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Apparatus and method for nonlinear normalization of image

  • US 5,757,979 A
  • Filed: 10/28/1992
  • Issued: 05/26/1998
  • Est. Priority Date: 10/30/1991
  • Status: Expired due to Fees
First Claim
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1. An apparatus for nonlinear normalization of an image, which performs pre-processing for computing the correlation between an unknown character and a reference pattern, the unknown character being formed of lines and having a line pitch in the X direction and a line pitch in the Y direction, said apparatus comprising:

  • means for obtaining a local spatial density function ρ

    (Xi, Yj) (i=1-I, j=1-J) from a two-dimensional pattern f(Xi, Yj) which is obtained by sampling said unknown character at a sampling interval γ

    . said spatial density function ρ

    (Xi, Yj) being obtained as a correlate of both the line pitch in the X direction and the line pitch in the Y direction;

    means for computing an X-direction cumulative function hx(Xi) by successively adding said spatial density function ρ

    (Xi, Yj) while Yj is varied from Y1 to YJ and Xi is fixed;

    means for computing a Y-direction cumulative function hy(Yj) by successively adding said spatial density function ρ

    (Xi, Yj) while Xi is varied from X1 to XI and Yj is fixed;

    means for extending said cumulative functions hx(Xi) and hy(Yj) into continuous cumulative functions hx(X) and hy(Y), respectively;

    means for determining new sampling points (Xi, Yj) at new sampling intervals (δ

    i, ε

    j) in the X and Y directions, the new sampling intervals satisfying the condition that the product of said cumulative function hx(Xi) and δ

    i takes a first fixed value, and the product of said cumulative function hy(Yj) and ε

    j takes a second fixed value; and

    means for computing normalized sampled values at said new sampling points (Xi, Yj) by resampling said unknown character or by performing a computation on said two-dimensional pattern f(Xi, Yj),wherein said correlate of both the line pitch in the X direction and the line pitch in the Y direction is a function of the product of the reciprocals of said line pitches in the X and Y directions.

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