TRANSMISSIVE-TYPE LIQUID CRYSTAL DISPLAY DEVICE

• US 20080150863A1
• Filed: 12/17/2007
• Published: 06/26/2008
• Est. Priority Date: 12/21/2006
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Tanaka, Hiroshi, Morisue, Takashi, Muramatsu, Tsuyoshi, Aoki, Atsushi
• Granted Patent: US 8,233,013 B2
• Time in Patent Office: Days
• US Class Current: 345/88
• CPC Class Codes: G09G 2300/0452 Details of colour pixel setup, e.g. pixel composed of a red, a blue and two green components
• CPC Class Codes: G09G 2320/0238 Improving the black level
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336

Abstract

In a transmissive-type liquid crystal display device including a liquid crystal panel and a backlight, the liquid crystal panel has pixels each divided into four subpixels red (R), green (G), blue (B), and white (W). The backlight is a white backlight by which luminance of emitted light is controllable. A color-saturation reducing section carries out a process of reducing color saturation on a first RGB input signal, which is an original input signal, so that the first RGB input signal becomes a second RGB input signal. Thereafter, an output signal generating section obtains a transmissivity and a backlight value on the basis of the second RGB input signal.

Claims

1. A transmissive-type liquid crystal display device, comprising:

a liquid crystal panel having pixels each divided into four subpixels red (R), green (G), blue (B), and white (W);

a white-color active backlight by which a luminance of light that is to be emitted is controllable;

a color-saturation reducing section that carries out a process of reducing color saturation on pixel data that is high in luminance and in color saturation, among pixel data contained in a first RGB input signal which is an input image, so that the first RGB input signal is converted into a second RGB input signal;

an output signal generating section that generates, from the second RGB input signal, a transmissivity signal of each of the subpixels R, G, B, W of each pixel of the liquid crystal panel, and calculates a backlight value in the active backlight;

a liquid crystal panel controlling section that controls and drives the liquid crystal panel on the basis of the transmissivity signal generated in the output signal generating section; and

a backlight controlling section that controls, on the basis of the backlight value calculated in the output signal generating section, the luminance of light that is to be emitted from the backlight.

2. The device of claim 1, wherein the color-saturation reducing section reduces only the color saturation of the pixel data on which the process of reducing color saturation is carried out, without changing luminance and hue of the pixel data before and after the process of reducing color saturation.

3. The device of claim 1, wherein a level of the process of reducing color saturation is changeable by the color-saturation reducing section.

4. The device of claim 3, wherein the color-saturation reducing section determines, on the basis of a white-color luminance ratio WR, the range of change of the level of the process of reducing color saturation,

where the white-color luminance ratio WR is a ratio P2/P1 of a display luminance P2, in a case in which a transmissivity of each of the subpixels RGB is 0% and a transmissivity of the subpixel W is x %, to a display luminance P1, in a case in which the transmissivity of each of the subpixels RGB is x % and the transmissivity of the subpixel W is 0%.

5. The device of claim 1, wherein the color-saturation reducing section extracts, from the pixel data contained in the first RGB input signal which is the input image, pixel that is high in luminance and in color saturation, in accordance with process (A) below, and carries out, in accordance with process (B) below, a process of reducing the color saturation on the pixel data thus extracted:

(A) calculating an upper limit MAXw of the backlight by

MAXw=MAX×

Bl Ratio,

and extracting, as the pixel data that is high in luminance and in color saturation, target pixel data that satisfies

MAXw<

maxRGB−

minRGB,

where;

WR is a white-color luminance ratio (this is a ratio P2/P1 of a display luminance P2 in a case in which a transmissivity of each of the subpixels RGB is 0% and a transmissivity of the subpixel W is x %, with respect to a display luminance P1 in a case in which the transmissivity of each of the subpixels RGB is x % and the transmissivity of the subpixel W is 0%);

MAX is the upper limit of the backlight value in a case in which the process of reducing color saturation is not carried out;

Bl Ratio is a backlight value determination ratio (1/(1+WR)≦

Bl Ratio≦

1.0);

maxRGB=max(Ri,Gi,Bi);

minRGB=min(Ri,Gi,Bi);

Ri, Gi, Bi (i=1, 2, . . . , Np) are RGB values of the target pixel in the first RGB input signal;

Np is the number of pixels in the input image;

max (A, B, . . . ) is a maximum value of A, B, and

min (A, B, . . . ) is a minimum value of A, B, . . . ); and

(B) obtaining, on the basis of the pixel data thus extracted,

Rsi=α

×

Ri+(1−

α

)×

Yi,

Gsi=α

×

Gi+(1−

α

)×

Yi, and

Bsi=α

×

Bi+(1−

α

)×

Yi,

pixel data after the process of reducing color saturation, where;

Rsi, Gsi, Bsi (I=1, 2, . . . , Np) are RGB values of the target pixel in the second RGB input signal after the process of reducing color saturation;

Yi (i=1, 2, . . . , Np) is a luminance of the target pixel; and

α

=MAXw/(maxRGB−

minRGB).

6. The device of claim 5, wherein the output signal generating means includes:

a W transmission-amount calculating section that calculates a transmission amount (Wtsi) of the subpixel W in accordance with process (A) of calculating the W transmission amount (Wtsi) by

Wtsi=min(maxRGBs/(1+1/WR),minRGBs),

where maxRGBs=max (Rsi, Gsi, Bsi), and minRGBs=min (Rsi, Gsi, Bsi);

an RGB transmission-amount calculating section that calculates a transmission amount (Rtsi, Gtsi, Btsi) of each of the subpixels RGB in accordance with process (B) of calculating the RGB transmission amounts (Rtsi, Gtsi, Btsi) by

Rtsi=Rsi−

Wtsi,

Gtsi=Gsi−

Wtsi, and

Btsi=Bsi−

Wtsi;

a backlight value calculating section that calculates a backlight value (Wbs) in accordance with process (C) of calculating the backlight value (Wbs) by

Wbs=max(Rts1,Gts1,Bts1,Wts1/WR, . . . RtsNp,GtsNp,BtsNp,WtsNp/WR);

and

a transmissivity calculating means for calculating a transmissivity (rsi, gsi, bsi, wsi) of each of the subpixels RGBW in accordance with process (D) of calculating the RGBW transmissivities (rsi, gsi, bsi, wsi) by

rsi=Rtsi/Wbs,

gsi=Gtsi/Wbs,

bsi=Btsi/Wbs, and

wsi=Wtsi/Wbs/WR,

where rsi=gsi=bsi=wsi=0 when Wbs=0.

7. The device of claim 1, wherein:

a plurality of active backlights are provided with respect to the liquid crystal panel; and

controlling a transmissivity of the liquid crystal panel and controlling the backlight value of the backlight are carried out on individual areas that correspond to the plurality of active backlights, respectively.

8. A control program, causing a computer to execute respective processes of the sections defined in claim 5 and of the means defined in claim 5.

9. A control program, causing a computer to execute respective processes of the sections defined in claim 6 and of the means defined in claim 6.