System and method for correcting luminance non-uniformity of obliquely projected images

• US 7,018,050 B2
• Filed: 09/08/2003
• Issued: 03/28/2006
• Est. Priority Date: 09/08/2003
• Status: Expired due to Fees

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Ulichney, Robert Alan, Sukthankar, Rahul
• Primary Examiner(s): Perkey, W. B.
• Assistant Examiner(s): VALENTIN, JUAN D
• Application Number:
  US10/657,527
• Publication Number:
  US 20050052618A1
• Time in Patent Office: 932 Days
• Field of Search: 349/8, 349/10, 349/42, 349/58, 349/61, 349/110, 349/158, 349/161, 349/201, 349/5, 348/744, 348/745, 348/750, 348/766, 348/771, 348/746, 348/747, 359/619, 359/858, 353/69, 353/70, 353/30, 353/31, 353/99, 353/119, 353/37, 353/78, 353/84, 353/33, 353/34, 353/38, 353/101, 353/81, 353/94, 353/121, 353/122, 345/698, 345/596, 358/3.13, 382/275
• US Class Current: 353/69
• CPC Class Codes: G03B 21/26 Projecting separately subsidiary matter simultaneously with main image
• 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 9/3185 Geometric adjustment, e.g. keystone or convergence optical or mechanical adjustment of convergence H04N9/317; using scanning means H04N3/22; optical or mechanical adjustments of projectors not peculiar to the presence of an electronic spatial light modulator G03B21/14
• CPC Class Codes: H04N 9/3194 including sensor feedback

Abstract

A system and method corrects luminance non-uniformity caused by images being obliquely projected onto a screen. A camera is used to record the geometry of the obliquely displayed image. Utilizing this recorded geometry, a homography is then derived that maps pixels between the projector'"'"'s coordinate system and the screen'"'"'s coordinate system. Utilizing the homography, the projector pixel that attends to the largest projected area on the screen is identified. Next, the ratio of each pixel'"'"'s projected area to the largest projected area is computed. These ratios are then organized into an attenuation array that is used to produce “corrected” luminance information from input image data. The projector is then driven with the “corrected” luminance information.

Claims

1. A method for correcting non-uniformity in luminance of an image generated by a projector and displayed obliquely on a screen having a surface, wherein the projector has a plurality of pixels for use in generating images and each projector pixel subtends to a corresponding projected area on the screen, the method comprising the steps of:

identifying, with a camera, the projector pixel that subtends to the largest projected area on the screen;

determining a ratio between the projected area of each pixel and the largest projected area;

organizing the ratio determined for each pixel into an attenuation array;

modifying luminance information of an input image received by the projector by the ratios of the attenuation array; and

utilizing the modified luminance information to drive the projector such that the image produced on the screen is uniform in luminance.

2. The method of claim 1 further comprising the step of generating a homography that maps between a first coordinate system relative to the projector, and a second coordinate system relative to the surface, and wherein the step of identifying is based on the homography.

3. The method of claim 2 wherein

the first coordinate system includes an x_p coordinate and a y_p coordinate;

the projector to surface homography includes parameters h₇, h₈ and h₉;

the step of identifying comprises the step of calculating a value, w, far each pixel represented by coordinates x_p, y_p, wherein w is equal to |h₇x_p+h₈y_p+h₉| and determining which projector pixel has the smallest calculated value of w.

4. The method of claim 2 wherein the stop of generating the projector to surface homography comprises the steps of:

capturing one or more images produced by the projector on the screen with the camera;

determining the coordinates of each of at least four projector pixels in the first coordinate system, which is relative to the projector, and in a third coordinate system that is relative to the camera; and

processing the coordinates of the at least four projector pixels in both the first and third coordinate systems to generate the projector to surface homography.

5. The method of claim 4 wherein the camera has an optical axis that is perpendicular with the surface in all planes, and the step of generating the projector to surface homography comprises the steps of:

generating a projector to camera homography based upon the determination of the coordinates of the at least four projector pixels in both the first and third coordinate systems; and

equating the projector to camera homography with the projector to surface homography.

6. The method of claim 1 further comprising the step of positioning the camera substantially perpendicular to the surface of the screen, the camera and the projector having different optical axes relative to the surface of the screen.

7. A system for correcting luminance of an image displayed with an oblique shape on a screen having a surface, the system comprising:

a projector for generating the image, the projector having a non-perpendicular optical axis relative to the surface of the screen;

a camera for capturing the image, the camera having a substantially perpendicular optical axis relative to the surface of the screen;

a luminance correction engine for receiving the captured image from the camera, said luminance correction engine being configured to determine a ratio between a projected area of each pixel and the largest projected area on the screen, to organize the ratio determined for each pixel into an attenuation array, and to send the attenuation array to the projector, wherein the projector receives the attenuation or ray and modifies the luminance of the image.

8. The system of claim 7, wherein the attenuation array includes a first coordinate system representing the projector, a second coordinate system representing the surface, and a homography between the first coordinate system and the second coordinate system.

9. The system of claim 8, wherein the homography includes parameters h₇, h₈ and h₉ the first coordinate system includes an x_p and a y_p coordinate, and a value |h₇x_p+h₈y_p+h₉|.

10. The system of claim 7, wherein the luminance correction engine includes a spatial attenuation array for modifying the shape of the image.

11. An apparatus for correcting non-uniformity in luminance of an image generated by a projector and displayed obliquely on a screen having a surface, wherein the projector has a plurality of pixels for use in generating images and each projector pixel subtends to a corresponding projected area on the screen, the apparatus comprising:

means for capturing the image;

means for calculating an attenuation array based upon the captured image, wherein the means for calculating an attenuation array is configured to determine a ratio between the projected area of each pixel and the largest projected area on the screen to calculate the attenuation array;

means for modifying luminance information of an input image received by the projector by the attenuation array; and

means for driving the projector with the modified luminance information such that the image produced on the screen is uniform in luminance.

12. The apparatus of claim 11, further comprising:

means for calculating homographies between the means for capturing, the screen, and the projector; and

means for modifying a shape of the image based upon the homographies.

13. The apparatus of claim 11, further comprising:

means for identifying the projector pixel that subtends to the largest projected area on the screen; and

means for organizing the ratio determined for each pixel into an array.