US9270958B2 - Liquid crystal display apparatus for generating an output video signal based on an input video signal and a lighting signal - Google Patents

Liquid crystal display apparatus for generating an output video signal based on an input video signal and a lighting signal Download PDF

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US9270958B2
US9270958B2 US13/181,765 US201113181765A US9270958B2 US 9270958 B2 US9270958 B2 US 9270958B2 US 201113181765 A US201113181765 A US 201113181765A US 9270958 B2 US9270958 B2 US 9270958B2
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signal
video signal
pixel
sub
liquid crystal
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US20120026211A1 (en
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Ken Kikuchi
Tomoya Yano
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Sony Corp
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Sony Corp
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    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
    • G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
    • G09G3/3607—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals for displaying colours or for displaying grey scales with a specific pixel layout, e.g. using sub-pixels
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/64—Circuits for processing colour signals
    • H04N9/67—Circuits for processing colour signals for matrixing
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/06—Adjustment of display parameters
    • G09G2320/0626—Adjustment of display parameters for control of overall brightness
    • G09G2320/0646—Modulation of illumination source brightness and image signal correlated to each other
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2340/00—Aspects of display data processing
    • G09G2340/06—Colour space transformation
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2360/00—Aspects of the architecture of display systems
    • G09G2360/16—Calculation or use of calculated indices related to luminance levels in display data
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
    • G09G3/3406—Control of illumination source

Definitions

  • the present disclosure relates to a liquid crystal display apparatus having a sub-pixel structure made up of sub-pixels of four colors of red (R), green (G), blue (B), and white (W), for example.
  • an active-matrix liquid crystal display (LCD) apparatus in which TFT (Thin Film Transistor) is disposed in each pixel is often used.
  • a video signal is line-sequentially written to a subsidiary capacitive device and a liquid crystal device of each pixel from the upper portion to the lower portion of the screen, thereby driving each pixel.
  • each of pixels in a liquid crystal display panel includes sub-pixels of four colors (see Japanese Examined Patent Application Publication No. Hei 4-54207, Japanese Unexamined Patent Application Publication No. Hei 04-355722, and Japanese Patent No. 4354491, for example) have been proposed.
  • the sub-pixels of four colors include sub-pixels of three colors, red (R), green (G), blue (B), and a sub-pixel of a color higher in luminance than the three colors (Z; white (W) or yellow (Y), for example).
  • a light incident on a liquid crystal layer from a back light is modulated according to the signal level of a video signal, and a light amount (luminance) of transmitted light (display light) is controlled.
  • spectroscopic characteristic of the transmitted light from the liquid crystal layer generally shows gradation dependency, and transmittance peak shifts to the short wavelength side (blue light side) as the signal level of the video signal lowers.
  • color filters for selectively transmitting light of predetermined wavelength region is disposed in each sub-pixel. Therefore, even if a chromaticity point at the maximum signal level in each of video signals for each color is set as a reference, the above mentioned wavelength shift of transmittance peak is not a major problem.
  • a sub-pixel of Z shows high luminance characteristic, so that spectroscopic characteristic of transmitted light from the sub-pixel of Z largely changes according to a signal level of a video signal. Therefore, a chromaticity point of transmitted light (display light) from whole pixels also largely shifts in response to the signal level of the video signal.
  • a sub-pixel of W is employed as the sub-pixel of Z, since no color filter is disposed in the sub-pixel of W, variation of the chromaticity point of the display light according to the signal level is large.
  • a transmittance in a sub-pixel of W shows relatively high liquid crystal spectroscopic characteristic, in other words, that a transmittance peak is in the vicinity of a wavelength region of G
  • the result is as follows. That is, at a signal level lower than the maximum signal level in the sub-pixel of W, a transmittance peak is located in the wavelength region of B.
  • the liquid crystal display apparatus having the sub-pixel structure of four colors of R, G, B, and Z shows a nonlinearity as follows. Specifically, the nonlinearity is shown in a relationship between a signal level of a Z-sub-pixel video signal (Z signal), and, in the case where the signal level of the Z-sub-pixel video signal is replaced by a set of R-, G-, and B-sub-pixel intermediate video signals.
  • Z signal Z-sub-pixel video signal
  • a signal level of a video signal also nonlinearly changes to cause a variation (color shift) of a chromaticity point, thereby lowering image quality.
  • a complicate arithmetic processing for the nonlinearity becomes necessary upon signal processing, which leads to a complicate device configuration.
  • the present disclosure has been made in view of the above circumstances and provides a liquid crystal display apparatus which can realize, in a simple configuration, a dimming processing while suppressing a lowering of image quality due to color shift in the case of performing a video display using a sub-pixel structure of four colors of R, G, B, and Z.
  • a liquid crystal display apparatus includes: a light source section; a liquid crystal display panel including a plurality of pixels each of which having sub-pixels of three colors of red (R), green (G), and blue (B), and a sub-pixel of a color (Z) showing luminance higher than those of the three colors, the liquid crystal display panel being configured to modulate light emitted from the light source section, based on input video signals corresponding to the respective three colors of R, G, and B to perform a video display; and a display control section including an output signal generation section adapted to generate, based on the input video signals, output video signals corresponding to the respective four colors of R, G, B, and Z, and to generate a lighting signal of the light source section, the display control section being configured to perform a display drive on the sub-pixels of R, G, B, and Z in the liquid crystal display panel with use of the respective output video signals, and perform a lighting drive on the light source section with use of the lighting signal.
  • a display control section including an output signal generation section
  • the output signal generation section generates the lighting signal, based on the input video signals, to carry out a predetermined dimming processing, based on both the input video signals and the generated lighting signal, and the output signal generation section generates the output video signals through carrying out, based on a resultant video signal from the dimming processing, a predetermined color conversion processing.
  • output video signals corresponding to respective four colors of R, G, B, and Z and a lighting signal of the light source section are generated based on input video signals corresponding to respective three colors of R, G, and B, a display drive of each of the sub-pixels of R, G, B, and Z is carried out with use of the output video signals, and a lighting drive on the light source section is carried out with use of the lighting signal.
  • the lighting signal is generated based on the input video signals, and a predetermined dimming processing is carried out based on both the input video signals and the lighting signal, and thereafter, a predetermined color conversion processing based on a resultant video signal from the dimming processing is carried out, to thereby generate the output video signals.
  • the generation and the dimming processing of the lighting signal are carried out to the input video signals which correspond to the three colors of R, G, and B, and thereafter, a color conversion processing is carried out to generate the output video signals which correspond to four colors of R, G, B, and Z.
  • the color shift of the display light due to variation of peak wavelength region in irradiating light from the sub-pixel of Z is suppressed with a simple arithmetic processing (dimming processing).
  • the lighting signal is generated based on the input video signals corresponding to respective three colors of R, G, and B, and a predetermined dimming processing is carried out based on the input video signals and the lighting signal, and thereafter, a predetermined color conversion processing is carried out based on a resultant video signal from the dimming processing, to thereby generate the output video signals corresponding to respective four colors of R, G, B, and Z, so that it is possible to reduce the color shift of the display light due to the nonlinearity with a simple arithmetic processing (dimming processing). Therefore, when a video display is carried out using a sub-pixel structure of four colors of R, G, B, and Z, it is possible to realize a dimming processing while lowering of image quality due to color shift is suppressed with a simple configuration.
  • FIG. 1 is a block diagram illustrating a general configuration of a liquid crystal display apparatus according to an embodiment of the present disclosure.
  • FIGS. 2A and 2B are schematic plan views illustrating exemplary sub-pixel structures of the pixel shown in FIG. 1 .
  • FIG. 3 is a circuit diagram illustrating a specific configuration example of the sub-pixels shown in FIGS. 2A and 2B .
  • FIG. 4 is a block diagram illustrating a specific configuration of an output signal generation section shown in FIG. 1 .
  • FIG. 5 is a block diagram illustrating a specific configuration of an RGB/RGBW conversion section shown in FIG. 4 .
  • FIGS. 6A and 6B are characteristic charts for describing an example of a limiting processing of a signal level when the RGB/RGBW conversion is carried out.
  • FIG. 7 is a characteristic chart illustrating an example of wavelength dependency of spectral transmittance according to a signal level of W signal according to a comparative example.
  • FIG. 8 is a characteristic chart illustrating an example of wavelength dependency of spectral transmittance in each sub-pixel of R, G, B, and W according to the comparative example.
  • FIG. 9 is a characteristic chart illustrating an example of ideal color reproduction characteristic in an RGBW sub-pixel structure in HSV color space.
  • FIG. 10 is a characteristic chart illustrating an example of color reproduction characteristic in the RGBW sub-pixel structure according to the comparative example in HSV color space.
  • FIG. 11 is a characteristic chart illustrating an example of a relationship between a signal level of the W signal and signal levels of R, G, and B in the case where the signal level of W is replaced by a set of R-, G-, and B-sub-pixel intermediate video signal in the RGBW sub-pixel structure according to the comparative example.
  • FIGS. 12A and 12B are characteristic charts illustrating an example of a common LUT which is used in a BL level calculation section according to a modification 1.
  • FIG. 13 is a block diagram illustrating a specific configuration example of a BL level calculation section according to a modification 2.
  • FIG. 14 is a characteristic chart illustrating an example of a LUT for R which is used in the BL level calculation section shown in FIG. 13 .
  • FIG. 15 is a characteristic chart illustrating an example of a LUT for G which is used in the BL level calculation section shown in FIG. 13 .
  • FIG. 16 is a characteristic chart illustrating an example of a LUT for B which is used in the BL level calculation section shown in FIG. 13 .
  • FIGS. 17A and 17B are characteristic charts illustrating another example of a LUT for R which is used in the BL level calculation section shown in FIG. 13 .
  • FIGS. 18A and 18B are characteristic charts illustrating another example of a LUT for G which is used in the BL level calculation section shown in FIG. 13 .
  • FIGS. 19A and 19B are characteristic chart illustrating another example of a LUT for B which is used in the BL level calculation section shown in FIG. 13 .
  • FIGS. 20A and 20B are schematic plan views illustrating exemplary sub-pixel structures of a pixel according to a modification 3.
  • Embodiment (example of liquid crystal display apparatus using RGBW panel)
  • Modification 1 (example in which common LUT is used between R, G, and B in BL level calculation section)
  • Modification 2 (example in which individual LUTs are used for each of R, G, and B in BL level calculation section)
  • FIG. 1 is a block diagram illustrating a general configuration of a liquid crystal display apparatus 1 according to an embodiment of the present disclosure.
  • the liquid crystal display apparatus 1 carries out a video display based on an input video signal Din which is externally input.
  • the liquid crystal display apparatus 1 includes a liquid crystal display panel 2 , a back light 3 (light source section), a video signal processing section 41 , an output signal generation section 42 , a timing control section 43 , a back light driving section 50 , a data driver 51 , and a gate driver 52 .
  • the video signal processing section 41 , the output signal generation section 42 , the timing control section 43 , the back light driving section 50 , the data driver 51 , and the gate driver 52 correspond to a specific example of “a display control section” of the present disclosure.
  • the liquid crystal display panel 2 modulates light emitted from the back light 3 (described later) based on an input video signal Din to carry out a video display based on the input video signal Din.
  • the liquid crystal display panel 2 includes a plurality of pixels 20 arranged in a matrix as a whole.
  • FIGS. 2A and 2B are schematic plan views each illustrating an exemplary sub-pixel structure in each pixel 20 .
  • Each pixel 20 has, a sub-pixel 20 R corresponding to red (R), a sub-pixel 20 G corresponding to green (G), a sub-pixel 20 B corresponding to blue (B), and a sub-pixel 20 W corresponding to white (W) which is higher in luminance than these three colors.
  • the sub-pixels 20 R, 20 G, 20 B, and 20 W of four colors of R, G, B, and W
  • the sub-pixels 20 R, 20 G, and 20 B respectively corresponding to three colors of R, G, and B have color filters 24 R, 24 G, and 24 B respectively corresponding to colors of R, G, and B.
  • the color filter 24 R corresponding to R is disposed to the sub-pixel 20 R corresponding to R
  • the color filter 24 G corresponding to G is disposed to the sub-pixel 20 G corresponding to G
  • the color filter 24 B corresponding to B is disposed to the sub-pixel 20 B corresponding to B.
  • no color filter is disposed to the sub-pixel 20 W corresponding to W.
  • luminance efficiency of video display can be enhanced compared with the case of the sub-pixel structure of three colors of R, G, and B. Details will be described later.
  • FIG. 3 illustrates an exemplary circuit configuration of a pixel circuit in each of the sub-pixels 20 R, 20 G, 20 B, and 20 W.
  • Each of the sub-pixels 20 R, 20 G, 20 B, and 20 W has a liquid crystal device 22 , a TFT device 21 , and a subsidiary capacitive device 23 .
  • a gate line G for line-sequentially selecting a pixel to be driven
  • a data line D for supplying to a pixel to be driven a video voltage (a video voltage supplied from the data driver 51 described later), and a subsidiary capacitive line Cs are connected.
  • the liquid crystal device 22 carries out a display operation according to a video voltage supplied to one end thereof from the data line D through the TFT device 21 .
  • the liquid crystal device 22 is a device in which a liquid crystal layer (not shown) made up of a liquid crystal such as VA (Vertical Alignment) mode liquid crystal or TN (Twisted Nematic) mode liquid crystal is sandwiched between a pair of electrodes (not shown).
  • a liquid crystal layer made up of a liquid crystal such as VA (Vertical Alignment) mode liquid crystal or TN (Twisted Nematic) mode liquid crystal is sandwiched between a pair of electrodes (not shown).
  • One of, or one end of, the pair of electrodes in the liquid crystal device 22 is connected to a drain of the TFT device 21 and one end of the subsidiary capacitive device 23 , the other of, or the other end of, the pair of electrodes is grounded.
  • the subsidiary capacitive device 23 is a capacitive device for stabilizing an accumulated charge of the liquid crystal device 22 .
  • One end of the subsidiary capacitive device 23 is connected to one end of the liquid crystal device 22 and the drain of the TFT device 21 , and the other end is connected to the subsidiary capacitive line Cs.
  • the TFT device 21 is a switching device for supplying, to both of one end of the liquid crystal device 22 and one end of the subsidiary capacitive device 23 , a video voltage based on a video signal D 1 , and is a MOS-FET (Metal Oxide Semiconductor-Field Effect Transistor).
  • a gate and a source of the TFT device 21 are connected to the gate line G and the data line D, respectively, and the drain of the TFT device 21 is connected to both of one end of the liquid crystal device 22 and one end of the subsidiary capacitive device 23 .
  • the back light 3 is a light source section for irradiating light to the liquid crystal display panel 2 , and is made up of, for example, Cold Cathode Fluorescent Lamp (CCFL), Light Emitting Diode (LED), or the like as a light emitting device.
  • the back light 3 carries out a lighting drive (active control or dynamic control of luminance) according to a luminance level or signal level of an input video signal Din, and the detail will be described later.
  • the video signal processing section 41 carries out, for example, a predetermined image processing (e.g., sharpness processing, gamma correction, or the like) for improving image quality on an input video signal Din of the pixel signal corresponding to three primary colors of R, G, and B.
  • a video signal D 1 of the pixel signal corresponding to three colors of R, G, and B that is, a pixel signal D 1 r for R, a pixel signal D 1 g for G, and a pixel signal D 1 b for B
  • a video signal D 1 of the pixel signal corresponding to three colors of R, G, and B is generated.
  • the output signal generation section 42 carries out a predetermined signal processing described later based on a video signal D 1 (D 1 r , D 1 g , and D 1 b ) supplied from the video signal processing section 41 .
  • a lighting signal BL 1 which shows luminance level (lighting level) in the back light 3
  • a video signal D 4 pixel signal D 4 r for R, pixel signal D 4 g for G, pixel signal D 4 b for B, and pixel signal D 4 w for W
  • an output video signal are generated.
  • the lighting signal BL 1 is generated based on the video signal D 1 , and a predetermined dimming processing described later is carried out based on the video signal D 1 and the generated lighting signal BL 1 . Then, a predetermined color conversion processing described later is carried out based on the resultant video signal from the dimming processing (video signal D 2 described later), thereby generating a video signal D 4 . It is to be noted that, specific configuration of the output signal generation section 42 will be described later ( FIG. 4 to FIG. 6B ).
  • the timing control section 43 controls the drive timing of the back light driving section 50 , the gate driver 52 , and the data driver 51 , and supplies a video signal D 4 supplied from the output signal generation section 42 to the data driver 51 .
  • the gate driver 52 line-sequentially drives each of the pixels 20 (each of sub-pixels 20 R, 20 G, 20 B, and 20 W) in the liquid crystal display panel 2 along the gate line G.
  • the data driver 51 supplies the video voltage based on the video signal D 4 supplied from the timing control section 43 to each of the pixels 20 (each of the sub-pixels 20 R, 20 G, 20 B, and 20 W) of the liquid crystal display panel 2 .
  • the data driver 51 supplies the pixel signal D 4 r for R to the sub-pixel 20 R, supplies the pixel signal D 4 g for G to the sub-pixel 20 G, supplies the pixel signal D 4 b for B to the sub-pixel 20 B, and supplies the pixel signal D 4 w for W to the sub-pixel 20 W. More specifically, the data driver 51 converts the video signal D 4 from digital to analog (D/A) to generate a video signal (above mentioned video voltage) as an analog signal, and outputs the resulting signal to each of the pixels 20 (each of the sub-pixels 20 R, 20 G, 20 B, and 20 W). In this manner, the display drive of each of the pixels 20 (each of the sub-pixels 20 R, 20 G, 20 B, and 20 W) in the liquid crystal display panel 2 based on the video signal D 4 is carried out.
  • D/A digital to analog
  • a video signal above mentioned video voltage
  • the back light driving section 50 carries out a lighting drive (lighting drive) of the back light 3 based on the lighting signal BL 1 output from the output signal generation section 42 .
  • a lighting drive active control or dynamic control of luminance
  • the detail will be described later.
  • FIG. 4 illustrates a block configuration of the output signal generation section 42 .
  • the output signal generation section 42 has a BL level calculation section 421 , an LCD level calculation section 422 , a chromaticity point adjustment section 423 , and an RGB/RGBW conversion section 424 .
  • the BL level calculation section 421 generates a lighting signal BL 1 in the back light 3 based on a video signal D 1 (D 1 r , D 1 g , and D 1 b ). Specifically, the BL level calculation section 421 analyses a luminance level (signal level) of the video signal D 1 to obtain a lighting signal BL 1 corresponding to the luminance level. Specifics of the generating operation for the lighting signal BL 1 in the BL level calculation section 421 will be described later.
  • the LCD level calculation section 422 Based on the video signal D 1 (D 1 r , D 1 g , and D 1 b ) and the lighting signal BL 1 output from the BL level calculation section 421 , the LCD level calculation section 422 generates a video signal D 2 (pixel signal D 2 r for R, pixel signal D 2 g for G, and pixel signal D 2 b for B). Specifically, the LCD level calculation section 422 carries out a predetermined dimming processing (here, the signal level of the video signal D 1 is divided by the signal level of the lighting signal BL 1 ) based on the video signal D 1 and the lighting signal BL 1 to generate the video signal D 2 .
  • a predetermined dimming processing here, the signal level of the video signal D 1 is divided by the signal level of the lighting signal BL 1
  • the LCD level calculation section 422 generates the video signal D 2 with use of the following expressions (1) to (3).
  • D 2 r ( D 1 r/BL 1) (1)
  • D 2 g ( D 1 g/BL 1) (2)
  • D 2 b ( D 1 b/BL 1) (3)
  • the chromaticity point adjustment section 423 carries out a predetermined chromaticity point adjustment of a video signal D 2 (D 2 r , D 2 g , and D 2 b ) to generate a video signal D 3 (D 3 r , D 3 g , and D 3 b ).
  • a video signal D 2 (D 1 ) is a video signal indicating white (W)
  • the chromaticity point adjustment is carried out so that a chromaticity point of display light emitted from the liquid crystal display panel 2 based on emitted light from the back light 3 is white chromaticity point.
  • a video signal D 2 (D 1 ) is a video signal indicating white (W)” corresponds to the case when a luminance level (signal level or luminance gradation) of each of the pixel signals D 2 r , D 2 g , and D 2 b (D 1 r , D 1 g , and D 1 b ) is at the maximum value.
  • the chromaticity point adjustment section 423 carries out a chromaticity point adjustment with use of, for example, a transformation matrix M d2 ⁇ d3 specified by the following expression (4).
  • the video signal D 2 (pixel signals D 2 r , D 2 g , and D 2 b ) is multiplied by the transformation matrix M d2 ⁇ d3 , in other words, a matrix operation is carried out, thereby generating the video signal D 3 (pixel signals D 3 r , D 3 g , and D 3 b ).
  • the transformation matrix M d2 ⁇ d3 can be obtained by multiplying the transformation matrix M d2 ⁇ XYZ by the transformation matrix M XYZ ⁇ d3 (matrix operation).
  • the transformation matrix M d2 ⁇ XYZ is a transformation matrix from the video signal D 2 to the tristimulus values (X, Y, Z) in the white color chromaticity point.
  • the transformation matrix M XYZ ⁇ d3 is a transformation matrix from this tristimulus values (X, Y, Z) to the video signal D 3 , and can be obtained with use of the following expression (5).
  • (Xw, Yw, Zw) represent tristimulus values in the sub-pixel 20 W
  • (Wr, Wg, Wb) represent the signal level of each sub-pixel intermediate video signal in the case where the signal level of the video signal (W signal) for the sub-pixel 20 W is replaced by a set of the intermediate video signals for each of the sub-pixels 20 R, 20 G, and 20 B.
  • the RGB/RGBW conversion section 424 carries out a predetermined RGB/RGBW conversion processing (color conversion processing) on the video signal D 3 (D 3 r , D 3 g , and D 3 b ) which corresponds to the three colors of R, G, and B and is output from the chromaticity point adjustment section 423 .
  • a video signal D 4 (D 4 r , D 4 g , D 4 b , and D 4 w ) corresponding to four colors of R, G, B, and W is generated.
  • FIG. 5 illustrates a block configuration of the RGB/RGBW conversion section 424 .
  • the RGB/RGBW conversion section 424 has LUTs (Look-Up Tables) 61 R, 61 G, and 61 B for each color of R, G, and B; a Min selection section 62 ; LUTs 63 R, 63 G, and 63 B for each color of R, G, and B; a Max selection section 64 ; a Min selection section 65 ; LUTs 66 R, 66 G, and 66 B for each color of R, G, and B; and subtraction sections 67 R, 67 G, and 67 B.
  • LUTs Look-Up Tables
  • the pixel signals D 3 r , D 3 g , and D 3 b which are input signals, are described as Sr, Sg, and Sb, respectively.
  • the LUTs 61 R, 61 G, and 61 B are LUTs which respectively correspond to inverse functions invfr, invfg, and invfb described later. Therefore, in the figure, the LUTs 61 R, 61 G, and 61 B are respectively shown as “Invfr-LUT”, “Invfg-LUT”, and “Invfb-LUT”.
  • the LUTs 63 R, 63 G, and 63 B are LUTs which respectively correspond to inverse functions invFr, invFg, and invFb described later. Therefore, in the figure, the LUTs 63 R, 63 G, and 63 B are respectively shown as “InvFr-LUT”, “InvFg-LUT”, and “InvFb-LUT”. Further, LUTs 66 R, 66 G, and 66 B are LUTs which respectively correspond to functions fr, fg, and fb described later. Therefore, in the figure, the LUTs 66 R, 66 G, and 66 B are respectively shown as fr-LUT, fg-LUT, and fb-LUT.
  • LUTs representing which set of signal levels can realize the process, when a signal level of a video signal D 4 w (Sw) for a sub-pixel 20 W is replaced by a set of the intermediate video signals for sub-pixels 20 R, 20 G, and 20 B (which correspond to above-mentioned Wr, Wg, and Wb, respectively), is used.
  • LUTs 66 R, 66 G, and 66 B (first LUT) which are LUTs prepared according to nonlinearity (nonlinearity in a relationship between a signal level of Sw and signal levels of Wr, Wg, and Wb) to be described later and shown in FIG. 11 , are used.
  • LUTs 61 R, 61 G, and 61 B respectively corresponding to the inverse function invfr (Sr), invfg (Sg), and invfb (Sb) are provided.
  • signal levels of inputs (Sr, Sg, and Sb) exceed the maximum value of each color in the vertical axis in the graph shown in FIG.
  • the signal level of each of pixel signals D 4 r , D 4 g , D 4 b , and D 4 w after the RGB/RGBW conversion will also be near 1.0, which is the upper limit. Therefore, if the signal level of the pixel signal D 4 w (W signal Sw) is changed, the signal level will exceed upper limit, which means the W signal Sw will be uniquely determined and there is no degree of freedom in signal level.
  • pixels 20 other than the pixel showing the highest luminance level in all of the pixels 20 of the liquid crystal display panel 2 , have a degree of freedom in the signal level of W signal Sw, in a range of the condition (restriction) specified by the expression (10) and the restriction that the signal level of each pixel signals D 4 r , D 4 g , D 4 b , and D 4 w is 1.0, which is the upper limit of them, or lower. Therefore, in such pixels 20 , in order to uniquely determine the signal level of the W signal Sw, another constraint condition may be required in addition to the expression (10).
  • the signal level (signal amplitude) of each of pixel signals D 4 r , D 4 g , D 4 b , and D 4 w should be at the smallest level.
  • display light is emitted in such a manner that there is no unevenness in luminance (in such a manner as to make luminance even) as far as possible, thereby advantageously making it possible to reduce graininess (graininess caused by sub-pixel structure) of the image when displayed in one color.
  • an RGB/RGBW conversion processing be carried out in the RGB/RGBW conversion section 424 so that signal levels of pixel signals D 4 r , D 4 g , D 4 b , and D 4 w making up the video signal D 4 are substantially equal to each other.
  • the signal level of the W signal is evaluated.
  • the solution in this case will be equal to the highest signal level in the pixel signals D 4 r , D 4 g , and D 4 b , so that the solution will be the one having the highest level in the above described solutions.
  • This can be expressed by the following expressions (11) to (14).
  • functions Fr (Sw), Fg (Sw), and Fb (Sw) set by the following expressions (14) to (16) are provided.
  • the signal level Sw_ 2 of W signal which is evaluated by the following expression (17) using inverse functions invFr (Sw), invFg (Sw), and invFb (Sw) respectively corresponding to the functions Fr (Sw), Fg (Sw), and Fb (Sw), is the signal level of W signal which satisfies the other constraint condition.
  • the highest value in the values of inverse functions invFr (Sw), invFg (Sw), and invFb (Sw) is the Sw_ 2 .
  • a condition (Sw_ 2 ⁇ Sw_ 1 ) that the signal level after the RGB/RGBW conversion has positive value may be required to be satisfied.
  • Sw_ 2 which makes one of the pixel signals D 4 r , D 4 g , and D 4 b into “0” will be selected. Therefore, the W signal Sw finally evaluated upon an RGB/RGBW conversion processing is expressed by the following expression (18). In other words, of Sw_ 1 and Sw_ 2 , the signal level having the lower value (the lowest value) is W signal Sw.
  • a LUT 61 R is a LUT which corresponds to the above described inverse function invfr (Sr), and outputs a value (signal level) indicated by the inverse function invfr (Sr) in response to input of a pixel signal D 3 r (Sr).
  • a LUT 61 G is a LUT which corresponds to the above described inverse function invfg (Sg), and outputs a value (signal level) indicated by the inverse function invfg (Sg) in response to input of a pixel signal D 3 g (Sg).
  • a LUT 61 B is a LUT which corresponds to the above described inverse function invfb (Sb), and outputs a value (signal level) indicated by the inverse function invfb (Sb) in response to input of a pixel signal D 3 b (Sb).
  • a Min selection section 62 is a section in which an arithmetic processing corresponding to the above described expression (10) is carried out, and from values (signal levels) output from LUTs 61 R, 61 G, and 61 B, the signal level having the lowest value is selected and output as Sw_ 1 .
  • a LUT 63 R is a LUT which corresponds to the above described inverse function invFr (Sr), and outputs a value (signal level) indicated by the inverse function invFr (Sr) in response to input of a pixel signal D 3 r (Sr).
  • a LUT 63 G is a LUT which corresponds to the above described inverse function invFg (Sg), and outputs a value (signal level) indicated by the inverse function invFg (Sg) in response to input of a pixel signal D 3 g (Sg).
  • a LUT 63 B is a LUT which corresponds to the above described inverse function invFb (Sb), and outputs a value (signal level) indicated by the inverse function invFb (Sb) in response to input of a pixel signal D 3 b (Sb).
  • a Max selection section 64 is a section in which an arithmetic processing corresponding to the above described expression (17) is carried out, and from values (signal levels) output from LUTs 63 R, 63 G, and 63 B, the signal level having the highest value is selected and output as Sw_ 2 .
  • a Min selection section 65 is a portion in which an arithmetic processing corresponding the above described expression (18) is carried out, and from Sw_ 1 and Sw_ 2 , the signal level having the lowest value (lower value) is selected and output as Sw.
  • a LUT 66 R is a LUT which corresponds to the above described function fr (Sw), and outputs a value (signal level) indicated by the function fr (Sw) in response to input of a W signal Sw.
  • a LUT 66 G is a LUT which corresponds to the above described function fg (Sw), and outputs a value (signal level) indicated by the function fg (Sw) in response to input of a W signal Sw.
  • a LUT 66 B is a LUT which corresponds to the above described function fb (Sw), and outputs a value (signal level) indicated by the function fb (Sw) in response to input of a W signal Sw.
  • a processing for limiting a signal level during the RGB/RGBW conversion processing in the RGB/RGBW conversion section 424 so that a signal level of pixel signals D 4 r , D 4 g , D 4 b , and D 4 w does not exceed a predetermined upper limit (e.g., 1.0).
  • a predetermined upper limit e.g., 1.0
  • the total number of sub-pixels is four thirds times larger than that in a liquid crystal display panel having a sub-pixel structure of three colors of R, G, and B, and therefore aperture ratio of each sub-pixel of the sub-pixel structure of four colors is relatively small.
  • display luminance of each sub-pixel in the sub-pixel structure of four colors tends to be relatively lower than luminance of each sub-pixel in the sub-pixel structure of three colors.
  • the signal level (luminance level) thereof may be made higher.
  • the video signal may exceed a predetermined upper limit (e.g., 1.0). If a configuration where signals which exceed the upper limit are all (evenly) set to the upper limit is adopted, then a gradation thereof will be lost (gradation thereof will be roughened), causing a discontinuity in luminance gradation.
  • gain coefficient (shown in FIG. 6A ) determined corresponding to the highest level in signal levels of video signals (pixel signals D 4 r , D 4 g , D 4 b , and D 4 w ) is multiplied by each of the signals, thereby carrying out a correction (limiting processing) of signal levels. More specifically, when the signal level is above the threshold level, as shown by the arrow in the figure, the value of gain coefficient is gradually (here, linearly) decreased. Thus, as shown in FIG.
  • the signal level of the video signal after the correction is made higher than before the correction
  • the signal level can be prevented from exceeding a predetermined upper limit (here, 1.0).
  • a predetermined upper limit here, 1.0
  • the increase rate of the signal level of the video signal after correction is gradually decreased, as shown by the arrow in the figure, and the upper limit can be reached exactly when the signal level before correction reaches the maximum value (here, 1.5).
  • the pixel signal D 4 w (W signal Sw) can be prevented from exceeding the upper limit of 1.0, so that it is also possible to carry out the above described signal level limiting processing only on the pixel signals D 4 r , D 4 g , and D 4 b.
  • a relationship between a signal level of Sw (described later) and signal levels of Wr, Wg and Wb supposedly shows linearity (proportional relationship), not nonlinearity as shown in FIG. 11 , for example, a video signal after RGB/RGBW conversion also shows nonlinearity. In that case, if the signal level is multiplied by constant after the signal level is converted to video signals corresponding to four colors of R, G, B, and W, chromaticity point will not be changed.
  • the signal level of the lighting signal BL 1 can be obtained.
  • the relationship between the signal level of Sw and the signal levels of Wr, Wg, and Wb shows, for example, nonlinearity as shown in FIG. 11 . Therefore, in the present embodiment, the above described method is not usable in the case where the signal level of the lighting signal BL 1 is to be computed.
  • a method may be adopted in which a solution of expression is obtained so that the maximum value of a video signal D 4 obtained through an RGB/RGBW conversion after the a video signal D 3 output from the chromaticity point adjustment section 423 is multiplied by constant (k fold) is 1.0.
  • this method is described in four cases. It is to be noted that, in the description below, three colors composing the video signal are denoted as c 1 , c 2 , and c 3 , each of which corresponds to any of R, G, and B.
  • a solution can be obtained from a condition that all the pixel signals D 4 r , D 4 g , D 4 b , and D 4 w after an RGB/RGBW conversion have positive value.
  • the pixel signal corresponding to one of the rest of the three colors c 1 to c 3 is a value within the range from 0 to 1, so that the following expressions (19) to (21) can be obtained.
  • the expressions (19) to (21) with use of the expressions (19) and (20), the following expression (22) can be obtained.
  • function G c1,c2 (Sw) specified by the following expression (23) is defined.
  • inverse function G ⁇ 1 c1,c2 (Sc 1 /Sc 2 ) corresponding to function G c1,c2 (Sw) specified by the following expression (24) is obtained to prepare a Look-Up Table.
  • a W signal Sw and a multiplying factor k are obtained with use of the following expression (25). If the W signal Sw and the multiplying factor k thus obtained satisfy the above described expression (21), then the multiplying factor k is the maximum multiplying factor in question.
  • a value of a W signal Sw indicating a peak value is expressed as Sw_p.
  • a value V of a video signal D 3 before a RGB/RGBW conversion is higher than that in the case where a W signal Sw is 1.
  • each of pixel signals D 4 r and D 4 g other than the pixel signal D 4 b only needs to be a value within the range from 0 to 1, so that expressions (30) to (32) can be obtained. If there exists a multiplying factor k which satisfies these expressions (30) to (32), the multiplying factor k is the maximum multiplying factor in question, and can be expressed by the following expression (33).
  • the factor k having the highest value is the multiplying factor k in question.
  • the right-hand value in the expression (36) monotonically decreases in the range larger than the value Sw_p of the W signal Sw at peak value.
  • the multiplying factor k should be lower than the right-hand value in the expression (36) with respect to all the colors of c 1 to c 3 ; therefore, in the range where the right-hand value in the expression (36) has larger value, a point where the multiplying factor k gives the maximum value is as follows.
  • the multiplying factor k can be evaluated, and the value V which is evaluated by multiplying the multiplying factor k by a video signal D 3 before a RGB/RGBW conversion is the maximum value in that case.
  • the video signal processing section 41 carries out a predetermined image processing on the input video signal Din, thereby generating a video signal D 1 (D 1 r , D 1 g , and D 1 b ).
  • the output signal generation section 42 carries out a predetermined signal processing on the video signal D 1 .
  • a lighting signal BL 1 in the back light 3 and a video signal D 4 (D 4 r , D 4 g , D 4 b , and D 4 z ) in the liquid crystal display panel 2 are generated.
  • the video signal D 4 and the lighting signal BL 1 thus generated are input to the timing control section 43 .
  • the video signal D 4 is supplied from the timing control section 43 to the data driver 51 .
  • the data driver 51 converts the video signal D 4 from digital to analog so as to generate a video voltage serving as analog signal.
  • the display drive operation is carried out.
  • the display drive based on the video signal D 4 (D 4 r , D 4 g , D 4 b , and D 4 w ) is carried out to the pixel 20 (each of the sub-pixels 20 R, 20 G, 20 B, and 20 W) in the liquid crystal display panel 2 .
  • the lighting signal BL 1 is supplied from the timing control section 43 to the back light driving section 50 .
  • the back light driving section 50 carries out, based on the lighting signal BL 1 , a lighting drive (lighting drive) for each light source (each light emitting device) in the back light 3 .
  • a lighting drive active control of luminance (dynamic control)
  • a luminance level signal level of an input video signal Din.
  • the video display is carried out with use of video signals corresponding to the sub-pixels 20 R, 20 G, 20 B, and 20 W of four colors. Therefore, in comparison with the known apparatus in which a video display is carried out with use of video signals corresponding to sub-pixels of three colors of R, G, and B, enhanced luminance efficiency can be achieved. In addition, since an active drive of the back light 3 is carried out with use of luminance according to the luminance level of the input video signal Din, lower power consumption and expansion of dynamic range can be realized while keeping a display luminance.
  • an operation for generating an output signal (operation in the output signal generation section 42 ) in the case of using a sub-pixel structure of four colors of R, G, B, and W is specifically described in comparison with comparative example.
  • incident light on a liquid crystal layer from a back light is modulated according to a signal level of a video signal, and amount of light (luminance) of transmitted light (display light) is controlled.
  • Spectroscopic characteristic of transmitted light from the liquid crystal layer indicates gradation dependency, and as the signal level of the video signal lowers, a transmittance peak shifts to the short wavelength side (blue color light side) (see FIG. 7 , for example).
  • a sub-pixel of Z (W) shows a high luminance characteristic, so that spectroscopic characteristic of the transmitted light from the sub-pixel of Z (W) changes according to a signal level of a video signal.
  • FIG. 8 illustrates spectroscopic transmittance in each of sub-pixels R, G, B, and W.
  • color reproduction characteristic in a sub-pixel structure of four colors of R, G, B, and W is illustrated in HSV color space, if it is assumed that there is no variation in transmittance peak in sub-pixel of W, the result is ideally as shown in FIG. 9 , for example.
  • shown in FIG. 9 is a rotationally symmetric color space with the white-color chromaticity point as the center.
  • color reproduction characteristic in the sub-pixel structure of four colors of R, G, B, and W according to comparative example (known) will be as shown in FIG. 10 , for example.
  • a bright (value of value V is high) region exists in colors (color phase) from white (W) to blue (B) side, while dark (value of value V is low) region exists in color region (color phase) from magenta (M) to cyan (C) with yellow (Y) at the center thereof.
  • M magenta
  • C cyan
  • Y yellow
  • FIG. 11 illustrates an exemplary relationship between a signal level of a W-sub-pixel video signal (signal level of W signal) and, above described Wr, Wg, and Wb (signal level of each of R-, G-, and B-sub-pixel intermediate video signals in the case where a signal level of W signal is replaced by a set of the R-, G-, and B-sub pixel intermediate video signals) in the sub-pixel structure of four colors of R, G, B, and W according to the comparative example. If it is assumed that there is no variation in transmittance peak in the sub-pixel of W as in the case shown in FIG. 9 , for example, the relationship between the signal level of W signal and Wr, Wg, and Wb will be proportional (will show linearity).
  • each of Wr, Wg, and Wb is a function having a gradient depending on a signal level of W signal (shows nonlinearity).
  • a signal level of the video signal is also nonlinearly changed to cause a variation (color shift) in chromaticity point in some cases, thereby lowering image quality. Further, in order to reduce such a lowering of image quality due to the color shift, a complicated arithmetic processing for the nonlinearity becomes necessary during a signal processing (dimming processing), which results in a complicated device configuration.
  • signal processing are carried out in the output signal generation section 42 as follows. Specifically, firstly, the BL level calculation section 421 generates a lighting signal BL 1 based on a video signal D 1 , and then, the LCD level calculation section 422 carries out a predetermined dimming processing (division operation) based on the video signal D 1 and the lighting signal BL 1 to generate a video signal D 2 .
  • the RGB/RGBW conversion section 424 carries out a RGB/RGBW conversion processing on a video signal D 3 based on the resultant video signal D 2 from the dimming processing to generate a video signal D 4 .
  • the generation and dimming processing of the lighting signal BL 1 are carried out on the video signal D 1 (D 1 r , D 1 g , and D 1 b ) corresponding to the three colors of R, G, and B, and thereafter, the RGB/RGBW conversion processing is carried out to generate the video signal D 4 corresponding to four colors of R, G, B, and W.
  • the result is as follows. That is, the color shift of the display light due to variation of peak wavelength region (above-described nonlinearity) in emitted light (transmitted light) from the sub-pixel 20 W is suppressed with a simple arithmetic processing (dimming processing).
  • the chromaticity point adjustment section 423 in the output signal generation section 42 carries out a predetermined chromaticity point adjustment on the video signal D 2 (D 2 r , D 2 g , and D 2 b ) to generate a video signal D 3 (D 3 r , D 3 g , and D 3 b ). More specifically, when the video signal D 2 (D 1 ) is a video signal which indicates W, the chromaticity point adjustment is carried out so that the chromaticity point of display light emitted from the liquid crystal display panel 2 based on the emitted light from the back light 3 is a white-color chromaticity point.
  • the RGB/RGBW conversion section 424 carries out the RGB/RGBW conversion processing for the video signal D 3 (D 3 r , D 3 g , and D 3 b ) after the chromaticity point adjustment in order to generate the video signal D 4 (D 4 r , D 4 g , D 4 b , and D 4 w ) which corresponds to four colors of R, G, B, and W.
  • the chromaticity point adjustment section 423 carries out the chromaticity point adjustment, by using, for example, the transformation matrix M d2 ⁇ d3 specified by the expression (4).
  • the video signal D 2 (pixel signals D 2 r , D 2 g , and D 2 b ) is multiplied by the transformation matrix M d2 ⁇ d3 (or, matrix operation is carried out), thereby to generate the video signal D 3 (pixel signals D 3 r , D 3 g , and D 3 b ).
  • the chromaticity point of the display light indicates a white-color chromaticity point.
  • the chromaticity point of the peak wavelength region in emitted light from the sub-pixel 20 W is adjusted, and the color shift of the display light is suppressed.
  • the LUTs 66 R, 66 G, and 66 B provided in advance according to, for example, the nonlinearity shown in FIG. 11 (nonlinearity in the relationship between a signal level of Sw and signal levels of Wr, Wg, and Wb) are used.
  • a characteristic e.g., the above described nonlinearity
  • the lighting signal BL 1 is generated based on the video signal D 1 corresponding to three colors of R, G, and B and the predetermined dimming processing based on the video signal D 1 and the lighting signal BL 1 is carried out, and thereafter, the predetermined RGB/RGBW conversion processing based on the video signal D 2 after the dimming processing is carried out, thereby to generate the video signal D 4 corresponding to four colors of R, G, B, and W. Consequently, it is possible to reduce the color shift of the display light caused by the nonlinearity with a simple arithmetic processing (dimming processing). Therefore, in the case where a video display is carried out using the sub-pixel structure of four colors of R, G, B, and W, the dimming processing can be realized in a simple configuration with the lowering of image quality due to color shift being suppressed.
  • the pixel 20 of the embodiment is configured to include the sub-pixel 20 W corresponding to W as an example of a sub-pixel 20 Z which will be described later, it is not necessary to provide any color filter in this sub-pixel 20 W, and therefore enhanced efficiency in luminance (lower power consumption) can be realized in particular.
  • the BL level calculation section 421 in the liquid crystal display apparatus 1 of the embodiment uses a common LUT shared by R, G, and B hereinafter described (common LUT 70 described later). Specifically, when generating a lighting signal BL 1 , as opposed to the embodiment, the BL level calculation section 421 uses a LUT (second Look-Up Table) in which a relationship between chromaticity of the video signal D 1 and the highest signal level which can be expressed in the chromaticity or the inverse of the signal level is specified in advance.
  • LUT second Look-Up Table
  • the reason for this is as follows. That is, although the highest signal level (signal amplitude) which can be expressed can be obtained by using the circuit configuration as in the embodiment, the configuration (circuit configuration) may be complicated. In view of this, in the modification 1, the highest signal level which can be expressed for chromaticity of the video signal D 1 is calculated in advance, and the resulting level is retained as a LUT for the video signal D 1 . In this manner, through comparison with the signal level of the video signal D 1 , the lighting signal BL 1 can be calculated. Methods for preliminarily calculating the highest signal level which can be expressed for the chromaticity of the video signal D 1 are described below.
  • the highest signal level which can be expressed may be obtained with use of the methods for obtaining solutions in each of the cases (1) to (4) explained in the above described embodiment.
  • a video signal D 1 before an RGB/RGBW conversion may be obtained through a back calculation of a video signal D 4 after the RGB/RGBW conversion.
  • a pixel signal corresponding to either of colors of R, G, or B is 1 as the upper limit.
  • a reverse conversion (RGBW/RGB conversion) of a video signal in which a pixel signal corresponding to either of colors is made to be 1 and at the same time the other pixel signals corresponding to the other colors are minutely changed is carried out to thereby generate a video signal D 3 , and through inverse matrix calculation, or the like, of the video signal D 3 , the video signal D 1 is obtained.
  • the video signal D 1 obtained in this way is divided by chromaticity, and the signal having amplitude of the largest value V in the chromaticity is obtained as the highest signal.
  • a repeated computation may be adopted and the computation method is as follows. Firstly, an arbitrary video signal D 1 is multiplied by constant until its signal level (amplitude) is, for example, almost 2, and then, a matrix conversion, and an RGB/RGBW conversion which gives the minimum amplitude are carried out. At this point of time, a W signal Sw is converted up to 1 as the upper limit of LUT while pixel signals corresponding to R, G, and B exceed 1.
  • d the signal level (amplitude) of the video signal D 1 is denoted by h.
  • the next input signal is a signal wherein the video signal D 1 is multiplied by (h ⁇ d)/h
  • the matrix operation and the RGB/RGBW conversion are carried out to evaluate the difference value d between the upper limit and 1.
  • This computation is repeatedly carried out until the difference value d becomes below a predetermined threshold level (minute value), and amplitude of value V of the input signal at that time is used as the highest expressible signal level.
  • a LUT of HSV type as the common LUT 70 shown in FIGS. 12A and 12B , can be given as an example.
  • the common LUT 70 is a LUT in which hue H and saturation S in chromaticity of the video signal D 1 are obtained, and the highest expressible signal level for those is used as value V.
  • the lighting signal BL 1 can be obtained with use of the highest value (the highest value in all pixels 20 ) of the ratio which can be obtained by dividing the video signal D 1 by the highest expressible signal level (value V) which is obtained from the common LUT 70 .
  • luminance of the back light causes bouncing (color skipping) and other problems, so that luminance of the back light is changed with a certain amount of time constant.
  • luminance of the back light changes only in a certain amount of time constraint, so that the luminance and chromaticity of the region will not be correctly expressed, thereby generating “dark” portion.
  • the signal level variation in the lighting signal BL 1 in response to chromaticity variation in the video signal D 1 be limited to equal to or lower than a predetermined threshold level.
  • a predetermined threshold level a value of sensitivity of the human eye (for example, ⁇ E ⁇ 1.0) can be given.
  • ⁇ E is color difference between two colors which is defined in CIE1976 L*u*v* color system and CIE1976 L*a*b* color system, and values around ⁇ E ⁇ 1 are the allowable tolerance of color difference.
  • the common LUT 70 is set in this manner, it is possible to reduce the rapid change in luminance, bouncing (color skipping), and the like which are caused by a steep change in luminance of the back light due to a shape of a color space.
  • a liquid crystal display apparatus includes a BL calculation section 421 A described below disposed in place of the BL level calculation section 421 in the liquid crystal display apparatus 1 of the above mentioned embodiment.
  • the BL level calculation section 421 A uses individual LUTs (LUTs 74 R, 74 G, and 74 B described later) for each of pixel signals corresponding to R, G, and B.
  • the BL level calculation section 421 A of the modification 2 includes three kinds of LUTs each of which is used when each of pixel signals of R, G, and B is at the maximum value.
  • the input signal is divided by the maximum value of R, G, and B, and chromaticity is specified by values other than the maximum value.
  • FIG. 13 illustrates an exemplary block configuration of the BL level calculation section 421 A.
  • the BL level calculation section 421 A includes a Max selection section 71 , a division section 72 , a selection output section 73 , and LUTs 74 R, 74 G, and 74 B for each color of R, G, and B.
  • the Max selection section 71 selects a pixel signal which has the highest signal level from pixel signals D 1 r , D 1 g , and D 1 b in a video signal D 1 , and outputs the selected signal.
  • the division section 72 is a section in which each of pixel signals D 1 r , D 1 g , and D 1 b in a video signal D 1 is divided by the highest signal level output from the Max selection section 71 .
  • the selection output section 73 selects a part of the divided values of the pixel signals D 1 r , D 1 g , and D 1 b output from the division section 72 , and outputs the selected part to each of LUTs 74 R, 74 G, and 74 B. Specifically, the selection output section 73 outputs the divided values of the pixel signals D 1 g and D 1 b individually to the LUT 74 R, outputs the divided values of the pixel signals D 1 r and D 1 b individually to the LUT 74 G, and outputs the divided values of the pixel signals D 1 r and D 1 g individually to the LUT 74 B.
  • the LUTs 74 R, 74 G, and 74 B are LUTs in which hue H and saturation S in chromaticity of the video signal D 1 , and inverse of the corresponding highest expressible signal level (1/value V) are related. This is because, as mentioned above, the ratio obtained by dividing a pixel signal by the signal level having the highest expressible value is used when calculating back light luminance, so that the use of the inverse of value V leads to a simple configuration.
  • signal level variation of the lighting signal BL 1 responding to chromaticity variation in the video signal D 1 be limited to equal to or lower than a predetermined threshold level.
  • portions (regions) shown, for example, by symbols P 31 in FIG. 18A and P 41 in FIG. 19A are preferably limited in the signal level variation as shown, for example, by symbols P 32 in FIG. 18B and P 42 in FIG. 19B .
  • a liquid crystal display apparatus includes a liquid crystal display panel having a pixel 20 - 1 described below in place of the liquid crystal display panel 2 having the pixel 20 in the liquid crystal display apparatus 1 of the embodiment.
  • FIGS. 20A and 20B are schematic plan views illustrating exemplary configurations of sub-pixels of each pixel 20 - 1 according to the modification 3.
  • FIGS. 20A and 20B correspond to FIGS. 2A and 2B , respectively.
  • Each pixel 20 - 1 includes the same sub-pixels 20 R, 20 G, and 20 B corresponding to three colors of R, G, and B as in the embodiment, and a sub-pixel 20 Z which shows luminance higher than those of the three colors.
  • the color (Z) which shows the high luminance includes yellow (Y), white (W), and the like, and, in the modification 3, the color (Z) is described as a broader concept of these exemplified colors.
  • the sub-pixels 20 R, 20 G, 20 B, and 20 Z of four colors of R, G, B, and Z are provided with, as in the embodiment, the color filters 24 R, 24 G, and 24 B corresponding to each color of R, G, and B, respectively.
  • the layout of each of the sub-pixels 20 R, 20 G, 20 B, and 20 Z is not limited to these examples, and other layouts may be adopted.
  • liquid crystal display apparatus in the modification 3 configured in this manner, it is possible to obtain the same effects as in the liquid crystal display apparatus 1 of the embodiment, through the same functions. More specifically, in the case where a video display is performed with use of the sub-pixel structure of four colors of R, G, B, and Z, it is possible to realize in a simple configuration a dimming processing while suppressing lowering of image quality due to color shift.
  • the series of processing described in the embodiment and so forth may be carried out by hardware or software.
  • the program configuring the software is installed to the general-purpose computer or the like.
  • the program may be stored in advance in the recording medium incorporated in the computer.

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