BACKLIGHT LEVEL SELECTION FOR DISPLAY DEVICES

• US 20110025592A1
• Filed: 07/29/2009
• Published: 02/03/2011
• Est. Priority Date: 07/29/2009
• Status: Active Grant

• Current Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Original Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Inventors: BOTZAS, Anthony, HWANG, Sarah Sunyoung
• Granted Patent: US 8,184,089 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• 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

Abstract

Display systems and methods for adjusting backlight illumination are disclosed for selecting a backlight illumination level that is low enough to reduce backlight power consumption while maintaining a desired level of image quality. The method 1) determines the peak illumination level requested by a frame to satisfy all pixels in a frame, 2) determines a histogram-based statistical illumination value for the frame, and 3) selects the lower of the two values. The histogram-based statistical illumination value is calculated using an error function for different ranges of illumination levels, wherein the error function correlates with luminance error introduced by selecting next lower range of illumination levels.

Claims

1. A method of selecting an illumination level for a backlight in a display system, the method comprising:

determining a first value, wherein the first value is the highest illumination level requested by a pixel in a frame;

determining a second value for the frame, wherein the second value is calculated by;

dividing possible illumination levels into a predetermined number of bins, each of the bins covering a range of illumination levels;

determining an error function for at least the bin covering the highest range of illumination levels, wherein the error function correlates with luminance error introduced by selecting an illumination level of a neighboring bin covering a lower range of illumination levels;

identifying a critical bin of the bins, wherein the critical bin has an error function exceeding a threshold number and has the highest range of illumination levels out of the bins having error functions exceeding the threshold number; and

calculating the second value based on the illumination level of the critical bin;

selecting a lower value between the first and second values.

2. The method of claim 1, further comprising determining a local peak value of a bin based on number of pixels in the frame requesting a particular illumination level in the range of illumination levels covered by the single bin.

3. The method of claim 2, wherein selecting a lower value between the first and second values comprises selecting a lower value between the first value and the local peak value of the critical bin.

4. The method of claim 1, further comprising determining an average illumination value for a bin based on illumination levels requested by pixels in the bin.

5. The method of claim 4, wherein selecting a lower value between the first and second values is selecting a lower value between the first value and the average illumination value of the critical bin.

6. The method of claim 1, wherein determining the error function comprises counting the number of pixels requesting an illumination level that falls in the range covered by at least one of the bins.

7. The method of claim 6, wherein the number of pixels requesting an illumination level that falls in one of the bins is counted up to a predetermined cap number.

8. The method of claim 6, wherein the illumination level requested by a pixel is determined using max (R, G, B, W) in a multiprimary display system.

9. The method of claim 1, wherein calculating the second value further comprises selecting a particular illumination level out of the range of illumination levels covered by the critical bin.

10. The method of claim 9, wherein the bins are arranged in a histogram and selecting the particular illumination level comprises:

identifying a first point defined as an intersection of the lowest illumination level covered by the critical bin and the cumulative error function (E_sum[i]) in the critical bin;

identifying a second point defined as an intersection of the lowest illumination level covered by an adjacent bin and the cumulative error function (E_sum[i+1]) of the adjacent bin, the adjacent bin covering the next highest range of illumination levels compared to the critical bin;

drawing a straight line through the first point and the second point;

identifying a third point defined as an intersection of the straight line and the threshold number; and

determining the particular illumination level based on the third point.

11. The method of claim 9, wherein the bins are arranged in a histogram and selecting the particular illumination level comprises:

identifying a first point defined as an intersection of the lowest illumination level covered by the critical bin and the cumulative error function (E_sum[i]) in the critical bin;

identifying a second point defined as an intersection of the highest illumination level covered by the critical bin and a second threshold number, the second threshold number being higher than the first threshold number;

drawing a straight line through the first point and the second point;

identifying a third point defined as an intersection of the straight line and the cumulative error function of the critical bin (E_sum[i]); and

determining the particular illumination level based on the third point.

12. The method of claim 1, wherein dividing possible illumination levels into a predetermined number of bins includes using digital illumination values to define the bins.

13. A display system comprising:

a display for displaying images;

a backlight for illuminating said display, said backlight comprising a set of illumination levels; and

a backlight level selection module including;

a block for dividing possible illumination levels into a predetermined number of bins, each of the bins covering a range of illumination levels;

a block for determining an error function for at least the bin covering the highest range of illumination levels, wherein the error function correlates with luminance error introduced by selecting an illumination level of a neighboring bin covering a lower range of illumination levels;

a block for identifying a critical bin of the bins, wherein the critical bin has an error function exceeding a threshold number and has the highest range of illumination levels out of the bins having error functions exceeding the threshold number; and

a block for calculating the second value based on the illumination level of the critical bin; and

a block for selecting a lower value between the first and second values.

14. The display system of claim 13, wherein the backlight level selection module further includes a block for determining a local peak value of a bin based on number of pixels in the frame requesting a particular illumination level in the range of illumination levels covered by the single bin.

15. The display system of claim 14, wherein the block for selecting a lower value between the first and second values comprises a block for selecting a lower value between the first value and the local peak value of the critical bin.

16. The display system of claim 13 further comprising a block for determining an average illumination value for a bin based on illumination levels requested by pixels in the bin.

17. The display system of claim 16, wherein the block for selecting a lower value between the first and second values comprises a block for selecting a lower value between the first value and the average illumination value of the critical bin.

18. The display system of claim 13, wherein the block for determining the error function comprises a block for counting the number of pixels requesting an illumination level that falls in the range covered by at least one of the bins.

19. The display system of claim 18, wherein the block counting the number of pixels counts up to a predetermined cap number.

20. The display system of claim 18, wherein the illumination level requested by a pixel is determined using max (R, G, B, W) in a multiprimary display system.

21. The display system of claim 13, wherein the bins are arranged in a histogram and the block selecting the particular illumination level comprises:

a block identifying a first point defined as an intersection of the lowest illumination level covered by the critical bin and the cumulative error function (E_sum[i]) in the critical bin;

a block identifying a second point defined as an intersection of the lowest illumination level covered by an adjacent bin and the cumulative error function (E_sum[i+1]) of the adjacent bin, the adjacent bin covering the next highest range of illumination levels compared to the critical bin;

a block drawing a straight line through the first point and the second point;

a block identifying a third point defined as an intersection of the straight line and the threshold number; and

a block determining the particular illumination level based on the third point.

22. The display system of claim 21, wherein the bins are arranged in a histogram and selecting the particular illumination level comprises:

a block identifying a first point defined as an intersection of the lowest illumination level covered by the critical bin and the cumulative error function (E_sum[i]) in the critical bin;

a block identifying a second point defined as an intersection of the highest illumination level covered by the critical bin and a second threshold number, the second threshold number being higher than the first threshold number;

a block drawing a straight line through the first point and the second point;

a block identifying a third point defined as an intersection of the straight line and the cumulative error function of the critical bin (E_sum[i]); and

a block determining the particular illumination level based on the third point.

23. The display system of claim 13, wherein the block for dividing possible illumination levels into a predetermined number of bins includes using digital illumination values to define the bins.