LCD image compensation for LED backlighting

• US 10,163,408 B1
• Filed: 09/05/2014
• Issued: 12/25/2018
• Est. Priority Date: 09/05/2014
• Status: Active Grant

• Current Assignee: Pixelworks Semiconductor Technology Company Limited
• Original Assignee: Pixelworks Incorporated
• Inventors: Chen, Tao, Zhang, Bob
• Primary Examiner(s): Eurice, Michael J
• Application Number:
  US14/478,378
• Time in Patent Office: 1,572 Days
• CPC Class Codes: G09G 2320/0271 Adjustment of the gradation levels within the range of the gradation scale, e.g. by redistribution or clipping
• CPC Class Codes: G09G 2320/0285 using tables for spatial correction of display data
• CPC Class Codes: G09G 2320/0606 Manual adjustment
• CPC Class Codes: G09G 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• CPC Class Codes: G09G 2320/066 for control of contrast
• CPC Class Codes: G09G 2360/144 the light being ambient light
• 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 3/36 using liquid crystals

Abstract

A method includes determining a display backlight level based upon an ambient light level, using image content of incoming image data to adjust the display backlight level based upon image content to produce an image-compensated backlight value, and adjusting pixel values in the image data as needed based upon the image-compensated backlight value.

Claims

1. A method, comprising:

determining a display backlight level based upon an ambient light level;

determining a weighted histogram of image pixel values of incoming image data, wherein each count added to a histogram bin in the weighted histogram is weighted by a value of an image pixel, and each histogram bin of the weighted histogram is mapped to a bin backlight value;

using the weighted histogram of image pixel values of incoming image data to produce a content backlight value and content-based compensation weights for each pixel in the incoming image data;

finding a final backlight level based upon the display backlight level and the content backlight values;

limiting the final backlight level to find an actual backlight level; and

adjusting the image pixel values of the incoming image data as needed based upon initial pixel values in the incoming image data, the content backlight value, the content-based compensation weights, the final backlight level, and the actual backlight level.

2. The method of claim 1, further comprising:

designating at least some pixels in the image data as bright pixels based upon the histogram bin identified by gray scale values of the bright pixels;

applying a contrast adjustment gain identified in the histogram bin.

3. The method of claim 1, wherein each bin value is adjusted using a piece-wise linear function.

4. The method of claim 1, wherein determining the display backlight level comprises:

measuring the ambient light level in an environment; and

mapping measured ambient light to a display backlight value.

5. The method of claim 4, wherein mapping the measured ambient light level comprises applying a piece-wise linear function to the measured ambient light to produce the display backlight level.

6. The method of claim 4, wherein the display backlight value is set by a user.

7. The method of claim 6, wherein the display backlight value set by the user is adjusted based upon the ambient light to determine the display backlight level.

8. The method of claim 6, wherein the display backlight level is adjusted to be higher than the display backlight value set by the user if an actual ambient light value is brighter than set by the user.

9. The method of claim 6, wherein the display backlight level is adjusted to be lower than the display backlight value set by the user if an actual ambient light value is darker than set by the user.

10. A method, comprising:

determining a backlight value for a display; and

determining a weighted histogram of image pixel values of original image data, wherein each count added to a histogram bin in the weighted histogram is weighted by a value of an image pixel, and each histogram bin of the weighted histogram is mapped to a bin backlight value;

adjusting pixel values in the original image data to compensate for the backlight value to produce compensated pixel values, wherein adjusting the original image data comprises using the backlight value and the pixel values in the original image data as indexes into two one-dimensional look-up tables developed using the weighted histogram to produce a content backlight value and content-based compensation weights for each pixel in the incoming image data.

11. A method, comprising:

receiving image data at a processor;

determining a weighted histogram of image pixel values of image data, wherein each count added to a histogram bin in the weighted histogram is weighted by a value of an image pixel, and each histogram bin of the weighted histogram is mapped to a bin backlight value;

using input pixel values in the image data to index a one-dimensional look-up table stored in memory to access adjusted pixels values for the image data, wherein the adjusted pixel values are based upon a weighted histogram of the image data;

applying a compensation weight to the adjusted pixels values to produce compensated pixel values;

adjusting a value for a backlight based upon an average pixel value, an average adjusted pixel value and the compensation weight.

12. The method of claim 11, further comprising:

designating at least some pixels in the image data as bright pixels based upon the histogram bin identified by gray scale values of the bright pixels;

applying a contrast adjustment gain identified in the histogram bin.

13. The method of claim 11, wherein determining a display backlight level comprises:

measuring ambient light in an environment; and

mapping measured ambient light to the display backlight value.

14. The method of claim 13, wherein mapping the measured ambient light comprises applying a piece-wise linear function to the measured ambient light to produce a display backlight value.

15. The method of claim 11, wherein determining the display backlight value comprises the value for a backlight set by a user.

16. The method of claim 15, wherein value for a backlight set by the user is adjusted based upon an ambient light.

17. The method of claim 15, wherein the value for a backlight set by the user is adjusted to be lower than set by the user if an actual ambient light value is darker than set by the user.

18. The method of claim 15, wherein the value for a backlight set by the user is adjusted to be higher than set by the user if an actual ambient light value is brighter than set by the user.