JPH04306787A - Production of pattern recognition filter and pattern recognition device using this filter - Google Patents

Abstract

PURPOSE:To provide the method for production of pattern recognition filter capable of holding intercorrelation signals and the pattern recognition device with high reliability using this filter. CONSTITUTION:By cutting off the component of frequency higher than the frequency including information for pattern width and a, zero-order light component from the Fourier spectrum of the coherent light according to the reference pattern picture and recording the result on a hologram dry plate 6, and a matched filter 15 is produced. The correlation signal of the Fourier conversion spectrum of a pattern to be recognized 19 and the matched filter 15 are observed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a pattern recognition filter and a pattern recognition apparatus for reading characters on printed matter using the pattern recognition filter.

0002

2. Description of the Related Art For example, as a method for reading characters on printed matter, there is an optical method using holography. As a pattern recognition method using holography, there is a method in which the Fourier spectrum of a reference character is recorded on a hologram dry plate together with a reference light, a matched filter is created, and the intensity of the correlation signal between the input character and the reference character is observed. .

0003

However, the method of observing the strength of a correlation signal between an input character and a reference character using a matched filter has the following problems. In other words, if the shape of the character to be recognized is exactly the same as the shape of the character used when creating the matched filter, it is possible to identify it, but if the character to be recognized is chipped or faded, etc. , the strength of the autocorrelation signal decreases, making it impossible to distinguish between the autocorrelation signal and the cross-correlation signal, and the recognition rate decreases.

An object of the present invention is to provide a method for manufacturing a pattern recognition filter capable of suppressing cross-correlation signals, and a highly reliable pattern recognition device using this filter.

[0005]

Means and Effects for Solving the Problems In order to achieve the above object, the present invention provides a method for converting a Fourier spectrum of coherent light corresponding to an image of a reference pattern into a zero-order light component,
A frequency component higher than a frequency component containing information about the thickness of the pattern is cut and recorded on a hologram dry plate.

[0006] The present invention also provides an imaging device for capturing an image of a recognized pattern, a coherent light creating means for creating coherent light according to an image of the recognized pattern captured by the imaging device, irradiation means that converts the coherent light created by the coherent light creation means into a Fourier transform spectrum image and irradiates it onto the pattern recognition filter, and images a correlation signal between the Fourier transform spectrum of the pattern to be recognized and the pattern recognition filter. and an imaging device for imaging correlation signals. Further, the present invention makes it possible to suppress cross-correlation signals and improve reliability of pattern recognition.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

FIGS. 1 to 3 show an embodiment of the present invention. FIG. 1 shows how a matched filter is manufactured as a filter for pattern recognition, and FIG. 3 shows how pattern recognition is performed.

A method for manufacturing a matched filter will be explained based on FIG. This manufacturing method uses a CCD camera 1, a monitor 2, a spatial light modulator 3, a polarizing beam splitter 4, a Fourier transform lens 5, and a hologram dry plate 6. Furthermore, a laser oscillator 7, an enlarged collimating lens system 8, a half mirror 9, and a full mirror 10 are used in this manufacturing method.

First, the CCD camera 1 scans the reference pattern 11.
is photographed, and an image of the reference pattern 11 is displayed on the monitor 2. Furthermore, the reference pattern 11 displayed on the monitor 2
is written on the spatial light modulator 3 facing the monitor 2.

Further, a laser beam is emitted from the laser oscillator 7, and this laser beam is converted into an expanded collimated beam by an expanded collimating lens system 8. This expanded collimated beam is split into two directions by a half mirror 9, and one laser beam is guided to the spatial light modulator 3 by a polarizing beam splitter 4.

[0012] Then, the spatial light modulator 3 reflects this laser light and emits a coherent image corresponding to the image displayed on the monitor 2. This coherent image passes through the polarizing beam splitter 4 and reaches the Fourier transform lens 5,
A Fourier spectral image of the reference pattern 11 is obtained at the back focal position of the Fourier transform lens 5.

A hologram dry plate 6 is placed at the rear focal point of the Fourier transform lens 5. Then, the other of the laser beams divided into two by the half mirror 9 is irradiated onto the hologram dry plate 6 by the full mirror 10. Then, the Fourier spectrum image formed by the Fourier transform lens 5 is transferred to the hologram dry plate 6 along with the other laser beam as a reference beam.
is irradiated and recorded. Here, it is possible to arrange an imaging lens or the like between the monitor 2 and the spatial light modulator 3. Furthermore, it is possible to use a He-Ne laser oscillator as the laser oscillator 7. Furthermore, the polarizing beam splitter 4 only needs to pass the coherent light emitted from the spatial light modulator 3. When the Fourier spectrum image of the reference pattern 11 is recorded on the hologram dry plate 6, a cut filter 12 as shown in FIG.
is used.

That is, this cut filter 12 is formed by forming a perfectly circular aperture 13 on a plate-shaped body, for example, and further includes a perfectly circular light shielding plate 14 in the center of the aperture 13. have. And this cut filter 1
2 is, for example, a Fourier transform lens 5 and a hologram dry plate 6.
An aperture 13 and a light shielding plate 14 are interposed between the Fourier transform lens 5 and the hologram dry plate 6. Then, the cut filter 12 passes only specific frequency components of the Fourier spectrum image.

For example, if the reference pattern 11 is a character,
If the size is 4 mm square and the focal length of the Fourier transform lens 5 is 1 m, then the Fourier spectrum will be 0.
The size of the secondary light is calculated to be approximately 0.2 mm in diameter. Furthermore, if the thickness of the character is 1 mm, the size of the main portion of the Fourier spectrum is calculated to be about 1.0 mm in diameter. Then, if the diameter A of the percher 13 is set to 1.0 mm and the diameter B of the light shielding plate 14 is set to 0.2 mm,
It is possible to remove the zero-order light of the Fourier spectrum and information about the thickness of characters included in the Fourier spectrum. Then, specific frequency components that only each pattern has are recorded on the hologram dry plate 6 without including unnecessary frequency components.

The hologram dry plate 12 on which the Fourier spectrum and reference light from which unnecessary frequency components have been removed by the cut filter 12 described above is recorded is subjected to a development process, and a matched filter 15 is formed.

Next, the pattern recognition device 16 and the pattern recognition method using this pattern recognition device 16 will be explained based on FIG. In addition, matched filter 15
Equipment that can be used in conjunction with the equipment used in the production of is given the same number, and the explanation thereof will be omitted.

In the pattern recognition device 16, a CCD camera 1 for capturing an image of a pattern to be recognized is connected to a monitor 2, and a spatial light modulator 3 has its writing side facing in front of the monitor 2. Further, on the readout side of the spatial light modulator 3, a polarizing beam splitter 4 and a Fourier transform lens 5 are coaxially arranged. Here, it is possible to arrange an imaging lens between the monitor 2 and the spatial light modulator 3.

Further, a laser oscillator 7, an enlarged collimating lens system 8, and a full mirror 17 are provided. The enlarged collimating lens system 8 converts the laser light emitted from the laser oscillator 7 into an enlarged collimated beam, and the full mirror 17 guides the enlarged collimated beam to the polarizing beam splitter 4.

Furthermore, a matched filter 15 is arranged at the rear focal position of the Fourier transform lens 5,
On the back side of the matched filter 15, there is a C for correlation signal imaging.
A CD camera 18 is provided. The CCD camera 18 for imaging the correlation signal is tilted with respect to the matched filter 15, and its orientation is adjusted to a predetermined direction with respect to the optical axis on the readout side of the spatial light modulator 3.

In the pattern recognition device 16, first, the CCD camera 1 photographs the pattern to be recognized 19, and the image of the pattern to be recognized 19 is displayed on the monitor 2. Further, the image of the recognized pattern 19 displayed on the monitor 2 is written to the spatial light modulator 3 facing the monitor 2.

Further, a laser beam is emitted from the laser oscillator 7, and this laser beam is converted into an expanded collimated beam by the expanded collimating lens system 8. This expanded collimated beam is sent to the full mirror 17 and polarized beam splitter 4.
reflect towards. The expanded collimated beam is then guided to the spatial light modulator 3 by the polarizing beam splitter 4,
A coherent image corresponding to the image displayed on the monitor 2 is emitted to the readout side of the spatial light modulator 3.

This coherent image passes through the polarizing beam splitter 4 and reaches the Fourier transform lens 5, and a Fourier spectrum image of the pattern to be recognized 19 is obtained at the rear focal position of the Fourier transform lens 5. This Fourier spectrum image then enters a matched filter 15 placed at the rear focal point of the Fourier transform lens 5.

Then, on the back side of the matched filter 15, a CCD camera 18 for photographing a correlation signal photographs the diffracted light from the matched filter 15, and the correlation between the pattern to be recognized and the reference pattern is determined.

That is, the diffracted light of the Fourier spectrum image is formed on the back side of the matched filter 15. When the correlation between the recognized pattern 19 and the reference pattern 11 recorded on the matched filter is stronger, a stronger diffracted light is generated in the direction in which the reference light travels when the matched filter 15 is manufactured. Therefore, by observing the diffracted light on the back side of the matched filter 15, the pattern to be recognized 19 can be recognized.

That is, in the method for manufacturing the matched filter 15 described above, only specific frequency components necessary for pattern recognition are recorded on the hologram dry plate 6, and interference fringes from which unnecessary frequency components have been removed are recorded on the matched filter 15. is formed.

Furthermore, in the pattern recognition device 16 using the matched filter 15, it is possible to correlate only specific frequency components effective for pattern recognition between the pattern to be recognized 19 and the reference pattern 11. In addition, compared to the case where correlations are taken based on all frequency components of the pattern to be recognized 19, cross-correlation signals can be suppressed and the recognition rate can be improved. Furthermore, even if there is a chip or blur, the recognition pattern 19 can be reliably recognized, and the reliability of pattern recognition can be improved.

[0028]

[Table 1]

[Table 1] above shows the recognition results when a matched filter 15 was created using the cut filter 12 and pattern recognition was performed, and the recognition results when a matched filter was created without using the cut filter 12 and pattern recognition was performed. This shows the recognition results obtained when

[0030] In [Table 1], S and N represent recognition conditions, respectively. Condition S means that the matched filter 15 is created using the character "0" as the reference pattern, and the character "0" is used as the pattern to be recognized. This means that it has been entered. Moreover, condition N means a case where the matched filter 15 is created using the character "0" as a reference pattern, and the character "8" is input as the recognized pattern.

Furthermore, the numerical values in the column of condition S and the column of condition N are the strength of the correlation signal (autocorrelation signal) in case of condition S and the strength of the correlation signal (cross-correlation signal) in case of condition N, respectively. ) represents the strength of Further, the numerical value in the S/N column represents the ratio between the strength of the autocorrelation signal and the strength of the cross-correlation signal.

As shown in [Table 1], cut filter 1
When pattern recognition was performed using a matched filter 15 prepared using 2, the ratio of the strength of the autocorrelation signal to the strength of the cross-correlation signal was improved by 3.4 times. Note that the present invention is not limited to the above-mentioned embodiments, and can be modified in various ways without departing from the spirit of the invention.

For example, in this embodiment, the spatial light modulator 3 is used to obtain a coherent image corresponding to the monitor image, but a liquid crystal light valve or the like may be used instead of the spatial light modulator 3. . Further, instead of the hologram dry plate 6, it is also possible to use an optical converter such as a liquid crystal display device or a nonlinear optical element.

[0034]

Effects of the Invention As explained above, the present invention divides the Fourier spectrum of coherent light corresponding to an image of a reference pattern into a zero-order light component and a frequency component higher than the frequency component containing information about the thickness of the pattern. is cut and recorded on a holographic plate.

The present invention also provides an imaging device for imaging a recognized pattern, a coherent light generating means for creating coherent light according to an image of the recognized pattern captured by the imaging device, irradiation means that converts the coherent light created by the coherent light creation means into a Fourier transform spectrum image and irradiates it onto the pattern recognition filter, and images a correlation signal between the Fourier transform spectrum of the pattern to be recognized and the pattern recognition filter. and an imaging device for imaging correlation signals. Further, the present invention has the effect of suppressing cross-correlation signals and improving reliability of pattern recognition.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of the filter manufacturing method of the present invention.

FIG. 2 is a front view of a cut filter.

FIG. 3 is a configuration diagram showing an embodiment of the pattern recognition device of the present invention.

[Explanation of symbols]

1... CCD camera for imaging the pattern to be recognized, 2... Monitor,
3...Spatial light modulator, 4...Polarizing beam splitter, 5...Fourier transform lens, 6...Hologram dry plate, 7...Laser oscillator, 8...Enlargement collimator lens system, 9...Half mirror, 10, 17...Full mirror, 11...Reference pattern, 12
... cut filter, 13 ... aperture, 14 ... light shielding plate,
15...Matched filter, 16...Pattern recognition device, 1
8... CCD camera for correlating signal imaging, 19... Pattern to be recognized.

Claims (2)

[Claims] Claim 1: A Fourier spectrum of coherent light corresponding to an image of a reference pattern is recorded on a hologram dry plate by cutting out a zero-order light component and a frequency component higher than a frequency component containing information about the thickness of the pattern. A method for manufacturing a pattern recognition filter, characterized in that: 2. An imaging device for imaging a recognized pattern that images a recognized pattern, a coherent light creating means that creates coherent light according to an image of the recognized pattern taken by the imaging device, and irradiation means for converting the coherent light created by the light creation means into a Fourier transform spectrum image and irradiating the pattern recognition filter; and imaging a correlation signal between the Fourier transform spectrum of the recognized pattern and the pattern recognition filter. A pattern recognition device comprising: an imaging device for imaging correlation signals;