Field sequential LCD device and color image display method thereof

• US 20020060662A1
• Filed: 11/23/2001
• Published: 05/23/2002
• Est. Priority Date: 11/23/2000
• Status: Active Grant

• Current Assignee: LG Display Co., Ltd.
• Original Assignee: LG Display Co., Ltd.
• Inventors: Hong, Hyung-Ki
• Granted Patent: US 7,365,729 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G09G 2310/0235 Field-sequential colour display
• CPC Class Codes: G09G 2340/06 Colour space transformation
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/2025 the sub-frames having all the same time duration
• CPC Class Codes: G09G 3/2077 by a combination of two or more gradation control methods
• CPC Class Codes: G09G 3/3413 Details of control of colour illumination sources

Abstract

In a liquid crystal display device, a field sequential liquid crystal display device includes a liquid crystal panel having an upper substrate, a lower substrate and a liquid crystal layer therebetween; a backlight device under the liquid crystal panel for irradiating light to the liquid crystal panel and having three color light sources; and an image signal processor controlling a sequential lighting order and combination of the three color light sources.

Claims

1. A field sequential liquid crystal display device, comprising:

a liquid crystal panel having an upper substrate, a lower substrate and a liquid crystal layer therebetween;

a backlight device under the liquid crystal panel for irradiating light to the liquid crystal panel and having three color light sources; and

an image signal processor controlling a sequential lighting order and combination of the three color light sources.

2. The device according to claim 1, wherein each of the three color light sources has one of colors Cyan, Magenta and Yellow.

3. The device according to claim 1, wherein each of the three color light sources has one of colors Red, Green and Blue.

4. The device according to claim 1, wherein the image signal processor changes the lighting order and combination of the three color light sources depending on image characteristics displayed in the liquid crystal panel.

5. The device according to claim 1, wherein the liquid crystal layer is Optical Compensated Birefringent (OCB) mode.

6. The device according to claim 1, wherein the liquid crystal layer is Ferroelectric Liquid Crystal (FLC) mode.

7. The device according to claim 1, wherein the three color light sources are sequentially lit for up to about {fraction (1/180)} second at three subframes when one frame period is approximately {fraction (1/60)} second.

8. The device according to claim 7, wherein a lighting time of each of the light sources at each subframe is less than {fraction (1/180)} second.

9. A color image display method for a field sequential liquid crystal display device that includes a liquid crystal panel having an upper substrate, a lower substrate, a liquid crystal layer therebetween, and a plurality of pixels;

a backlight device under the liquid crystal panel for irradiating light to the liquid crystal panel and having Red, Green and Blue light sources; and

an image signal processor controlling a sequential lighting order and combination of the Red, Green and Blue light sources, the method comprising the steps of;

dividing one frame into first, second and third subframes, wherein each subframe has a period of approximately one-third of one frame period;

applying an image signal to each pixel of the liquid crystal panel through the image signal processor, the image signal depending on image characteristics displayed in the liquid crystal panel; and

lighting the Red, Green and Blue light sources at the subframes through the image signal processor by way of combining the lighting order of the Red, Green and Blue light sources.

10. The method according to claim 9, wherein the combination of the Red (R), Green (G), and Blue (B) light sources turned on each subframe is one of sequential combinations consisting of B+G, R+B and R+G to display Cyan (C), Magenta (M) and Yellow (Y) colors, respectively, when the displayed image requires a higher brightness.

11. The method according to claim 10, wherein the image signal processor converts the image signal into a signal corresponding to a C-M-Y mode when the C, M and Y colors are generated, and applies the converted signal to the plurality of the pixels.

12. The method according to claim 11, wherein the image signal processor sequentially lights the R, G and B light sources at each subframe in accordance with the C-M-Y mode.

13. The method according to claim 9, wherein one frame period is approximately {fraction (1/60)} period.

14. The method according to claim 9, a lighting time of each of the Red, Green and Blue light sources is less than about {fraction (1/180)} second.

15. The method according to claim 9, wherein one of the R, G and B light sources are turned on and off more frequently than the other two light sources when the displayed image needs an emphasized color.

16. The method according to claim 15, wherein the R light sources is turned on and off not only at the first subframe but also at least one of the second and third subframes when the emphasized color is Red.

18. The method according to claim 17, wherein the number of the turned-on light sources at each subframe is less than two.

19. The method according to claim 17, wherein classifying the cases depends on a range of the average brightness values of the component R, G and B.

20. The method according to claim 17, wherein turning on the light sources is determined by a value that doubles respective minimum values of the components R, G and B in chromaticity coordinates.

21. The method according to claim 17, wherein the liquid crystal layer is Optical Compensated Birefringent (OCB) mode.

22. The method according to claim 17, wherein the liquid crystal layer is Ferroelectric Liquid Crystal (FLC) mode.

17. A color image display method for a field sequential liquid crystal display device that includes a liquid crystal panel having an upper substrate, a lower substrate, a liquid crystal layer therebetween, and a plurality of pixels;

a backlight device under the liquid crystal panel for irradiating light to the liquid crystal panel and having Red (R), Green (G) and Blue (B) light sources; and

an image signal processor controlling an image signal and a sequential lighting order and combination of the Red, Green and Blue light sources, the method comprising the steps of;

expressing a brightness of each component R, G and B with a gray level having 256 levels;

setting the brightness of each component R, G and B as a maximum brightness when the brightness of each component R, G and B has a value of gray level of at least 127;

calculating the average brightness value of each of the components R, G and B;

classifying cases in accordance with the image signal by which the average brightness values of the components R, G and B is greater than the maximum brightness of the displayed image; and

determining which light sources are turned on at the subframes in each case.