JP2676562B2 - Optical pattern recognition device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a CCD in the field of optical information processing and optical measurement.
For two-dimensional images obtained from imaging devices such as cameras,
The present invention relates to a device that automatically performs pattern recognition and measurement by performing optical correlation processing.

[Summary of the Invention]

The present invention is based on the Joint Transform Correlator.
in ator), the congruent Fourier transform intensity distribution of at least one or more reference images containing the required target recorded in the spatial light modulator and at least one or more newly input signal images is newly input. At least one or more signal images are read out by Fourier transform light, and Fourier transform is performed again to obtain a correlation signal,
The present invention relates to an optical pattern recognition device that can quickly obtain a correlation signal with less noise even if many reference images are used at one time.

[Conventional technology]

In the conventional optical pattern recognition device and correlation processing device, the joint transform correlator
r) was often used. For example, FIG. 4 shows an example using an optical writing type spatial light modulator. In this method, the input image is an image in which a reference image serving as a reference for recognition and a signal image to be recognized are simultaneously arranged adjacent to each other.
36. The light beam emitted from the laser 1 is expanded by the beam expander 2 and then split into two light beams by the beam splitter 25. The light beam that has passed through the beam splitter 25 irradiates the input image 36 and converts the input image 36 into a coherent image. This coherent image is a Fourier transform lens 7
Fourier transform is performed by using, and the liquid crystal light valve 37 arranged on the transform surface stores the light intensity distribution of the Fourier transform image of the congruent Fourier transform image of the reference image and the signal image.

Next, the light beam reflected by the beam splitter 25 is reflected by the mirrors 4 and 9 and the deflecting beam splitter 38 and illuminates the liquid crystal light valve 37, and the light intensity distribution of the stored combined Fourier transform image is converted into a coherent image. Convert. This coherent image is read out as a negative image or a positive image by passing through the deflecting beam splitter 38 acting as an analyzer, is Fourier transformed by the Fourier transform lens 8, and is received by the CCD camera 13 arranged on the transform surface. To be done. By doing so, a correlation peak representing a two-dimensional cross-correlation coefficient between the signal image and the reference image can be obtained.

In the above example, a reflection type liquid crystal light valve is used with the optical writing type space as a modulator, but when used in a transmission type, a BSO crystal (Bi ₁₂ SiO ₂₀ ) or the like is well known. Also, instead of using the optical writing type spatial light modulator, there is also a method of capturing a combined Fourier transform image with a CCD camera and displaying it on an electrically writing type spatial light modulator such as a liquid crystal television.

An example of the input image 36 is shown in FIG. 5, and a CCD camera 1 is shown in FIG.
3 shows a pair of correlation peaks representing a two-dimensional cross-correlation coefficient between the signal image and the reference image obtained from FIG.

More recently, binarization of the Fourier transform image of the reference image and the signal image has been found to make the correlation peaks sharper and sharper and improve the S / N ratio (for example, B-Javidi and C Jay Kuo, Applied Optics, 27, 663 (1988): B. Javidi and CJK.
uo, Applied Optics, 27, 663 (1988). ).

Further, as an optical pattern recognition device using a method other than the congruential transform correlator, a hologram of the Fourier transform image of the reference image is arranged on the Fourier transform plane of the signal image, and the Fourier transform image of the signal image is filtered by this. After that, a matched filter type optical correlator that obtains a correlation signal by performing the Fourier transform again has also been known for a long time.

[Problems to be solved by the invention]

However, generally, in this method, the number of signal images and reference images is one each. Therefore, in the case of recognizing an alphabet, for example, one character of the alphabet to be recognized is used as a signal image, and in order to obtain correlation with all the alphabets, the alphabet must be rewritten one by one as a reference image and the correlation processing must be performed in time series. No, it takes a lot of time. However, in order to solve it, for example, when increasing the number of reference images and trying to correlate with many reference images at once, the intensity of the correlation peak due to the correlation processing between each reference image and the signal image is significantly reduced, Since the noise component increases, the correlation peak is buried by the noise component, which makes it difficult to separate the peaks, and may cause incorrect recognition.

Also, when using a matched filter type correlator,
It is known that noise is less affected when the number of reference images is increased than when using a congruential transform correlator [Francis TS You, QW Song, YS Cheng and Don A. Gregory, Applied Optics. ,
29,225 (1990): Francis TS, Yu, QWSong, YSCheng, a
nd Don A. Gregory, Applied Optics, 29,225 (1990)],
In order to increase the number of reference images, it is necessary to prepare the same number of reference light beams as the number of reference images, which causes a problem that the optical system becomes complicated.

[Means for solving the problem]

In order to solve the above problems, in the present invention, means for converting at least one reference image including a desired target and at least one newly input signal image into a coherent image, and Fourier transforming the coherent image, A unit for obtaining a congruent Fourier transform image of the reference image and the signal image; a unit for converting the congruent Fourier transform image into an intensity distribution image and displaying the intensity distribution on a spatial light modulator; Means for converting at least one signal image only into a coherent image; and Fourier transforming the coherent image of only the signal image, and irradiating so as to match it with the recording center of the intensity distribution image recorded in the spatial light modulator. And means for reading the intensity distribution image, and Fourier transforming the read intensity distribution image,
By using an optical pattern recognition device having a means for converting the image into a correlation signal using an image pickup device, a correlation signal with less influence of noise can be obtained even if the number of reference images increases, and a simple optical An optical pattern recognition device that can be configured with a system can be provided, and the above-mentioned problems are solved.

In particular, the means for converting the joint Fourier transform image into an intensity distribution image and displaying the intensity distribution on the spatial light modulator uses a ferroelectric liquid crystal having a bistable memory property between the light reflectance and the applied voltage. An optical pattern recognition device capable of recognizing an optical pattern in real time is provided by irradiating and storing a congruent Fourier transform image in the previously described optical writing type spatial light modulator.

[Action]

According to the above configuration, among the interference fringes generated by the interference between the Fourier transforms of the plurality of reference images and the signal images recorded in the optical writing type spatial light modulator on the Fourier transform surface of the input image, Do not read the part of the interference fringes caused by the interference between the Fourier transforms of the reference image and the signal image other than the required target or between the Fourier transforms of the reference images, and by the Fourier transform of the reference image and the signal image that are the required target. Read only the part of the generated interference fringes,
An image that includes a correlation signal by Fourier transforming it again (for example, if the signal image is represented by f and the reference image is represented by g, the correlation between g and f and the convolution of f: f * (g ☆ f) is included) Therefore, an optical pattern recognition device that is as strong in noise as a matched filter type optical correlator can be obtained. In addition, since the Fourier transform image is converted into the intensity distribution image in the same manner as the congruential transform correlator, the signal image and the 1
Since it is frequently correlated with many reference images, high-speed and accurate pattern recognition can be performed.

〔Example〕

An embodiment of an optical pattern recognition device according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an embodiment of an optical pattern recognition device of the present invention. At least one reference image including the desired goal and at least one newly input
The means for converting one signal image into a coherent image includes a laser 1, a beam expander 2, a first beam splitter 3, and a first liquid crystal television 5, and Fourier transforms the coherent image to convert the reference image and the signal image. The means for obtaining a congruent Fourier transform image is composed of a first Fourier transform lens 7 and a second mirror 9, and converts the congruent Fourier transform image into an intensity distribution image and displays the intensity distribution image on a spatial light modulator. The means for converting comprises a light writing type liquid crystal light valve 10, and means for converting only at least one newly input signal image into a coherent image is a laser 1, a beam expander 2, a first mirror 4 and a second mirror 4. The liquid crystal television 6 is used, the coherent image of only the signal image is subjected to Fourier transform, and this is subjected to intensity distribution recorded in the spatial light modulator. Means for reading the intensity distribution image by irradiating to match the recording center of the image is, the polarizer and the second Fourier interchangeable lens 8 and the second beam splitter 11
The third Fourier transform lens 12 and the CCD camera 1 are provided as means for performing a Fourier transform on the read intensity distribution image and transforming the image into a correlation signal by using an imaging device.
Consists of three. Computer 14 and first D / A converter 15 and first
The drive unit 31 of the liquid crystal television is used for displaying on the first liquid crystal television 5 at least one reference image including the required target and at least one newly input signal image, and the computer 14 and the second D The / A converter 16 and the drive unit 32 of the second liquid crystal television are used to display only at least one newly input signal image on the second liquid crystal television 6, and the computer 14 and the optical writing type liquid crystal light valve are used. Driver 17
Is used to drive the optically writable liquid crystal light valve 10.

The coherent light emitted from the laser 1 and expanded by the beam expander 2 is split into two light beams by the beam splitter 3. The light flux reflected by the beam splitter 3 is
The input image composed of the signal image and the reference image is converted into a coherent image by irradiating the first liquid crystal television 5 in which the signal image and the reference image are simultaneously arranged in parallel and displayed. The coherent image is Fourier-transformed by the first Fourier transform lens 7 via the second mirror 9, and is applied to the optical writing type liquid crystal light valve 10. Here, if the TN (Twist Nematic) liquid crystal is used as the light modulation material as the light writing type liquid crystal light valve 10, the Fourier transform screen is recorded as an image having a gray scale, and the light reflection material is used as the light modulation material. If a ferroelectric liquid crystal having a bistable memory property between the rate and the applied voltage is used, the image will be binarized entirely by a certain threshold, so the binarized intensity distribution of the Fourier transform image. Are recorded in the optically writable liquid crystal light valve 10.

On the other hand, the other light flux transmitted through the beam splitter 3 is
By irradiating the second liquid crystal television 6 that displays only the newly input signal image in the same arrangement as that displayed on the first liquid crystal television 5 after being reflected by the first mirror 4. Convert only the signal image to a coherent image. The coherent image of only the signal image is Fourier-transformed by the second Fourier transform lens 8 via the second beam splitter 11 and the polarizer 39, and the optical writing type liquid crystal light valve 10 is provided.
It is irradiated to the reading surface of and is reflected again. However, since the optically writable liquid crystal light valve 10 is a reflective type, the reading surface is the surface in the direction opposite to the surface on which the Fourier transform image is recorded. As a result, the gray scale or binarized intensity distribution image of the Fourier transform image recorded on the optical writing type liquid crystal light valve 10 is converted into a coherent image. The coherent image is read out as a negative image by passing through the polarizer 39, and is Fourier-transformed by the third Fourier transform lens 12, so that it is received by the CCD camera 13 as an image including a correlation output. Here, the first liquid crystal television 5 is arranged on the front focal plane of the first Fourier transform lens 7, and the optical writing type liquid crystal light valve 10 is arranged on the rear focal plane. Further, the second liquid crystal television 6 is arranged on the front focal plane of the second Fourier transform lens 8 and the optical writing type liquid crystal light valve 10 is arranged on the rear focal plane. Further, the optical writing type liquid crystal light valve 10 is arranged on the front focal plane of the third Fourier transform lens 12, and the CCD camera 13 is arranged on the rear focal plane.

Since the first liquid crystal television 5 and the second liquid crystal television 6 display image information by the drive unit 31 of the first liquid crystal television and the drive unit 32 of the second liquid crystal television, respectively, using the video signal, the computer 14 The digital image information output from each of them is converted into a video signal by the first D / A converter 15 and the second D / A converter 16, respectively. Further, the optically writable liquid crystal light valve 10 is driven by its driving unit 17, which is driven by the computer 14 to the first D / A converter 15 and the second D / A converter 15.
Of the digital image information sent to the D / A converter 16 of FIG.

In the first liquid crystal television 5, for example, as shown in FIG.
An image in which a plurality of reference images are arranged around the circumference of one signal image is displayed. This is because the distance between the signal image and the reference image is made constant, and at the same time, the influence of the Gaussian distribution of the intensity distribution of the laser light is reduced.
Further, the second liquid crystal television 6 is replaced by the first liquid crystal television 5
Only the signal image that is completely the same as the signal image displayed in Fig. 3 and has the same size, position, and rotation direction is displayed. Using the example of FIG. 7, only the signal image E is displayed at exactly the same size and at the same position in the rotation direction as shown in FIG.

In this state, from the CCD camera 13, a plurality of correlation peaks based on the correlation between the signal image and the reference image (correctly, the correlation between the signal image and the reference image and the convolution of the signal image, but for simplicity, This is called the correlation peak of the signal image and the reference image). For example, the seventh
In the case of the input image shown in the figure, there are four reference images, so 4
Pairwise correlation peaks may be obtained. In this case, the light intensity of each correlation peak is smaller than that in the case of one reference image, and the noise component is increased,
It becomes difficult to distinguish the correlation peak from the noise, and the conventional congruential transform correlator may make an erroneous recognition. Therefore,
The SN ratio of the optical pattern recognition device of the present invention and the conventional congruential conversion correlator when the number of reference images is increased by using the TN liquid crystal as the optical modulation material as the optical writing type liquid crystal light valve 10. Fig. 8 shows the SN ratio of the. As can be seen from FIG. 8, as the number of reference images increases, the optical pattern recognition apparatus of the present invention exhibits better SN characteristics than the conventional joint transform correlator. of course,
The slope of the curve shown in FIG. 8 also differs depending on the type of reference image and signal image used (for example, alphabet, kanji, fingerprint, painting, photograph, etc.). In FIG. 8,
Capital letters of the alphabet are used as the signal image and the reference image.

Next, the optical writing type liquid crystal light valve 10 according to the present invention using an optical writing type spatial light modulator using a ferroelectric liquid crystal having a bistable memory property between the light reflectance and the applied voltage. Before describing the characteristics of the pattern recognition device, an optical writing type spatial light modulator using a ferroelectric liquid crystal having a bistable memory property between the light reflectance and the applied voltage will be described first.

FIG. 9 is a sectional view showing the structure of an optical writing type spatial light modulator using a ferroelectric liquid crystal. Transparent substrates 40a, 40b such as glass or plastic for holding liquid crystal molecules
Is provided with transparent electrode layers 41a and 41b on its surface, and alignment film layers 42a and 42b in which silicon monoxide is obliquely vapor-deposited at an angle in the range of 75 to 85 degrees from the normal direction of the transparent substrate. Transparent substrates 40a and 4
In 0b, the alignment film layers 42a and 42b are opposed to each other by controlling a gap via a spacer 48 to sandwich the ferroelectric liquid crystal layer 43.

Further, a photoconductive layer 44, a light shielding layer 45, and a dielectric mirror 46 are laminated and formed on the transparent electrode layer 41a on the writing side by light between the alignment film 42a and the transparent substrate 40a on the writing side and the transparent on the reading side. Non-reflective coatings 47a and 47b are formed on the cell outer surface of the substrate 40b.

Next, a method for initializing the optical writing type spatial light modulator 10 using the ferroelectric liquid crystal having the above structure will be described. The first method is to irradiate the entire writing surface of the optical writing type spatial light modulator 10 using a ferroelectric liquid crystal once with a direct current bias voltage sufficiently higher than the maximum value of the threshold voltage at the time of bright or
A DC bias voltage in which an AC voltage of 100 Hz to 50 kHz is superposed is applied between the transparent electrode layers 41a and 41b to align the ferroelectric liquid crystal molecules in a stable state in one direction and store the state. The second method is a DC bias voltage of 100Hz or 100Hz, which is sufficiently higher than the maximum value of the threshold voltage in the dark without light irradiation.
A DC bias voltage in which an AC voltage of -50 kHz is superimposed is applied between the transparent electrode layers 41a and 41b to align the ferroelectric liquid crystal molecules in a stable state in one direction and store the state.

Further, the operation after the optical writing type spatial light modulator 10 using the ferroelectric liquid crystal is initialized as described above will be described. The threshold voltage of the optical writing type spatial light modulator using the ferroelectric liquid crystal is equal to or less than the minimum value of the threshold voltage of the optical writing type spatial light modulator using the ferroelectric liquid crystal in the dark without light irradiation, and the threshold value of the optical writing type spatial light modulator using the ferroelectric liquid crystal in the light irradiation. An image is written by laser light or the like while applying a DC bias voltage of a reverse polarity that is equal to or higher than the maximum value of the voltage or a DC bias voltage in which an AC voltage of 100 Hz to 50 kHz is superimposed between the transparent electrode layers 41a and 41b. . Carriers are generated in the photoconductive layer 44 in the region irradiated with the laser, and as a result, the specific resistance of the photoconductive layer is reduced, and the generated carriers drift in the direction of the electric field due to the DC bias, and are generated in the region irradiated with the laser. Is applied to the ferroelectric liquid crystal layer with a reverse polarity voltage equal to or higher than the threshold voltage, and the ferroelectric liquid crystal undergoes inversion of molecules accompanying the inversion of spontaneous polarization and shifts to the other stable state. The value is processed and stored.

The binarized and stored image is irradiated with light for reading linearly polarized light whose polarization axis is aligned with the alignment direction of liquid crystal molecules aligned by initialization (or the direction orthogonal thereto), and by the dielectric mirror 46. It is possible to read in a positive state or a negative state by passing an analyzer arranged such that the polarization axis is perpendicular (or parallel) to the polarization direction of the reflected light. In the embodiment shown in FIG. 1, a polarizer 39 is used instead of the analyzer.

The threshold voltage for binarizing an image is the transparent electrodes 41a, 4a.
By changing the frequency of the AC voltage or the value of the DC bias voltage applied during 1b to change the voltage, the same effect as when the threshold value is changed can be obtained.

In the above embodiment, when the visible light reflectance of the dielectric mirror 46 is sufficiently high and the influence of the reading light on the photoconductive layer 44 is extremely small, the light shielding layer 45 can be omitted. Further, when the read light reaching the photoconductive layer 44 is sufficiently small and the effect of the read light on the photoconductive layer 44 is extremely small, the dielectric mirror 46 can be omitted.

The characteristics of the optical writing type spatial light modulator using the ferroelectric liquid crystal described above applied to the optical pattern recognition apparatus of the present invention will be described. FIG. 10 shows the S / N ratio and the optical writing type space using the TN liquid crystal when the optical writing type spatial modulator using the ferroelectric liquid crystal is used as the liquid crystal light valve 10 of the optical pattern recognition device of the present invention. The S / N ratio when using an optical modulator is
It shows how the number of reference images changes as the number of reference images increases. The S / N when using the optical writing spatial light modulator using ferroelectric liquid crystal is SN _F , and the S / N when using the optical writing spatial light modulator using TN liquid crystal is SN _T. When I did
SN _F / SN _T when the number of reference image is changed, decreases as the number of reference images increases. However, when the number of reference images is small, it is understood that the use of the photo-writing type spatial light modulator using the ferroelectric liquid crystal enables the pattern recognition with a high S / N and high sensitivity. Further, even if the number of reference images increases, in the example of FIG. 10, if the number of reference images is up to 8, it is better to use the optical writing type spatial light modulator using the ferroelectric liquid crystal. It turns out that is large. In addition,
In the embodiment of FIG. 10, alphabets are used as the signal image and the reference image. Needless to say, the above relationship does not change essentially although it differs slightly depending on the type of image used as the input image.

Next, FIG. 2 shows an example in which the optical pattern recognition device of the present invention can be constructed using only one image information input means. In FIG. 2, the means for converting at least one reference image including a desired target and at least one newly input signal image into a coherent image comprises a laser 1, a beam expander 2 and a liquid crystal television 18, and the coherent The means for obtaining the congruent Fourier transform image of the reference image and the signal image by Fourier transforming the image comprises a first Fourier transform lens 7 and a mirror 21, and transforms the congruent Fourier transform image into an intensity distribution image to obtain its intensity. The means for displaying the distribution image on the spatial light modulator is an optical writing type liquid crystal light valve.
The means for converting only at least one newly input signal image into a coherent image is composed of a laser 1, a beam expander 2, a liquid crystal television 18, and a first beam splitter 3, and the coherent only the signal image is provided. The means for performing Fourier transform on the image, irradiating the image so as to coincide with the recording center of the intensity distribution image recorded in the spatial light modulator, and reading out the intensity distribution image, includes the second Fourier transform lens 8 and the second Fourier transform lens 8. Beam splitter 11 of
The means for Fourier-transforming the read intensity distribution image and converting the image into a correlation signal using the image pickup device is
It is composed of a third Fourier transform lens 12 and a CCD camera 13.
Computer 14, D / A converter 34, and LCD TV driver 24
Is used to display at least one reference image including a desired target and at least one newly input signal image on the liquid crystal television 18, and the computer 14 and the first optical shutter driving unit 23 are the second optical shutters. A computer 14 which is used to perform switching for recording a Fourier transform image of at least one reference image including the desired target and at least one newly input signal image for driving in the optically writable liquid crystal light valve 10. And the first optical shutter drive unit
Reference numeral 22 drives the first optical shutter 19 and irradiates the optical writing type liquid crystal light valve 10 with a Fourier transform image of at least one newly input signal image, and performs switching for reading the information recorded therein. Used for computer 14 and optical writing type liquid crystal light valve driver 17
Is used to drive an optically writable liquid crystal light valve. In the writing / reading of the image of the optical writing type liquid crystal light valve 10, if the reading light intensity is weaker than the writing light intensity intensity to the extent that the reading light does not affect the writing of the Fourier transform image, the first The optical shutter 19, the first optical shutter drive unit 22, the second optical shutter 20 and the second optical shutter drive unit 23 may be omitted.

The coherent light emitted from the laser 1 and expanded by the beam expander 2 illuminates a liquid crystal television 18 in which a signal image and a reference image are arranged in parallel and displayed to convert an input image into a coherent image. Of the coherent image, only one part corresponding to the signal image is split into two light beams by the beam splitter 3. Beam splitter 3
The coherent image that has passed through is subjected to Fourier transform by the first Fourier transform lens 7 via the second optical shutter 20, and is irradiated on the optical writing type liquid crystal light valve 10. here,
When the optical writing type liquid crystal light valve 10 using a TN liquid crystal as a light modulating material is used, the Fourier transform image is recorded as an image having a gray scale, and as a light modulating material, it is between the light reflectance and the applied voltage. If a liquid crystal with a ferroelectric liquid crystal having a bistable memory property is used,
Since the image is all binarized by a certain threshold,
The binarized intensity distribution of the Fourier transform image is recorded in the optically writable liquid crystal light valve 10.

On the other hand, the coherent image of only the signal image reflected by the beam splitter 3 passes through the first optical shutter 19 and then
Second beam splitter by the second Fourier transform lens 8
It is Fourier-transformed through 11 and the polarizer 39, is irradiated to the reading surface of the optical writing type liquid crystal light valve 10, and is reflected again. However, since the optically writable liquid crystal light valve 10 is a reflective type, the reading surface is the surface in the direction opposite to the surface on which the Fourier transform image is recorded. As a result, the gray scale or binarized intensity distribution image of the Fourier transform image recorded on the optical writing type liquid crystal light valve 10 is converted into a coherent image. The coherent image is read out as a negative or positive image by passing through the polarizer 39, and the third Fourier transform lens
By being Fourier-transformed by 12, the CCD camera 13 receives the image as an image including the correlation output. Here, the liquid crystal television 18 is arranged on the front focal plane of the first Fourier transform lens 7, and the optical writing type liquid crystal light valve 10 is arranged on the rear focal plane.
The liquid crystal television 18 is provided on the front focal plane of the second Fourier transform lens 8 and the optical writing type liquid crystal light valve 10 is provided on the rear focal plane.
Place. Further, the optical writing type liquid crystal light valve 10 is arranged on the front focal plane of the third Fourier transform lens 12, and the CCD camera 13 is arranged on the rear focal plane.

Since the liquid crystal television 18 uses the video signal to display image information by the drive unit 24 of the liquid crystal television, the computer 14
The digital image information output from the D / A converter 34 is converted into a video signal. Further, the optically writable liquid crystal light valve 10 is driven by its driving unit 17, which operates in synchronization with a clock of digital image information sent to the D / A converter 34 by the computer 14. Further, the first optical shutter 19 and the second optical shutter 20 are
The optical shutter drive unit 22 and the second optical shutter drive unit 23 of FIG. A mechanical optical shutter may be used for these optical shutters, but it is preferable to use a high-speed optical shutter using a ferroelectric liquid crystal or an electro-optic crystal as a light modulation material. Furthermore, these optical shutters are configured so that the reading light is not emitted when the writing liquid crystal light valve 10 is irradiated with the writing light, and the writing light is not emitted when the reading light is irradiated. Is controlled by.

The characteristics of one embodiment of the optical pattern recognition apparatus of the present invention shown in FIG. 2 are almost the same as the characteristics of the optical pattern recognition apparatus of the present invention shown in FIG. The feature is that the input process of the reference image to the optical system becomes simpler.

Next, without using the optical writing type spatial light modulator,
An embodiment of the optical pattern recognition device of the present invention, which is constructed by using all of the electric writing type spatial light modulators, will be described.
FIG. 3 is a block diagram of an embodiment of the optical pattern recognition apparatus of the present invention, which is constructed by using all of the electric writing type spatial light modulators. In FIG. 3, the means for converting at least one reference image containing the desired target and at least one newly input signal image into a coherent image comprises a laser 1, a beam expander 2 and a first liquid crystal television 5. ,
Means for Fourier transforming the coherent image to obtain a congruent Fourier transform image of the reference image and the signal image is a first means.
The means for converting the congruent Fourier transform image into an intensity distribution image and displaying the intensity distribution image on the spatial light modulator comprises a first CCD camera 26 and a third liquid crystal television 27. The means for converting at least one newly input signal image into a coherent image, which comprises the third liquid crystal television drive unit 35, is a laser 1, a beam expander 2, a beam splitter 25, and a second liquid crystal television 6
The means for Fourier transforming the coherent image of only the signal image, and irradiating the coherent image of the signal image so that it coincides with the recording center of the altitude distribution image recorded in the spatial light modulator, and reading the intensity distribution image, The second Fourier transform lens 8 and the means for performing the Fourier transform on the read intensity distribution image and converting the image into the correlation signal by using the image pickup device are the third Fourier transform lens 12 and the second CC.
It consists of D camera 29. The signal image captured by the third CCD camera 30 is converted into a digital signal by the A / D converter 33 and captured by the computer 14, and at the same time, transferred to the second liquid crystal television 6 through the second liquid crystal television drive unit 32. Display only the signal image. Computer 14 and D / A converter 34
And the first liquid crystal television drive unit 31 causes the first liquid crystal television 5 to receive at least one reference image including a desired target and at least one newly input signal image captured from the third CCD camera 30. Used to display. 1st CC
The Fourier transform intensity distributions of the signal image and the reference image obtained by the D camera 26 are displayed on the third liquid crystal television 27 through the third liquid crystal television driving unit 35.

The embodiment shown in FIG. 3 can be constructed with a spatial light modulator which is cheaper and more readily available. Also, since it has a feature that it can be easily connected to an electric system, it can be easily connected to a conventional machine vision or the like.

In the above embodiment, as shown in FIG.
Although one signal image and a plurality of reference images are used, it goes without saying that a plurality of signal images and one reference image may be used, or a plurality of signal images and reference images may be provided. .

In the above embodiment, it goes without saying that the laser 1 may be a gas laser, a semiconductor laser, or any other laser with good coherence.

In the above embodiment, a liquid crystal television was used as the input means for the reference image and the signal image to be newly input, but as the light modulating material, an electro-optical material such as PLZT or LiNO3 or yttrium iron garnet or gadolinium iron garnet was used. It is also possible to use an electrically writable spatial light modulator using a magneto-optical material, a spatial light modulator using a deformable material that is electrically deformable, or an optically writable spatial light modulator. Not to mention good things.

In the embodiment shown in FIGS. 1 and 2,
The second beam splitter without the polarizer 39 used for reading the Fourier transform interference fringe distributions of the signal image and the reference image recorded in the optical writing type spatial light modulator.
A polarizing beam splitter may be used instead of 11, and a polarizer may be inserted between the second beam splitter 11 and the second Fourier transform lens 8 to provide the second beam splitter 11 and the third Fourier transform lens 12 It goes without saying that an analyzer may be inserted between the polarizers and the polarizer may be arranged orthogonally (or in parallel).

[Effects of the Invention] As described above, according to the present invention, in order to correlate with many reference images at one time, a joint transform correlator (Joint Transf
orm correlator), a new Fourier transform intensity distribution of at least one reference image including a desired target recorded in the spatial light modulator and at least one newly input signal image is newly input. At least 1
One or more signal images are read out with Fourier transform light, and the Fourier transform is performed again to obtain a correlation signal. Even if many reference images are used at a time, a correlation signal with less noise can be obtained at high speed. Pattern recognition can be performed with the same accuracy as in the case of one reference image. Therefore, it can be faster than rewriting one reference image one after another and performing correlation in time series, which also leads to cost reduction.

[Brief description of the drawings]

1 and 2 are configuration diagrams of an embodiment of an optical pattern recognition apparatus of the present invention, and FIG. 3 shows an optical pattern recognition apparatus of the present invention when an electric writing type spatial light modulator is used. 1
FIG. 4 is a configuration diagram of an embodiment, FIG. 4 is a configuration diagram showing an example of a conventional congruential conversion correlator using an optical writing type spatial light modulator, and FIG. 5 is an input image 36 of FIG. FIG. 6 is a diagram showing an example, FIG. 6 is a diagram showing a pair of correlation peaks representing a two-dimensional cross-correlation coefficient between the signal image and the reference image in FIG. 4, and FIG. 7 is using a plurality of reference images. 1 of the input image in the case
FIG. 8 is a diagram showing an example, and FIG. 8 is a graph showing changes in the SN ratio of the optical pattern recognition device of the present invention and the SN ratio of the conventional congruential conversion correlator when the number of reference images increases. , 9th
FIG. 10 is a cross-sectional view showing the structure of an optical writing type spatial light modulator using a ferroelectric liquid crystal, and FIG. 10 is a view showing a structure using a ferroelectric liquid crystal as a liquid crystal light valve of the optical pattern recognition device of the present invention. SN ratio and TN when using a writable spatial light modulator
In the case of using an optical writing type spatial light modulator using liquid crystal
6 is a graph showing how the ratio of the SN ratio changes as the number of reference images increases. 1 ... Laser 2 ... Beam Expander 3 ... First Beam Splitter 4 ... First Mirror 5 ... First Liquid Crystal Television 6 ... Second Liquid Crystal Television 7 ... First Fourier Transform Lens 8 …… Second Fourier transform lens 9 …… Second mirror 10 …… Optical writing type liquid crystal light valve 11 …… Second beam splitter 12 …… Third Fourier transform lens 13 …… CCD camera 14 …… Computer 15 …… First D / A converter 16 …… Second D / A converter 17 …… Optical writing type liquid crystal light valve drive 18 …… LCD TV 19 …… First optical shutter 20… … Second optical shutter 21 …… Mirror 22 …… First optical shutter driver 23 …… Second optical shutter driver 24 …… LCD TV driver 25 …… Beam splitter 26 …… First CCD camera 27 …… Third LCD TV 29 …… Second CCD camera 30 …… Third CCD camera LA 31 …… First LCD TV driver 32 …… Second LCD TV driver 33 …… A / D converter 34 …… D / A converter 35 …… Third LCD TV driver 36 Input image 37 Liquid crystal light valve 38 Polarizing beam splitter 39 Polarizer 40a, 40b Transparent substrate 41a, 41b Transparent electrode layer 42a, 42b Alignment layer 43. Ferroelectric Liquid crystal layer 44 …… Photoconductive layer 45 …… Shading layer 46 …… Dielectric mirrors 47a, 47b …… Anti-reflection coating layer 48 …… Spacer SN _F …… Optical writing type spatial light modulator using ferroelectric liquid crystal SN ratio in the case of using SN _T ...... TN ratio in the case of using the optical writing type spatial light modulator using TN liquid crystal

Claims (2)

(57) [Claims] 1. An optical pattern recognition device for automatically recognizing and measuring a required pattern by performing optical processing using coherent light on a two-dimensional image obtained from an image pickup device, Means for converting at least one reference image including a target and at least one newly input signal image into a coherent image, and means for Fourier transforming the coherent image to obtain a congruent Fourier transform image of the reference image and the signal image A unit for converting the congruent Fourier transform image into an intensity distribution image and displaying the intensity distribution on a spatial light modulator; and a unit for converting at least one newly input signal image into a coherent image, Fourier transform of the coherent image of only the signal image is performed, and this is recorded as the intensity distribution image recorded in the spatial light modulator. Optical pattern recognition having means for irradiating the intensity distribution image so as to coincide with the center and reading the intensity distribution image, and means for Fourier transforming the intensity distribution image read out and converting the image into a correlation signal using an imaging device. apparatus. 2. Means for converting a congruent Fourier transform image into an intensity distribution image and displaying the intensity distribution on a spatial light modulator has ferroelectricity having a bistable memory property between the light reflectance and the applied voltage. 2. The optical pattern recognition device according to claim 1, wherein the optical writing type spatial light modulator using liquid crystal is irradiated with a congruent Fourier transform image and stored.