JP2952322B2 - Optical pattern recognition device with automatic adjustment of light intensity - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to the field of optical information processing and optical measurement.
The present invention relates to an apparatus that automatically performs pattern recognition and measurement by performing an optical correlation process using coherent light on a two-dimensional image obtained from an imaging device such as a D camera.

[Summary of the Invention] Joint Transform Correlato
r) and the improved correlator based on it, if the state of the input image such as the type, size, or number of reference images or correlated images changes, the visibility of interference fringes or changes in the spatial frequency domain The state of the intensity distribution image of the joint Fourier transform image displayed on the spatial light converter changes. As a result, the light intensity and S / N ratio of the obtained correlation peak change, so that the light intensity of the correlation peak is out of the appropriate light receiving range of the image pickup device or the light receiving element, and the accurate correlation peak intensity cannot be measured. There was a problem that recognition and measurement could not be performed. In order to solve the above problems, the present invention has means for measuring the light intensity of the joint Fourier transform image or the correlation output image or the amount of change thereof, and the light intensity or the sensitivity of the light receiving element or the space By automatically adjusting the display characteristics of the optical modulator, the appropriate joint Fourier transform image intensity distribution image is displayed on the spatial light modulator, and the correlation peak is received by the imaging device or the light receiving element. By measuring the intensity with a good S / N ratio, accurate recognition and measurement are always possible.

[Prior Art] Conventional optical pattern recognition devices and correlation processing devices include a joint transform correlator (Joint Transform Correlator).
ator) is widely known. For example, patents in this system include JP-A-57-138616 and JP-A-57-21.
No. 0316 and JP-A-58-21716 have been proposed.

FIG. 2 shows a basic configuration diagram of the joint transform correlator. As a spatial light modulator for displaying an intensity distribution image of a congruent Fourier transform image, an optical writing type and reflection type liquid crystal light valve will be described as an example. An image in which a reference image serving as a reference for recognition and a correlated image to be recognized are simultaneously arranged adjacently is referred to as an input image 4. The light beam emitted from the laser 19 is expanded by the beam expander 3 and then split by the beam splitter 31 into two light beams. Beam splitter
The light beam transmitted through 31 irradiates input image 4 and converts input image 4 into a coherent image. This coherent image is
When the Fourier transform is performed using the lens 5 for the transform, a congruent Fourier transform image of the reference image and the correlated image is obtained on the transform plane. On this joint Fourier transform image,
Interference fringes due to interference between the Fourier transform images of the reference image of the correlated image are superimposed. Therefore, by disposing the writing surface of the liquid crystal light valve 6 on the conversion surface, the liquid crystal light valve 6 can display the intensity distribution image of the joint Fourier-transformed image.

Next, the light beam reflected by the beam splitter 31 is reflected by a mirror.
32, 33, the light is reflected by the polarizing beam splitter 11, illuminates the reading surface of the liquid crystal light valve 6, and converts the displayed intensity distribution image into a coherent image. This coherent image is read as a negative image or a positive image by transmitting through a polarizing beam splitter 11 used as a substitute for an analyzer, and is subjected to Fourier transform by a Fourier transform lens 12, thereby obtaining A correlation output image including the correlation peak is obtained on the conversion plane. Therefore, by receiving the correlation output image with the light receiving element 13 arranged on the conversion surface, a correlation peak representing a two-dimensional cross-correlation coefficient between the correlated image and the reference image can be obtained as a correlation signal.

In principle, a BSO crystal (a transmissive spatial light modulator using Bi ₁₂ SiO ₂₀ as a light modulating material) may be used instead of the liquid crystal light valve 6 which is a light writing type and a reflective spatial light modulator. The same Fourier transform image is received by an image pickup device such as a CCD camera, and the output is input to an electric writing type spatial light modulator such as a liquid crystal television to obtain an intensity distribution. The same applies in principle to the method of displaying an image.

FIG. 3 shows an example of the input image 4 in the joint transform correlator. One correlated image and one reference image are arranged adjacent to each other. FIG. 4 shows an example of the correlation peak between the correlated image obtained on the light receiving element 13 and the reference image. The zero dimension appears at the center, and a pair of correlation peaks is obtained on the left and right sides.

Conventionally, in a correlator based on this method, as shown in FIG. 3, one correlated image to be recognized has one reference image which is a database for performing a correlation process with the correlated image. When performing correlation processing with a large number of reference images, the reference images are often rewritten one after another. Moreover, in order to make the correlator more multifunctional at a higher speed, a plurality of reference images and a correlation process with a large number of reference images at once are required to reduce the number of correlation peaks obtained as a result of the correlation process and noise. S / N due to increased components
It was difficult due to reasons such as a decrease in the ratio.

In order to solve the above drawback, we have developed a joint transform correlator having a feedback system [June 1990
Optical pattern recognition device filed on the 15th]. This means that in a normal joint transform correlator, each two-dimensional correlation coefficient between at least one correlated image and at least one reference image obtained as a result of the correlation processing is input to a linear or non-linear transfer function. Then, a feedback system is configured to substantially change the light intensity transmitted through each reference image corresponding to each correlation coefficient in accordance with the output of the transfer function.

FIG. 5 shows a basic configuration diagram of a joint transform correlator having the above feedback system. As the spatial light modulator for displaying the intensity distribution image of the joint Fourier transform image, an optical writing type and reflection type liquid crystal light valve will be described as an example, as in FIG. Until the correlation output image is received by the light receiving element 13, it is the same as FIG. For example, 1
When a plurality of correlated images and a plurality of reference images are used as input images, a plurality of pairs of correlation peaks are obtained on the light receiving element 13.
Hereinafter, for simplicity, only the correlation peak intensity on one side of the pair of correlation peaks will be considered. Each correlation signal representing each correlation peak intensity is output from the light receiving element 13 and is normalized.
34, each correlation signal is normalized by the largest correlation signal among the correlation signals. Then, the normalized correlation signal is input to the liquid crystal mask driving circuit 35, and drives the liquid crystal mask 36 disposed immediately before the input image 4. Thereby,
A feedback system is configured to change the transmittance of a portion corresponding to each reference image on the liquid crystal mask 36 to substantially change the light intensity transmitted through each reference image.

FIG. 6 shows an example of an input image used in a joint transform correlator having a feedback system. The correlated image is arranged at the center, and 13 reference images are arranged on the circumference thereof.

[Problems to be Solved by the Invention] However, generally, the state of an input image is not always constant, and the type, size, number, contrast, and the like of a correlated image and a reference image change. For example, the type or size of the correlated image or the reference image changes depending on what the target is, such as a case where the object to be recognized or measured is a character or a human face. Further, as described in the related art, usually, the joint transform correlator usually performs the correlation process between one correlated image and one reference image. In some cases, a plurality of reference images or images to be correlated is used and many correlation processes are performed at one time so that a higher-speed correlation process can be performed. In such a case, the intensity of the combined Fourier-transformed image and its intensity distribution change due to a change in the amount of light transmitted through the input image or a change in the pattern of the Fourier-transformed image itself. Also, when the number of reference images increases, the visibility of interference fringes superimposed on the joint Fourier transform image decreases. In such a state, when this joint Fourier transform image is displayed on an optical writing type spatial light modulator such as a liquid crystal light valve, these spatial light modulators have an appropriate writing light intensity range. In the joint Fourier-transformed image, an image in a region outside the light intensity range is not properly displayed, for example, is crushed or cannot be displayed, and the state of the displayed intensity distribution image is greatly changed. The same can be said when the combined Fourier-transformed image is received by a CCD camera or the like and displayed on an electric writing type spatial light modulator.

For example, when the type of the correlated image or the reference image changes and the amount of light transmitted through the input image increases, the intensity distribution of the joint Fourier transform image naturally changes, but not only that but also the overall intensity increases. . Therefore, the image is crushed in the low frequency region where the light intensity is strong, and the higher frequency region is displayed on the spatial light modulator, and the displayed spatial frequency region changes.

Also, for example, when the number of reference images is increased,
The visibility of interference fringes superimposed on the joint Fourier-transformed image is reduced. Therefore, the visibility of the interference fringes on the intensity distribution image displayed on the spatial light modulator may be reduced, or the interference fringes may be completely crushed or not displayed in a certain area. In addition, the amount of light transmitted through the input image is larger than in the case of one reference image, and the light intensity of the joint Fourier transform image itself is increased, so that the image is displayed on the spatial light modulator as described above. The spatial frequency domain of the intensity distribution image changes.

As described above, as the state of the input image changes,
When the visibility of the interference fringes decreases, the correlation peak intensity in the correlation output image decreases and the noise component also increases, so that the S / N ratio greatly decreases. When such a correlation output image is received by the light receiving element, there is a problem that the light receiving element has an appropriate light receiving intensity range, so that the correlation peak of the light intensity outside the range cannot be measured accurately.
Also, if the displayed spatial frequency domain changes,
There is also a problem that the characteristics of the correlation processing change significantly.

Further, in a joint transform correlator having a feedback system, by performing feedback, correlation processing with more reference images can be performed than in a normal joint transform correlator, but the feedback changes the light intensity transmitted through the reference image. Therefore, the light intensity and the visibility of interference fringes of the joint Fourier-transformed image change, thereby causing the same problems as described above.

[Means for Solving the Problems] In the present invention, means for converting at least one reference image including a required target and at least one newly input correlated image into a coherent image; Means for performing a Fourier transform to obtain a joint Fourier transform image of the reference image and the correlated image; and converting the joint Fourier transform image into an intensity distribution image, and converting the intensity distribution image to spatial light. Means for displaying on a modulator, means for reading out the intensity distribution image displayed on the spatial light modulator using coherent light, and a correlation output image obtained by again performing Fourier transform on the read out intensity distribution image Means for converting the image into a correlation signal using an imaging device or a light receiving element; and measuring the light intensity of the joint Fourier transform image or the correlation output image or a change in the light intensity. Means for changing the light intensity according to the light intensity or the change in the light intensity, means for changing the light receiving sensitivity of the imaging device or the light receiving element, or changing display characteristics of the spatial light modulator. The above-mentioned subject was solved by having a means.

In order to further enhance the function at a higher speed, a normalization circuit for normalizing the correlation signal with a maximum correlation signal; and a signal before or after the reference image based on the signal normalized by the normalization circuit. The above-mentioned problem has been solved by providing a means for changing linearly or non-linearly the transmittance or the reflectance of a portion corresponding to each of the reference images in the spatial light modulator for a mask arranged in (1).

[Operation] According to the above-described configuration, in a normal joint conversion correlator or a joint conversion correlator having a feedback system, when the state of the input image such as the number or type of reference images changes, When the light intensity for irradiating the image changes, it is possible to measure the light intensity of the joint Fourier transform image or the correlation output image or the amount of change thereof. Then, in accordance with the light intensity or the amount of change, the light intensity of the joint Fourier transform image or the correlation output image is changed, or the light receiving sensitivity of an image pickup device or a light receiving element that receives the correlation output image is changed. Alternatively, the display characteristics of a spatial light modulator that displays an intensity distribution image can be changed.

By using any of the above methods or a combination thereof, an appropriate spatial frequency region in the intensity distribution image can be displayed on the spatial light modulator, and a wide range can be obtained even if the visibility of interference fringes is reduced. The interference fringes can be displayed on the spatial light modulator in an appropriate area. In addition, the correlation output image can be received in an appropriate light receiving range of the imaging device or the light receiving element.

As a result, without changing the characteristics of the correlation processing,
Since a correlation coefficient with a good N ratio can be obtained, the pattern can be optically recognized and measured accurately.

Example An example according to the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an embodiment according to the present invention. As the spatial light modulator, a liquid crystal light valve of an optical writing type and a reflection type will be described as an example. The means for converting at least one reference image including a required target and at least one newly input correlated image into a coherent image,
A writing laser 1, a writing laser controller 2, a beam expander 3, and an input image 4. The coherent image is subjected to Fourier transform, and a joint Fourier transform image of the reference image and the correlated image is obtained. The means for obtaining
Means for converting the combined Fourier transformed image into an intensity distribution image and displaying the intensity distribution image on a spatial light modulator comprises a liquid crystal light valve 6 and a liquid crystal light valve driving circuit 7; The means for reading out the intensity distribution image displayed on the spatial light modulator using coherent light comprises a reading laser 8, a reading laser control unit 9, a beam expander 10, and a polarization beam splitter 11. Means for converting a correlation output image obtained by Fourier-transforming the read-out intensity distribution image again into a correlation signal using an imaging device or a light receiving element;
Lie transform lens 12, light receiving element 13, and light receiving element drive circuit 14
The means for measuring the light intensity of the joint Fourier transform image or the correlation output image or a change in the light intensity comprises a beam splitter 21, an intensity monitoring light receiving element 22, an intensity monitoring circuit 23, and a peak intensity measurement. Consists of circuit 15,
Means for changing the light intensity according to the light intensity or the change in the light intensity, means for changing the light receiving sensitivity of the imaging device or the light receiving element, or means for changing the display characteristics of the spatial light modulator, And a reading laser control unit 9.

The writing laser 1 has its output light intensity controlled by the writing laser controller 2 and emits coherent light. The luminous flux of the coherent light emitted from the writing laser 1 is expanded by the beam expander 3, and the input image 4 in which the correlated image and the reference image are simultaneously arranged in parallel is irradiated to convert the input image 4 into a coherent image. Convert. The coherent image is Fourier-transformed by the Fourier-transforming lens 5, and is applied to the writing surface of the liquid crystal light valve 6 arranged on the conversion surface. As a result, the intensity distribution image of the joint Fourier transform image is displayed on the liquid crystal light valve 6. Here, the liquid crystal light valve 6
Are driven by a liquid crystal light valve drive circuit 7. Part of the joint Fourier transform image is a beam splitter
The light is radiated to a light receiving element 22 for intensity monitoring. The output from the intensity monitoring light receiving element 22 is input to an intensity monitoring circuit 23, which can measure the light intensity of the combined Fourier transform image or the amount of change thereof. The output from the intensity monitor circuit 23 is input to the writing laser controller 2 and changes the output light intensity of the writing laser 1.

The coherent light emitted from the reading laser 8 whose output light intensity is controlled by the reading laser control unit 9 is expanded by a beam expander 10 and reflected by a polarizing beam splitter 11 to be reflected by a liquid crystal light valve. The reading surface of No. 6 is irradiated. When the coherent light reflected on the reading surface of the liquid crystal light valve 6 passes through the polarizing beam splitter 11, the intensity distribution image displayed on the liquid crystal light valve 6 becomes a coherent image as a positive image or a negative image. Is converted to The image is Fourier-transformed by a Fourier transform lens 12, and a light-receiving element 13 disposed on the conversion surface receives a correlation output image including a correlation peak. The light receiving element 13 is driven by a light receiving element driving circuit 14 and converts a correlation output image into a correlation signal. The correlation signal is input to the peak intensity measurement circuit 15, where the correlation peak intensity is measured and output. The correlation peak intensity measured by the peak intensity measurement circuit 15 is input to the reading laser control unit 9 and changes the output light intensity of the reading laser 8.

Here, the input image 4 can be arranged at any position from the front focal plane to the rear focal plane of the Fourier transform lens 5, but in order to perform a strict Fourier transform, the front focal plane or the It is preferable to arrange between the Fourier transform lens 5 and the back focal plane. Therefore, in this embodiment, the input image 4 is arranged on the front focal plane of the Fourier transform lens 5, and the liquid crystal light valve 6 is arranged on the rear focal plane. Further, for the same reason, the liquid crystal light valve 6 is disposed on the front focal plane of the Fourier transform lens 12, and the light receiving element 13 is disposed on the rear focal plane.

Next, the operation will be described. For example, the sixth input image
As shown in the figure, an image in which a plurality of reference images are arranged around one correlated image is used. When the state of the input image such as the number of reference images or the size of the correlated image or the reference image changes, the amount of light transmitted through the input image naturally changes, so that the light intensity of the joint Fourier transform image changes. For example, when the number of reference images increases, the light intensity of the joint Fourier transform image increases, and the light intensity in a region where the spatial frequency is low becomes too strong. Furthermore, the visibility of interference fringes is reduced. Therefore, in the intensity distribution image displayed on the liquid crystal light valve 6, high frequency components are displayed, but low frequency components are crushed, and the visibility of interference fringes is low. Therefore, the light intensity of the joint Fourier-transformed image or the amount of change thereof is determined by the intensity monitoring light receiving element 22 and the intensity monitoring circuit 23.
Measure with As described above, when the light intensity of the joint Fourier transform image increases, a signal is output from the intensity monitor circuit 23 to the writing laser control unit 2 so that the light intensity is always constant, The output light intensity of the writing laser 1 is reduced. Of course, instead of changing the output light intensity of the writing laser 1 so that the light intensity of the joint Fourier transform image is always constant, the change of the light intensity of the joint Fourier transform image and the writing laser A functional relationship such as a proportional relationship may exist between the change of the output light intensity and the change of the output light intensity. Contrary to the above example, when the light intensity of the joint Fourier transform image decreases, the output light intensity of the writing laser 1 may be increased.

Here, when measuring the light intensity of the joint Fourier transform image or the amount of change thereof, the light intensity of the entire joint Fourier transform image or the amount of change thereof may be measured, or only in the vicinity of the optical axis. Alternatively, the light intensity in only a specific spatial frequency region and the change amount thereof may be measured.

As described above, the light intensity of the congruent Fourier-transformed image or the change amount thereof is measured by the light-receiving element 22 for intensity monitoring, and is fed back to the output light intensity of the writing laser 1, thereby obtaining the reference image. When the state of the input image such as the number or the size of the correlated image or the reference image changes, the change in the light intensity of the joint Fourier transform image can be corrected. An appropriate intensity distribution image can be displayed.

Next, consider a correlation output image. If the number of reference images is large, or if the reference image and the correlated image are not very similar, even if an intensity distribution image in an appropriate spatial frequency region is displayed on the liquid crystal light valve 6, the intensity distribution image The visibility of the interference fringes superimposed on it is low. In that case, the correlation peak intensity in the correlation output image received by the light receiving element 13 is weak and the noise component also increases. In such a state, the correlation peak cannot be received in an appropriate light receiving range of the light receiving element 13, for example, in a linear range of the γ characteristic, and the S / H ratio is reduced, so that accurate measurement of the correlation peak intensity cannot be performed. Therefore, the correlation peak intensity is read out from the peak intensity measurement circuit 15 and output to the laser control unit 9 so that the sum of the correlation peak intensity is constant or the maximum correlation peak intensity is close to the upper limit of the appropriate light receiving range. By increasing the output light intensity of the reading laser 8 so as to satisfy the following condition, the correlation peak can be received in an appropriate light receiving range of the light receiving element 13.

As described above, even if the correlation peak intensity changes depending on the state of the input image 4, the correlation peak intensity is fed back to the output light intensity of the reading laser 8 to change the output light intensity. The correlation peak intensity can be measured in an appropriate light receiving range.

By performing one or both of the above-described feedback of the light intensity of the joint Fourier transform image and the feedback of the light intensity of the correlation output image, even if the state of the input image 4 changes, S / The correlation peak intensity can be measured with a good N ratio.

Another embodiment according to the present invention will be described with reference to the drawings.
FIG. 7 is a block diagram of another embodiment of the optical pattern recognition device of the present invention. The optical system after the liquid crystal light valve 6 is omitted. The means for changing the light intensity according to the change of the light intensity or the light intensity or the means for changing the light receiving sensitivity of the imaging device or the light receiving element or the means for changing the display characteristics of the spatial light modulator is variable. formula
ND filter 24, stepping motor 25, and motor control circuit
The other components are the same as those of the embodiment shown in FIG.
That is, the difference is that a variable ND filter 24 whose transmittance changes in the circumferential direction in the light beam on the writing side of the liquid crystal light valve 6, a stepping motor 25 for rotating the variable ND filter 24, The point is that a motor control circuit 26 for controlling the motor 25 is provided. Strength monitor circuit 23
Is output to the motor control circuit 26, and the variable ND filter 24 is rotated by the stepping motor 25 in accordance with the light intensity of the joint Fourier transform image or its change, thereby changing the transmittance of the variable ND filter 24. This changes the light intensity of the joint Fourier-transformed image. Variable ND filter 24
May be basically set at any position in the light beam from the writing laser 1 to the liquid crystal light valve 6, but it is arranged between the writing laser 1 having a small diameter of the light beam and the beam expander 3. This is preferable because the light intensity of the coherent light can be easily changed.

FIG. 8 is a block diagram of another embodiment of the optical pattern recognition device of the present invention. The optical system after the liquid crystal light valve 6 is omitted. Means for changing the light intensity according to the change of the light intensity or the light intensity or means for changing the light receiving sensitivity of the imaging device or the light receiving element or means for changing the display characteristics of the spatial light modulator, The other components are the same as those of the embodiment shown in FIG. That is, the difference is that the output of the intensity monitor circuit 23 is input to the liquid crystal light valve drive circuit 7. Thereby, the liquid crystal light valve 6 is changed according to the light intensity of the joint Fourier-transformed image or the change amount thereof.
Is changed. Specifically, the light receiving sensitivity characteristic can be changed by a method such as changing a voltage applied to the liquid crystal light valve 6, a DC bias voltage, or a driving frequency. In general, a method of changing the applied voltage is easy. .

FIG. 9 is a block diagram of another embodiment of the optical pattern recognition device of the present invention. The optical system before the liquid crystal light valve 6 is omitted. The means for changing the light intensity according to the change of the light intensity or the light intensity or the means for changing the light receiving sensitivity of the imaging device or the light receiving element or the means for changing the display characteristics of the spatial light modulator is variable. An ND filter 16, a stepping motor 17, and a motor control circuit 18 are the same as those in the embodiment shown in FIG. That is, the difference is that a variable ND filter 16, a stepping motor 17 for rotating the variable ND filter 16, and a motor control circuit 18 are provided in the optical path on the reading side of the liquid crystal light valve 6. is there. The peak intensity measurement circuit 15 measures the correlation peak intensity or its change amount,
The output is input to the motor control circuit 18. Then, the variable ND filter 16 is rotated by the stepping motor 17 according to the correlation peak intensity or the amount of change thereof, and the light intensity of the correlation output image is changed by changing the transmittance of the variable ND filter 16. The variable ND filter 16 can be installed at any position in the optical path from the reading laser 8 to the light receiving element 13, but the reading laser 8 having a small light beam diameter and the beam extractor can be basically used. It is preferable to dispose it between the pandas 10 or immediately before the light receiving element 13 because the intensity of the correlation peak in the correlation output image can be easily changed.

FIG. 10 is a block diagram of another embodiment of the optical pattern recognition device of the present invention. The optical system before the liquid crystal light valve 6 is omitted. Means for changing the light intensity in accordance with the light intensity or the change in the light intensity, means for changing the light receiving sensitivity of the imaging device or the light receiving element, or means for changing the display characteristics of the spatial light modulator, The other components are the same as those of the embodiment shown in FIG. That is, the difference is that the peak intensity measurement circuit 15
Is input to the light receiving element drive circuit 14 to change the sensitivity of the light receiving element 13. The peak intensity measuring circuit 15 measures the correlation peak intensity or the amount of change thereof, and outputs the output to the light receiving element driving circuit 14. Then, the sensitivity of the light receiving element 13 is changed so that the correlation peak can be received within an appropriate light receiving range of the light receiving element 13.

In the above embodiment, the writing laser 1, the reading laser 8 and the two lasers are used. Needless to say, the light beam from the writing laser 1 may be separated into two light beams by using a beam splitter. . Needless to say, the writing laser 1 and the reading laser 8 may be any laser having good coherence, such as a gas laser or a semiconductor laser.

In the above embodiment, one correlated image and a plurality of reference images are used as the input image 4 as shown in FIG. 6, but a plurality of correlated images and one reference image may be used. It goes without saying that there may be a plurality of images and a plurality of reference images.

As the input image 4 in the above embodiment, the correlated image and the reference image are written on an electric writing type spatial light modulator such as a liquid crystal television, an optical writing type spatial light modulator such as a liquid crystal light valve, or a photographic dry plate. Needless to say, the displayed one may be used. When the input image 4 is displayed on a spatial light modulator such as a liquid crystal television, by changing the contrast of the liquid crystal television,
It goes without saying that the amount of transmitted light of the input image 4 can be changed to change the light intensity of the joint Fourier-transformed image.

The light receiving element 22 for intensity monitoring in the above embodiment is a beam splitter 21 disposed immediately before the liquid crystal light valve 6.
A part of the congruent Fourier-transformed image may be received, or a part of the transmitted light of the input image 4 may be received by disposing the beam splitter 21 immediately before the input image 4. Needless to say.

It goes without saying that, instead of the variable ND filters 24 and 16 in the above embodiment, any device that can change the transmittance or the reflectance as required, such as a liquid crystal television, may be used.

It goes without saying that the light receiving element 13 in the above embodiment may be an imaging device such as a CCD camera, or a light receiving element array in which light receiving elements are arranged at positions where correlation peaks appear.

In general, a liquid crystal light valve using a nematic liquid crystal as a light modulating material is well known. However, as the liquid crystal light valve 6 in the above embodiment, a liquid crystal light valve using a ferroelectric liquid crystal as a light modulating material may be used. It goes without saying that it is good. In addition to the liquid crystal light valve, it goes without saying that a transmission type spatial light modulator using BSO crystal (Bi ₁₂ SiO ₂₀ ) or the like as a light modulation material can be used.

In the above embodiment, as the spatial light modulator 6, a liquid crystal light valve whose image input is an optical writing type is taken as an example. However, the principle is the same in a method of receiving a joint Fourier-transformed image with a CCD camera and displaying the image on a spatial light modulator whose image input is an electric writing type like a liquid crystal television. In this case, the light intensity of the joint Fourier transform image and the amount of change thereof may be measured by the light-receiving element 22 for intensity monitoring, or may be measured by the CCD camera itself that receives the joint Fourier transform image. Needless to say, it's good. Then, according to the measured light intensity of the joint Fourier transform image and the amount of change thereof, CC
It goes without saying that the light receiving sensitivity of the D camera may be changed or the transmittance of the liquid crystal television may be changed.

In the above embodiment, the Fourier transform lenses 5 and 12 are used.
It is not necessary to use lenses having the same focal length.

It goes without saying that all the above methods are applicable not only to the conventional joint transform correlator but also to a joint transform correlator having a feedback system as shown in FIG. In this case, as a method of changing the light intensity of the joint Fourier-transformed image, it is also possible to change the transmittance of the liquid crystal mask 36. Further, for example, when the input image 4 is displayed on the liquid crystal television, it is also possible to change the transmittance of the reference image portion of the liquid crystal television displaying the input image 4 instead of using the liquid crystal mask 36. Needless to say, there is.

In the embodiment having the feedback system, the liquid crystal mask 36 is used as a mask for changing the light intensity for irradiating the reference image, but the spatial light modulator can change the transmittance and the reflectance as required at a high speed. Needless to say, it is good.

In the embodiment having the feedback system, the input image 4 is disposed immediately after the liquid crystal mask 36. However, if the input image 4 is disposed close to each other, even if the input image 4 is disposed in front of the liquid crystal mask 36. It goes without saying that it is good.

By combining some of the above embodiments, the light intensity of the joint Fourier transform image or the correlation output image can be changed, or the display characteristics of the spatial light modulator for displaying the intensity distribution image or the light reception can be obtained. It goes without saying that the sensitivity of the element may be changed.

[Effects of the Invention] As described above, the number of reference images in the input image,
Even when the state of the input image changes, such as the size of the correlated image or the reference image, or the degree of similarity between the reference image and the correlated image, an appropriate joint intensity distribution image of the Fourier transform image is always obtained.
Even if the S / N ratio of the correlation peak is poor, the intensity of the correlation peak can be accurately measured, so that the accuracy and reliability of the result obtained by the correlation procedure are improved. This also gives
Since the number of reference images can be increased as compared with the related art, the correlator can have more functions and a higher speed.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of an optical pattern recognition apparatus capable of automatically adjusting light intensity according to the present invention, FIG. 2 is a block diagram showing an example of a conventional joint conversion correlator, and FIG. The figure which shows an example of the input image in a conversion correlator, 4th
The figure shows an example of a correlation output image in a joint transform correlator, FIG. 5 is a configuration diagram showing an example of a joint transform correlator having a feedback system, and FIG. 6 is a diagram of a joint transform correlator having a feedback system. FIG. 7 shows an example of an input image, FIG. 7 is a block diagram showing another embodiment of an optical pattern recognition device capable of automatically adjusting light intensity according to the present invention, and FIG. 8 is automatic light intensity adjustment according to the present invention. FIG. 9 is a block diagram showing another embodiment of a possible optical pattern recognition device, FIG. 9 is a block diagram showing another embodiment of an optical pattern recognition device capable of automatically adjusting light intensity according to the present invention, and FIG. FIG. 9 is a configuration diagram showing another embodiment of the optical pattern recognition device capable of automatically adjusting the light intensity according to the present invention. DESCRIPTION OF SYMBOLS 1 ... Writing laser 2 ... Writing laser control part 3 ... Beam expander 4 ... Input image 5 ... Fourier conversion lens 6 ... Liquid crystal light valve 7 ... Liquid crystal light valve drive circuit 8 ... ... Reading laser 9 ... Reading laser controller 10 ... Beam expander 11 ... Polarizing beam splitter 12 ... Fourier transform lens 13 ... Light receiving element 14 ... Light receiving element driving circuit 15 ... Peak intensity measuring circuit 16 Variable ND filter 17 Stepping motor 18 Motor control circuit 19 Laser 21 Beam splitter 22 Light receiving element for intensity monitoring 23 Intensity monitoring circuit 24 Variable ND filter 25 Stepping motor 26 Motor control circuit 31 Beam splitter 32 Mirror 33 Mirror 34 Normalization circuit 35 Liquid crystal mask drive circuit 36: LCD mask fL: Focal length of Fourier transform lens

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Claims (2)

(57) [Claims] An optical pattern recognition apparatus for automatically recognizing and measuring a required pattern by performing an optical correlation process using coherent light on a two-dimensional image obtained from a CCD camera or the like. At least one reference image containing the required target and at least one newly input image
Means for converting the two correlated images into a coherent image; Fourier transforming the coherent image to obtain a congruent Fourier transform image of the reference image and the correlated image; and intensifying the congruent Fourier transform image. Convert to distribution image,
Means for displaying the intensity distribution image on a spatial light modulator, means for reading the intensity distribution image displayed on the spatial light modulator using coherent light, and Fourier transforming the read intensity distribution image again A means for converting the obtained correlation output image into a correlation signal using an imaging device or a light receiving element; a means for measuring a light intensity of the joint Fourier transform image or the correlation output image or a change in the light intensity; and the light Means for converting the light intensity in accordance with a change in intensity or the light intensity, or means for changing the light receiving sensitivity of the imaging device or the light receiving element, or means for changing the display characteristics of the spatial light modulator. An optical pattern recognition device capable of automatically adjusting light intensity. 2. The optical pattern recognition device according to claim 1, wherein the light intensity is automatically adjusted. A normalization circuit for normalizing the correlation signal with a maximum correlation signal, and a signal normalized by the normalization circuit. Based on the spatial light modulator for the mask arranged before or after the reference image, means for linearly or non-linearly changing the transmittance or reflectance of the portion corresponding to each reference image An optical pattern recognition device capable of automatically adjusting light intensity.