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

• Current Assignee: Agency of Industrial Science & Technology (Government of Japan)
• Original Assignee: Agency of Industrial Science & Technology (Government of Japan)
• Inventors: Ohtani, Kazuo, Okuyama, Hironobu, Matsuoka, Katunori
• Primary Examiner(s): Moore, David K.
• Application Number:
  US07/827,526
• Time in Patent Office: 636 Days
• Field of Search: 382/31, 382/42, 382/11, 359/11, 359/559-561
• US Class Current: 382/211
• CPC Class Codes: G06E 3/003 forming integrals of products, e.g. Fourier integrals, Laplace integrals, correlation integrals; for analysis or synthesis of functions using orthogonal functions
• CPC Class Codes: G06V 10/88 Image or video recognition using optical means, e.g. reference filters, holographic masks, frequency domain filters or spatial domain filters

Abstract

A pattern recognition method and apparatus wherein an optical correlator and a feedback light path are provided. In the optical correlator, an input pattern whose image is formed on a first spatial light modulator (valve) is read by the irradiation of coherent light, and an image of a correlation peak image of this reading light is formed by the use of a correlation filter on which a plurality of reference patterns are recorded in the form of modified patterns. In the feedback light path, the correlation peak image is formed on a second spatial light modulator (valve), the correlation peak image is read out by the irradiation of coherent light, and the light having read the correlation image is made to pass a display filter on which display reference patterns are recorded. Further, an optical system is provided for feeding back the coherent light to the optical correlator after the coherent light having passed the display filter is once formed, thereby reading the correlation peak image by a light intensity measuring device. Moreover, there is disclosed a pattern displaying method and apparatus wherein the feedback light from the feedback light path is formed on a displaying member.

Claims

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, and

wherein 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.

2. A pattern display 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 read-out 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 on 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

displaying the display pattern obtained by the second optical correlator,

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, and

wherein 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.

3. A pattern recognition apparatus comprising:

means for imaging an input pattern, such as a letter or picture, on a first spatial light modulator;

lighting means including a first light source for radiating coherent light and reading out the input pattern imaged on the first spatial light modulator;

a first optical correlator for obtaining a correlation pattern of the read-out pattern on the first spatial modulator and a reference array of a plurality of reference patterns;

a second spatial light modulator having a non-linear input-output response characteristic and putting out a difference among input values in magnification;

another lighting means including a second light source for radiating coherent light and reading out the non-linearly transformed correlation pattern on the second spatial light modulator;

a second optical correlator for correlating together a display array including a plurality of display patterns and the read-out correlation pattern from the second spatial light modulator;

feedback means for 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 input pattern;

a light controller for detecting a sum of the light intensities of the correlation pattern obtained by the first optical correlator, adjusting the intensity of coherent light to be radiated on the first spatial light modulator and making substantially constant the sum of light intensities of the correlation pattern; and

a light detector for detecting the position of a strongest optical peak of the correlation pattern appearing on the second spatial light modulator, using the light read out by the coherent light, and determining the correspondence of the input pattern to a reference pattern,

wherein said first optical correlator further comprises a first lens, a second lens and a correlation filter stored with Fourier transforms of reference patterns,

wherein said second optical correlator comprises a third lens, a fourth lens and a display filter stored with Fourier transforms of display patterns,

wherein said reference array includes a plurality of reference patterns and stored with Fourier transforms thereof to form a reference filter, each reference pattern including a plurality of patterns representing a similar pattern category and a display pattern and forming a sub-group, the reference filter forming a bright correlation peak on a prescribed position on the input plane of the second spatial light modulator, and

wherein said display array includes a display pattern for each pattern category and stored with Fourier transforms thereof to form a display filter, the display array 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.

4. A pattern display apparatus comprising:

means for imaging an input pattern, such as a letter or picture, on a first spatial light modulator;

lighting means including a first light source for radiating coherent light and reading out the input pattern imaged on the first spatial light modulator;

a first optical correlator for obtaining a correlation pattern of the read-out pattern on the first spatial modulator and a reference array of a plurality of reference patterns;

a second spatial light modulator having a non-linear input-output response characteristic and putting out a difference among input values in magnification;

another lighting means including a second light source for radiating coherent light and reading out the non-linearly transformed correlation pattern on the second spatial light modulator;

a second optical correlator for correlating together a display array including a plurality of display patterns and the read-out correlation pattern from the second spatial light modulator;

feedback means for 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 input pattern;

a light controller for detecting a sum of the light intensities of the correlation pattern obtained by the first optical correlator, adjusting the intensity of coherent light to be radiated on the first spatial light modulator and making substantially constant the sum of light intensities of the correlation pattern; and

means for displaying the display pattern obtained through the second optical correlator,

wherein said first optical correlator comprises a first lens, a second lens and a correlation filter stored with Fourier transforms of reference patterns,

wherein said second optical correlator comprises a third lens, a fourth lens and a display filter stored with Fourier transforms of display patterns,

wherein said reference array includes a plurality of reference patterns and stored with Fourier transforms thereof to form a reference filter, each reference pattern including a plurality of patterns representing a similar pattern category and a display pattern and forming a sub-group, the reference filter forming a bright correlation peak on a prescribed position on the input plane of the second spatial light modulator, and

wherein said display array includes a display pattern for each pattern category and stored with Fourier transforms thereof to form a display filter, the display array 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.