Method and apparatus for calibrating a tiled display

• US 20020027608A1
• Filed: 06/08/2001
• Published: 03/07/2002
• Est. Priority Date: 09/23/1998
• Status: Active Grant

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Chandrasekhar, Rajesh, Chen, Chung-Jen, Johnson, Michael J.
• Granted Patent: US 6,525,772 B2
• Time in Patent Office: Days
• US Class Current: 348/383
• CPC Class Codes: H04N 17/04 for receivers
• CPC Class Codes: H04N 9/12 Picture reproducers H04N9/11 takes precedence
• CPC Class Codes: H04N 9/3147 Multi-projection systems displays in general H04N9/12; video walls G06F3/1446, G09G2300/026
• CPC Class Codes: H04N 9/3194 including sensor feedback

Abstract

A display system that can be calibrated and re-calibrated with a minimal amount of manual intervention. To accomplish this, one or more cameras are provided to capture an image of the display screen. The resulting captured image is processed to identify any non-desirable characteristics, including visible artifacts such as seams, bands, rings, etc. Once the non-desirable characteristics are identified, an appropriate transformation function is determined. The transformation function is used to pre-warp the input video signal that is provided to the display such that the non-desirable characteristics are reduced or eliminated from the display. The transformation function preferably compensates for spatial non-uniformity, color non-uniformity, luminance non-uniformity, and other visible artifacts.

Claims

1. In a system for controlling a tiled display system that receives an input video signal, the tiled display system having two or more displays, each manifesting one of a number of discrete images separately onto a viewing surface or screen to form a composite image, the improvement comprising:

camera means for providing a capture image of at least a portion of the composite image;

determining means for determining if the capture image has one or more non-desirable characteristics; and

identifying means for identifying a transformation function that can be used to process the input video signal and provide processed input video signals to selected displays to reduce the non-desirable characteristics.

2. A tiled display system according to claim 1, wherein the two or more displays are projection type displays.

3. A tiled display system according to claim 1, wherein the two or more displays are front projection displays.

4. A tiled display system according to claim 1, wherein the two or more displays are rear projection displays.

5. A tiled display system according to claim 1, wherein the one or more non-desirable characteristics include spatial non-uniformity.

6. A tiled display system according to claim 1, wherein the one or more non-desirable characteristics includes color non-uniformity.

7. A tiled display system according to claim 1, wherein the one or more non-desirable characteristics includes luminance non-uniformity.

8. A tiled display system according to claim 1, wherein the camera means is a colorimeter.

9. A tiled display system according to claim 8, wherein the colorimeter comprises one or more video cameras.

10. A tiled display system according to claim 1, wherein the tiled display system has a viewing side with said camera means located on the viewing side.

11. A tiled display system according to claim 1 wherein the tiled display system has a viewing side with said camera means located on the opposite of the viewing side.

12. A tiled display system according to claim 1, wherein said camera means periodically captures a new capture image during normal functional operation of the tiled display system.

13. A system according to claim 12, wherein said determining means periodically determines if the new capture image has one or more non-desirable characteristics, and said identifying means periodically identifies a new transformation function that can be used to process the input video signal and provide processed input video signals to selected displays to reduce the non-desirable characteristics.

14. A system according to claim 1, wherein said camera means captures the capture image during a calibration period.

15. A tiled display system according to claim 1, wherein the camera means captures a portion of the composite image that substantially corresponds to one of the number of discrete images.

16. A system according to claim 1, wherein the camera means sequentially captures a portion of the composite image, wherein each sequentially captured portion substantially corresponds to one of the number of discrete images.

18. A method according to claim 17, wherein said capturing, determining and identifying steps are repeated periodically during normal functional operation of the projection display.

19. A method according to claim 17, wherein said determining step compares the capture image with a predetermined data set to determine if the capture image has one or more non-desirable characteristics.

20. A method according to claim 17, wherein said transformation function is determined during a calibration procedure.

21. A method according to claim 20, wherein said calibration procedure includes the steps of:

sequentially inputting one or more input signals that correspond to a flat field image of varying intensities;

capturing a capture image of selected flat images;

identifying a luminance dome in the capture images; and

determining a transformation function that will at least partially remove the luminance domes from the composite image.

22. A method according to claim 21, wherein the transformation function is represented by a color look up table of captured color domes, a nearest neighbor detection and identification block and an interpolation block among the nearest neighbors to determine the input level needed at the display to output the desired linear output level.

23. A method according to claim 22, wherein the transformation function is represented, at least in part, by a number of coefficients.

24. A method according to claim 22, wherein the transformation function is a bilinear transformation function.

25. A method according to claim 20, wherein said calibration procedure includes the steps of:

causing the at least one of the two or more displays to manifest a discrete image that has a predetermined pattern with a number of features;

capturing a capture image of a selected portion of the composite image;

identifying a spatial distortion in the capture image by examining the relative location of selected features in the capture image;

determining a transformation function that will at least partially remove the spatial distortion from the composite image.

26. A method according to claim 25, wherein said predetermined pattern includes a dot pattern.

27. A method according to claim 26, further comprising the steps of:

locating the dots in the capture image; and

identifying a transformation function that will at least partially remove the spatial distortion from the composite image by comparing the location of the dots in the capture image relative to an expected location.

28. A method according to claim 27, wherein said locating step includes the steps of:

calculating the dot locations by subtracting a black capture image from the capture image that includes the dots;

examining the resulting image content above a noise threshold using spatial filters which have an all-pass kernel;

measuring the center of gravity of the dots to find the corresponding dot locations;

eliminating dots whose energy threshold is below the threshold;

sorting the dot locations for correlation with known or expected dot patterns and deriving corrective transformation functions therefrom.

30. A method according to claim 29, wherein each display projects one of the number of discrete images separately onto a screen in an overlapping manner to form a composite image having one or more overlapping regions.

31. A method according to claim 30, wherein at least one of the overlapping regions corresponds to more than 25% of the corresponding discrete images.

32. A method according to claim 30, wherein at least one of the overlapping regions corresponds to more than 50% of the corresponding discrete images.

33. A method according to claim 30, wherein said determining step includes the steps of:

identifying a selected feature in a selected overlapping region, wherein the selected feature is manifested by a selected display;

identifying a selected feature in the selected overlapping region, wherein the selected feature is correlated to a corresponding feature;

determining the spatial relationship among the selected features; and

identifying one or more transformation functions for the display, said transformation functions effectively moving the location of the selected features on the viewing surface or screen toward a corrective location when applied to the input signal of the selected display.

34. A method according to claim 33, wherein said first transformation function effectively moves the location of the selected features toward the corrective location by an amount that is weighted by a blending function of the tile exhibiting the selected feature.

35. A method according to claim 33, wherein the predetermined pattern has a predetermined linear relationship among selected features.

36. A method according to claim 35, wherein said first transformation function effectively moves the location of the selected feature toward the corresponding feature, and said second transformation function effectively moves the location of the corresponding feature toward the selected feature, while maintaining the predetermined linear relationship between the features.

38. A method according to claim 37, wherein the inputting, capturing, determining and identifying steps are repeated for each of two or more colors.

39. A method according to claim 37, wherein said projection display includes a number of pixels, and said determining step determines a distortion using more than one of the pixels.

40. A method according to claim 39, wherein said determining step determines an X-distortion by examining more than one pixel in an X-direction, and a Y-distortion by examining more than one pixel in a Y-direction, so that an X-Y dependence of the distortion can be determined.

41. A method according to claim 40, wherein said identifying step identifies the transformation function by examining the X-Y dependence of the distortion determined by the determining step.

17. A method for controlling a display system that has two or more displays, each display manifesting one of a number of discrete images separately onto a viewing surface or screen to form a composite image, the method comprising the steps of:

capturing a capture image of at least a portion of the composite image;

determining if the capture image has one or more non-desirable characteristics; and

identifying a transformation function that can be used to process an input video signal and provide a processed input video signal to selected displays to reduce the non-desirable characteristics.

29. A method for calibrating a tiled display system, the tiled display system having two or more displays, each receiving an input signal and each manifesting one of a number of discrete images separately onto a viewing surface or screen to form a composite image, the method comprising the steps of:

providing an input signal to selected projectors to project a number of discrete images, each discrete image having a predetermined pattern with a number of corresponding features;

capturing a capture image of at least a portion of the screen using a camera device;

determining a distortion in the composite image by isolating the location of selected features in the capture image;

identifying a transformation function that can be applied to the input signal of selected displays to at least partially remove the distortion from the composite image.

37. A method for calibrating a tiled projection display, the tiled projection display having two or more projectors, each receiving an input signal and each projecting one of a number of discrete images separately onto a screen to form a composite image, the method comprising the steps of:

sequentially inputting to selected projectors an input signal that correspond to a flat field image of a first color for each of a number of luminance intensities;

capturing a capture image of selected flat field images;

determining a distortion in the projection display by examining the captured flat field images; and

identifying a transformation function that can be applied to the input signal that will at least partially remove the distortion from the composite image.

42. A method for calibrating a tiled projection display, the tiled projection display having two or more projectors, each receiving an input signal and each projecting one of a number of discrete images separately onto a screen to form a composite image, the method comprising the steps of:

providing a physical template that includes a predetermined pattern adjacent the screen;

capturing a capture image of at least a portion of the physical template using a camera device; and

determining a camera distortion that is introduced by the camera device by comparing the capture image with a predetermined expectation.

43. A method according to claim 42, further comprising the steps of:

removing the physical template;

providing an input signal to selected projectors to project a number of discrete images, each exhibiting a predetermined pattern;

capturing a capture image of at least a portion of the screen using a camera device; and

determining a projection system distortion that is introduced by the projection system by comparing the capture image with a predetermined expectation.

44. A method according to claim 43, further comprising the step of removing the camera distortion before determining the projection system distortion.