Patent ID: 8330689

Claim:
A transmissive liquid crystal display device, comprising: a liquid crystal panel containing pixels each divided into four subpixels, a red (R), a green (G), a blue (B), and a white (W) subpixel; a white active backlight emitting light with controllable emission luminance; a luminance lowering section for performing luminance lowering processing on high luminance pixel data of pixel data contained in input RGB signals representing an input image to transform the input RGB signals to luminance-lowered RGB signals: an output signal generating section for generating transmittance signals for individual R, G, B, W subpixels in the pixels in the liquid crystal panel from the luminance-lowered RGB signals and also calculating a backlight value for the active backlight from the luminance-lowered RGB signals; a liquid crystal panel control section for controlling driving of the liquid crystal panel according to the transmittance signals generated in the output signal generating section; a backlight control section for controlling the emission luminance of the backlight according to the backlight value calculated in the output signal generating section; wherein the luminance lowering section performs the luminance lowering processing by following procedures (A) to (B): (A) calculating a luminance-lowering maximum backlight value MAXwy by equation (1), MAXwy=MAX×B1Ratioy (1) where MAX is a maximum value of the input RGB signals (i.e., the maximum one of backlight values when neither chroma lowering nor luminance lowering is preformed) and B1Ratioy is a luminance-lowering backlight value setup ratio (0≦B1Ratioy≦1), (B) transforming the input RGB signals (R[i], G[i], B[i]) to the luminance-lowered RGB signals (Ry[i], Gy[i], By[i]) (i=1, 2, . . . , Np; Np is the number of pixels in the image) by if inequality (2) is satisfied, calculating the luminance-lowered-RGB signals by equations (3) to (6), MAXwy<max(maxRGB/2,maxRGB−minRGB) (2) Ry[i]=βy×R[i] (3) Gy[i]=βy×G[i] (4) By[i]=βy×B[i] (5) βy=MAXwy/max(maxRGB/2,maxRGB−minRGB) (6) where maxRGB=max(R[i], G[i], B[i]), minRGB=min(R[i], G[i], B[i]), max(A, B, . . . ) is a maximum value of A, B, . . . , and min (A, B, . . . ) is a minimum value of A, B, . . . , and if inequality (2) is not satisfied, transforming the luminance-lowered RGB signals to similar levels to the input RGB signals by equations (7) to (9) Ry[i]=R[i] (7) Gy[i]=G[i] (8) By[i]=B[i] (9).