SYSTEM AND METHOD FOR IMPROVING COLOR AND BRIGHTNESS UNIFORMITY OF BACKLIT LCD DISPLAYS

• US 20110285763A1
• Filed: 04/29/2011
• Published: 11/24/2011
• Est. Priority Date: 01/05/2007
• Status: Active Grant

• Current Assignee: Geo Semiconductor Incorporated
• Original Assignee: Geo Semiconductor Incorporated
• Inventors: Bassi, Zorawar Singh, Alavi-Harati, Ashkan
• Granted Patent: US 8,442,316 B2
• Time in Patent Office: Days
• US Class Current: 345/694
• CPC Class Codes: G06T 2207/10004 Still image; Photographic image
• CPC Class Codes: G06T 2207/10152 Varying illumination
• CPC Class Codes: G06T 5/94 based on local image properties, e.g. for local contrast enhancement
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 2320/0242 Compensation of deficiencies in the appearance of colours
• CPC Class Codes: G09G 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• CPC Class Codes: G09G 2340/06 Colour space transformation
• CPC Class Codes: G09G 3/2003 Display of colours specific for liquid crystal displays G09G3/3607
• CPC Class Codes: H04N 1/60 Colour correction or control H04N1/54 takes precedence

Abstract

Systems and methods for improving color and brightness uniformity of an image displayed on a backlit LCD are disclosed. In one example, a correction map is computed and applied to the LCD pixel values. In another example, the voltage settings of the backlight source components are also corrected in addition to the LCD pixel values. For efficient hardware implementation, corrections are applied using function representation of a grid data transformation relating measured values to corrected values. In one particular exemplary embodiment, the backlight source is provided by a plurality of LEDs. In another exemplary embodiment, the display consists of a plurality of OLEDs wherein the light source and the display panels coincide.

Claims

1. A method for improving color and brightness uniformity of a Liquid Crystal Display (LCD) backlit by a plurality of light source components, said method comprising:

setting at least one backlight voltage common to all the light source components;

for each of the at least one backlight voltage settings, displaying a plurality of reference input images having pre-determined flat RGB pixel values across the display for at least one signal level;

measuring the display uniformity at a selected set of grid points on the display in response to said plurality of reference input images, the uniformity being characterized by at least one of the tristimulus values, luminance and chrominance components;

generating a display response function from the measured uniformity data, the response function being the sum of responses for R, G and B components for every pixel of the display;

computing a pixel correction grid data map that results in a constant uniformity value for all pixels at each said at least one signal level;

converting the pixel correction grid data map into a functional form represented by a set of coefficients; and

applying the pixel correction functions to the input signal and the display for all pixel positions and color values.

2. The method of claim 1, wherein the response function further depends on the backlight voltage setting and the correction grid data includes a backlight correction map applying to the backlight source components.

3. The method of claim 2, wherein the pixel map is regenerated after application of the backlight correction, and the backlight and pixel corrections are iterated until required degree of uniformity is achieved.

4. The method of claim 2, wherein the backlight response function is represented as a linear function.

5. The method of claim 2, wherein the backlight correction is obtained using tristimulus Point Spread Functions (PSF) of each light source component.

6. The method of claim 5, wherein the PSF is provided as a specification of the light source components.

7. The method of claim 5, wherein the PSF is approximated using mathematical models.

8. The method of claim 5, wherein the PSF is directly measured.

9. The method of claim 1, wherein the reference input images are a plurality of pure grey levels for brightness only corrections,

10. The method of claim 1, wherein each said light source component is a Light Emitting Diode (LED).

11. The method of claim 1, wherein each said light source component is a Cold Cathode Fluorescent Lamp (CCFL) tube.

12. The method of claim 1, wherein each said light source component is a Laser Diode (LD).

13. The method of claim 1, wherein the reference input images are a plurality of levels of pure red, pure green, and pure blue levels.

14. The method of claim 13, wherein the reference input images further include a plurality of pure grey levels, implemented to compensate for LCD black level offset of RGB components.

15. The method of claim 1, wherein the display response function is obtained using a polynomial fit to the measured grid points.

16. The method of claim 15, wherein the polynomial is a cubic function;

17. The method of claim 1, wherein the display response function is obtained by interpolating the measured grid point data.

18. The method of claim 1, wherein the display response function is estimated by modeling the function as a power law;

19. The method of claim 1, wherein the response function is a plurality of local polynomial fits to a vicinity of the measured grid points, such that the local fits are monotonic functions.

20. The method of claim 15, wherein the response function is shifted and scaled to make the function monotonic.

21. The method of claim 1, wherein the constant uniformity value of the response function is set as the average measured value.

22. The method of claim 1, wherein the constant uniformity value of the response function is set as the minimum measured value in case the corrected pixel values go above the allowable bit range for high signal levels.

23. The method of claim 1, wherein the constant uniformity value of the response function is set to be the maximum measured value in case the corrected pixel values go below the allowable bit range for low signal levels.

24. The method of claim 1, wherein a plurality of said set of coefficients for several pixel correction maps is computed and stored corresponding to several settings of ambient temperature.

25. The method of claim 1, wherein a plurality of said set of coefficients for several pixel correction maps is computed and stored corresponding to several settings of ambient light.

26. An electronic system for improving color and brightness uniformity of a backlit LCD, said system comprising:

a display panel consisting of arrays of pixels, each said pixel being characterized by a controllable digital RGB value;

a backlight source panel consisting of a plurality of light source components, each said light source component characterized by an adjustable voltage control;

an image generator unit for displaying a plurality of reference input images on the display;

an image capture and measurement unit to measure the display uniformity at a selected set of grid points on the display in response to said plurality of reference input images, the uniformity being characterized by at least one of the tristimulus values, luminance and chrominance components;

a first processing means to generate a display response function from the measured uniformity data, and compute a pixel correction grid data map that results in a constant uniformity value for all pixels at each said at least one signal level; and

a second processing means to convert the pixel correction grid data map into a functional form represented by a set of coefficients, and applying the pixel correction functions to the input signal and the display for all pixel positions and color values.

27. The system of claim 26, wherein the response function further depends on the backlight voltage setting and the correction grid data includes a backlight correction applying to the backlight voltage controls.

28. The system of claim 26, wherein each said light source component is a Light Emitting Diode (LED).

29. The system of claim 27, wherein the LED components are arranged in a direct backlighting architecture.

30. The system of claim 27, wherein the LED components are arranged in an edge-lit backlighting architecture.

31. The system of claim 26, wherein each said light source component is a Cold Cathode Fluorescent Lamp (CCFL) tube.

32. The system of claim 26, wherein each said light source component is a Laser Diode (LD).

33. The system of claim 26, wherein the first processing means and the second processing means are integrated into one processor.

34. The system of claim 26, wherein the first processing means is a software tool run on a computer system.

35. The system of claim 26, wherein the second processing means is integrated into the display.

36. The system of claim 26, wherein the capture device is a two-dimensional (2D) camera.

37. The system of claim 26, wherein the capture device is a spot meter.

38. An electronic system for improving color and brightness uniformity of an Organic LED Display (OLED), said system comprising:

A display panel consisting of arrays of pixels, each pixel being an OLED component and characterized by a controllable digital RGB value;

an image generator unit for displaying a plurality of reference input images on the display;

an image capture and measurement unit to measure the display uniformity at a selected set of grid points on the display in response to said plurality of reference input images, the uniformity being characterized by at least one of the tristimulus values, luminance and chrominance components;

a first processing means to generate a display response function from the measured uniformity data, and compute a pixel correction grid data map that results in a constant uniformity value for all pixels at each said at least one signal level; and

a second processing means to convert the pixel correction grid data map into a functional form represented by a set of coefficients, and applying the pixel correction functions to the input signal and the display for all pixel positions and color values.