US 4,817,176 A · Method and apparatus for pattern recognition

Abstract

A method and apparatus for recognizing an unknown character, pattern, or indicia, or the like as being a particular one of a group of known reference characters, patterns, indicia, or the like. In the preferred embodiment, the system converts scanned and digitized MICR data and uses it to identify the character. The reference characters and the unknown character are Fourier Transformed and various corrections are made for eliminating the absolute amplitude difference from the recognition process, while simultaneously providing a method of correcting for position differences between the reference charcter and the unknown character. Provisions are made for weighting the phase differences proportional to the expected accuracy of the phase data to minimize the effects of noise on the measurement, and for combining the amplitude and phase data to define a single "best match" criteria for the unknown character. The input data is stored in memory and later converted to real and imaginary frequency components through the Fourier Transform process. The real and imaginary parts are converted to amplitude and phase as a function of frequency and both the amplitude and the phase data are corrected for position errors and the like. They are then compared to a set of amplitude and phase data for the group of standard known characters. The particular one of the known reference characters which is closest to the transform of the unknown character is designated as the "best match". The second minimum is located, and the percentage that the best match is better than the second best match is used to determine a margin of error criteria.

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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Method and apparatus for pattern recognition

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Method and apparatus for pattern recognition

Life of this patent

Abstract

Claims27