JP3486214B2 - Pattern recognition device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pattern recognition device for performing pattern recognition by performing optical correlation calculation.

[0002]

2. Description of the Related Art Several methods have been proposed for performing pattern correlation using optical calculation. For example, a method using a hologram (Vander-Lugt type optical correlator) or a joint transform correlator using two spatial light modulators (Joint Transform Corr
elation: JTC) has been reported. Of these, the method using a hologram has the drawback that accurate alignment is required for the wavelength accuracy of the hologram mask.
The JTC system is more practical.

FIG. 9 is a block diagram showing the configuration of a conventional pattern recognition apparatus for performing optical correlation calculation of an input pattern and a reference pattern by using the joint transform correlation method. The recognition device shown in the figure is a high-resolution spatial light modulator (SLM) 200,
201 is used, an input image 210 composed of an input pattern and a reference pattern is drawn by the liquid crystal projector 202,
It is to detect the coincidence of both patterns. The input pattern and the reference pattern are written in the SLM 200, and the lens 2
Fourier transform is performed at 03 to form a Fourier pattern 211 on the SLM 201. This Fourier pattern 21
1 is again Fourier-transformed by the lens 204, and the correlation signal image 212 according to the correlation value of the input pattern and the reference pattern is given to the CCD camera 205. CC
The correlation signal image 212 given to the D camera 205 is image-processed by the image measuring device 206, and it is detected whether the input pattern and the reference pattern are the same pattern.

When the input pattern and the reference pattern coincide with each other, in the correlation signal image 212 given to the CCD camera 205, a point of 0th-order light corresponding to the intensity of the original pattern appears in the center, and two luminances are obtained. The points of the ± 1st order light having a high intensity appear on the left and right corresponding to the distance between the input pattern and the reference pattern. Here, the distance d between the 0th-order light spot and the -1st-order light spot of this correlation signal image 212 is proportional to the distance d1 between the input pattern and the reference pattern.

A conventional pattern recognition device using such a JTC device is disclosed in Japanese Patent Application No. 56-23925, Japanese Patent Application Laid-Open No. 3-204625, Japanese Patent Application Laid-Open No. 3-280179.
JP-A-4-116710, JP-A-4-115241
It is described in documents such as Japanese Patent Laid-Open No. 4-158332.

[0006]

By the way, the conventional pattern recognition apparatus uses S in order to perform the Fourier transform twice.
Two sets of LM and Fourier transform lens are required. Therefore, the scale of the system becomes large, which is a problem.

It is an object of the present invention to solve such a problem and to provide a compact and low cost pattern recognition apparatus which operates with a simple system configuration.

[0008]

In order to solve the above-mentioned problems, the pattern recognition apparatus of the present invention comprises: (a) a Fourier transform lens for performing Fourier transform of coherent light; (b) an input pattern and at least one or more. First spatial light modulation means for inputting a reference pattern and causing first coherent light having information on these patterns to enter a Fourier transform lens; and (c) converting the first coherent light by the Fourier transform lens. The first Fourier transform image obtained by inputting is input, and the second Fourier transform image having the information of the first Fourier transform image is input.
Fourier coherent light from the same side as the first coherent light at an incident angle different from that of the first coherent light so that the optical axis of the second coherent light does not coincide with the optical axis of the first coherent light. The input pattern and the reference pattern are the same, by inputting the second spatial light modulation means to be incident on the conversion lens and (d) the second Fourier transform image obtained by converting the second coherent light by the Fourier transform lens. And a detection means for detecting whether or not the pattern is the pattern, the first spatial light modulation means is arranged on the optical axis of the Fourier transform lens and in such a manner that the optical axis and a predetermined output surface are perpendicular to each other. A first spatial light modulator for outputting a first coherent light from the input device, and an input device for inputting an input pattern and at least one or more reference patterns on a surface opposite to an output surface of the first spatial light modulator. And the second spatial light modulator is arranged on the optical axis between the first spatial light modulator and the Fourier transform lens and at a tilt of 45 degrees with respect to the optical axis, and emits the first coherent light. A half mirror that transmits the second coherent light and that reflects the second coherent light, and is arranged on a straight line perpendicular to the optical axis on the surface of the half mirror, along a surface including an optical axis perpendicular to the surface of the half mirror, A second spatial light modulator for outputting a second coherent light from the output surface, the predetermined output surface being adjusted to be slightly inclined with respect to the surface perpendicular to this straight line; Is
The first coherent light passing through the Fourier transform lens is input to the surface opposite to the output surface of the second spatial light modulator,
An optical system is also provided for inputting the second coherent light that has passed through the Fourier transform lens to a predetermined detection surface of the detection means.

[0009]

According to the pattern recognition apparatus of the present invention, the input pattern and at least one or more reference patterns are input to the first spatial light modulator, and the first coherent light having the information of these patterns is emitted. To be done. The first coherent light is incident on the Fourier transform lens, and a first Fourier transform image is formed. This first Fourier transform image is input to the second spatial light modulator, and the second coherent light having the information of this first Fourier transform image is emitted. The second coherent light is again incident on the Fourier transform lens, and a second Fourier transform image is formed. This second Fourier transform image is input to the detecting means, and it is detected from the correlation pattern appearing on the second Fourier transform image whether the input pattern and the reference pattern are the same pattern.

Thus, the first coherent light and the second coherent light
The coherent light of is incident on the same Fourier transform lens. However, since the angles of incidence of these coherent lights on the Fourier transform lens are different, the first Fourier transform image obtained by Fourier transforming the first coherent light and the second coherent light are obtained by Fourier transform. The image formation points of the second Fourier transform image are at different positions.
Therefore, the second Fourier transform image can be taken out separately from the first Fourier transform image.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing the outline of the pattern recognition apparatus according to this embodiment. As shown in the figure, the pattern recognition apparatus of the present embodiment is provided with a spatial light modulator (hereinafter referred to as an SLM) 10 that inputs an input pattern and a reference pattern and converts the input pattern and a reference pattern into coherent light 11 having information on these patterns. A Fourier transform lens 20 for optically Fourier transforming the coherent light 11 and 31 and an SLM 30 for inputting a Fourier transform image 21 and converting it into coherent light 31 having information of this Fourier transform image 21 are provided. In addition, the coherent light 31 is reflected by the Fourier transform lens 2
A Fourier transform image 22 converted by 0 is input, and a photodetector 40 that detects correlation value data from a correlation pattern appearing on the Fourier transform image 22 and an input based on the correlation value detected by the photodetector 40 The control device 50 is provided for determining whether the pattern and the reference pattern are the same pattern. Furthermore, a CRT 6 displaying an input pattern and a reference pattern
0, and a writing lens 70 for forming an image of the input pattern and the reference pattern displayed on the CRT 60 on the input surface 10a of the SLM 10.

Next, the operation of the pattern recognition apparatus of this embodiment will be described. The input pattern and the reference pattern are displayed side by side on the CRT 60 according to an instruction from the control device 50. An example of the display image at this time is shown in FIG. FIG. 2A is a display example using a fingerprint pattern, where the left image is the input pattern and the right image is the reference pattern.

The input image composed of the input pattern and the reference pattern as shown in the figure is transmitted by the writing lens 70 to the SLM.
An image is formed on the input surface 10a of 10 and the information of the input image is written. Then, by irradiating the SLM 10 with the read laser light, the coherent light 11 having the information of the input image is obtained.
Is emitted. The coherent light 11 enters a Fourier transform lens 20 and is converted into a Fourier transform image 21. This Fourier transform image 21 is the input surface 3 of the SLM 30.
0a and the information of the Fourier transform image 21 is written. An example of this Fourier transform image 21 is shown in FIG.

By irradiating the SLM 30 with the read laser beam, the coherent light 31 having the information of the Fourier transform image is emitted. This coherent light 31
Enters the Fourier transform lens 20 again and is converted into a Fourier transform image 22. On this Fourier transform image 22, a correlation pattern between the input pattern and the reference pattern appears. An example of this Fourier transform image 22 is shown in FIG.
Here, the incident angle of the coherent light 31 is different from that of the coherent light 11. Therefore, the Fourier transform image 22
Is an image forming position of the Fourier transform image 11 S
The position is different from the input surface 30a of the LM 30. A photodetector 40 is provided at this image forming position, and the correlation value data of the correlation pattern appearing on the Fourier transform image 22 is detected as the light intensity. The correlation value data is given to the control device 50, and it is determined whether the input pattern and the reference pattern are the same pattern by, for example, threshold value processing.
That is, when the intensity value indicating the correlation is equal to or greater than the predetermined threshold value, it is determined that the patterns are the same. This determination result is displayed on a CRT or the like, and the operator can be informed as a pattern recognition result.

Next, a concrete example showing the present embodiment in detail will be described with reference to FIG. In the pattern recognition apparatus according to this specific example, the SLM 10 and the Fourier transform lens 20 are arranged to face each other, and the half mirror 80 is formed between the SLM 10 and the Fourier transform lens 20 at an angle of 45 degrees with the optical axis of the Fourier transform lens 20. Are arranged. Furthermore, at one end on the line orthogonal to the optical axis of the Fourier transform lens 20, S
The LM 30 is provided with the laser light source 90 and the collimator lens 91 at the other end. Therefore, the laser light source 9
Of the read laser light emitted from 0, the half mirror 8
The SLM 30 is irradiated with the laser light transmitted through 0, and the SLM 10 is irradiated with the laser light reflected by the half mirror 80. Then, the coherent light 11 read out (emits) by irradiating the SLM 10 with the laser light passes through the half mirror 80 and is given to the Fourier transform lens 20. Further, the coherent light 31 read (emitted) by irradiating the SLM 30 with the laser light is reflected by the half mirror 80 and given to the Fourier transform lens 20.

The Fourier transform image 21 converted by the Fourier transform lens 20 passes through the reflection mirrors 81 to 83 to S
An image is formed on the input surface 30a of the LM 30. Where SLM1
0 is the exit surface 10 with respect to the optical axis of the Fourier transform lens 20.
It is arranged so that b is vertical. On the contrary,
The SLM 30 is arranged at an angle with respect to a line segment orthogonal to the optical axis of the Fourier transform lens 20. Therefore, the angle at which the coherent light 11 emitted from the SLM 10 is incident on the Fourier transform lens 20, and the coherent light 31 emitted from the SLM 30 is calculated by the Fourier transform lens 2
The angle is different from the angle of incidence on 0. In this specific example, the reflection mirror 83 is
It uses a small area mirror. Therefore, the coherent light 31 that has passed through the Fourier transform lens 20 passes through the side of the reflection mirror 83 without being reflected by the reflection mirror 83, and the Fourier transform image 2 is formed on the detection surface 40 a of the photodetector 40.
2 is imaged. Thus, in this specific example, the SLM3
By arranging 0 at an angle, the image formation positions of the Fourier transform image 21 and the Fourier transform image 22 can be separated. For this reason, two Fourier transform lenses are required to detect the conventional correlation value, but only one Fourier transform lens 20 is required in this specific example (and this embodiment). As described above, the present specific example (and the present example) has a simpler system configuration than the conventional one, and can provide a compact and low-cost pattern recognition apparatus.

By the way, a conventional system for performing JTC using one Fourier transform lens has already been disclosed in Japanese Patent Laid-Open No. 4-3236.
It is devised in the document of the 23rd publication. However, in this conventional system, SLMs are arranged on both sides of the Fourier transform lens, and coherent light from each SLM enters from both sides of the Fourier transform lens. Therefore, Fourier transform images can be formed on both sides of the Fourier transform lens, and a space having the focal length f is required on each side of the Fourier transform lens. Therefore, although a single lens can be used, the size of the device cannot be made compact.

Further, as the Fourier transform lens, a combination lens is often used in order to improve accuracy and shorten the focal length (using a telephoto type lens). Such a combination lens is designed with the aberrations minimized after the light incident direction is determined. However, in a conventional system in which light is incident from both directions, such high performance Fourier transform lens cannot be used because of large aberration. In addition, this conventional system requires two lasers having different wavelengths, resulting in a complicated system configuration. The present specific example (and this example) is an excellent device that does not cause such a problem.

In the embodiment of FIG. 3, SLM 10 and SLM
An optical address type SLM is used for 30. In Figure 4,
A configuration of a typical optical address type SLM 100 is shown. As shown in the figure, the SLM 100 has a sandwich structure in which an amorphous silicon (a-Si) layer 103, a dielectric mirror 104, and a liquid crystal layer 105 are sandwiched between two glass substrates 102 having a transparent electrode 101 formed on the inner surface. Have
Then, the writing light 106 enters the a-Si layer 103 side, and the reading light 107 enters the liquid crystal layer 105 side. In the state where the writing light 106 is not given, aS
The impedance of the i layer 103 is very high, and even if a voltage is applied between the transparent electrodes 101, the voltage applied to the liquid crystal layer 105 is small. When writing light 106 is applied, a-Si
The impedance of the layer 103 decreases, the voltage applied to the liquid crystal layer 105 increases in response to the writing light 106, and the liquid crystal molecules move. By irradiating the liquid crystal layer 105 side with the reading light 107, the reading light 107 is modulated and a coherent light image is obtained.

A twisted nematic liquid crystal is used in a general liquid crystal TV or the like, and a TN using this liquid crystal is used.
The LC-SLM can be used for the SLMs 10 and 30. Further, a high-speed response can be realized by using a FLC-SLM using FLC (ferroelectric liquid crystal) as a light modulation material. Furthermore, a nematic liquid crystal SLM (a phase modulation type SLM) in which liquid crystal axes are aligned in parallel for the purpose of improving diffraction efficiency.
By using LM), it is possible to make the system highly functional. In this case, since it is phase modulation, a bright Fourier transform image is obtained. As a result, the S / N at the time of recognition can be improved, and at the same time, high-speed response (10 milliseconds or less) can be achieved. As can be seen from the graph of FIG. 5 showing the relationship between the sensitivity and the response speed of the phase modulation SLM, the operating characteristics of the phase modulation SLM are such that the higher the drive voltage, the faster the response speed. This is because it has a characteristic that sensitivity is deteriorated. Therefore, when a bright Fourier transform image is obtained, the drive voltage can be increased and the response speed of the system is improved. The horizontal axis of the graph of FIG. 5 is the drive voltage, and the vertical axis is the sensitivity and the rise time. here,
Sensitivity is the amount of light required to modulate the phase by π (unit: μW /
cm ² , wavelength 680 nm), and the rise time means a time required for rise of 10% to 90% (measured by intensity modulation, unit: msec) when the phase is π-modulated.

The SLM 10 is an electric address type SLM.
(For example, a liquid crystal TV). A specific example thereof is shown in FIG. The system configuration of the figure is different from the system configuration of FIG. 3 in that a signal of an input image (input pattern + reference pattern) from the control device 50 is directly input to the electrical address type SLM 110. The other configuration is the same as the system configuration of FIG. Therefore, the processing of this specific example is the same as that of the system of FIG. 3 except that the signal of the input image from the control device 50 is electrically written to the SLM 110. In this specific example, a transmissive liquid crystal TV may be used instead of the reflective electric address SLM. In this case, it is necessary to arrange the reading optical system (laser light source, collimator lens) so that the transmission image is input to the Fourier transform system.

Furthermore, when a nonlinear input / output characteristic is used as the SLM, a correlator with little influence of the input light intensity can be realized. FIG. 7 shows an example of the input / output characteristics of a SIM using a-Si (amorphous silicon) and nematic liquid crystal (vertical axis: phase modulation degree, horizontal axis: input light intensity). From this figure, it can be seen that the phase modulation degree of the SLM has a characteristic substantially proportional to the logarithm of the input light intensity.

FIG. 8 shows the relationship between the correlation intensity and the input light intensity when a correlator is constructed using an SLM having this characteristic. From this figure, it is understood that the region where 50% of the maximum correlation intensity is obtained is about 15 μW / cm ^{2 to 1} mW / cm ² .

Up to now, in the optical correlator, when the input light intensity changes, the correlation intensity changes in proportion to it, but by using the SLM having such a nonlinear input / output characteristic, the input light intensity It is possible to realize an optical correlator that is less affected by changes.

In this embodiment, instead of the CRT 60, another display device such as a liquid crystal display or a plasma display may be used.

[0026]

The pattern recognition apparatus of the present invention detects the correlation pattern by performing Fourier transform twice with one Fourier transform lens. Therefore, the system configuration is simpler than that of a conventional device that requires two Fourier transform lenses, and the device can be downsized and the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of a pattern recognition apparatus according to this embodiment.

FIG. 2 is a diagram showing an input image and a Fourier transform image.

FIG. 3 is a diagram showing a specific configuration of the present embodiment.

FIG. 4 is a sectional view showing the structure of an SLM.

FIG. 5 is a diagram showing a relationship between sensitivity and response speed with respect to a drive voltage of a phase modulation type SLM.

FIG. 6 is a diagram showing a specific configuration of the present embodiment.

FIG. 7 is a diagram showing input / output characteristics of a phase modulation type SLM.

FIG. 8 is a diagram showing an influence of a change in input light intensity on a correlation intensity.

FIG. 9 is a block diagram showing a configuration of a conventional pattern recognition device.

[Explanation of symbols]

10, 30, 100, 110 ... Spatial light modulator, 11, 3
1 ... Coherent light, 20 ... Fourier transform lens, 2
1, 22 ... Fourier transform image, 40 ... Photodetector, 50 ... Control device, 60 ... CRT, 70 ... Writing lens, 80 ...
Half mirror, 81-83 ... Reflective mirror, 90 ... Laser light source, 91 ... Collimator lens, 101 ... Transparent electrode, 1
02 ... glass substrate, 103 ... amorphous silicon layer,
104 ... Dielectric mirror, 105 ... Liquid crystal layer, 106 ... Write light, 107 ... Read light.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naohisa Kosaka 1 1126, Nomachi, Hamamatsu City, Shizuoka Prefecture 1126 Hamamatsu Photonics Co., Ltd. (72) Inventor Yuji Kobayashi 1 1126, Nomachi, Hamamatsu City, Shizuoka Prefecture Hamamatsu Photonics Co., Ltd. (72) Inventor Tsutomu Hara 1 1126, Nomachi, Hamamatsu-shi, Shizuoka 1 Hamamatsu Photonics Co., Ltd. (56) Reference JP-A-4-116710 (JP, A) JP-A-61-185719 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02F 3/00 502

Claims (2)

(57) [Claims] 1. A Fourier transform lens for Fourier transforming coherent light, and an input pattern and at least one or more reference patterns are inputted, and the first coherent light having information on these patterns is inputted to the Fourier transform lens. A first spatial light modulation means to be incident and a first Fourier transform image obtained by transforming the first coherent light by the Fourier transform lens are input, and information of the first Fourier transform image is stored. The second coherent light beam whose optical axis is the first coherent light beam
Of the first coherent light so that it does not coincide with the optical axis of the coherent light.
Second spatial light modulating means for entering the Fourier transform lens from the same side as the first coherent light at an incident angle different from that of the first coherent light, and converting the second coherent light by the Fourier transform lens. The obtained second Fourier transform image is input, and a detection unit that detects whether the input pattern and the reference pattern are the same pattern is provided, and the first spatial light modulation unit is the optical axis of the Fourier transform lens. A first spatial light modulator which is arranged above and in which the optical axis and a predetermined output surface are perpendicular to each other, and which outputs the first coherent light from the output surface; and the first spatial light modulation. An input device for inputting an input pattern and at least one or more reference patterns on a surface opposite to the output surface of the device, wherein the second spatial light modulator is the first spatial light modulator. A half mirror that is arranged on the optical axis between the Fourier transform lens and the optical axis so as to be inclined by 45 degrees and that transmits the first coherent light and reflects the second coherent light; It is arranged on a straight line perpendicular to the optical axis on the surface of the half mirror, along a surface including the optical axis perpendicular to the surface of the half mirror, and the predetermined output surface is a surface perpendicular to the straight line. A second spatial light modulator that outputs the second coherent light from the output surface, adjusted so as to be slightly inclined with respect to the first coherent light that has passed through the Fourier transform lens. Is input to the surface of the second spatial light modulator opposite to the output surface, and the second coherent light that has passed through the Fourier transform lens is input to a predetermined detection surface of the detection means. Pattern recognition apparatus comprising: a system. 2. The first spatial light modulator and the second spatial light modulator.
2. The pattern recognition device according to claim 1, wherein at least one of the spatial light modulators of 1. is a phase modulation type spatial light modulator.