognized in the 2 × 2 region.

  Furthermore, since the time pattern changes from 3 to 2 to 3 to 2 in 4 frames in one pixel of FIG. 10A, the transmittance is 13.3% → 20.0% → 13.3% → 20. It changes over time to 0.0%, and the average transmittance a which is an average value in four frames in one pixel is also 16.6%. In other words, the visual perception of the brightness obtained by multiplying the average transmittance by the backlight luminance is averaged in units of one pixel. The luminance difference of each pattern at this time is 6.7% as shown in FIG.

  By expressing the same transmittance (brightness) in space and time in this way, even in an image where the input image source breaks the space pattern (for example, pixels b and c as shown in FIG. 12 are black) in the time direction. The brightness recognized by the compensation is visually maintained, and the brightness recognized by the spatial compensation even in a video that breaks the time pattern (for example, frames 2 and 4 as shown in FIG. 13 are all black). Is visually maintained. This is the basic principle of multi-gradation that is unlikely to generate noise and flicker.

  However, in FIG. 10A, when viewed from a certain frame, there is always a difference in brightness from the adjacent pixel spatially, and from a certain pixel, there is always a difference from the adjacent frame in time. Therefore, in recent liquid crystal TVs, the luminance difference between pixels due to an increase in the pixels and the luminance difference between gradations due to an increase in contrast become large, and the spatial pattern is easily visible. Furthermore, the input video has also been refined by using FullHD, and has become a fine video expression that breaks the spatial pattern. Furthermore, flickering is easily recognized by making it possible to more clearly see the blinking of patterns that have not been recognized up to now due to the slow response speed of the liquid crystal due to the improved response speed of the liquid crystal. Furthermore, with the improvement of moving image performance such as 120 Hz driving of the liquid crystal panel, pattern interference noise due to line-of-sight tracking is easier to see than before.

  Here, FIG. 14 shows the principle of generation of pattern interference noise by line-of-sight tracking. Here, as shown in FIG. 14A, gradation 2 (transmittance 13.3%), gradation 2.5 (transmittance 16.6%), and gradation 3 (transmittance 20.0%). Consider that a two-dimensional image is displayed on the screen. The gradation 2.5 is a new gradation value (transmittance) generated by the spatiotemporal pattern.

  FIG. 14B shows a case where one line of the image is cut out and arranged in the order of frame time when the image is stationary. In the case of the same pixel position when standing still, for example, at the pixel position 5, the gradation becomes 3 → 2 → 3 → 2, and it can be seen that the gradation 2.5 is expressed by averaging over time. Also, spatially, for example, at pixel positions 5 and 6, gradations 3 and 2 indicate that gradation 2.5 is expressed.

  On the other hand, when the image is scrolled by one pixel to the right for each video frame, the eye follows the movement of the edge of the image as shown in FIG. The luminance of the image is projected on the retina in this direction. Therefore, every time the frame of the input video changes, the pixel at the pixel position 5 moves in the order of 5 → 6 → 7 → 8, and the line of sight follows it. However, since the gradation 2.5 is generated by being fixed at the pixel position by a temporal and spatial pattern of gradation 2 and gradation 3, the pattern is as shown in FIG. At this time, when the change in gradation is observed in the line-of-sight tracking direction of pixel positions 5 → 6 → 7 → 8, the gradation is 3 → 3 → 3 → 3, the pattern in the time direction is destroyed, and the same spatial pattern overlaps. The result is emphasized. In this way, noise due to pattern interference occurs.

  As a way to prevent this, it seems that the spatio-temporal pattern will be eliminated if it is generated in accordance with the scrolling of the image, but the motion scale of the image becomes necessary, so the hardware scale becomes large, and the line of sight moves the edge of the image. Since this does not necessarily follow exactly, it is impossible to completely eliminate this phenomenon.

  That is, when the TV has a large screen, the pixel size is increased, but the brightness difference from the adjacent pixels due to the spatial pattern is increased, so that the display quality is lowered.

  In order to improve the problems as described above, the luminance difference between the spatially adjacent pixels and the temporal luminance difference with the adjacent frame may be reduced as much as possible. The present invention realizes this by overlapping two liquid crystal panels.

  Therefore, in the present invention, as shown in FIG. 11A, when two liquid crystal panels are stacked, the combination of the two transmittances closest to the transmittance of 15% is used from the table shown in FIG. A spatiotemporal pattern can be formed. Specifically, the transmittance when the two liquid crystal panels are overlapped is a multiplication of the transmittance of the respective liquid crystal panels. Therefore, as shown in FIG. When the gradation 11 (transmittance 73.3%) of the second liquid crystal panel is superimposed on (transmittance 20.0%), the transmittance is 14.7% (= 20.0% × 73. 3%). Further, the transmittance when the gradation 7 (transmittance 46.7%) of the second liquid crystal panel is superimposed on the gradation 5 (transmittance 33.3%) of the first liquid crystal panel is 15. 6% (= 33.3% × 46.7%). The closest to 15% transmittance of one LCD panel is 13.3% and 20.0% of gradations 2 and 3 from FIG. 10 (a). The transmittances that can be selected when the liquid crystal panels are stacked are 14.7% and 15.6%. That is, if the combination of these two transmittances is used, it can be expressed by a spatio-temporal pattern with a smaller luminance difference, and the interference pattern and noise can be made inconspicuous. In this case, the average transmittance of the time pattern is 15.1%. The luminance difference of each pattern at this time is 0.9% as shown in FIG. 11B, which is considerably higher than the luminance difference of 6.7% in the case of the conventional spatiotemporal pattern shown in FIG. Can be small.

  That is, by overlapping two liquid crystal panels, it is possible to increase the degree of freedom in selecting the closest combination of transmittances that sandwiches the target transmittance (15%).

  At this time, the spatiotemporal patterns displayed on the front panel (first liquid crystal panel) and the rear panel (second liquid crystal panel) are different, and the pixels in the spatiotemporal pattern are as much as possible when the patterns overlap in time and space. Display control is performed so as to obtain a pattern in which the luminance difference between them is reduced.

  If two liquid crystal panels have the same spatiotemporal pattern, the number of selectable transmittances is the same as the number of transmittances for one liquid crystal panel (only the transmittance on the diagonal in FIG. 8). Therefore, the degree of freedom in selecting the optimum transmittance is reduced, which is a disadvantageous condition. Therefore, it is preferable that the space-time patterns of the two liquid crystal panels are different.

  Although the above explanation has been given for an example of a liquid crystal panel with 16 gradations, it can of course be applied to a liquid crystal panel with 16 gradations or more, and the number of sets that can be selected increases as the number of gradations increases, such as 256 gradations. It is possible to express more gradations with less luminance difference between dots. Furthermore, the same theory can be developed when creating a spatiotemporal pattern in which the chromaticity difference is as small as possible.

  Next, a case where the present invention is applied to a liquid crystal panel having 256 gradations as a liquid crystal panel having 16 gradations or more will be described below.

  FIGS. 15, 16 and 17 show an example when the liquid crystal panel has 256 gradations. FIG. 15 shows the number of sets of transmittance when two liquid crystal panels of 256 gradations are overlapped. FIG. 16 is a 3D graph of the transmittance shown in FIG. FIG. 17A is a diagram showing a spatio-temporal pattern when two liquid crystal panels are overlapped, and FIG. 17B is a graph showing a luminance difference in the pattern shown in FIG.

  As before, the combination closest to the transmittance of 15% can be selected from the transmittance combination table of FIG. Here, gradations 112 to 127 for the front panel and gradations 80 to 95 for the rear panel are selected as the point where the transmittance is 15% on account of the space on the paper, but naturally other gradation combinations exist. . Using the combination table of FIG. 15, the combination closest to 15% can be selected in the same manner as described above. Is the closest. The spatiotemporal pattern in this combination is shown in FIG. At this time, the luminance difference of each pattern was 0.9% at 16 gradations, but as much as 0.02% as shown in FIG. 17B.

  Note that the gradation range of the front panel and the rear panel described here is 15.56% when the combination of gradation 7 and gradation 5 in FIG. It can be said that one gradation of the 16 gradation panel is further divided into 16 and complemented more finely. Therefore, the same theory can be developed even if the panel gradation is further increased.

  In the above description, the same gradation data bit number n is used for the front panel and the rear panel. However, even if the front panel has gradation data n1 bits and the rear panel has gradation data n2 bits, As described above, only the number of combinations of transmittances that can be selected is changed, and the effect of reducing the luminance difference between patterns by overlapping two panels can be exhibited. For example, if the front panel has gradation data of 8 bits and the rear panel has gradation data of 4 bits, the effect of multi-gradation by the method of the present invention can be achieved while reducing the hardware scale as compared with the rear panel having the same 8 bits. To some extent.

  Here, a procedure for creating an actual spatiotemporal pattern will be described below. FIG. 18 is a flowchart showing a procedure for creating a spatiotemporal pattern.

  First, in step S1, the gradation-transmittance characteristics of each panel to be overlaid are measured.

  Next, in step S2, a combined transmittance table is created from the combinations of transmittances of the panels. That is, the transmittance obtained by multiplying the respective transmittances as in the example of the two-panel display shown in FIG. In step S1 and step S2, the measurement of each panel in step S1 can be omitted by measuring with the panels stacked.

  Next, the following steps S3 to S6 are repeated for each gradation k.

  In step S3, the target transmittance T is obtained from the following equation from the desired gradation k and the required γ curve.

T = (k / maximum gradation) ^ γ
Next, in step S4, the transmittances TU and TB closest to the target transmittance T are searched from the combined transmittance table. Here, TU and TB are transmittances that sandwich the target transmittance T as follows.

TU ≧ T ≧ TB
A spatio-temporal pattern having a minimum luminance difference may be displayed with these transmittances TU and TB. In step S5, the gradation value of each panel for realizing the transmittances TU and TB by a circuit is obtained. That is, as in the example of FIG. 19A, the combination gradation KU [1] of the panel 1 with the transmittance TU and the combination gradation KU [2] of the panel 2 and the combination gradation KB [ 1] and the combined gradation KB [2] of panel 2 are obtained from the combined transmittance table.

  In step S6, these are set as the spatio-temporal pattern gradations KU [p] and KB [p] for the gradation k in any panel p, and are registered in the spatio-temporal pattern candidate table of each panel.

  By performing steps S3 to S6 for all gradations, a candidate table of combinations of gradations of the spatiotemporal pattern for each gradation in each panel as shown in FIG. 19B is completed.

  The spatio-temporal pattern generator of the present invention shown in FIG. 2 incorporates the KU and KB spatio-temporal pattern candidate table in the candidate generation block, narrows down the gradation candidates KU and KB with m-bit gradation data K, and selects RGB. KU or KB is selectively output in a 1-bit state from the dither pattern generator.

  It is also possible to automate steps S3 to S6 by rearranging the combined transmittance table by transmittance and incorporating them as a table, and searching this table from the input gradation to obtain KU and KL. However, the combined transmittance table becomes large as the number of panel gradations and the number of panels increase.

  Here, the control circuit of the two liquid crystal panels of the present invention will be described with reference to the timing chart of FIG. The video data is composed of a plurality of frame data with a resolution (horizontal X pixel vertical Y line) of the liquid crystal panel, horizontal (column) W pixels including a blank period, and a period represented by vertical (row) H line as one frame. Let's say. In the NTSC standard, 60 frames are input as a video source signal per second. Further, the video data D is composed of m-bit gradation data of each RGB, and m> n with respect to the n-bit gradation data of each RGB of the liquid crystal panel.

  The video synchronization signal S includes a vertical synchronization signal VS, a horizontal synchronization signal HS, a data enable signal DE, and a pixel clock signal CK. FIG. 20 shows that every time the vertical synchronization signal VS becomes active (L), the video data is in the next frame period. Each time the horizontal synchronization signal HS becomes active (L), it represents that the video data has entered the next line period. When the data enable signal DE is (L), the video data represents a blank period, and when the data enable signal DE is (H), the video data represents a display period during which data is displayed on the liquid crystal panel. In these periods, the pixel clock signal CK is the minimum reference unit, the horizontal period of the video data is the W clock, and the display period is the X clock. Video data D is input in synchronization with the data enable signal DE and the pixel clock signal CK as shown in FIG.

  First, the distributor 101 in FIG. 1 outputs the same video data D1 and D2 as the two video synchronization signals S1 and S2 at the same timing. That is, the distributor 101 only shifts one clock timing. The video synchronization signals S1 and S2 are signals including VS1, HS1, DE1, CK1 and VS2, HS2, DE2, CK2, respectively. In the timing chart of FIG. 20, the timing of the data enable signals DE1 and DE2 is shown on behalf of the video synchronization signals S1 and S2.

  Subsequently, the first spatiotemporal pattern generator 103a receives the video synchronization signal S1 and the video data D1, and outputs the video data Q1 subjected to the spatiotemporal pattern processing. In FIG. 20, q1_0, q1_1, q1_2,... Of Q1 are output with a shift of two clock timings with respect to the pixel data d0, d1, d2,. Similarly, the second spatio-temporal pattern generator 103b receives the video synchronization signal S2 and the video data D2, and each pixel data d0, d1, d2,. Each pixel data q2_0, q2_1, q2_2... Of the video data Q2 is output.

  The video synchronization signal S1 is also input to the first timing controller 102a in FIG. 1, and a signal TC1 for controlling the driver is output. TC1 includes a data start pulse SP1, a latch pulse LS1, a dot clock DCK1, a gate start pulse GSP1, and a gate clock GCK1. As shown in FIG. 20, SP1 is active (H) to indicate the start position of video data Q1, and video data for one line is sequentially stored in the driver according to the clock timing of DCK1. Then, when LS1 becomes active (H), gradation voltages corresponding to digital values of video data for one line are applied to the first liquid crystal panel all at once. Further, the control for applying the gradation voltage to the first line of the screen display is reset when GSP1 becomes active (H) and the waveform of GCK1 rises. When GSP1 becomes (L) and the waveform of GCK1 rises, the control of applying the gradation voltage to the next screen line is shifted. In this way, the line to be controlled is sequentially selected from the upper end to the lower end of the screen, and LS1 becomes active, so that the gradation voltage is simultaneously applied to the pixels on one line on the liquid crystal panel.

  Similarly, the video synchronization signal S2 is also input to the second timing controller 102b of FIG. 1, and a signal TC2 for controlling the driver is output. TC2 includes a data start pulse SP2, a latch pulse LS2, a dot clock DCK2, a gate start pulse GSP1, and a gate clock GCK2. The timing is the same as TC1 as shown in FIG.

  FIG. 21 is a timing chart of the spatiotemporal pattern generator of FIG.

  The input video synchronization signal in FIG. 2 includes a vertical synchronization signal VS, a horizontal synchronization signal HS, a data enable signal DE, and a clock signal CK of the video signal.

  As shown in FIG. 21, the frame of the video signal is switched by the vertical synchronization signal VS, and the number of frames f is counted and output within the timing control block of FIG. The number of frames f is counted with the maximum number of frames constituting the spatiotemporal pattern. Here, the maximum is four frames, and FIG. 21 shows frame counts 1, 2, 3, and 4.

  Further, when the vertical period is expanded, a plurality of horizontal synchronizing signals HS are inputted between VS and the next VS, and the video signal lines are switched by the horizontal synchronizing signal HS, and the number of rows is changed in the timing control block of FIG. (Number of lines) y is counted.

  The number of lines y is counted with the maximum number of lines constituting the spatiotemporal pattern. Here, since the spatiotemporal pattern is assumed to have a 2 × 2 configuration, the number of rows y in FIG.

  Further, when the horizontal period is enlarged, a plurality of clock signals CK are inputted between the HS and the next HS, and the data enable signal DE becomes High level during the screen display period. At this time, the pixels of the video signal are switched by the clock signal CK, and the number of columns (number of pixels) x is counted inside the timing control unit 500 of FIG.

  The number of columns x is counted with the maximum number of columns constituting the spatiotemporal pattern. Here, since the space-time pattern is assumed to be 2 × 2, the number of columns x in FIG.

  At the above timing, the frame number f, the row number y, and the column number x are output from the timing control signal and input to the RGB dither pattern generator as a selection address signal for the spatiotemporal pattern.

  On the other hand, the RGB data constituting the input video data are processed independently. Each hardware configuration is the same. As shown in FIG. 21, m-bit video data (gradation data K) is synchronized with the timings of DE and CK at k0, k1, k2,. . . . Is entered. The gradation data K is input to the candidate generation block, and candidate gradations KU and KB expressing the gradation K are output from the built-in space-time pattern candidate table. In FIG. 21, (ku0, kb0), (ku1, kb1),. . . . Is output to the selection unit 303 in FIG.

  The gradation data K is also input to the data separation unit 301, and the low-order (mn) bit gradation KL is output. In FIG. 21, kl 0, kl 1, kl 2. . . . Is output. The low-order bit gradation KL is input to the RGB dither pattern generator 400 of FIG. 2, and 1-bit data PT indicating a dither pattern of an arbitrary pixel is output together with the position information of the spatiotemporal pattern of the timing control block.

  In FIG. 21, in synchronization with the timing of DE and CK, pt0, pt1, pt2,. . . Is output to the selection unit 303 in FIG. The selection unit 303 selects one of the gradation candidate data KU and KB from 0 and 1 of PT, and outputs the selected gradation data KX. In FIG. 21, kx0, kx1, kx2,. . . . Is output.

  With the above timing, a spatio-temporal pattern for expressing an arbitrary m-bit gradation K is composed of n-bit gradation data KU and KB.

  Further, FIG. 2 has a spatiotemporal pattern generator independently for each of R, G, and B, and can have the same spatiotemporal pattern at the same matrix position and the same number of frames, or separate spatiotemporal patterns. In addition, since the size of the spatiotemporal pattern and the number of frames can be freely set according to the number of counts, there are no particular restrictions other than the hardware scale.

  FIG. 22 shows an example of a case where RGB is the same in a 4 × 4, 4-frame spatiotemporal pattern (a) and RGB independent (b). In FIG. 22, the 1-bit PAT from which the candidate gradations KU and KB are selected by the spatio-temporal pattern generator of FIG. 2 is represented by 1 = white and 0 = gray. Thus, since the pattern becomes fine when RGB is made independent, the number of gradations can be increased without any noise or flicker.

  FIG. 8 shows an example in which the γ curve representing the change in transmittance with respect to the gradation of the two panels is γ = 1.0 for both the front and rear surfaces. Hereinafter, modified examples of the γ value in the panel will be described.

  In general, a panel such as a liquid crystal TV imitates the characteristics of a cathode ray tube TV, and γ = 2.2 and a value other than 1.0 is used. FIG. 23 shows a table showing combinations of transmittances when two 16-gradation panels with γ = 2.2 are stacked, and FIG. 24 shows a 3D graph at that time. In the graph of FIG. 24, it can be seen that one of the panels has a curve of γ = 2.2 when the transmittance is 100%.

  The calculation formula of the transmittance T of the gradation k when γ = 2.2 is given by the following.

T = (k / maximum gradation) ^ γ
From the table shown in FIG. 23, it can be seen that there are many combinations with low transmittance compared to the table shown in FIG. 8 where γ = 1.0. That is, it is possible to display with a large number of gradations and high accuracy at low luminance. On the other hand, there are fewer combinations with high transmittance.

  The brightness sensation Q = αLogL (α is an arbitrary constant) according to Weber-Fechner's law, which is a generally known visual characteristic. Therefore, even if the difference in the luminance values of the two gradations is the same, the higher the luminance, the lower the gradation difference. It becomes difficult to identify, and it becomes easier to identify the gradation difference as the luminance is lower.

  Therefore, by overlapping two panels with γ = 2.2, the number of gradations on the low gradation side can be increased, and the smoothness of the appearance of the image can be improved from the viewpoint of visual characteristics.

  FIG. 25 shows the transmittance when two 16-gradation panels are stacked when the first liquid crystal panel (front panel) is γ = 2.2 and the second liquid crystal panel (rear panel) is γ = 1.0. FIG. 26 is a diagram obtained by converting the table shown in FIG. 25 into a 3D graph. In the graph of FIG. 26, a curve of γ = 2.2 of the front panel is drawn when the rear panel has a transmittance of 100%, and a curve of γ = 1.0 of the rear panel when the front panel has a transmittance of 100%. You can see that is drawn.

  Although the number of combinations with lower transmittance is smaller than that when γ = 2.2, the number of combinations with higher transmittance is increasing. That is, it can be said that the gradations with low brightness and high gradations increase moderately. Also, compared to γ = 2.2, when γ = 1.0, the gradation voltage applied to the panel changes linearly, so it can be created by interpolating a few reference voltages, reducing the circuit scale. Can do. By the way, when γ = 2.2, the gradation voltage must be changed to a non-linear γ curve. Therefore, in order to interpolate along the γ curve, eight or more reference voltages are required, and the circuit scale is correspondingly increased. growing.

  A circuit for generating a gradation voltage is provided in the driver, and the circuit scale increases especially when the number of gradations of the panel increases. For example, FIG. 27 shows an example of a circuit configuration for generating a gradation voltage of 256 gradations at γ = 2.2. The reference voltage setting circuit is composed of a resistance voltage dividing circuit R1-R9 for setting a reference voltage V0-V9 at an arbitrary point of the γ curve and interpolating between them on a broken line, and 256 gradation voltages Is generated. The driver selects a corresponding gradation voltage from these gradation voltages from the input video data, and drives the liquid crystal panel by applying the voltage. Thus, a large number of reference voltages are required. If γ is close to 1.0, a linear voltage change occurs, so that a large number of such reference voltages are not necessary, and the circuit scale can be reduced.

  As described above, if the input gradation of the liquid crystal panel and the γ value of the transmittance are large, the gradation of low luminance can be increased. If the γ value is small, the high luminance gradation can be increased. By mixing both, it is possible to increase the number of combinations that reduce the brightness difference where smoothness is required according to the video expression. This can be done by fixing the γ of the liquid crystal panel in advance aiming at an arbitrary gradation range, or by actively changing it according to the gradation range concentrated in the screen histogram of the input video. Conceivable.

  In FIG. 28, the front panel has γ = 2.2, the rear panel has gradation 0 to gradation 7 and γ = 1.0, and the transmittance changes from 0% to 100%. FIG. 29 is a diagram showing a 3D graph of the table shown in FIG. 28. FIG.

  From the table shown in FIG. 28, all the gradations 7 and above are the same as when the transmittance is one panel (front panel). For this reason, at gradation 7 or higher, only gradation performance equivalent to that of a single panel can be obtained. However, the low gradation part where the gradation difference (brightness difference) is easy to understand visually, here there are a large number of gradation combinations below the gradation 7, so a transmission combination that reduces the visual luminance difference is selected. The number of selected gradations can be increased. Nevertheless, the display brightness of the transmittance of 0% (not completely 0) and the transmittance of 100% does not change, and the same high contrast can be maintained.

  Further, since gradation 8 or higher is equivalent to gradation 7, a circuit for recording a combination of gradation 8 or higher and a circuit for processing become unnecessary, and the circuit scale can be reduced to ½. Although it seems that it is not so much with a panel with 16 gradations, it can be easily imagined that, for example, a panel with 256 gradations greatly contributes to a reduction in circuit scale.

  Here, a description will be given below of which gradation can be used to obtain the above-described effect when the rear panel is set to have a transmittance of 100%.

Experience has shown that a liquid crystal panel with a maximum luminance of 600 cd / m ² makes the dither pattern conspicuous at low gradations from around 64 gradations in the case of gradation 256. The 64 gradations are about 28 cd / m ² in terms of luminance according to the following formula when γ = 2.2 of the panel.

Luminance = Maximum luminance × (Grayscale required / Maximum grayscale) ^ γ = 600 × (64/255) ^ 2.2
Further, it is generally known that the range in which Weber-Fechner's law (brightness sensation Q is proportional to the logarithm of luminance L) is 30 to 1000 cd / m ² (FIG. 3.12 of the non-patent document). . This means that if it is less than 30 cd / m ^2, it is not proportional to the logarithm and the visual sensitivity related to brightness is further increased. Therefore, since the display luminance of the gradation changes depending on the luminance of the backlight, it is desirable that the transmittance of the rear panel is set to 100% with the gradation of the luminance of 30 cd / m ² or more instead of the gradation value as it is. It is also conceivable to set a lower gradation by balancing the circuit scale and the actual appearance.

  In this way, by limiting the gradation range for different patterns on the two panels to an appropriate place, the increase in contrast due to the overlapping of the two panels is maintained while suppressing an increase in circuit scale, and noise and flicker are suppressed. The smoothness of the image can be increased by suppressing the number of gradations and increasing the number of gradations.

  Up to this point, the case where two liquid crystal panels are stacked has been described. However, the present invention is not limited to this, and the present invention can be applied to a case where three or more liquid crystal panels are stacked.

  FIG. 30 is a configuration diagram showing a panel control circuit 600 in a display device in which p (p> 2) liquid crystal panels are stacked. Note that members having the same functions as those included in the panel control circuit 100 shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 30, the panel control circuit 600 includes a distributor 101, timing controllers (first timing controller 102a to p-th timing controller 102p) corresponding to the number (p) of liquid crystal panels, and a spatio-temporal pattern generator. (First spatiotemporal pattern generator 103a to pth spatiotemporal pattern generator 103p). The signals from the timing controllers and the spatiotemporal pattern generator are output to the corresponding liquid crystal panel drivers.

  According to the display device having the above configuration, it is possible to increase the number of combinations of gradations in which the luminance difference between patterns is smaller than in the case shown in FIG. Thus, the video expression can be further smoothed.

  Electronic devices to which the display device of the present invention can be applied include a TV, a PC monitor, a medical monitor, a projector, an information display, and the like. It is suitable for.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims. That is, embodiments obtained by combining technical means appropriately changed within the scope of the claims are also included in the technical scope of the present invention.

  The display device of the present invention is suitable for a display device in which the number of gradations is important as an application and the pixel size is large.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram illustrating a main configuration of a driving device of a panel control unit according to an embodiment of a driving device of a display device of the present invention. It is a block diagram which shows the principal part structure of the spatiotemporal pattern generator with which the panel control part shown in FIG. 1 was equipped. It is a schematic block diagram of the display apparatus driven by the drive device of the display apparatus shown in FIG. It is a schematic sectional drawing which shows the principal part of the display apparatus shown in FIG. It is a block diagram which shows the principal part structure of the panel control part in case the display panel as a comparative example is 1 sheet structure. It is a block diagram which shows the principal part structure of the spatiotemporal pattern generator with which the panel control part shown in FIG. 5 was equipped. It is a figure which shows the group number table | surface of the transmittance | permeability when two 2 gradation liquid crystal panels are piled up. It is a figure which shows the group number table | surface of the transmittance | permeability when two 16 gradation liquid crystal panels are piled up. It is the graph which made the transmittance | permeability shown in FIG. 8 3D graph. FIG. 10A is a diagram illustrating a spatiotemporal pattern of one liquid crystal panel, and FIG. 10B is a graph illustrating a luminance difference in the pattern illustrated in FIG. FIG. 11A is a diagram showing a spatio-temporal pattern when two liquid crystal panels are overlapped, and FIG. 11B is a graph showing a luminance difference in the pattern shown in FIG. 11A. It is a figure which shows the spatiotemporal pattern which shows the example in which a spatial pattern is destroyed. It is a figure which shows the spatiotemporal pattern which shows the example where a time pattern is destroyed. It is a figure which shows the principle that pattern interference noise generate | occur | produces by a gaze tracking. It is a figure which shows the group number table | surface of the transmittance | permeability when two liquid crystal panels of 256 gradation are piled up. It is the graph which made the 3D graph of the transmittance | permeability shown in FIG. FIG. 17A is a diagram showing a spatio-temporal pattern when two liquid crystal panels are overlapped, and FIG. 17B is a graph showing a luminance difference in the pattern shown in FIG. It is a flowchart which shows the preparation procedure of a spatiotemporal pattern. FIG. 19A is a diagram showing the concept of a combined transmittance table and a spatio-temporal pattern candidate table when two panels of the present invention are overlapped, and FIG. 19B is a spatio-temporal pattern candidate table. FIG. It is a timing chart of the control circuit of two liquid crystal panels of the present invention. 3 is a timing chart of the spatiotemporal pattern generator of FIG. It is a figure which shows the example of a spatio-temporal pattern of 4x4 and 4 frames in the case where RGB is the same (A) and the case where RGB is independent (B). It is a figure which shows the combination table of the transmittance | permeability when two 16 gradation panels of (gamma) = 2.2 are piled up. It is the graph which made the 3D graph of the transmittance | permeability shown in FIG. Combination table of transmittance when two 16 gradation panels are stacked when the first liquid crystal panel (front panel) is γ = 2.2 and the second liquid crystal panel (rear panel) is γ = 1.0. FIG. It is the graph which made the 3D graph of the transmittance | permeability shown in FIG. It is a figure which shows the example of the circuit structure which produces | generates the gradation voltage of 256 gradations at (gamma) = 2.2. The front panel has γ = 2.2, the rear panel has gradations 0 to 7, and γ = 1.0, and the transmittance changes from 0% to 100%. It is a figure which shows the combination table of the transmittance | permeability when two tones panels are piled up. It is the graph which made 3D graph of the transmittance | permeability shown in FIG. It is a block diagram which shows the panel control circuit 600 in the display apparatus which piled up the liquid crystal panel p (p> 2).

Explanation of symbols

1 Transparent substrate 2 Color filter 3 Counter electrode 4 Pixel electrode 6 TFT
7 Interlayer insulating film 8 Black matrix 10 Counter substrate 11 Active matrix substrate 100 Panel control circuit (panel control means)
101 Distributor 102a First timing controller 102b Second timing controller 103a First space-time pattern generator (pattern generation circuit)
103b Second space-time pattern generator (pattern generation circuit)
200a First driver 200b Second driver 300 Data converter 301 Data separator 302 Candidate generator 303 Selector 400 RGB dither pattern generator (dither pattern generator)
500 Timing control unit 600 Panel control circuit A Polarizing plate B Polarizing plate C Polarizing plate m Number of gradation bits n Number of gradation bits

Claims (6)

A driving device that receives video data of m bits and outputs it to a display device in which two or more transmissive display panels of n (m> n) bit gradation are stacked,
In order to express the gradation of the input video data, a luminance pattern that is transmitted through each of the transmissive display panels is configured, and the luminance difference between pixels that configure the luminance pattern is minimized. A drive device for a display device, comprising panel control means for generating a combination of gradation values to be output to a transmissive panel and outputting the combination to each transmissive display panel. The panel control means includes
2. The display device driving device according to claim 1, wherein among the transmissive display panels, at least two transmissive display panels are controlled to have different dither patterns. The panel control means includes
A distributor for distributing video data included in the input video source signal to the number of transmissive display panels;
A pattern generation circuit provided for the number of video data distributed by the distributor, generating a dither pattern of the video data output from the distributor, and outputting the dither pattern to a corresponding transmissive display panel. The display device driving device according to claim 2, wherein the driving device is a display device. The pattern generation circuit
A data conversion unit that is provided for each color component of the video data included in the input video source signal and converts the input video data to output video data having a number of gradation bits smaller than the number of gradation bits of the input video data;
A dither pattern generator for generating a dither pattern to be supplied to the data converter;
4. The display device driving apparatus according to claim 3, further comprising a timing control unit for timing the generation of a dither pattern in the dither pattern generator. The data converter is
a data separator that separates input video data of m-bit gradation into lower (mn) bits and outputs to the dither pattern generator;
A candidate generating unit that acquires and generates two n-bit gradation candidates from an LUT based on the m-bit gradation input video data;
A selection unit that selects any one of the two n-bit gradation candidates supplied from the candidate generation unit and outputs video data of n-bit gradation;
The dither pattern generator generates 1-bit pattern data based on lower (mn) bit data supplied from the data separation unit and a timing signal from the timing control unit, and selects the selection unit. Output to
5. The display device driving device according to claim 4, wherein the selection unit selects one of two n-bit gradation candidates from the 1-bit pattern from the dither pattern generator. An electronic device provided with a display device,
The electronic device according to claim 1, wherein the driving device that drives the display device is the display device driving device according to claim 1.

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