Optical pattern recognition apparatus with coordinate conversion function

• US 5,528,702 A
• Filed: 05/20/1992
• Issued: 06/18/1996
• Est. Priority Date: 05/31/1991
• Status: Expired due to Term

• Current Assignee: Sumitomo Osaka Cement Company Limited
• Original Assignee: Seiko Instruments Incorporated (Seiko Group), Sumitomo Osaka Cement Company Limited
• Inventors: Mitsuoka, Yasuyuki, Iwaki, Tadao
• Primary Examiner(s): Boudreau, Leo
• Assistant Examiner(s): Anderson, David R.
• Application Number:
  US07/886,331
• Time in Patent Office: 1,490 Days
• Field of Search: 382/32, 382/42, 382/43, 382/44, 382/211, 382/280, 382/278, 382/294, 382/210
• US Class Current: 382/211
• CPC Class Codes: G06E 3/005 using electro-optical or opto-electronic means
• CPC Class Codes: G06V 10/92 using spatial domain filters, e.g. joint transform correlators

Abstract

An optical pattern recognition apparatus has an optical coordinate converter unit which simultaneously and in parallel converts an entered reference image and an entered input image from an entered coordinate system to a desired coordinate system to produce a coordinate-converted reference image and a coordinate-converted input image. A joint transform correlator receives the coordinate-converted reference image and the coordinate-converted input image and generates a correlation coefficient between the coordinate-converted reference image and the coordinate-converted input image so that a correlation between each entered reference and each entered input image is obtained to effect pattern recognition in real time. A feedback circuit normalizes the generated correlation coefficient between the coordinate-converted reference image and the coordinate-converted input image with a maximum correlation coefficient. The feedback circuit changes a subsequently generated correlation coefficient between the coordinate-converted reference image and the coordinate-converted input image depending on the normalized correlation coefficient so that, if the coordinate-converted reference image is obtained from a plurality of entered reference images, a particular entered reference image having the highest correlation with the entered input image is systematically obtained.

Claims

1. An optical pattern recognition apparatus for automatically identifying and measuring specified patterns by performing optical correlation processing, by using coherent light, on two-dimensional images obtained from a photographing means, the optical pattern recognition apparatus comprising:

an optical coordinate convertor unit for converting simultaneously and in parallel at least one entered reference image and at least one entered input image from an entered coordinate system to a desired coordinate system to produce a coordinate-converted reference image of each entered reference image and a coordinate-converted input image of each entered input image,

the optical coordinate convertor unit comprising

means for producing a two-dimensional reference image and input image of said each reference image and said each input image, respectively,

at least one coherent light source,

at least one object image spatial light modulator for recording the two-dimensional reference image and the two-dimensional input image,

at least one coordinate conversion optical filter placed close to the object image spatial light modulator, and

at least one lens; and

a joint transform correlator for generating a correlation coefficient between each coordinate-converted reference image and each coordinate-converted input image, the joint transform correlator comprising

means for converting said each coordinate-converted reference image add said each coordinate-converted input image produced by the optical coordinate convertor into respective coordinate-converted intensity distribution images and then displaying the coordinate-converted intensity distribution images on a coordinate-converted image spatial light modulator,

means for converting the coordinate-converted intensity distribution images displayed on the coordinate-converted image spatial light modulator into respective coherent images,

means for converting the coherent images into a joint Fourier-transformed image of the coordinate-converted intensity distribution images using a Fourier-transform lens,

means for converting the joint Fourier-transformed image into a Fourier-transformed intensity distribution image and displaying the Fourier-transformed intensity distribution image on a Fourier-transformed image spatial light modulator,

means for reading the Fourier-transformed intensity distribution image displayed on the Fourier-transformed image spatial light modulator using coherent light,

means for generating a correlation output image by Fourier-transforming the Fourier-transformed intensity distribution image,

means for converting the correlation output image into a correlation signal using either a photographing device or light receiving element, and

means for processing the correlation signal to determine two-dimensional correlation coefficients of said each two-dimensional reference image and said each two-dimensional input image so that a correlation between said each entered reference image and said each entered input image is obtained to effect pattern recognition in real time.

2. An optical pattern recognition apparatus according to claim 1;

further comprising a feedback circuit, the feedback circuit comprising

a normalization circuit for normalizing the two-dimensional coefficients with a maximum correlation coefficient,

a mask spatial light modulator placed immediately adjacent to one of the object image spatial light modulator and the coordinate-converted image spatial light modulator, and

means for changing at least one of the transmission factor and the reflection factor of parts of the mask spatial light modulator that correspond to either of said each reference image or the coordinate-converted intensity distribution image in either of a linear or non-linear relationship according to the correlation coefficient normalized by the normalization circuit.

3. An optical pattern recognition apparatus according to claim 2;

wherein at least one of the transmission factor and the reflection factor of the parts of the mask spatial light modulator that correspond to either of said each reference image and said each input image or to the coordinate-converted intensity distribution images is changed according to one of (1) a ratio of areas between said each reference image and said each input image, (2) a ratio of areas between the coordinate-converted intensity distribution images, and (3) either the transmitted or the reflected light intensity; and

further comprising normalization means for making equal the intensities of the Fourier-transformed images of the coordinate-converted intensity distribution images.

4. An optical pattern recognition apparatus according to claim 2;

wherein the non-linear relationship in the feedback circuit is represented by one of a saturation type function, a step function with more than one stage, and a combination of both a saturation type function and a step function with more than one stage.

5. An optical pattern recognition apparatus according to claim 1;

wherein the means for converting said each coordinate-converted reference image and said each coordinate-converted input image into respective coordinate-converted intensity distribution images and then displaying the coordinate-converted intensity distribution images on the coordinate-converted image spatial light modulator comprises means for converting the coordinate-converted images into binarized coordinate-converted intensity distribution images and displaying the binarized coordinate-converted intensity distribution images on the coordinate-converted image spatial light modulator.

6. An optical pattern recognition apparatus according to claim 5;

wherein the coordinate-converted image spatial light modulator comprises a light-addressed spatial light modulator using a ferroelectric liquid crystal having a bistable memory capability.

7. An optical pattern recognition apparatus according to claim 5;

wherein the means for converting the coordinate-converted images into the binarized coordinate-converted intensity distribution images and displaying the binarized coordinate-converted intensity distribution images on the coordinate-converted image spatial light modulator comprises a photographing device for converting the coordinate-converted images to an image signal, binarizing means for binarizing the image signal, and an electrically addressed coordinate-converted image spatial light modulator for displaying the binarized image signal.

8. An optical pattern recognition apparatus according to claim 5;

wherein the coordinate-converted image spatial light modulator comprises an electrically addressed spatial light modulator using a ferroelectric liquid crystal having a bistable memory capability.

9. An optical pattern recognition apparatus according to claim 1;

wherein the means for converting the joint Fourier-transformed image into the Fourier-transformed intensity distribution image and displaying the Fourier-transformed intensity distribution image on the Fourier-transformed image spatial light modulator includes means for converting the joint Fourier-transformed image into a binarized Fourier-transformed intensity distribution image and displaying the binarized Fourier-transformed intensity distribution image on the Fourier-transformed image spatial light modulator.

10. An optical pattern recognition apparatus according to claim 9;

wherein the Fourier-transformed image spatial light modulator comprises a light-addressed spatial light modulator using a ferroelectric liquid crystal having a bistable memory capability.

11. An optical pattern recognition apparatus according to claim 9;

wherein the means for converting the joint Fourier-transformed image into the binarized Fourier-transformed intensity distribution image and displaying the binarized Fourier-transformed intensity distribution image on the Fourier-transformed-image spatial light modulator comprises a photographing device for converting the joint Fourier-transformed image into an image signal,

binarizing means for binarizing the image signal, and

a Fourier-transformed image spatial light modulator for displaying the binarized image signal.

12. An optical pattern recognition apparatus according to claim 9;

wherein the Fourier-transformed image spatial light modulator comprises an electrically addressed spatial light modulator using a ferroelectric liquid crystal having a bistable memory capability.

13. An optical pattern recognition apparatus according to claim 1;

further comprising an automatic light regulator, the automatic light regulator including

means for measuring one of the light intensity and change in the light intensity of one of the coordinate-converted image, the joint Fourier-transformed image and the correlation output image, and

one of (1) means for changing the light intensity according to either the light intensity or the change in the light intensity, and (2) means for changing the light reception sensitivity of one of the coordinate-converted image spatial light modulator, the Fourier-transformed image spatial light modulator, the photographing device and the light receiving element.

14. An optical pattern recognition apparatus for automatically identifying and measuring specified patterns by performing optical correlation processing, using coherent light, on two-dimensional images obtained from a photographing means, the optical pattern recognition apparatus comprising:

an optical coordinate converter unit for converting simultaneously and in parallel at least one reference image and at least one input image from an entered coordinate system to a desired coordinate system to produce a coordinate-converted reference image of each entered reference image and a coordinate-converted input image of each entered input image, the optical coordinate converter unit comprising a least one coherent light source, means for producing a two-dimensional reference image from said each entered reference image and a two-dimensional input image from said each entered input image, converting means for optically or electronically converting said each two-dimensional reference image and said each two-dimensional input image into a respective shift-invariable image and then displaying each shift-invariable reference image and each shift-invariable input image on at least one shift-invariable image spatial light modulator, at least one coordinate conversion optical filter placed close to each shift-invariable image spatial light modulator, and at least one lens; and

a joint transform correlator for generating a correlation coefficient between each coordinate-converted reference image and each coordinate-converted input image, the joint transform correlator comprising means for converting said each coordinate-converted reference image and said each coordinate-converted input image into respective coordinate-converted intensity distribution images for display on a coordinate-converted image spatial light modulator, means for converting the coordinate-converted intensity distribution images displayed on the coordinate-converted image spatial light modulator into respective coherent images, means for converting the coherent images into a joint Fourier-transformed image of the coordinate-converted intensity distribution images using a Fourier-transforming lens, means for converting the joint Fourier-transformed image into a Fourier-transformed intensity distribution image and displaying the Fourier-transformed intensity distribution image on a Fourier-transformed image spatial light modulator, means for reading the Fourier-transformed intensity distribution image displayed on the Fourier-transformed image spatial light modulator using coherent light, means for generating a correlation output image by Fourier-transforming the Fourier-transformed intensity distribution image, means for converting the correlation output image into a correlation signal using either a photographing device or a light receiving element, and means for processing the correlation signal to determine two-dimensional correlation coefficients of said each two-dimensional reference image and said each two-dimensional input image so that a correlation between said each entered reference image and said each entered input image is obtained to effect pattern recognition in real time.

15. An optical pattern recognition apparatus according to claim 14;

wherein the converting means further comprises

means for Fourier-transforming said each two-dimensional reference image and said each two-dimensional input image by using coherent light into the shift-invariable images, and

means for converting the shift-invariable images into shift-invariable intensity distribution images and displaying the shift-invariable intensity distribution images on said each shift-invariable image spatial light modulator.

16. An optical pattern recognition apparatus according to claim 14;

wherein the converting means further comprises means for converting said each two-dimensional reference image and said each two-dimensional input image into respective shift-invariable intensity distribution images by computer image processing and for displaying the shift-invariable intensity distribution images on said each shift-invariable image spatial light modulator.

17. An optical pattern recognition apparatus according to claim 14;

wherein the converting means further comprises means for converting the shift-invariable images into binarized shift-invariable intensity distribution images and then displaying the shift-invariable intensity distribution images on said each shift-invariable image spatial light modulator.

18. An optical pattern recognition apparatus according to claim 17;

wherein said each shift-invariable image spatial light modulator comprises a light-addressed, shift-invariable image spatial light modulator including a ferroelectric liquid crystal having a bistable memory capability, and the converting means further comprises means for radiating the shift-invariable images onto each light-addressed, shift-invariable image spatial light modulator to store the binarized shift-invariable intensity distribution images.

19. An optical pattern recognition apparatus according to claim 17;

wherein the converting means further comprises a photographing device for converting the shift-invariable images to image signals,

binarizing means for binarizing the image signals, and

wherein said each shift-invariable image spatial light modulator comprises an electrically addressed shift-invariable image spatial light modulator for displaying the binarized image signal.

20. An optical pattern recognition apparatus according to claim 17;

wherein each shift-invariable image spatial light modulator is an electrically addressed spatial light modulator using a ferroelectric liquid crystal having a bistable memory capability.

21. An optical pattern recognition apparatus, comprising:

an optical coordinate converter unit for concerting simultaneously and in parallel at least one entered reference image and at least one entered input image from an entered coordinate system to a desired coordinate system to produce a coordinate-converted reference image of each entered reference image and a coordinate-converted input image of each entered input image; and

a joint transform correlator for receiving said each coordinate-converted reference image and said each coordinate-converted input image and generating a correlation coefficient between said each coordinate-converted reference image and said each coordinate-converted input image so that a correlation between said each entered reference image and said each entered input image is obtained to effect pattern recognition in real time.

22. An optical pattern recognition apparatus according to claim 21;

wherein the optical coordinate converter unit comprises image producing means for producing a two-dimensional reference image and a two-dimensional input image of said each entered reference image and said each entered input image, respectively, a spatial light modulator for displaying said each two-dimensional reference image and said each two-dimensional input image oriented in the entered coordinate system, and a coordinate conversion optical filter disposed adjacent to the spatial light modulator for converting said each two-dimensional reference image and said each two-dimensional input image from the entered coordinate system to the desired coordinate system to produce the coordinate-converted reference image of said each entered reference image and the coordinate-converted input image of said each entered input image.

23. An optical pattern recognition apparatus according to claim 22;

wherein the spatial light modulator includes a ferroelectric liquid crystal having a bistable memory capability and comprises either a light-addressed modulator or an electrical-addressed modulator.

24. An optical pattern recognition apparatus according to claim 21;

wherein the joint transform correlator comprises means for converting said each coordinate-converted reference image and said each coordinate-converted input image into respective coordinate-converted intensity distribution images, means for converting the respective coordinate-converted intensity distribution images into respective coherent images, means for converting the respective coherent images into a joint Fourier-transformed image, means for converting the joint Fourier-transformed image into a Fourier-transformed intensity distribution image, means for generating a correlation output image by Fourier-transforming the Fourier-transformed intensity distribution image, means for converting the correlation output image into a correlation signal, and means for processing the correlation signal to determine two-dimensional correlation coefficients between said each two-dimensional reference image and said each two-dimensional input image so that a correlation between said each entered reference image and said each entered input image is obtained to effect pattern recognition in real time.

25. An optical pattern recognition apparatus according to claim 24;

wherein the means for converting said each coordinate-converted reference image and said each coordinate-converted input image into respective coordinate-converted intensity distribution images comprises means for converting said each coordinate-converted reference image and said each coordinate-converted input image into respective binarized coordinate-converted intensity distribution images.

26. An optical pattern recognition apparatus according to claim 24;

wherein the means for converting the joint Fourier-transformed image into a Fourier-transformed intensity distribution image comprises means for converting the joint Fourier-transformed image into a binarized Fourier-transformed intensity distribution image.

27. An optical pattern recognition apparatus according to claim 21;

further comprising a feedback circuit comprising normalizing means for normalizing the generated correlation coefficient between said each coordinate-converted reference image and said each coordinate-converted input image with a maximum correlation coefficient, and means for changing a subsequently generated correlation coefficient between said each coordinate-converted reference image and said each coordinate-converted input image depending on the normalized correlation coefficient between each said coordinate-converted reference image and said each coordinate converted input image.

28. An optical pattern recognition apparatus according to claim 21;

wherein the optical coordinate converter unit comprises means for producing a two-dimensional reference image from said each entered reference image and a two-dimensional input image from said each entered input image, converting means for optically or electronically converting said each two-dimensional reference image and said each two-dimensional input image into a respective shift-invariable image and then displaying said each shift-invariable reference image and said each shift-invariable input image on at least one shift-invariable image spatial light modulator, and at least one coordinate conversion optical filter placed close to said each shift-invariable image spatial light modulator for producing said each coordinate-converted reference image of said each entered reference image and said each coordinate-converted input image of said each entered input image.