Color correction method and apparatus for displays

• US 8,773,451 B2
• Filed: 05/03/2011
• Issued: 07/08/2014
• Est. Priority Date: 05/03/2011
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Marcu, Gabriel Gheorghe, Chen, Wei, Lum, David W., Drolet, Jean-Jacques P.
• Primary Examiner(s): Hoang, Phi
• Application Number:
  US13/100,146
• Publication Number:
  US 20120281008A1
• Time in Patent Office: 1,162 Days
• Field of Search: None
• US Class Current: 345/589
• CPC Class Codes: G09G 2320/0242 Compensation of deficiencies in the appearance of colours
• 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 2320/041 Temperature compensation
• CPC Class Codes: G09G 2320/0666 for control of colour parameters, e.g. colour temperature
• CPC Class Codes: G09G 2320/0673 for control of gamma adjustment, e.g. selecting another gamma curve
• CPC Class Codes: G09G 2320/0693 Calibration of display systems
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 3/006 Electronic inspection or testing of displays and display drivers, e.g. of LED or LCD displays testing individual LED's G01R31/2635; testing lamps G01R31/44; testing of optical features of LCD displays G02F1/1309
• CPC Class Codes: G09G 3/2003 Display of colours specific for liquid crystal displays G09G3/3607

Abstract

Method and apparatus for adjusting the display characteristics of an electronic display, such as a computer or television display. The display is color corrected, e.g., at the factory, to measure its white point correction, gamma and gray tracking correction, and the gain correction over time as the display warms up. Moreover the white point correction and the gamma correction are performed on a per unit basis for each individual display to be manufactured. The resulting correction parameters are stored in memory or firmware associated with the display. Thereby when the display is in use, it performs compensation for white point, gray tracking and gain correction as the display warms up, each time it is powered up or when its thermal operation conditions change.

Claims

1. A method of correcting characteristics of a display, comprising the acts of:

for a display unit, determining a per-unit gamma correction, a per-unit white point correction, and a per-unit gray tracking correction;

determining a set of generic gain corrections for a plurality of temperatures for the display unit; and

storing the determined corrections in a computer readable memory associated with the display unit,

whereby in use, the display unit applies the stored corrections to a displayed image.

2. The method of claim 1, wherein the gain corrections are normalized for a plurality of display units.

3. The method of claim 1, wherein each of the gamma, gray tracking and white point corrections is determined, and each is determined unit-by-unit.

4. The method of claim 1, wherein determining the gain corrections includes:

measuring temperatures at a plurality of locations adjacent the display unit;

combining the measured temperatures into one value; and

associating the one value with a set of gain correction values.

5. The method of claim 4, wherein the one value is a function of a temperature of the display at a center of its screen.

6. The method of claim 1, wherein the plurality of temperatures are up to a full warm up of the display unit.

7. The method of claim 1, wherein the computer readable memory is organized as a look up table and is a programmable read only memory device.

8. The method of claim 1, wherein the storing includes:

transmitting at least one of the corrections to a video input port of the display; and

coupling the at least one of the corrections from the video input port to the computer readable memory.

9. A computing apparatus that carries out the method of claim 1.

10. A display unit comprising:

a screen;

a display driver coupled to drive the screen; and

a controller coupled to receive image data to display on the screen and to output the data to the display driver, the controller including;

a computer readable memory storing for the display unit, a gamma correction, a white point correction, and a set of gain corrections for a plurality of temperatures;

at least one combiner adapted to combine the corrections with the image data; and

an output port coupled to the combiner and to the display driver.

11. The display unit of claim 10, further comprising a second combiner coupled to combine the white point correction and set of gain corrections.

12. The display unit of claim 10, further comprising:

an input temperature port coupled to receive a temperature parameter; and

a logic coupled to the input temperature port and a portion of the computer readable memory storing the set of gain corrections.

13. The display unit of claim 12, wherein the temperature parameter is a function of a plurality of temperatures sensed adjacent the display.

14. The display unit of claim 12, further comprising a plurality of temperature sensors disposed adjacent the display;

and a logic coupled to each of the temperature sensors;

wherein the logic computes the temperature parameter from data provided by the temperature sensors.

15. The display unit of claim 14, wherein initially the temperature parameter is one of the plurality of sensed temperatures or a predetermined value, and thereafter the temperature parameter is computed by the logic.

16. The display unit of claim 10, wherein the computer readable memory is at least partly on the same integrated circuit as the controller and display driver.

17. The display unit of claim 10, wherein the computer readable memory stores a gray tracking correction for the display unit.

18. A method of operating a display unit having a screen driver driven by a controller, the controller being coupled to receive image data to display on the screen and to output data to the screen, the method comprising the acts of:

storing in a computer readable memory a gamma correction, a white point correction, and a set of gain corrections for a plurality of temperatures;

correcting the image data, wherein correcting the image data comprises;

applying the gamma correction to the image data,

applying the white point correction to the image data, and

applying the set of gain corrections to the image data; and

outputting the image data to the screen.

20. The method defined in claim 18, wherein correcting the image data by applying the gamma correction, the white point correction, and the set of gain corrections to the image data comprises:

generating a combined correction by combining the set of gain corrections and the white point correction; and

combining the image data with the combined correction.

19. A controller adapted to control a display unit, the controller comprising:

an input port adapted to received image data;

an output port adapted to drive the display unit;

a computer readable memory storing for the display unit a temperature-independent gamma correction, a temperature-independent white point correction, and a temperature-dependent set of gain corrections for a plurality of temperatures; and

at least one combiner coupled to combine the temperature-independent gamma correction, the temperature-independent white point correction, and the temperature-dependent set of gain corrections with the image data;

wherever an output port of the combiner is coupled to the output port.