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Methods and systems for camera characterization in terms of response function, color, and vignetting under non-uniform illumination

  • US 10,504,239 B2
  • Filed: 04/13/2016
  • Issued: 12/10/2019
  • Est. Priority Date: 04/13/2015
  • Status: Active Grant
First Claim
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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 custom character, the set of points with albedo ρ

    n;

    iii. deriving equations for the estimation using
    f

    1
    (d(x))=u(x



    (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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