JP3988011B2 - Feature extraction method and feature extraction device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for extracting image features by optical Hough transform.
[0002]
[Prior art]
As a method for extracting image features, an electrical method or an optical method is known. In particular, recently, optical methods have attracted attention because of the development of two-dimensional input / output electronic devices and the expectation of high-speed processing due to optical parallelism. As an optical method, there is holographic filtering using a hologram as a spatial filter, and it has been proposed to perform various image processing by giving the filter various functions.
[0003]
The Hough transform, which is a kind of wavelet transform, is a useful tool for detecting straight lines and curves, and is used in fields related to image processing and object recognition. Therefore, methods for optically performing Hough conversion have been studied.
[0004]
Specifically, the literature “Dong-Hak Shin and Ju-Seog Jang: Optical impulsion of the Hough transform by use of rotary 3PT OPD3. A method of optically performing Hough conversion has been proposed.
[0005]
FIG. 7 shows the method. In this method, as shown in FIG. 5A, the parallel light 52 is transmitted through the slit 53 to form the signal light 54, and the signal light 54 is Fourier-transformed by the lens 55 to irradiate the hologram medium 51 at the same time. The reference light 56 is applied to the hologram medium 51. The slit 53 is rotated to rotate the angle θ of the line segment image of the signal light 54 on the hologram medium 51 by 10 degrees, and the hologram of the reference light 56 is adjusted accordingly. The irradiation direction on the medium 51 is rotated by 10 degrees to multiplex record a plurality of line segment image holograms on the hologram medium 51.
[0006]
Thus, the hologram medium 51 on which the hologram is rotationally multiplexed can be used to detect the direction and position of the line segment. In this case, as shown in FIG. 7B, the input image 61 is illuminated by the parallel light 62 to form the signal light 63, and the signal light 63 is Fourier transformed by the lens 64 to irradiate the hologram medium 51. To do. Accordingly, the hologram medium 51 functions as a Hough conversion filter, and the light passing through the hologram medium 51 is subjected to inverse Fourier transform by the lens 65 and irradiated to the detection surface 66, so that the detection surface 66 is included in the input image 61. A light peak 67 is obtained according to the direction and position of the line segment to be detected, and the direction and position of the line segment included in the input image 61 can be detected by detecting this with a CCD camera or the like.
[0007]
[Problems to be solved by the invention]
However, in the conventional feature extraction method described above, the direction θ in which the light peak 67 appears on the detection surface 66 changes according to the direction of the line segment included in the input image 61, as shown in FIG. In addition, the radial position R at which the light peak 67 appears also changes according to the position of the line segment included in the input image 61. Therefore, in this method, the optical peak 67 appears discretely over a wide range, so that there is a problem that it is difficult to reduce the size of the device, thereby reducing the cost of the device.
[0008]
Although it is conceivable that the light peak 67 appears at a position near the center of the detection surface 66, the light peaks at adjacent angular positions overlap so that the direction of the light peak and the radial position are detected with high accuracy. I can't do that. For this reason, it is difficult to achieve both miniaturization and cost reduction of the apparatus and high accuracy of feature extraction.
[0009]
Accordingly, the present invention is capable of realizing high accuracy of feature extraction and miniaturization / cost reduction of an apparatus in a method of extracting image features by optical Hough transformation.
[0010]
[Means for Solving the Problems]
In the feature extraction filter creation method of the present invention,
Optical recording of a plurality of signal lights holding line segment image information having different directions depending on the spatial intensity distribution, by changing the polarization angle of the reference light or the polarization angle of each signal light according to the direction, respectively. Record in the same area of the medium.
[0011]
In the feature extraction method of the present invention,
A plurality of signal lights that hold line segment image information having different directions depending on the spatial intensity distribution, the polarization angle of the reference light or the polarization angle of each signal light is changed according to the direction, respectively, and is the same as a hologram The optical recording medium recorded in the region is irradiated with signal light that retains image information to be extracted by spatial intensity distribution, and hologram diffraction light is read from the optical recording medium onto the optical path of the reference light. Each polarization component of the diffracted light is extracted and its spatial intensity distribution is detected.
[0012]
[Action]
A material exhibiting light-induced birefringence (light-induced anisotropy, light-induced dichroism) is sensitive to the polarization state of light incident thereon and can record the polarization angle (polarization direction) of incident light. . For example, a polymer or liquid crystal having a photoisomerizable group in the side chain, or a polymer in which a photoisomerizable molecule is dispersed is irradiated with linearly polarized light, so that photoisomerization is induced and linearly polarized light Depending on the direction, anisotropy of the refractive index occurs, and the polarization direction can be recorded and stored. At this time, if the reference light is irradiated simultaneously, the polarization angle of the signal light can be recorded as a hologram.
[0013]
A normal hologram is recorded with the signal light and the reference light having the same polarization direction (parallel). In contrast, a material exhibiting light-induced birefringence can record a hologram by changing the polarization directions of signal light and reference light.
[0014]
Focusing on this point, the applicant previously disclosed in Japanese Patent Laid-Open No. 10-340479, a plurality of signal lights each holding two-dimensional data information by a spatial intensity distribution, a polarization angle of reference light for each, or A method has been proposed in which the polarization angle of each signal light is changed, and each hologram is recorded in the same area of the optical recording medium and reproduced from the same area.
[0015]
By utilizing this, in the feature extraction filter creating method of the present invention, as described above, a plurality of signal lights holding line segment image information having different directions depending on the spatial intensity distribution are converted into the polarization angles of the reference lights or the The polarization angle of each signal light is changed according to the direction, and each hologram is recorded in the same area of the optical recording medium.
[0016]
When a feature extraction filter created in this way, that is, an area on which an optical recording medium is recorded with multiple holograms is irradiated with signal light that holds information about an image whose feature is to be extracted by spatial intensity distribution, Each hologram that is multiplexed and recorded on the recording medium functions as a Hough conversion filter, and polarization according to the direction of the line segment included in the target image as hologram diffracted light on the optical path of the reference light at the time of recording each hologram. A diffracted light beam having a light peak at a spatial position corresponding to the position of the line segment included in the target image is obtained.
[0017]
For example, when each hologram is multiplexed and recorded by changing the polarization angle of the reference light according to the direction of the line segment, the line in the direction of 0 degrees (a predetermined direction is defined as the direction of 0 degrees) in the target image When a minute is included, a diffracted light having the same polarization angle as the reference light at the time of recording the hologram is obtained from the hologram in which the line segment in the direction of 0 degree is recorded. When a minute is included, diffracted light having the same polarization angle as the reference light at the time of recording the hologram is obtained from a hologram in which a line segment in the direction of 10 degrees is recorded, and is included in the target image. From the hologram in which the line segment in the same direction as the line segment is recorded, diffracted light having the same polarization angle as the reference light at the time of recording the hologram is obtained, and the diffracted light of each polarization angle is included in the target image. Spatial position according to the position of the line segment In the indicates the photopeak.
[0018]
Therefore, the direction and position of the line segment included in the target image are detected by extracting each polarization component of the hologram diffracted light using an analyzer and detecting the spatial intensity distribution of each polarization component using a photodetector. can do.
[0019]
In this case, since each hologram is recorded by the reference light in the same optical path, diffracted light of any polarization angle from the hologram in which the line segment in any direction is recorded is obtained in the same direction, and the light peak However, since it appears within a limited range in that direction, it is possible to reduce the size of the device and to realize a reduction in the cost of the device. In addition, since the direction of the line segment included in the target image is detected by the polarization angle of the diffracted light, feature extraction can be performed with high accuracy even if the light peak appears within a limited range.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
[Example of optical recording medium]
FIG. 1 shows an example of an optical recording medium used in the method of the present invention, in which a polarization sensitive layer 12 is formed on one surface side of a transparent substrate 11 such as a glass substrate.
[0021]
The polarization sensitive layer 12 may be any material as long as it exhibits light-induced birefringence and can record polarization information as a hologram, but as a preferred example, a polymer having a photoisomerizable group in the side chain. Alternatively, a polymer liquid crystal or a polymer in which molecules to be photoisomerized are dispersed can be used. As the photoisomerizable group or molecule, for example, those containing an azobenzene skeleton are suitable.
[0022]
As one preferred example of the polarization sensitive layer 12, a polyester having cyanoazobenzene in the side chain represented by the chemical formula shown in FIG. 2 can be used. As described in detail in Japanese Patent Application Laid-Open No. 10-340479, this material can record, reproduce and erase holograms having polarization information by photoinduced anisotropy by photoisomerization of side chain cyanoazobenzene. It is.
[0023]
In order to record the hologram in a volumetric (three-dimensional) manner, the thickness of the polarization sensitive layer 12 needs to be at least about 10 μm, and the storage capacity can be increased as the thickness is increased. The entire optical recording medium 10 can also be formed as a polarization sensitive layer exhibiting light induced birefringence.
[0024]
[Example of Feature Extraction Device, Feature Extraction Filter Creation Method, and Feature Extraction Method]
FIG. 3 shows an example of the feature extraction device of the present invention, which is a case where it also serves as an optical recording device that is a feature extraction filter creation device.
[0025]
A light source 21 that emits sensitive coherent light to the polarization sensitive layer 12 of the optical recording medium 10 is used. For example, when a polyester having cyanoazobenzene in the side chain shown in FIG. 2 is used as the polarization sensitive layer 12, an argon ion laser having a wavelength of 515 nm sensitive to this is used.
[0026]
The polarization of the light 1 from the light source 21 is, for example, P-polarized light perpendicular to the paper surface (hereinafter referred to as a 0 degree polarization angle), and the P-polarized light 1 passes through the spatial filter 22 and the wave front is disturbed. Then, the light is converted into parallel light by the lens 23 and further divided into two light beams by the beam splitter 24.
[0027]
(Hologram recording (filter creation))
At the time of hologram recording, the shutter 25 is opened, and the P-polarized light 2 transmitted through the beam splitter 24 is incident on the spatial light modulator 26 for forming signal light, and the spatial light modulator 26 is controlled by a control circuit not shown in the figure. In addition, a binary two-dimensional line segment image is displayed. As a result, the light 4 transmitted through the spatial light modulator 26 is spatially modulated according to the value of each pixel of the line segment image, and is P-polarized signal light that retains the line segment image information by the spatial intensity distribution. It becomes. As such a spatial light modulator 26, a liquid crystal panel or the like can be used.
[0028]
The P-polarized signal light 4 from the spatial light modulator 26 is Fourier-transformed by the lens 27, and the P-polarized signal light 5 after the conversion is applied to the optical recording medium 10.
[0029]
Further, at the time of hologram recording, the shutter 28 is opened and the P-polarized light 3 reflected by the beam splitter 24 is incident on the polarization rotation element 29, and the polarization rotation element according to a control signal from the control circuit not shown in the figure. The polarization angle of the light passing through 29 is rotated. As the polarization rotation element 29 that can rotate the polarization angle of transmitted light in this way, a liquid crystal bulb, a Pockels element, a Faraday element, a half-wave plate, or the like can be used.
[0030]
At the time of hologram recording, the light transmitted through the polarization rotating element 29 is reflected by the mirror 31, converted into parallel light having a reduced beam diameter by the lenses 32 and 33, and further reflected by the mirrors 34, 35 and 36, and is referred to. As the light 6, the region irradiated with the signal light 5 of the optical recording medium 10 is irradiated simultaneously with the signal light 5.
[0031]
As a result, the spatial intensity distribution of the P-polarized signal light 5 is recorded as a hologram in the optical recording medium 10.
[0032]
In this case, first, a line segment in the direction of 0 degrees as shown in FIG. 4A (the vertical direction in FIG. 4 is taken as the direction of 0 degrees) as shown in FIG. Is polarized light of 0 degree (P-polarized light), and P-polarized signal light holding the line segment information in the direction of 0 degree by the spatial intensity distribution is recorded on the optical recording medium 10 as a hologram.
[0033]
Next, a line segment in the direction of 10 degrees as shown in FIG. 4B is set on the spatial light modulator 26 (the direction rotated 10 degrees in the clockwise direction with respect to the vertical direction is the direction of 10 degrees). The reference light 6 is polarized at 10 degrees (the polarization direction rotated by 10 degrees in the predetermined direction with respect to the polarization direction of P-polarized light is set to 10 degrees polarization), and the line in the direction of 10 degrees is determined by the spatial intensity distribution. P-polarized signal light holding minute information is multiplexed and recorded as a hologram in the same area of the optical recording medium 10.
[0034]
Thereafter, similarly, the direction of the line segment displayed on the spatial light modulator 26 is changed by 10 degrees up to 170 degrees, and the polarization angle of the reference light 6 is changed by 10 degrees up to 170 degrees accordingly. Multiple holograms are recorded in the same area.
[0035]
Therefore, an 18-page line segment image whose line direction changes by 10 degrees from 0 degrees to 170 degrees is converted into a 18-page hologram by reference light whose polarization angle changes by 10 degrees from 0 degrees to 170 degrees. Are recorded in the same area of the optical recording medium 10.
[0036]
(Feature extraction method)
At the time of feature extraction, the shutter 28 is closed to block the reference light 6, the shutter 25 is opened, and the P-polarized light 2 transmitted through the beam splitter 24 is incident on the spatial light modulator 26. Thus, a binary two-dimensional target image whose features are to be extracted is displayed on the spatial light modulator 26. Thereby, the light 4 transmitted through the spatial light modulator 26 is spatially intensity-modulated according to the value of each pixel of the target image, and becomes P-polarized signal light that retains the target image information by the spatial intensity distribution. .
[0037]
The P-polarized signal light 4 from the spatial light modulator 26 is Fourier-transformed by the lens 27, and the P-polarized signal light 5 after the conversion is a feature extraction filter, that is, an optical recording medium, created as described above. 10 areas of 18-page holograms are recorded in a multiplexed manner.
[0038]
At this time, each hologram that is multiplexed and recorded on the optical recording medium 10 functions as a Hough transform filter, and the direction of the line segment included in the target image as the hologram diffracted light 7 on the optical path of the reference light 6 at the time of recording. Diffracted light having a light angle at a spatial position corresponding to the position of the line segment included in the target image and having a polarization angle corresponding to the light angle is obtained.
[0039]
That is, when the target image includes a line segment in the direction of 0 degree, diffraction from the hologram in which the line segment in the direction of 0 degree is recorded has the same polarization angle of 0 degree as the reference light at the time of recording the hologram. When light is obtained and the target image includes a line segment in the direction of 10 degrees, the polarization of 10 degrees is the same as the reference light at the time of recording the hologram from the hologram in which the line segment in the direction of 10 degrees is recorded. A diffracted light having the same polarization angle as the reference light at the time of recording the hologram is obtained from a hologram in which a line segment in the same direction as the direction of the line segment included in the target image is recorded. In addition to being obtained, diffracted light of each polarization angle exhibits a light peak at a spatial position corresponding to the position of the line segment included in the target image.
[0040]
The hologram diffracted light 7 is reflected by the mirror 41, and further, the analyzer 42 sequentially extracts each polarization component having a different polarization angle by 10 degrees from 0 degrees to 170 degrees of the diffracted light 7, and the extracted polarization component 7a. Is imaged on the photodetector 43 in a two-dimensional array. Therefore, the direction and position of the line segment included in the target image can be detected from the detection signal of the photodetector 43.
[0041]
In this case, since the hologram for 18 pages is recorded by the reference light 6 in the same optical path, diffracted light with any polarization angle from the hologram in which the line segment in any direction is recorded can be obtained in the same direction. Since the light peak also appears within a limited range in the direction, the device can be downsized and the cost of the device can be reduced. In addition, since the direction of the line segment included in the target image is detected by the polarization angle of the diffracted light, feature extraction can be performed with high accuracy even if the light peak appears within a limited range.
[0042]
[Verification by experiment]
With the method and apparatus described above, an attempt was made to actually create a feature extraction filter and extract features of the target image. As the optical recording medium 10, the polarization sensitive layer 12 formed of polyester having cyanoazobenzene in the side chain was used, and as the light source 21, the above-described argon ion laser having a wavelength of 515 nm was used. Signal light and reference light at the time of hologram recording (when creating filters) is about 0.5 W / cm ^2, the signal light at the time of feature extraction, was 0.15 W / cm ^2. As the spatial light modulator 26, a liquid crystal panel for a projector having a size of one pixel of 42 μm × 42 μm and 640 × 480 pixels was used.
[0043]
In order to create a feature extraction filter, first, a line segment in the direction of 0 degrees as shown in FIG. 4A is displayed on the spatial light modulator 26, the polarization angle of the reference light 6 is set to 0 degrees, A hologram was recorded on the recording medium 10. At this time, on the spatial light modulator 26, the width of the line segment is 10 pixels and the length is 240 pixels.
[0044]
Next, a line segment in the direction of 10 degrees as shown in FIG. 4B is displayed on the spatial light modulator 26, the polarization angle of the reference light 6 is set to 10 degrees, and the hologram is formed in the same region of the optical recording medium 10. Was recorded multiple times. Thereafter, similarly, the direction of the line segment displayed on the spatial light modulator 26 is changed by 10 degrees up to 170 degrees, and the polarization angle of the reference light 6 is changed by 10 degrees up to 170 degrees, so that the same area of the optical recording medium 10 is obtained. Multiple holograms were recorded.
[0045]
However, the display of the line segment image on the spatial light modulator 26 is digital, and when the line segment is tilted, the width and length of the line segment are as accurate as when the line segment is oriented at 0 degrees or 90 degrees. Since it cannot be the same, the line segment is set to a value close to 0 degrees or 90 degrees.
[0046]
Next, feature extraction of the target image was performed using the feature extraction filter created in this way. First, the spatial light modulator 26 displays a target image having one line segment in the direction of 0 degrees at the center in the left-right direction as shown in FIG. Was irradiated to an area in which holograms for 18 pages of the optical recording medium 10 were recorded in a multiplexed manner.
[0047]
As a result, when the transmission axis direction of the analyzer 42 is set to 0 degree, as a diffraction image detected by the photodetector 43, one light peak is observed in the center as shown in FIG. It was confirmed that the target image has one line segment in the direction of 0 degree at the center in the left-right direction.
[0048]
Next, as shown in FIG. 6A, the spatial light modulator 26 displays a target image having two line segments in the direction of 90 degrees up and down across the center point, and is subjected to Fourier transform. The P-polarized signal light was irradiated to the area where the holograms for 18 pages of the optical recording medium 10 were recorded in a multiplexed manner.
[0049]
As a result, when the transmission axis direction of the analyzer 42 is set to 90 degrees, as shown in FIG. 6B, the diffraction image detected by the photodetector 43 is light at two points above and below the center point. A peak was observed, and it was confirmed that the target image had two line segments in the direction of 90 degrees up and down across the center point.
[0050]
【The invention's effect】
As described above, according to the present invention, it is possible to improve the accuracy of feature extraction by optical Hough transform and reduce the size and cost of the apparatus.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of an optical recording medium used in the method of the present invention.
FIG. 2 is a diagram illustrating a chemical formula of an example of a material of a polarization sensitive layer of an optical recording medium.
FIG. 3 is a diagram illustrating an example of a feature extraction apparatus according to the present invention.
FIG. 4 is a diagram showing an example of a line segment image to be hologram-recorded by the feature extraction filter creation method of the present invention.
FIG. 5 is a diagram illustrating an example of a feature extraction target image and a feature extraction result diffraction image;
FIG. 6 is a diagram illustrating another example of a feature extraction target image and a diffraction image of a feature extraction result.
FIG. 7 is a diagram illustrating a conventional feature extraction filter creation method and feature extraction method.
[Explanation of symbols]
4, 5 ... Signal light 6 ... Reference light 7 ... Diffracted light 7a ... Polarized component 10 ... Optical recording medium 12 ... Polarization sensitive layer 21 ... Light source 24 ... Beam splitter 25, 28 ... Shutter 26 ... Spatial light modulator 29 ... Polarization rotation Element 42 ... Analyzer 43 ... Photodetector

Claims (5)

Optical recording of a plurality of signal lights holding line segment image information having different directions depending on the spatial intensity distribution by changing the polarization angle of the reference light or the polarization angle of the respective signal light according to the direction. A feature extraction filter creation method for recording in the same area of a medium. A plurality of signal lights holding line segment image information having different directions depending on the spatial intensity distribution are converted into light as holograms by changing the polarization angles of the reference light or the respective signal lights according to the directions. A feature extraction filter recorded in the same area of the recording medium. A plurality of signal lights that hold line segment image information having different directions depending on the spatial intensity distribution, the polarization angle of the reference light or the polarization angle of each signal light is changed according to the direction, and each is the same as a hologram The optical recording medium recorded in the region is irradiated with signal light that retains image information to be extracted based on spatial intensity distribution, and hologram diffraction light is read from the optical recording medium onto the optical path of the reference light. A feature extraction method for extracting each polarization component of diffracted light and detecting its spatial intensity distribution. A light source that emits coherent light;
A spatial light modulator that modulates the intensity of light from the light source in accordance with image information of a feature extraction target, and obtains signal light that retains the image information by a spatial intensity distribution;
The signal light obtained from this spatial light modulator has a plurality of signal lights that hold line segment image information having different directions depending on the spatial intensity distribution, and the polarization angle of the reference light or the polarization angle of each signal light is different. An imaging optical system that is changed according to the direction and irradiates an optical recording medium recorded in the same area as a hologram,
The signal light obtained from the spatial light modulator is irradiated onto the optical recording medium by the imaging optical system, so that from the hologram diffracted light read from the optical recording medium onto the optical path of the reference light Diffracted light optical system for extracting each polarization component;
A photodetector for detecting the spatial intensity distribution of each extracted polarization component;
A feature extraction apparatus comprising: A light source that emits coherent light;
A space that obtains signal light that retains the line segment image information or the feature extraction target image information by spatial intensity distribution by intensity-modulating the light from the light source according to the line segment image information or the feature extraction target image information. An optical modulator;
An imaging optical system for irradiating the optical recording medium with the signal light obtained from the spatial light modulator;
A reference light optical system that obtains reference light from light from the light source and irradiates the optical recording medium;
A polarization rotation element that rotates a polarization angle of the reference light or the signal light;
By irradiating the optical recording medium with signal light that holds the image information of the feature extraction target, each polarization component is extracted from the hologram diffracted light read from the optical recording medium onto the optical path of the reference light. A diffracted light optical system to be extracted;
A photodetector for detecting the spatial intensity distribution of each extracted polarization component;
An optical recording feature extraction apparatus comprising:

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