JPH0244043B2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field) This invention detects spatial periodicity of a horizontally adjustable specific period included in an input image, and constructs and displays an image indicating the position of the spatial periodicity of the image. The present invention relates to a frequency detection device or a pattern detection device having a specific spatial frequency. The apparatus of the present invention is capable of displaying feature extraction, defect inspection, etc. in pattern recognition as an image in relation to the position of the object to be measured.

(Prior Art) Conventionally, an image is inputted with a television camera, and a horizontal scanning direction correlation image of the image is obtained by performing spatial real-time correlation calculation processing using an electro-optical method.
There are image correlation devices that display this on a receiver screen. In such a device, the 2
Since the two signals are both processed signals such as television image video signals, even if a correlated output image is detected,
It is difficult to detect spatial frequency components contained in television images. That is, in the autocorrelation output image, only the periodicity of the input image can be detected, and in the cross-correlation output image, only the degree of similarity (degree of overlap) with respect to the specific target signal can be measured.

In addition, in the image spatial frequency analyzer (Japanese Patent Application No. 183810/1989) that the inventors invented earlier, a spatial frequency spectrum image that indicates the detected spatial frequency in the horizontal direction and its position in the vertical direction in the vertical direction. can be displayed.

However, this device does not display the horizontal position of the detected spatial frequency component. In other words, with this device, the horizontal axis of the output screen is indicated by a spatial frequency scale, and there is no information about the position of the detected spatial frequency component in the input image, that is, the spatial phase information of the specific spatial frequency component. No information is obtained, and the two-dimensional position of the detected spatial frequency component cannot be determined.

Furthermore, since only the position and brightness of one bright spot representing a part of the spatial frequency spectrum of the output image can be obtained from the video signal obtained by horizontally scanning the input image once, the horizontal scanning of the image pickup device for image input is The horizontal scanning speed of the output image becomes significantly slower than the speed.

This problem becomes more noticeable when the number of bright spots indicating spatial frequencies in the image is increased in order to increase the resolution of the output image, and as a result, the time required to construct one output image becomes longer. In other words, resolution and processing speed conflict with each other, and their upper limit is limited by the horizontal scanning speed of the image pickup device for image input. Therefore, when used in applications requiring high resolution or applications in which the entire image of a high-speed moving object is processed in real time, an expensive imaging device for inputting images with a very high horizontal scanning speed is required.

Furthermore, it can be used for feature extraction in pattern recognition that focuses only on spatial periodicity of a certain period included in an input image and detects its frequency and location, and for industrial applications such as defect inspection. To use,
A method that simply displays all the frequencies detected in the horizontal direction has the problem of being difficult to analyze in terms of operating time and desired position information, and is hardly suitable for practical use.

(Objective of the present invention) The present invention improves the conventional image correlation device as described above, and applies correlation calculation to spatially adjust a specific horizontally adjustable period in an input image. By providing an apparatus for detecting a pattern having a spatial frequency that detects periodicity, constructs an image indicating its position in both horizontal and vertical directions, and further displays an output image at the same horizontal scanning speed as the horizontal scanning speed of the input image. be.

(Summary of the Invention) Therefore, in the present invention, an acousto-optic correlator using an ultrasonic optical modulator and a Fourier transform optical system, or a correlator having an equivalent function, is capable of calculating the correlation of electrical signals in real time. One of the two signals input to the correlator is used as a reference signal having a specific externally adjustable temporal frequency that corresponds to the spatial frequency to be detected, and the other input signal is used as a unidirectional horizontal The video signal obtained by scanning is obtained by performing a cross-correlation calculation on these two signals to obtain an output signal, which is displayed on the screen by horizontal and vertical sweeping of the image pickup device for image input, and is then returned to the original input. The horizontal spatial frequency of a specific period included in the image is displayed at a position corresponding to the original input image where it was detected.

(Configuration of the Present Invention) In describing the embodiments of the present invention, first, a description will be given of the configuration and operation of an acousto-optic correlator using an ultrasonic optical modulator and a Fourier transform optical system. FIG. 1 is a block diagram of an embodiment of an image spatial frequency detection apparatus according to the present invention. In the same figure, 6
is an acousto-optic correlator or a correlator with equivalent functionality.

In this acousto-optic correlator, two electrical signals to be subjected to a correlation calculation are applied as external modulation signals to a pair of amplitude modulated sine wave oscillators 8 and 9. The oscillation frequency of the oscillator is the resonance frequency of the ultrasonic transducers disposed within the pair of ultrasonic light modulators 12 and 13. The sine waves output from the pair of oscillators undergo appropriate power amplification by a pair of amplifiers 10 and 11, and are applied to the ultrasonic transducer to generate two spatial ultrasonic signals within the pair of ultrasonic light modulators. form. These two ultrasound signals propagate within the ultrasound light modulator at the speed of sound. next,
These two ultrasonic signals are transferred to the Fourier transform optical system 1.
The operating principle of correlation calculation in real time using 4 will be described below. The light source of the conversion optical system is a laser 15, and the beam width of the laser beam emitted from the laser beam is expanded by a lens, and the beam width within the pair of ultrasonic light modulators is divided into two ultrasonic signals. It crosses at right angles and undergoes phase modulation. When this phase-modulated light is converged again by a lens, several diffracted light spots are generated on the focal plane of the lens. Of these diffraction light spots, two in the pair of ultrasonic light modulators
A spatial light intensity filter 16 detects only the bright spot resulting from the two-degree diffraction by crossing two ultrasonic signals, and the amount of light is photoelectrically converted and amplified by a photoelectric conversion device 17 to generate a current value I(t). Detect. in this case,
The envelope of the spatial phase pattern due to the two ultrasound signals in the pair of ultrasound light modulators is defined as U ₁ (x),
If U ₂ (-x), it is known that the following equation holds according to Rayleigh's theorem. However, U ₂ (−
_The (-) _sign of Since the ultrasound transducers are arranged facing each other, the use of the same spatial axis x represents opposite spatial positions.

∫｜U ₁ (x)｜ ² ｜U ₂ (−x)｜ ₂ dx＝∫｜F｛U ₁ (x)
U ₂ (−x)} | ² dα……(1) Here, F{U ₁ (x) U ₂ (−x)} is the ultrasound signal envelope U ₁ (x), U ₂ (−x ), and α represents a spatial axis parallel to the time axis x on the Fourier transform plane. The right side of equation (1) is U ₁ (x) and U ₂ (−x)
The output current I of the photoelectric converter indicates the total light amount of the optical image obtained by Fourier transforming the product of
(t). Also, the ultrasound signal envelope U ₁
Considering that (x) and U ₂ (-x) move in opposite directions within the ultrasonic optical modulator at an ultrasonic velocity v, the following equation can be derived from equation (1).

In equation (2), d represents the width of the luminous flux. From equation (2), it can be seen that the photoelectric converter output current C(t) represents the calculation result of the square value superposition of each of the ultrasound signal envelopes U ₁ (t) and U ₂ (t). However, the squared value superposition integral shown by equation (2) is different from the general format, and has a format in which both U ₁ (t) and U ₂ (t) move (delay). In addition, if U ₂ (t) is periodic like a continuous sine wave and has symmetry, consider U ₂ (t) = U ₂ (-t) ......(3), and ( 2) The formula is , which represents the square value cross-correlation calculation of U ₁ (t) and U ₂ (t).

In other words, the superposition of two signals within the optical system is expressed as a product operation, and the convergence effect of a lens is expressed as an integral operation. Since real-time cross-correlation calculation is performed within the device, its output signal becomes the correlation output shown in equation (4).

Here, a periodic and symmetrical waveform such as a continuous sine wave or a rectangular wave is used as U ₂ (t), the frequency is set to a specific value appropriately set by external adjustment, and U ₁ (t ), the output signal C(t) is U ₁ (t)
The correlation output has an amplitude depending on the amount of temporal frequency components included in the correlation output. Therefore, the specific temporal frequency contained in the video signal can be determined by the amplitude of the correlation output C(t).

Next, the entire configuration of the present invention will be explained.

The configuration of the embodiment of the image spatial frequency detection device of the present invention shown in FIG. 1 will be described.

In Fig. 1, 6 is an acousto-optic correlator using an ultrasonic optical modulator and a Fourier transform optical system, or a correlator having an equivalent function, which performs square cross-correlation calculation of two input signals according to the above-mentioned operating principle. Run in real time. The video signal of the input image 1 obtained by the imaging device 2 is sent through a synchronization pulse separation circuit 3 that removes horizontal and vertical synchronization pulses to a square compression circuit 4 that performs square compression of the signal amplitude, and its output is It is applied to the correlator 6 as one input signal. In other words, the video signal after the synchronization pulse is removed is h(x)
Then, the output signal of the square compression circuit 4 is √
(x). The reference signal generator 5 in the figure generates a reference signal having a periodic and symmetrical waveform such as a continuous sine wave or a rectangular wave having a specific frequency appropriately set by external adjustment, and The signal is input to the correlator 6 as a signal. Correlator 6
As mentioned above, the output signal C(t) of is the video signal h
(t), and is input to the output image display 7 together with the horizontal and vertical sweep signals output from the imaging device, and the frequency components are Construct and display an image showing the detected location.

(Operating principle of the present invention) Next, the operating principle of the present invention will be explained using the drawings. FIG. 2 is a diagram of typical input images and output images showing the operation of the embodiment of the present invention, and was drawn based on the results of an operation experiment of the embodiment.
In the figure, a shows an input image, the upper and lower right parts of which are images with a horizontal spatial frequency A, and the center left part has a smaller directional spatial frequency.
There is an image with A′. b in the figure is an output image in which the horizontal spatial frequency A included in the input image is detected and its position is shown. The temporal frequency of the video signal when the imaging device scans a portion having the spatial frequency A in the input image is expressed as in equation (5), where S is the scanning speed of the imaging device.

=S/A (5) Therefore, by setting the frequency of the reference signal generator to , the correlation output C(t) detects the temporal frequency in the video signal. This means that the spatial frequency A in the input image has been detected. An output image b is obtained by sweeping this correlation output C(t) with the same horizontal and vertical sweep signals as the input image a. When sweeping the upper middle and lower right parts of the image, C
(t) detects the spatial frequency A and has a large amplitude, so a striped image appears in the output image.
However, in other parts of the image, spatial frequency A is not detected and no image is generated. In the figure, c shows an output image when the horizontal spatial frequency A' is detected. The set frequency of the reference signal generator at this time is S/A' by calculation similar to equation (5). Similarly to b, a striped image appears only in the center left part where a predetermined spatial frequency is detected.

Next, the relationship between the present invention and the earlier applications filed by the same applicant (described in Japanese Patent Laid-Open No. 57-91086 and Japanese Patent Laid-open No. 57-91087) will be mentioned.

The "television image analog correlation device" described in JP-A-57-91086 is the "image spatial frequency analyzer" described in JP-A-57-91087 and the "detection device for patterns having spatial frequencies (image Although the configurations of the "spatial frequency detection device", the optical system, and the image correlator are similar, these three inventions have very different electrical signal processing systems.

In a TV image analog correlator, a delay circuit for delaying a synchronization signal is an essential component in order to obtain an autocorrelation image and display the autocorrelation image on either the left or right half of the receiver screen. It is said that

The image spatial frequency analyzer and the detection device for a pattern having a spatial frequency according to the present application are different in the following points.

(1) “Analyzer” performs frequency analysis.
A linear FM signal repetition generator that generates a linear FM signal at a constant repetition period is an essential component, and this linear FM signal is used as one input of a correlator that directs the cross-correlation signal.
In order to perform phase detection, the "detection device" requires a reference signal generator that generates a reference signal of a specific frequency that can be adjusted externally. There is a significant difference in configuration in that the reference signal is used as one input of the correlator that outputs the cross-correlation signal.

(2) “Analyzer” is an analyzer whose purpose is to display the spatial frequency spectrum of a TV input image in the form of an image on a TV screen. On the other hand, the “detection device” of this application refers to the position on the screen of a TV input image. This is a specific pattern detection device whose purpose is to detect whether a specific repeating pattern (checkered stripes) exists in the . Because of this difference in purpose, although the correlation optical systems of the two devices are similar, the electrical systems and operation contents are completely different.

(3) Comparing the operations of the two, the “analyzer” has the function of a spectrum analyzer that targets general TV images as an image measurement device, whereas the “detection device” of this application is used for defect detection and pattern recognition. It can be seen as a type of spatial filter used for feature detection. A spatial filter called a “detection device” can be considered to have the function of a processor, whereas
An "analyzer" does not have such processor functionality.

(4) Another difference between the two operations is the operation time.
In the case of the Analyzer, each scan line is output in near real time, but it takes several seconds to construct the entire spectral screen with average density.

On the other hand, in the "detection device" of the present application, the entire screen is output almost in real time with a delay of one scanning line (63 ms). For this reason, an "analyzer" cannot obtain sufficient results unless the image remains static for at least several seconds, but a "detection device" can process any object that can be tracked by a TV camera. .

(Effects of the present invention) Since the present invention has the above-described configuration, if it is used, it is possible to detect in real time the horizontal spatial frequency of any period included in the input image, and
Dimensional position can be displayed. Note that since the output image is swept at the same speed as the input image is swept horizontally and vertically, it is suitable for processing images of moving objects or for processing a large number of still images in a fixed period of time. Unlike the conventional image spatial frequency analyzer described above, a high-speed sweep imaging device is not required.

In the present invention, the spatial frequency to be detected can be fixed and used, or the spatial frequency to be detected can be adjusted as appropriate with a dial etc. while observing the output image, and the spatial frequency to be detected can be adjusted as appropriate. It can also be applied to a type of display that can be called a three-dimensional spectrum analyzer in which frequency is made to correspond to the time axis by sweeping in time, and can be used for a very wide range of applications.

If the imaging device is used in a fixed manner, it is also possible to measure the spatial frequency contained in the input image. is also possible. Furthermore, the video signal to be input is not limited to a signal directly obtained by an imaging device, but also a video signal recorded on a videotape or the like can be used.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing an input image and an output image. 1 is an input image, 2 is an imaging device, 3 is a synchronous pulse separation circuit, 4 is a square compression circuit, 5 is a reference signal generator, 6 is a correlator, 7 is an output image display device, 8, 9
is a sine wave oscillator, 10 and 11 are wideband amplifiers, 1
2 and 13 are ultrasonic optical modulators, 14 is a Fourier transform optical system, 15 is a laser, 16 is a photodetection filter, and 17 is a photoelectric conversion device.

Claims (1)

[Scope of Claims] 1. An image spatial frequency detection device for detecting and displaying the presence or absence of a pattern having a specific horizontal spatial frequency in an input image 1 and its location, comprising: an imaging device 2 that outputs a composite video signal obtained by horizontal scanning; a sync pulse separation circuit 3 that removes horizontal and vertical synchronization pulses from the composite video signal; and a square compression circuit that squares the output signal of the separation circuit. 4: a reference signal generator 5 that generates a reference signal of a specific frequency that can be adjusted from the outside; and a correlator 6 that receives the output signal of the square compression circuit and the reference signal and outputs a cross-correlation signal.
and: Receive the horizontal and vertical sweep signals output from the imaging device and the cross-correlation signal output from the correlator, and make the position of the pattern in the input image having the frequency of the reference signal correspond to the input image. 1. An apparatus for detecting a pattern having a spatial frequency, comprising: an output image display device 7 for displaying a pattern as an output image. 2. The correlator 6 includes a pair of amplitude modulated sine wave oscillators 8 and 9:
wideband amplifiers 10 and 11 whose input signals are the output signals of the sine wave oscillators; and a pair of ultrasonic optical modulators 12 and 13 whose ultrasonic propagation directions are opposite to each other and whose input signals are the output signals of the amplifiers. A Fourier transform optical system 14 having: a laser 15 that is a light source of the optical system; a photodetection filter 16 that detects the output light of the optical system; and a photoelectric conversion device 17 that photoelectrically converts and amplifies the output light. Claim 1 characterized in that it is an acousto-optic correlator
A device for detecting a pattern having the spatial frequency described in 1.