Methods and systems for camera characterization in terms of response function, color, and vignetting under non-uniform illumination
First Claim
1. A method for estimating a color model of an imaging device, comprised of the response function and the color mapping, under generic illumination, the method comprising:
- i. acquiring at least one calibration image of a scene with at least two regions of constant albedo from an arbitrary pose;
ii. segmenting the calibration image into regions of constant albedo and grouping the pixels in each region into a set , the set of points with albedo ρ
n;
iii. deriving equations for the estimation using
f−
1(d(x))=u(x)ρ
′
(x)where x are the pixel coordinates that correspond to a scene point, d(x) is the acquired image and is defined as a vector of Nc elements dc(x) that correspond to values on pixel x and channel c, f−
1(d) is the inverse camera response function, a function vector of elements f c−
1(dc), u(x) is the albedo-normalized irradiance, a scalar function, and ρ
′
is the albedo vector of size Nc in the color space of the camera and is defined by elements ρ
′
c for each channel c such that
ρ
=Mρ
′
with ρ
being the albedo vector of size Ns in the output color space and is defined by elements ρ
s for each channel s, and M being a color mapping matrix of size Ns by Nc and composed of rows msT; and
iv. determining the color model of the imaging device by solving the equations derived in step iii using a suitable solver or optimization scheme.
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Abstract
Methods and systems for describing a camera radiometrically, in terms of camera response function and vignetting, and in terms of color, suitable for non-uniform illumination set-ups. It estimates the camera response function and the camera color mapping from a single image of a generic scene with two albedos. With a second same-pose image with a different intensity of the near-light the vignetting is also estimated. The camera response function calibration involves the segmentation of the two albedos, the definition of the system of equations based on the assumption that can be made about the image formation process, and the actual estimation. For the modelling the vignetting there are three steps: computing the albedo-normalized irradiance, finding points of equal vignetting, when needed, and estimation.
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Citations
22 Claims
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1. A method for estimating a color model of an imaging device, comprised of the response function and the color mapping, under generic illumination, the method comprising:
-
i. acquiring at least one calibration image of a scene with at least two regions of constant albedo from an arbitrary pose; ii. segmenting the calibration image into regions of constant albedo and grouping the pixels in each region into a set , the set of points with albedo ρ
n;iii. deriving equations for the estimation using
f−
1(d(x))=u(x)ρ
′
(x)where x are the pixel coordinates that correspond to a scene point, d(x) is the acquired image and is defined as a vector of Nc elements dc(x) that correspond to values on pixel x and channel c, f−
1(d) is the inverse camera response function, a function vector of elements f c−
1(dc), u(x) is the albedo-normalized irradiance, a scalar function, and ρ
′
is the albedo vector of size Nc in the color space of the camera and is defined by elements ρ
′
c for each channel c such that
ρ
=Mρ
′with ρ
being the albedo vector of size Ns in the output color space and is defined by elements ρ
s for each channel s, and M being a color mapping matrix of size Ns by Nc and composed of rows msT; andiv. determining the color model of the imaging device by solving the equations derived in step iii using a suitable solver or optimization scheme. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A method for estimating a vignetting model of an imaging device comprising:
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i. acquiring at least one set of at least two calibration images with the same relative pose and a different intensity of a near-light source; ii. segmenting the calibration images into regions of constant albedo; iii. computing the albedo-normalized irradiance for each pair of same-pose images, u1(x) and u2(x); iv. deriving the equations of the vignetting model using
m(x)=K1u1(x)+K2u2(x)
where K1 and K2 are the two model unknowns; andv. finding a solution for the vignetting model with the equations created in step iv. - View Dependent Claims (20, 21, 22)
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Specification