Camera calibration using off-axis illumination and vignetting effects
First Claim
Patent Images
1. A method for calibrating a camera comprising the steps of:
- digitizing an image of a blank textureless surface having a uniform illumination;
from the digitized image, determining a pixel intensity drop off caused by a combination of a vignetting effect and an off-axis pixel projection effect due to camera defects;
from the determined pixel intensity drop off, approximating the vignetting effect and the off-axis pixel projection effect using a modeling equation; and
recovering an intrinsic parameter of the camera other than pixel intensity drop off using substantially only the determined pixel intensity drop off.
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Abstract
An imaging device is calibrated using a flat, featureless surface and uniform illumination, relying on the effect of off-axis illumination and vignetting on the reduction of light into the camera at off-axis angles. The effect of the tilt of the camera is also considered. These effects are used to extract intrinsic camera parameters including focal length, principal point, aspect ratio and skew.
68 Citations
40 Claims
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1. A method for calibrating a camera comprising the steps of:
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digitizing an image of a blank textureless surface having a uniform illumination; from the digitized image, determining a pixel intensity drop off caused by a combination of a vignetting effect and an off-axis pixel projection effect due to camera defects; from the determined pixel intensity drop off, approximating the vignetting effect and the off-axis pixel projection effect using a modeling equation; and recovering an intrinsic parameter of the camera other than pixel intensity drop off using substantially only the determined pixel intensity drop off. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A computer program product for calibrating a camera, the computer program product comprising a computer usable medium having computer readable code thereon, including program code which:
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retrieves a digitized image of a blank textureless surface having a uniform illumination; from the digitized image, determines a pixel intensity drop off caused by a combination of a vignetting effect and an off-axis pixel projection effect; from the determined pixel intensity drop off approximating the vignetting effect and the off-axis pixel projection effect using a modeling equation; and recovers an intrinsic parameter of the camera other than pixel intensity drop off based on substantially only the determined drop off. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
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17. A computer system comprising:
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a memory system; an I/O system connected to the memory system; a storage device connected to the I/O system; and a calibration routine located in the memory system responsive to a request for calibrating a camera which; retrieves a digitized image of a blank textureless surface having a uniform illumination; from the digitized image, determines a pixel intensity drop off caused by a combination of a vignetting effect and an off-axis pixel projection effect; from the determined pixel intensity drop off, approximating the vignetting effect and the off-axis pixel projection effect using a modeling equation; and recovers an intrinsic parameter of the camera other than pixel intensity drop off based on substantially only the determined drop off. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24)
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25. An apparatus for calibrating a camera comprising:
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means for digitizing an image of a blank textureless surface having a uniform illumination; means for determining a pixel intensity drop off in the digitized image caused by a combination of a vignetting effect and an off-axis pixel projection effect; means for approximating the vignetting effect and the off-axis pixel projection effect in the digitized image using a modeling equation; and means for recovering an intrinsic parameter of the camera other than pixel intensity drop off using substantially only the determined pixel intensity drop off. - View Dependent Claims (26, 27, 28, 29, 30, 31, 32)
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33. An apparatus for calibrating a camera comprising:
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a retrieval routine which retrieves a digitized image of a blank textureless surface having a uniform illumination; a routine which determines a pixel intensity drop off in the digitized image caused by a combination of a vignetting effect and an off-axis pixel projection effect; an approximating routine which approximates the vignetting effect and the off-axis pixel projection effect in a digitized image using a modeling equation; and a parameter computing routine which recovers an intrinsic parameter of the camera other than the pixel intensity drop off using substantially only the determined pixel intensity drop off. - View Dependent Claims (34)
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35. A method for calibrating a camera comprising the steps of:
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digitizing an image of a blank textureless surface having a uniform illumination; from the digitized image, determining a pixel intensity drop off caused by a combination of a vignetting effect and an off-axis pixel projection effect; from the determined pixel intensity drop off, approximating the vignetting effect and the off-axis pixel projection effect using a modeling equation; and recovering focal length of the camera using substantially only the determined pixel intensity drop off. - View Dependent Claims (36, 37)
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38. A method for calibrating a camera comprising the steps of:
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digitizing an image of a blank textureless surface having a uniform illumination; from the digitized image, determining pixel intensity drop off caused by a combination of a reduction in illumination of image points at the edge of the digitized image and a variation in illumination across the field of view in proportion to the fourth power of the cosine of an angle between a light ray and an optical path; from the determined pixel intensity drop off approximating the reduction in illumination of image points at the edge of the digitized image and the variation in illumination across the field of view in proportion to the fourth power of the cosine of an angle between a light ray and an optical path; and recovering an intrinsic parameter of the camera other than pixel intensity drop off using substantially only the determined pixel intensity drop off.
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39. A method for providing an estimate for a camera parameter comprising the steps of:
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digitizing an image of a blank textureless surface having a uniform illumination; from the digitized image, determining a pixel intensity drop off caused by a combination of a reduction in illumination of image points at the edge of the digitized image and a variation in illumination across the field of view in proportion to the fourth power of the cosine of an angle between a light ray and an optical path; from the determined pixel intensity drop off, approximating the reduction in illumination of image points at the edge of the digitized image and the variation in illumination across the field of view in proportion to the fourth power of the cosine of an angle between a light ray and an optical path, and recovering an intrinsic parameter of the camera other than pixel intensity drop off using substantially only the determined pixel intensity drop off. - View Dependent Claims (40)
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Specification