Computational methods and electronic camera apparatus for determining distance of objects, rapid autofocusing, and obtaining improved focus images

  • US 5,193,124 A
  • Filed: 06/15/1990
  • Issued: 03/09/1993
  • Est. Priority Date: 06/29/1989
  • Status: Expired due to Term
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First Claim
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1. A method of determining the distance of a surface patch of an object from a camera system having an aperture through which light enters, an image detector, an image forming optical system having first and second principal planes and a focal length, said second principal plane arranged closer to said image detector than said first principal plane, a light filter, a camera controller, and an image processor operatively connected to said image detector and to said camera controller, said method comprising:

  • a) setting said camera to a first set of camera parameters including at least one of (i) distance (s) between said second principal plane and said image detector, (ii) diameter (D) of said camera aperture, (iii) focal length (l) of said camera system, and (iv) spectral characteristic (λ

    ) of light transmitted by said light filter;

    b) forming a first image of said surface patch on said image detector;

    c) recording said first image in said image processor as a first digital image;

    d) preprocessing said first digital image to provide a first normalized image which is related to the point spread function of said camera system by a convolution operation;

    e) calculating a first set of Fourier coefficients of said first normalized image at a set of discrete spatial frequencies;

    f) changing at least one of said camera parameters;

    g) forming a second image of said surface patch on said image detector;

    h) recording said second image in said image processor as a second digital image;

    i) preprocessing said second digital image to provide a second normalized image which is related to the point spread function of said camera by a convolution operation;

    j) calculating a second set of Fourier coefficients of said second normalized image at said set of discrete spatial frequencies;

    k) dividing said first set of Fourier coefficients by said second set of Fourier coefficients to provide a set of ratio values;

    l) providing a signal mathematical relationship corresponding to each member of said set of ratios, said mathematical relationship provided without any intermediate parameter and representing the ratio of the optical transfer function of said first normalized image to the optical transfer function of said second normalized image, each said mathematical relationship dependent only on said camera parameters and having one unknown equal to said distance of said surface patch from said camera system;

    m) substituting each ratio value resulting from step (k) in the signal corresponding mathematical relationship provided in step (l) to obtain a set of equations; and

    n) solving said set of equations resulting from step (m) to determine said distance of said surface patch from said camera system.

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