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Method and apparatus for pattern recognition and display with optical correlator

  • US 5,257,322 A
  • Filed: 01/29/1992
  • Issued: 10/26/1993
  • Est. Priority Date: 09/20/1989
  • Status: Expired due to Fees
First Claim
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1. A pattern recognition method comprising the steps of:

  • forming an input pattern, such as a letter or picture, on a first spatial light modulator;

    irradiating coherent light to the first spatial light modulator and thereby reading out the inputted pattern;

    forming a correlation pattern between the inputted pattern and an array including a plurality of reference patterns preparatively stored in a correlation filter by a first optical correlator including the correlation filter and first and second lenses, the plurality of reference patterns being in several sub-groups, each containing more than one pattern which represent the same letter or picture;

    forming the formed correlation pattern in a second spatial light modulator having a non-linear input-output response characteristic for magnifying differences among a plurality of inputted values;

    reading out by coherent light the non-linearly transformed correlation pattern formed on the second spatial light modulator;

    correlating together an array including a plurality of display patterns preparatively stored in a display filter and the correlation pattern read out from the second spatial light modulator, using a second optical correlator including the display filter and third and fourth lenses;

    feeding back the light passed through the second optical correlator to the first optical correlator and mixing the fed-back light with the read-out light of the inputted pattern;

    detecting a sum of the light intensities of the correlation pattern formed by the first optical correlator and adjusting the intensity of the coherent light to be irradiated to the first spatial light modulator so that the sum of the light intensities can always be substantially constant; and

    detecting the position of a strongest optical peak of the correlation pattern appearing on the second spatial light modulator by the light read out by the coherent light and thereby determining the correspondence of the input pattern to a reference pattern,wherein the step for forming a correlation pattern includes the step of storing in the correlation filter Fourier transforms of the plurality of reference patterns in the array, each of the plurality of reference patterns including a plurality of patterns having a display pattern which form a sub-group for identifying a pattern category and form on a predetermined position on the input plane of the second spatial light modulator a bright correlation peak for each pattern category, andwherein the correlating step for forming a display pattern includes the step of storing in the display filter Fourier transforms of display patterns in the array included in the sub-group representing each pattern category, the array of display patterns converting each bright correlation peak formed by the correlation filter on the output plane of the second spatial light modulator to said display pattern included in the pattern category represented by the position of the correlation peak.

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