JP2898666B2 - Optical pattern identification device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical pattern identification device used in the field of optical information processing.

[Problems to be Solved by the Related Art and the Invention] Usually, as a method for identifying a pattern of an input image (that is, a test image), it is proposed to take a cross-correlation between a test image and a group of reference images. However, in general, as a method of obtaining the cross-correlation between the reference image group and the test image, a so-called hologram is conventionally formed by changing the direction of the Fourier transform hologram of the reference image by changing the direction of the reference light for each reference image. A first method of taking a multiplexed hologram and using it as a correlation filter, and a method of recording a joint Fourier transform image of a reference image group and a test image in the form of an intensity distribution, reading it out with coherent light, and performing a Fourier transform again. Method 2, i.e., JP-A-57-138616, 57-
The methods disclosed in 210316 and 58-21716 have been proposed.

However, in the first method, a hologram storage element is required. However, in the case of a photographic dry plate as a typical recording material, it takes time to develop the dry plate, and the direction of the reference light must be changed one by one. A very complicated operation is required to change each reference image, and it is impossible to perform real-time processing.

On the other hand, in the second method, although these disadvantages are solved, the joint Fourier transform image is a multiplexed interference fringe by each reference image and each reference image and the test image, Recording a joint Fourier transform image with too many reference images for the dynamic range and resolution of the spatial light modulator significantly reduces the visibility of interference fringes,
It cannot be used for recognition and identification by comparing a large number of test images.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and it is possible to quickly determine which of a plurality of reference images stored in a memory an input image (ie, a test image) is a pattern of. It is an object of the present invention to realize an optical pattern discriminating apparatus for detecting an image. According to the principle of the present invention, on the Fourier transform plane of the reference image, a mask of a transmittance distribution pattern obtained by binarizing the Fourier transform pattern of the input image or performing nonlinear processing close to the binarization is arranged. The amount of light of each reference image that reaches the imaging plane after passing through the mask is based on the fact that the amount of light changes according to the degree of coincidence with the input image. It is an object of the present invention to provide an optical pattern identification device that can easily create a mask and can easily increase the number of reference images.

[Means for Solving the Problems] In order to solve the above technical problem, the present invention provides at least a light source for generating coherent light,
A first spatial light modulator that outputs an input image as a coherent image, a first Fourier transform lens that optically Fourier transforms the input image displayed on the first spatial light modulator, and the Fourier transform lens A second spatial light modulator that binarizes the image pattern subjected to Fourier transform or reduces the halftone dynamic range, and outputs the pattern as a transmittance or reflectance pattern on an output surface; A group of reference images for comparison,
A second Fourier transform lens that optically Fourier-transforms the reference image group and causes the reference image group to enter an output surface of the second spatial light modulator, and optically transforms an output light distribution from the second spatial light modulator. A third Fourier transform lens for Fourier transforming the image, a photodetector array for receiving an image Fourier-transformed by the third Fourier transform lens, divided according to each image of the reference image group, and the photodetector An optical pattern identification apparatus, comprising: a calculator for multiplying a light amount incident on an array by a light amount ratio emitted from each reference image to calculate and compare an output light amount ratio from each reference image.

Preferably, the second spatial light modulator has a binary reflectance or transmittance made of ferroelectric liquid crystal. In addition, it is preferable that the transmittance of the reference image is set so that the amount of light emitted from each reference image is equal. And the second
Of the spatial light modulators described above, it is preferable that the light output near the optical axis be substantially zero.

[Operation] According to the configuration of the optical pattern identification device of the present invention as described above, when one of the reference images matches the input image, the reference image has almost no loss compared to the other reference images. , Transmitted through or reflected from the second spatial light modulator, and further imaged on the photodetector array through the second Fourier transform lens.

On the other hand, since the reference image that is not very similar to the input image does not match the Fourier transform pattern with the input image,
In the second spatial light modulator, many components are transmitted,
Alternatively, the amount of light that cannot be reflected and enters the photodetector array is significantly reduced. At this time, since the amount of light emitted from the original reference image is not equal in all the reference images, it is possible to know which reference image is closest to the input image pattern by compensating and comparing the amounts. it can.

The optical pattern identification device according to the present invention has the following configuration.

That is, it has a light source that generates at least coherent light, and a first spatial light modulator that outputs an input image as a coherent image.

The first Fourier transform lens for optically Fourier transforming the input image displayed on the first spatial light modulator binarizes the image pattern subjected to Fourier transform or reduces the halftone dynamic range, A second spatial light modulator that outputs the pattern as a transmittance or reflectance pattern on the output surface. A group of reference images to be compared with the input image is optically Fourier-transformed and made incident on the output surface of the second spatial light modulator. And
An image obtained by optically Fourier-transforming the output light distribution from the second spatial light modulator is received by a photodetector array divided according to each image of the reference image group. The light amount incident on the photodetector array (14) is multiplied by the light amount ratio emitted from each reference image, and the output light amount ratio from each reference image is calculated and compared by a computer.

Further, as the second spatial light modulator, a liquid crystal panel having a binary reflectivity or transmissivity constituted by using a ferroelectric liquid crystal can be used.

Preferably, the transmittance of the reference images is set such that the amount of light emitted from each reference image is equal.

In the second spatial light modulator, it is preferable that the optical output near the optical axis be substantially zero.

Next, the optical pattern identification device of the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

[Embodiment 1] Fig. 1 shows an optical pattern identification apparatus 1 according to the present invention.
It is a schematic block diagram which shows the function of an example.

In the optical arrangement of FIG. 1, an input image 1 is illuminated by incoherent light,
To the input surface of the spatial light modulator 3. The first spatial light modulator 3 forms an incoherent-coherent light modulator exhibiting a reflectivity distribution corresponding to the incident light amount distribution, and a liquid crystal light valve (Proc. SPIE. Vol. 684, pp. 96 to 100) and a spatial light modulator (see Proc. SPIE. Vol. 613, pp. 153 to 157) are typical.

Here, the light beam 8 emitted from the laser 6, which is a coherent light source, passes through a beam expander 7, has an appropriate beam diameter, is reflected by a beam splitter 9, and is reflected by a light beam 8a.
Then, the light is reflected by the mirror 26 and the beam splitter 4 and enters the output surface of the spatial light modulator 3. And, as described above, the output surface of the spatial light modulator 3 has a reflectance distribution according to the illuminance distribution by the imaging of the input image 1, so that the light beam 8a is spatially modulated according to the reflectance distribution. Is intensity-modulated, passes through the beam splitter 4, passes through the Fourier transform lens 5, and has an intensity pattern corresponding to the square of the spatial Fourier transform of the reflectance distribution on the output surface of the spatial light modulator 3, The light enters the input surface of the spatial light modulator 10.

By the way, here, the spatial light modulator 10 has a light input pattern to the input surface, when the input light intensity exceeds a certain threshold, the reflectance of the corresponding exit surface, 1
, Otherwise the reflectivity of the corresponding exit surface is close to 0, especially if the threshold is at a relatively low level, up to the relatively high spatial frequency of the input image. Can be reflected on the reflectivity distribution of the emission surface. Such a spatial light modulator can be obtained, for example, as a liquid crystal device having a liquid crystal light valve using a ferroelectric (smectic) liquid crystal.
In addition, such a spatial light modulator can be used as the first spatial light modulator 3.

By the way, a part of the light beam 8 passes through the beam splitter 9 to become a light beam 8b, and refers to the reference image group 16 displayed on the transmission type medium. In this reference image group, a plurality of images are recorded as a memory, and when the number is small, the image displayed on one slide film is most preferable. If the number is large, it is divided into a plurality of slide films and recorded, and they can be switched mechanically or recorded as multiple image holograms, and each hologram can be switched by changing the angle Alternatively, a group of reference images may be stored electrically and sequentially displayed on a matrix electrode type liquid crystal light valve.

The light beam 8b having passed through the reference image group 16 passes through the Fourier transform lens 11, is reflected by the beam splitter 12, and has a light amount pattern corresponding to the square of the spatial Fourier transform of the transmitted light amplitude distribution of the reference image group 16, The light enters the output surface of the spatial light modulator 10. This light beam 8b is reflected at the output surface of the spatial light modulator 10, but at this time, is modulated by the reflectance distribution, passes through the beam splitter 12, and exits the spatial light modulator 10. The light amount pattern corresponding to the square of the Fourier transform of the light amplitude distribution of
Light is incident on the photodetector array 14. Note that, regardless of where the reference image is located in the reference image group, the spatial spectrum image can be formed at the same location on the Fourier transform plane. If the spatial frequency coordinates with respect to the spatial spectrum of the reference image are substantially equal, if there is an image that matches the input image in the group of reference images, the spectral image is hardly lost and is reflected at the output surface of the spatial light modulator 10. In addition, since the reference image whose pattern does not match the input image is largely reflected on the output surface of the spatial light modulator 10 by the low reflectance portion,
In the photodetector array 14, a large electric signal is output from a photodetector on which a light beam having passed through a reference image that matches the input image is incident, and a relatively small electric signal is output from a photodetector that is not. . However, since the amount of light emitted from each reference image is not necessarily the same, the output from the photodetector corresponding to each reference image is normalized using the computer 15 by the light amount ratio when the reference image is emitted. Then, the reference image closest to the input image can be detected. At this time, the efficiency of transmitting the amount of light varies depending on the angle of view of the position of the reference image, so that a better result can be obtained by correcting the efficiency.

At this time, if the density of each reference image is adjusted in advance so that the amount of light emitted from each reference image of the reference image group 16 becomes equal, the output signal from the photodetector array 14 is corrected by the computer 15. You don't have to.

Further, in the spatial light modulator 10, the amount of incident light is large on the optical axis for any input image, that is, in the DC component of the image, and therefore, for any reference image, the reflectance of that portion is large. Therefore, it is preferable to mask the input surface or the output surface in a narrow range on the optical axis so that the reflectance is not increased.

Second Embodiment Next, FIG. 2 is a schematic diagram showing a configuration of another optical pattern identification device of the present invention. This will further explain the present invention.

In this embodiment, functions similar to those of the embodiment shown in FIG. 1 are realized by using a relatively inexpensive matrix liquid crystal panel as a spatial light modulator.

That is, the matrix liquid crystal panel used in the present embodiment is used for a liquid crystal television, a liquid crystal display for a personal computer, or the like, and shows a transmittance distribution according to an image by inputting an image signal such as a video signal. In the following, the liquid crystal panel is abbreviated.

The input image 1 is converted into an electric signal by the video camera 21 and displayed on the first liquid crystal panel 23. The light beam 8 emitted from the light source 6 such as a laser passes through the beam expander 7 to have an appropriate light beam diameter, and passes through the beam splitter 22 to become a light beam 8a. This light beam 8a illuminates the liquid crystal panel 23,
The transmitted luminous flux passes through the Fourier transform lens 5 and irradiates the CCD 24 with a light intensity pattern proportional to the square of the spatial Fourier transform of the light amplitude distribution of the input image on the liquid crystal panel 23. This pattern is generated by the image processing device 28.
A binary image is displayed on the second liquid crystal panel 29.

On the other hand, the light beam 8 reflected by the beam splitter 22 becomes a light beam 8b, is reflected by the mirror 25, and illuminates the reference image group 16. The reference image group 16 passes through the Fourier transform lens 11, and a light intensity pattern proportional to the square of the spatial Fourier transform of the light amplitude distribution on the reference image group 16 enters the liquid crystal panel 29. The light emitted from the liquid crystal panel 29 passes through the Fourier transform lens 13 and enters the photodetector array 14,
The process of detecting the reference image closest to the input image is as follows.
This is the same as the description of the embodiment shown in the figure. At this time, providing a mask for cutting the DC component before and after the liquid crystal panel 29 or in the input image to the liquid crystal panel 29 is also the same as the description of the above-described embodiment.

[Effects of the Invention] The above-described effects were obtained by the optical pattern identification device according to the present invention. In summary, the following remarkable technical effects were obtained.

That is, first, with a relatively simple configuration, it is possible to select a reference image that is optically closest to the input image.

Secondly, at this time, the image display can be sufficiently performed by the existing image display element, and there is no difficulty in separately recording the hologram of each reference image as in the first conventional method. The present invention provides an objective pattern identification device.

Third, even if the number of reference images simultaneously presented as a group of reference images is further increased, only the f-number of the optical system and the number of components of the photodetector array are increased. In addition, an optical pattern identification device that does not significantly reduce detection accuracy is provided.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing the configuration of an example of the optical pattern identification device of the present invention. FIG. 2 is a schematic configuration diagram showing the configuration of another example of the optical pattern identification device of the present invention. [Description of Signs of Main Parts] 1... Input image 2... Imaging lens 3, 10... Spatial light modulator 4, 9, 12… Beam splitter 5, 11, 13… Fourier transform lens 6. … Laser 7… Beam expander 8, 8a, 8b …… Light flux 10 …… Photodetector array 15 …… Calculator 16 …… Reference image group 21 …… Video camera 23, 29 …… LCD panel 24 …… CCD 26 …… Mirror 28 ... Image processing device

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G06T 7/00

Claims (4)

(57) [Claims] At least a light source for generating coherent light, a first spatial light modulator for outputting an input image as a coherent image, and an input image displayed on the first spatial light modulator are optically converted. A first Fourier transform lens for performing a Fourier transform, and binarizing or reducing a halftone dynamic range of the image pattern that has been Fourier transformed by the Fourier transform lens, and converting the pattern into a transmittance or reflectance pattern on an output surface. A second spatial light modulator that outputs as a reference image, a reference image group for comparison with an input image, and optically Fourier-transforms the reference image group so as to be incident on an output surface of the second spatial light modulator A second Fourier transform lens, a third Fourier transform lens that optically Fourier transforms an output light distribution from the second spatial light modulator, And a photodetector array divided according to each image of the reference image group, which receives an image subjected to Fourier transform by the Fourier transform lens of No. 3, and the amount of light incident on the photodetector array is emitted from each reference image. An optical pattern identification device, comprising: a calculator for multiplying a light amount ratio and calculating and comparing output light ratios from respective reference images. 2. The optical device according to claim 1, wherein said second spatial light modulator has a binary reflectance or transmittance made of ferroelectric liquid crystal. Pattern identification device. 3. The optical pattern identification according to claim 1, wherein the transmittance of the reference image is set so that the amount of light emitted from each reference image is equal. apparatus. 4. An optical pattern identification apparatus according to claim 1, wherein said second spatial light modulator makes an optical output near an optical axis substantially zero.