LCD Backlight Dimming, LCD / Image Signal Compensation and method of controlling an LCD display

• US 20090295705A1
• Filed: 05/29/2008
• Published: 12/03/2009
• Est. Priority Date: 05/29/2008
• Status: Active Grant

• Current Assignee: Hong Kong Applied Science And Technology Research Institute Co., Ltd.
• Original Assignee: Hong Kong Applied Science And Technology Research Institute Co., Ltd.
• Inventors: ZHANG, Wei, QIU, Guoping, CHEN, Min, PENG, Huajun, HUNG, Chun Kit
• Granted Patent: US 8,514,166 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G09G 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: G09G 3/3611 Control of matrices with row and column drivers

Abstract

A method of reducing power consumption in a liquid crystal display illuminated by a backlight device includes dimming the backlight and adjusting the intensity of the image to compensate for the dimmed backlight. A dimming factor for the backlight is based on a clipping point determining from the pixel intensity distribution of the image signal. The intensity of the image is adjusted based on the dimming factor, wherein a first tone mapping function is used to adjust pixel intensities below an intensity threshold and a second tone mapping function is used to adjust pixel intensities above the intensity threshold

Claims

1. A method of reducing power consumption in a liquid crystal display illuminated by a backlight device, the method comprising steps of:

determining a pixel intensity distribution for an image signal to be displayed on the liquid crystal display determining a clipping point based on the pixel intensity distribution of the image signal,

determining a dimming factor for the backlight based on the clipping point and illuminating the backlight according to the dimming factor,

adjusting the pixel intensity distribution of image pixels based on the dimming factor, wherein a first tone mapping function is used to adjust pixel intensities below an intensity threshold and a second tone mapping function is used to adjust pixel intensities above the intensity threshold

2. The method of claim 1 wherein the clipping point is between the 60^th and 99^th percentiles of the pixel intensity distribution.

3. The method of claim 1 wherein the pixel intensity distribution is based on achromatic intensities of pixels in the image signal.

4. The method of claim 1 wherein the pixel intensity distribution is based on maximum value of Red, Green and Blue channel intensities of pixels in the image signal.

5. The method of claim 1 wherein the dimming factor is determined by a equation of the form

$\mathrm{BLdim}={\left(\frac{\mathrm{CP}}{\mathrm{Imax}}\right)}^P,$

wherein CP is the clipping point value, Imax is the max display intensity, the p is a constant than not less than one. The value of p is determined according to the LCD input-output characteristics, usually close to the gamma value of the display.

6. The method of claim 1 wherein the intensity threshold is less than Clipping point.

7. The method of claim 6 wherein the threshold is determined by an equation of the form

|FP−

CP|=|CP−

Imax|,

where FP is the threshold, CP is the clipping point, Imax is the maximum display intensity of input image

8. The method of claim 1 wherein one of the first and second tone mapping functions is non-linear.

9. The method of claim 1 wherein the second mapping function is a non-linear mapping function

10. The method of claim 9 wherein the non-linear second tone mapping function is generated by the pixel intensity distribution.

11. A method of controlling a backlight illuminating and LCD display, the method comprising steps of:

determining a clipping point based on an pixel intensity distribution of a image signal,

determining an dimming factor for the backlight based on the clipping point, and

illuminating the backlight at the determined dimming factor.

12. The method of claim 11 wherein the clipping point is between the 60^th and 99^th percentiles of the pixel intensity distribution.

13. The method of claim 11 wherein the pixel intensity distribution is based on achromatic intensities of pixels in the image signal.

14. The method of claim 11 wherein the pixel intensity distribution is based on maximum value of Red, Green and Blue channel intensities of pixels in the image signal.

15. The method of claim 11 wherein the dimming factor is determined by a equation of the form

$\mathrm{BLdim}={\left(\frac{\mathrm{CP}}{\mathrm{Imax}}\right)}^P,$

wherein CP is the clipping point value, Imax is the max display intensity, the p is a constant than not less than one. The value of p is determined according to the LCD input-output characteristics, usually close to the gamma value of the display.

16. A method for maintaining the perceived brightness viewed of an image on a dimmed backlight liquid crystal display, the method comprising steps of:

dimming the backlight of a liquid crystal display by a dimming factor, and

adjusting the pixel intensity distribution of image pixels based on the dimming factor, wherein a first tone mapping function is used to adjust pixel intensities below an intensity threshold and a second tone mapping function is used to adjust pixel intensities above the intensity threshold.

17. The method of claim 16 wherein dimming the backlight of a liquid crystal display comprises steps of:

determining a clipping point based on an pixel intensity distribution of a image signal,

determining an dimming factor for the backlight based on the clipping point, and

illuminating the backlight at the determined dimming factor.

18. The method of claim 17 wherein the clipping point is between the 60^th and 99^th percentiles of the pixel intensity distribution.

19. The method of claim 17 wherein the pixel intensity distribution is based on achromatic intensities of pixels in the image signal.

20. The method of claim 17 wherein the pixel intensity distribution is based on maximum value of Red, Green and Blue channel intensities of pixels in the image signal.

21. The method of claim 17 wherein the dimming factor is determined by a equation of the form

$\mathrm{BLdim}={\left(\frac{\mathrm{CP}}{\mathrm{Imax}}\right)}^P,$

wherein CP is the clipping point value, Imax is the max display intensity, the p is a constant than not less than one. The value of p is determined according to the LCD input-output characteristics, usually close to the gamma value of the display.

22. The method of claim 18 wherein the intensity threshold is less than Clipping point.

23. The method of claim 18 wherein the threshold is determined by an equation of the form

|FP−

CP|=|CP−

Imax|,

where FP is the threshold, CP is the clipping point, Imax is the maximum display intensity of input image

24. The method of claim 18 wherein one of the first and second tone mapping functions is non-linear.

25. The method of claim 18 wherein the second mapping function is a non-linear mapping function

26. The method of claim 25 wherein the non-linear second tone mapping function is generated by the pixel intensity distribution.