System and method for automated calibration and correction of display geometry and color
View Patent ↗Various embodiments are described herein for a system and method for calibrating a display device to eliminate distortions due to various components such as one or more of lenses, mirrors, projection geometry, lateral chromatic aberration and color misalignment, and color and brightness non-uniformity. Calibration for distortions that vary over time is also addressed. Sensing devices coupled to processors can be used to sense display characteristics, which are then used to compute distortion data, and generate pre-compensating maps to correct for display distortions.
1. A calibration method to correct for image distortion of a camera that is positioned freely with respect to a viewing surface characterized by an aspect ratio and bounded by a rectangular frame, said method comprising:
displaying at least one test image comprising a set of reference markers with known shapes and coordinates on the viewing surface;
acquiring an image of the viewing surface such that the frame is captured in its entirety;
identifying the four corners of the frame and the markers, as distorted, in camera image space;
obtaining a transformation that corrects for perspective distortion of the acquired image by mapping the images of the four corners of the frame to a second set of four-corners forming a straight rectangle that maintains the aspect ratio and is characterized with an origin and a scale in the camera image space;
constructing a calibration grid that maps the identified markers to their respective undistorted positions with respect to the frame, onto the straight rectangle in the camera image space;
generating a camera distortion correction map from the calibration grid, that can be applied to all image pixels.
2. The calibration method of claim 1 , wherein the correction map is applied to images captured by the camera in a forward direction.
3. The calibration method of claim 1 , wherein inverse of the correction map is determined and applied to pre-distort input images such that images captured by the camera appear substantially distortion free.
4. The calibration method of claim 1 , wherein the camera position changes in time, and wherein said method dynamically calibrates the camera to correct for varying perspective distortions.
5. The calibration method of claim 1 , wherein the correction map is obtained as a fit to the calibration grid by a set of basis functions.
6. The calibration method of claim 1 , wherein the correction map is obtained as interpolation to the calibration grid by a set of basis functions.
7. The calibration method of claim 1 , wherein the scale and origin of the formed straight rectangle is optimized in the camera image space.
8. The calibration method of claim 7 , wherein the largest straight rectangle having the aspect ratio is chosen for maximum resolution.
9. The calibration method of claim 1 , wherein the aspect ratio of the viewing surface matches aspect ratio of the camera image space, and wherein the straight rectangle is adjusted to fill the camera image space.
10. The calibration method of claim 1 , wherein the camera distortion further includes lateral chromatic aberration, and wherein the at least one test image is repeated for each color component to construct a calibration grid independently for the each color component.
11. The calibration method of claim 1 , wherein the at least one test image is displayed on, attached to, or projected onto, the viewing surface.
12. The calibration method of claim 1 , wherein a plurality of missing markers in the image are determined and computed by extrapolation.
13. The calibration method of claim 1 , wherein the four corners are determined from equations of the four edge lines obtained by parameterization of the boundary.
14. The calibration method of claim 1 , wherein the frame is a physical bezel surrounding the viewing surface.
15. The calibration method of claim 1 , wherein the frame is an outline displayed on or projected on the viewing surface.
16. A calibration system to correct for image distortion of a camera, said system comprising:
a viewing surface characterized by an aspect ratio and bounded by a rectangular frame, wherein the camera is freely positioned with respect to the viewing surface;
a test image generator for generating at least one test image having a set of reference markers with known shapes and coordinates displayed on the viewing surface;
a calibration data generator configured to analyze the at least one test image as captured by the camera, and to construct calibration data by:
identifying the four corners of the frame and the markers, in camera image space;
obtaining a transformation that corrects for perspective distortion of the acquired image by mapping the images of the four corners of the frame to a second set of four-corners forming a straight rectangle that maintains the aspect ratio and is characterized with an origin and a scale in the camera image space;
mapping the identified markers to their respective undistorted positions with respect to the frame, onto the straight rectangle in the camera image space;
a warp generator to generate a camera distortion correction map from the calibration grid;
a digital warp unit to apply the correction map to the camera.
17. The calibration system of claim 16 , wherein at least one of the calibration data generator, the warp generator and the digital warp unit are integrated in a processor coupled to the camera.
18. The calibration system of claim 16 , wherein the camera position changes in time, and wherein said system is configured to dynamically calibrate the camera to correct for varying perspective distortions.
19. The calibration system of claim 16 , wherein the at least one test image is displayed on, attached to, or projected onto, the viewing surface.
20. The calibration system of claim 16 , wherein the frame is a physical bezel surrounding the viewing surface.
21. The calibration system of claim 16 , wherein the frame is an outline displayed on or projected on the viewing surface.