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Method and apparatus for pattern recognition

  • US 4,817,176 A
  • Filed: 02/14/1986
  • Issued: 03/28/1989
  • Est. Priority Date: 02/14/1986
  • Status: Expired due to Fees
First Claim
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1. A method for recognizing an unknown, machine-readable pattern as a particular one of a group of known reference patterns comprising:

  • providing a group of known reference patterns;

    computing the Fourier Transform of each of said group of known reference patterns such that each of the Fourier Transforms of each of said group of known reference patterns includes a center and a zero reference point;

    correcting the zero reference point to the center of each said Fourier Transform of each of said group of known reference patterns;

    converting the real and imaginary parts of each Fourier Transform to amplitude and phase angle form;

    correcting the converted phase angle for proper quadrature;

    providing a first memory;

    storing said corrected and converted Fourier Transformed reference patterns into a first memory;

    computing an amplitude normalization constant for each of said Fourier Transformed patterns;

    storing the computed normalization constant for each of said Fourier Transformed patterns in said first memory;

    scanning an unknown pattern to be recognized;

    generating an electrical signal indicative of said scanned unknown pattern;

    providing a second memory;

    digitizing said generated electrical signal;

    temporarily storing said digitized electrical signal in the second memory;

    retrieving said temporarily stored, digitized signal from said second memory;

    computing the Fourier Transform of each of said digitized electrical signals such that each Fourier Transform of each of said computed digitized electrical signals includes a center and a zero reference point;

    correcting the zero reference point to the center of each Fourier Transform of each of said computed digitized electrical signals indicative of said scanned unknown pattern;

    converting the real and imaginary parts of each Fourier Transform of each unknown pattern to amplitude and phase angle form;

    correcting the phase angle of each of said converted unknown patterns for proper quadrature;

    storing said corrected and converted Fourier Transformed unknown patterns into said second memory, each of said converted, Fourier Transformed unknown patterns having amplitude values with differences existing therebetween;

    computing an amplitude normalization constant for each of said Fourier Transformed unknown patterns;

    normalizing the amplitude values of the converted Fourier Transformed, unknown pattern stored in said second memory by multiplying same with said normalization constant to eliminate the absolute difference in amplitude value between the Fourier Transformed unknown pattern and each Fourier Transformed reference pattern;

    correcting for phase alignment error;

    correcting for quadrant error;

    computing the phase difference between the Fourier Transformed unknown pattern and each Fourier Transformed reference pattern;

    weighting the phase difference by the amplitude of the Fourier Transformed unknown pattern at each frequency point;

    comparing the absolute phase differences between the Fourier Transformed unknown pattern and the Fourier Transformed reference patterns;

    summing the amplitude and phase differences over all Fourier Transformed reference patterns;

    determining the best amplitude difference match between the Fourier Transformed unknown pattern and the Fourier Transformed reference pattern and the best phase difference match between the Fourier Transformed unknown pattern and the Fourier Transformed reference pattern, in combination;

    computing the average differences between the Fourier Transformed unknown pattern and the Fourier Transformed reference patterns;

    weighting the amplitude difference and phase difference, in combination, equally for each Fourier Transformed reference pattern and by the amount that they are less than the average differences, said weighted reference patterns having at least a first, and a second and minimum values; and

    locating the minimum value to identify the particular Fourier Transformed reference pattern which is the "best match" for the Fourier Transformed unknown pattern.

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