System and method for determining a gamma curve of a display device

• US 20090027523A1
• Filed: 07/25/2007
• Published: 01/29/2009
• Est. Priority Date: 07/25/2007
• Status: Active Grant

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Chang, Nelson Liang An, Damera-Venkata, Niranjan
• Granted Patent: US 7,986,356 B2
• Time in Patent Office: Days
• US Class Current: 348/254
• CPC Class Codes: H04N 17/04 for receivers
• CPC Class Codes: H04N 9/3147 Multi-projection systems displays in general H04N9/12; video walls G06F3/1446, G09G2300/026
• CPC Class Codes: H04N 9/3182 Colour adjustment, e.g. white balance, shading or gamut white balance per se H04N9/73; control of amplitude of colour signals H04N9/68; colour control circuits for displays in general G09G5/02, G09G3/2003, G09G3/3607
• CPC Class Codes: H04N 9/3194 including sensor feedback

Abstract

A method of determining a gamma curve of a display device includes identifying a region of interest of a display surface of the display device. A centroid of the region of interest is calculated. A plurality of input levels is applied to the display device to generate a corresponding plurality of displayed images on the display surface. At least one image of each of the displayed images is captured with a camera. A gamma curve of the display device is calculated based on the captured images and the centroid.

Claims

1. A method of determining a gamma curve of a display device, the method comprising:

identifying a region of interest of a display surface of the display device;

calculating a centroid of the region of interest;

applying a plurality of input levels to the display device to generate a corresponding plurality of displayed images on the display surface;

capturing at least one image of each of the displayed images with a camera; and

calculating a gamma curve of the display device based on the captured images and the centroid.

2. The method of claim 1, and further comprising:

capturing a set of dark images at each of a plurality of different exposure settings, thereby generating a plurality of sets of dark images;

averaging each set of dark images, thereby generating a fixed pattern noise image corresponding to each one of the exposure settings; and

determining an equation for each pixel of the camera for determining fixed pattern noise at that pixel as a function of exposure based on the fixed pattern noise images.

3. The method of claim 2, and further comprising:

removing fixed pattern noise from images captured by the camera based on the determined equations, thereby generating corresponding compensated images, and wherein the gamma curve is calculated based on the compensated images and the centroid.

4. The method of claim 1, wherein the display device is a projector.

5. The method of claim 1, wherein identifying a region of interest comprises:

displaying an all-white image;

capturing a first image of the all-white image with the camera;

displaying an all-black image;

capturing a second image of the all-black image with the camera;

computing a difference between the first and the second images, thereby generating a difference image; and

identifying a largest connected region in the difference image, wherein the largest connected region represents the identified region of interest.

6. The method of claim 1, wherein identifying a region of interest comprises:

displaying a plurality of all-white images;

capturing an image of each of the all-white images with the camera, thereby generating a first set of captured images;

averaging the first set of captured images, thereby generating a first average image;

displaying a plurality of all-black images;

capturing an image of each of the all-black images with the camera, thereby generating a second set of captured images;

averaging the second set of captured images, thereby generating a second average image;

computing a difference between the first and the second average images, thereby generating a difference image; and

identifying a largest connected region in the difference image, wherein the largest connected region represents the identified region of interest.

7. The method of claim 1, wherein capturing at least one image comprises:

capturing a plurality of images of each of the displayed images at a plurality of different exposures with the camera; and

integrating each plurality of images into a common exposure image.

8. The method of claim 1, wherein calculating a gamma curve comprises:

identifying a neighborhood region around the centroid; and

for each captured image, calculating an average value of pixels positioned within the identified neighborhood region, wherein the calculated average values represent output values of the gamma curve corresponding to the plurality of input levels.

9. The method of claim 8, wherein the input levels are in a range of zero to one, and wherein calculating a gamma curve further comprises:

shifting and scaling the average values to be in a range of zero to one.

10. The method of claim 9, and further comprising:

performing a curve fitting operation on the average values to smooth the gamma curve.

11. The method of claim 1, and further comprising:

generating sub-frames for display in a multi-projector system based on the calculated gamma curve.

12. The method of claim 1, wherein the plurality of displayed images are single color channel images, and the calculated gamma curve is representative of a single color channel of the display device.

13. A system for determining a gamma curve of a display device, comprising:

a first controller configured to apply a plurality of input levels to the display device to generate a corresponding plurality of displayed images on a display surface of the display device;

a camera configured to capture at least one image of each of the displayed images; and

a second controller configured to identify a region of interest of the display surface, calculate a centroid of the region of interest, and calculate a gamma curve of the display device based on the captured images and the centroid.

14. The system of claim 13, wherein the camera is configured to capture a set of dark images at each of a plurality of different exposure settings, thereby generating a plurality of sets of dark images, and wherein the second controller is configured to average each set of dark images, thereby generating a fixed pattern noise image corresponding to each one of the exposure settings, and wherein the second controller is configured to determine an equation for each pixel of the camera for determining fixed pattern noise at that pixel as a function of exposure based on the fixed pattern noise images.

15. The system of claim 14, wherein the second controller is configured to remove fixed pattern noise from images captured by the camera based on the determined equations, thereby generating corresponding compensated images, and wherein the gamma curve is calculated based on the compensated images and the centroid.

16. The system of claim 13, wherein the display device is a projector.

17. The system of claim 13, wherein the second controller is configured to identify a neighborhood region around the centroid, and, for each captured image, calculate an average value of pixels positioned within the identified neighborhood region, wherein the calculated average values represent output values of the gamma curve corresponding to the plurality of input levels.

18. The system of claim 17, wherein the input levels are in a range of zero to one, and wherein the second controller is configured to shift and scale the average values to be in a range of zero to one.

19. The system of claim 18, wherein the second controller is configured to perform a curve fitting operation on the average values to smooth the gamma curve.

20. A computer-readable medium having computer-executable instructions for performing a method of determining a gamma curve of a display device, the method comprising:

calculating a centroid of a region of interest of a display surface;

identifying a neighborhood region around the centroid;

applying a plurality of input levels to the display device to generate a corresponding plurality of displayed images on the display surface;

causing at least one image of each of the displayed images to be captured with a camera; and

for each captured image, calculating an average value of pixels positioned within the identified neighborhood region, wherein the calculated average values represent output values of a gamma curve corresponding to the plurality of input levels.