JPH0820916B2 - Optical coordinate transformation device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a coordinate conversion device for converting a two-dimensional image into a desired coordinate conversion image using coherent light in the fields of optical information processing and optical measurement. Is.

[Outline of Invention]

The present invention irradiates a liquid crystal light valve using a ferroelectric liquid crystal with a coordinate-converted image and stores the problem that the coordinate-converted image generally obtained in the optical coordinate-transformer has variations in intensity. Or the coordinate transformation image
The image is picked up by an image pickup device such as a CCD camera, converted into an image signal, and the image signal is binarized to binarize the intensity distribution of the wave-like converted image, thereby eliminating variations in intensity. .

[Conventional technology]

Conventionally, when optically measuring and recognizing objects having different shapes, sizes, orientations, positions, such as characters and parts, first convert the object into a two-dimensional image (input image),
Secondly, there is a general procedure of converting the input image into a desired coordinate system, and thirdly measuring and recognizing the coordinate converted image.

As for the type of coordinate conversion, when recognition or rotation angle measurement is performed on objects with different orientations, polar coordinate conversion is performed, or recognition, rotation angle, or magnification measurement is performed on objects with different orientations or sizes. In this case, various kinds of coordinate conversion such as 1nr-θ conversion are used depending on the purpose.

An example of the optical coordinate conversion method is shown in FIG. In this method, the coordinate conversion filter 5 of the input image 16 is placed on the front focal plane of the Fourier transform lens 6 so that the coherent light 15 is emitted from the back of the input image 16 so that the rear focus of the Fourier transform lens 6 is reduced. A desired coordinate conversion image can be obtained on the light receiving element 17 arranged on the surface. Here, the coordinate conversion filter 5 is made of a computer generated hologram.
Generally, a computer-generated hologram is obtained by dividing a two-dimensional diffraction grating into minute areas and calculating the grating pitch in each area by a computer so that the diffracted light from each minute area is diffracted in a desired direction. It is a hologram that has been created. Therefore, it is often produced by the same process as the semiconductor mask pattern based on the hologram pattern data obtained by a computer. More simply, a pattern output to a plotter or the like and transferred to a high resolution film or the like can be used. Light receiving element 17
As the optical writing type liquid crystal light valve using TN liquid crystal and an optical writing type spatial light modulator such as BSO crystal (Bi ₁₂ SiO ₂₀ ), a coordinate conversion image is often used for the spatial light modulator. After irradiating and memorizing, the coordinate conversion image memorized by irradiating with coherent light was read out and used for processing such as pattern recognition. In addition to this, there is also a method of using an imaging device such as a CCD camera instead of the optical writing spatial light modulator and inputting the obtained image signal to an electrically writing spatial light modulator such as a liquid crystal television.

[Problems to be solved by the invention]

However, the obtained coordinate transformed image has variations in intensity. Therefore, when pattern recognition or the like is performed using the coordinate-converted image, there is a problem that variations in the intensity have an adverse effect. There are many possible causes of variations in the intensity of the coordinate-transformed image. Typical causes are shown below. The first cause is the problem of the diffraction efficiency of the coordinate conversion filter. Since the coordinate conversion image is obtained by being diffracted by the coordinate conversion filter produced by the computer-generated hologram described above, the intensity of the portion distant from the optical axis is generally low and the intensity of the portion close to the optical axis is high. The second cause is that the intensity of coherent light has a Gaussian distribution. Therefore, since the intensity distribution exists in the input image itself, the intensity also varies in the coordinate conversion image. In addition, variations in intensity occur in the coordinate conversion image due to various causes such as poor adjustment of the optical system.

Due to the above reason, even if a certain coordinate transformation is applied to the input image, if the noise component is large, the weak portion of the coordinate transformed image is buried in the noise, and the boundary between the noise and the coordinate transformed image becomes large. May become ambiguous, and an accurate coordinate conversion image may not be obtained. Further, the intensity of the coordinate-transformed image of the characteristic portion of the input image may be relatively smaller than the intensity of other portions. In that case, even if pattern recognition or measurement is performed using the coordinate-converted image, the intensity of the coordinate-converted image of a characteristic portion is small, so that there is a problem that accurate recognition or measurement cannot be performed.

[Means for solving the problem]

In order to solve the above-mentioned problems, in the present invention, at least one coherent light source, a first spatial light modulator that holds a two-dimensional input image that is a target of coordinate conversion, and the first spatial light modulator. A means for obtaining a desired coordinate-transformed image by using a coordinate transformation filter arranged on the spatial light modulator and a lens, and an optical writing type liquid crystal light valve using a ferroelectric liquid crystal as a second spatial light modulator. Is stored in the image by irradiating it with a coordinate-converted image and storing it, or converting the image into an image signal by receiving the coordinate-converted image using an image pickup device, binarizing the image signal, and then electrically writing. Two
By inputting the intensity distribution of the coordinate-converted image to the second spatial light modulator and displaying it on the second spatial light modulator.

[Action]

With the above-described configuration, the intensity distribution of the obtained coordinate-converted image is binarized with a certain threshold, so that the binary image of the coordinate-converted image without intensity variations and noise components is obtained. Is obtained. Therefore, when pattern recognition or measurement is performed using the coordinate conversion image, accurate recognition or measurement can be performed.

〔Example〕

Embodiments according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an embodiment according to the present invention. In this embodiment, the second spatial light modulator is a liquid crystal light valve using a ferroelectric liquid crystal. The coherent light from the laser 1 is expanded by the beam expander 2 and then split into two light beams by the beam splitter 3.
The light beam that has passed through the beam splitter 3 passes through the shutter 11 in the open state, and illuminates the first spatial light modulator 4 in which the input image is written, thereby converting the input image into a coherent image. Then, the coherent image is transmitted through the coordinate conversion filter 5 arranged so as to overlap the first spatial light modulator 4, is Fourier-transformed by the Fourier transform lens 6, and illuminates the liquid crystal light valve 7. Here, the first spatial light modulator 4 and the coordinate conversion filter 5 are arranged on the front focal plane of the Fourier transform lens 6 in an overlapping manner, and the liquid crystal light valve 7 is arranged on the rear focal plane. As a result, the coordinate transformed image of the input image is stored on the liquid crystal light valve 7.

Here, the coordinate conversion filter 5 is made of a computer-generated hologram so that a desired coordinate conversion image can be obtained from the diffracted light in each minute area on the coordinate conversion filter 5. Therefore, the coordinate-transformed image irradiated onto the liquid crystal light valve 7, which is the back focal plane, naturally has an intensity distribution because it utilizes diffraction development.

The other light flux reflected by the beam splitter 3 is reflected by the mirrors 9 and 10 and the polarization beam splitter 8 and irradiated on the liquid crystal light valve 7 from the back surface to be reflected. At this time,
The shutter 11 is in a closed state. As a result, the coordinate conversion image stored in the liquid crystal light valve 7 is converted into a coherent image. This coherent image passes through the polarization beam splitter 8 and is used for the next processing system such as recognition and measurement.

The second spatial light modulator 7 is a photo-writing type liquid crystal light valve using a ferroelectric liquid crystal. The difference from the conventional liquid crystal light valve is that a ferroelectric liquid crystal having clear bistability between light transmittance or light reflectance and an applied voltage is used as a liquid crystal layer. By utilizing this property, the coordinate conversion image can be converted into a binarized image.

FIG. 3 shows a liquid crystal light valve 7 using a ferroelectric liquid crystal.
FIG. 3 is a cross-sectional view showing the structure of FIG. Transparent substrates 21a, 21b such as glass or plastic for sandwiching liquid crystal molecules have transparent electrode layers 22a, 22b on the surface and silicon monoxide at an angle in the range of 75 to 85 degrees with respect to the normal direction of the transparent substrate. Orientation film layers 23a and 23b obtained by oblique vapor deposition are provided. The transparent substrates 21a and 21b are arranged such that their alignment film layers 23a and 23b are opposed to each other with a gap controlled via a spacer 29 to sandwich the ferroelectric liquid crystal layer 24.

Further, a photoconductive layer 25, a light shielding layer 26, and a dielectric mirror 27 are laminated and formed on the transparent electrode layer 22a on the writing side by light between the alignment film 23a and the transparent substrate 21a on the writing side and the transparent on the reading side. Non-reflective coating layers 28a and 28b are formed on the cell outer surface of the substrate 21b.

Next, a method for initializing the liquid crystal light valve 7 having the above structure will be described. The first method is to use the liquid crystal light valve 7 once.
The entire writing surface is irradiated with light, and the DC bias voltage or 100Hz is sufficiently higher than the maximum threshold voltage when bright.
A DC bias voltage with an AC voltage of -50 KHz superimposed is applied between the transparent electrode layers 22a and 22b to align the ferroelectric liquid crystal molecules in a unidirectional stable state and store the state. The second method is, without light irradiation, a DC bias voltage sufficiently higher than the maximum threshold voltage in the dark or 100 Hz to 5 Hz.
A DC bias voltage with an AC voltage of 0 KHz superposed is applied between the transparent electrode layers 22a and 22b to align the ferroelectric liquid crystal molecules in a unidirectional stable state and store the state.

Furthermore, the operation after the liquid crystal light valve 7 is initialized as described above will be described. With no light irradiation, in the dark the threshold voltage is below the minimum value, and when the light is irradiated, the threshold voltage is above the maximum value.
An image is optically written by laser light or the like while applying a DC bias voltage in which an AC voltage of 100 Hz to 50 kHz is superimposed between the transparent electrode layers 22a and 22b. Carriers are generated in the photoconductive layer in the region irradiated with the laser, and the generated carriers drift toward the electric field due to the DC bias voltage, and as a result, the threshold voltage is lowered. When a bias voltage with a reverse polarity above the threshold voltage is applied, the ferroelectric liquid crystal undergoes inversion of molecules due to the inversion of spontaneous polarization, and the state transitions to the other stable state, so the image is binarized and stored. To be done.

The binarized and stored image is the direction of the alignment of liquid crystal molecules aligned by initialization (or the direction perpendicular to it).
By irradiating the reading light having a linear deviation with the polarization axis aligned with, and passing through an analyzer arranged so that the polarization axis is perpendicular (or parallel) to the polarization direction of the reflected light by the dielectric mirror 27, It can be read in the positive or negative state.

The threshold for binarizing an image is the transparent electrode layer 22a.
The voltage can be changed by adjusting the frequency of the AC voltage applied between 22 and 22b and the value of the DC bias voltage. Further, by adjusting the laser power to change the light intensity of the coordinate-converted image, the same effect as when the threshold value is substantially changed can be obtained.

Since the coordinate-converted image having the intensity distribution irradiated on the liquid crystal light valve 7 is binarized and stored, the threshold value is adjusted even if there are many noise components and are normally buried in noise. By doing so, it is possible to obtain an accurate coordinate conversion image without a noise component. Further, since the stored coordinate-converted image is binarized, the coordinate-converted image itself does not have variations in intensity, which makes it easy to use for the next optical system for recognition and measurement.

FIG. 4 shows a block diagram of another embodiment according to the present invention. In this embodiment, a liquid crystal television is used as the second spatial light modulator. It is the same as the above-described embodiment until the coordinate-converted image of the input image held by the first spatial light converter 4 is obtained, and the description thereof is omitted. CCD on the back focal plane of Fourier transform lens 6
The camera 12 is arranged. Thereby, the intensity distribution of the coordinate transformed image of the input image is transformed into an image signal. This image signal is binarized by determining a threshold value which is a binarization circuit 13.
Then, the intensity distribution of the binarized coordinate conversion image is displayed on the LCD TV.
Display on 14. The other light beam split by the beam splitter 3 is reflected by the mirror 9 and illuminates the liquid crystal television 14. Thereby, the binarized coordinate conversion image displayed on the liquid crystal television 14 can be converted into a coherent image.

Although the binarized image signal is displayed on the liquid crystal television 14 in the embodiment shown in FIG. 4, it may be stored in an optical writing type spatial light converter using a scanning optical system such as a laser scanner. Needless to say.

In the above embodiment, as the first spatial light modulator,
It goes without saying that it may be a spatial light modulator of optical writing type or electric writing type, or may be a film.

In the above embodiment, the light beam from the laser 1 is split into two light beams by using the beam splitter 3, but it goes without saying that two lasers may be used.

In the above embodiment, when the visible light reflectance of the dielectric mirror 27 is sufficiently high and the influence of the reading light on the photoconductive layer 25 is extremely small, the light shielding layer 26 can be omitted.
Further, when the reflectance of the photoconductive layer 25 with respect to the read light is sufficiently large, and the read light is sufficiently small and the influence of the read light on the photoconductive layer 25 is extremely small, the dielectric mirror 27 can be omitted. .

〔The invention's effect〕

As described above, since the image obtained by binarizing the coordinate-converted image of the input image is obtained, accurate recognition and measurement that is not affected by the variation in the intensity of the coordinate-converted image can be performed not only in pattern recognition but also in measurement. It will be possible.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment according to the present invention, FIG. 2 is a diagram showing an example of an optical coordinate conversion method, and FIG. 3 is a sectional view showing a structure of a liquid crystal light valve using a ferroelectric liquid crystal, FIG. 4 is a block diagram of another embodiment according to the present invention. 1 ... Laser 2 ... Beam expander 3 ... Beam splitter 4 ... First spatial light modulator 5 ... Coordinate conversion filter 6 ... Fourier transform lens 7 ... Liquid crystal light valve (second spatial light modulation) 8 …… Polarization beam splitter 9 …… Mirror 10 …… Mirror 11 …… Shutter 12 …… CCD camera 13 …… Binarization circuit 14 …… LCD TV (second spatial light modulator) 15 …… Coherent Light 16 …… Input image 17 …… Light receiving element 21a, 21b …… Transparent substrate 22a, 22b …… Transparent electrode layer 23a, 23b …… Alignment film layer 24 …… Ferroelectric liquid crystal layer 25 …… Photoconductive layer 26… … Shading layer 27 …… Dielectric mirror 28a, 28b …… Anti-reflection coating layer 29 …… Spacer

Claims (3)

[Claims] 1. A device for coordinate-converting a two-dimensional image obtained from an image pickup device such as a CCD camera using coherent light, wherein at least one coherent light source and a two-dimensional input image to be coordinate-converted are provided. A means for obtaining a desired coordinate-transformed image using the first spatial light modulator held therein, a coordinate transformation filter arranged to overlap the first spatial light modulator, and a lens; And a means for displaying the intensity distribution on the second spatial light modulator by binarizing the intensity distribution. 2. A light writing type liquid crystal light valve using a ferroelectric liquid crystal as a means for binarizing the intensity distribution of the coordinate conversion image and displaying it on a second spatial light modulator. The optical coordinate conversion device according to claim 1, wherein the spatial light modulator irradiates and stores the coordinate conversion image. 3. A means for binarizing the intensity distribution of a coordinate-transformed image and displaying it on a second spatial light modulator converts the coordinate-transformed image into an image signal by receiving light using an imaging device, The optical coordinate conversion device according to claim 1, wherein the image signal is binarized and then input to a second spatial light modulator of an electrical writing type.