JPH0477951B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention extracts a still image of a moving object, performs image processing to inspect the shape and defects of the object, and determines whether it is good or bad and sorts it. This invention relates to a binarization method for pattern inspection/discrimination scanning.

[Conventional technology]

FIG. 7 is a block diagram showing a conventional example of this type of pattern inspection/discrimination apparatus, and FIG. 8 is a timing chart for explaining its operation. In FIG. 7, 1 is an object, 2 is a conveyor, 3 is an imaging device such as a television camera, 4 is an illumination device, 5 is a position sensor consisting of a light emitting element and a light receiving element, and 6 is an amplifier 7, a binary value. conversion circuit 8, arithmetic determination section 9
This is an image processing device including a timing control circuit 10 and the like. The calculation/judgment section 9 further includes an image memory 91, a feature extraction circuit 92, an arithmetic processing circuit 93, a position detection/correction circuit 94, a setting device 95, and the like.

The operation of the conventional device will be described below with reference to FIGS. 7 and 8.

The object 1 is conveyed by a belt conveyor 2,
When this reaches a predetermined position within the field of view of the television camera 3, this is detected by the position sensor 5. The position sensor output is used as a test start signal, as shown in FIG. 8B, for example. Now, suppose that the television camera 3 has a built-in shutter and that this shutter is driven in synchronization with the vertical blanking period (vertical blanking period) V _BLK of the television camera 3. In this case, the shutter is 8th
As shown in Figure C, it is in the "open" state only once. Incidentally, the vertical blanking period is shown as in FIG. 8A.
When the shutter is opened in this manner, the optical image of the object 1 is converted into an image signal (video signal) and extracted by the television camera 3. In other words, the camera output of one field (1V; image) immediately after the shutter is opened is valid, and this is taken into the image processing device 6 as an image signal. The timing and duration of this image capture is shown as D in FIG. The image signal captured in this way is amplified by an amplifier 7 and binarized by a binarization circuit 8. 2
The digitized image signal is stored in an image memory 91, and a feature extraction circuit 92 extracts various characteristic quantities of the object from this memory 91. The arithmetic processing circuit 93 compares and discriminates each characteristic amount with a set value preset by the setting device 95, thereby determining whether the object is good or bad and sorting (sorting) the object, and outputs the results to a display device or the like. . The timing and period of this determination/calculation are shown as E in FIG. In addition,
A position detection/correction circuit 94 shown in FIG. 7 is provided to detect the amount of positional deviation of the object from the reference point and correct it.

The above is for a TV camera with a shutter, but when using a TV camera without a shutter, prepare a strobe instead of the shutter, and fire this strobe only once at the same timing as the shutter "opens". Accordingly, inspection and discrimination can be performed in the same manner as above.

In this way, shutters and strobes convert continuously moving images into still images, thereby extracting clear images without image blurring and ensuring highly accurate inspection and discrimination.

[Problem that the invention seeks to solve]

By the way, the threshold value of the binarization circuit in such devices is usually set at a fixed level set in advance, but this is because the circuit configuration and processing are easier and the processing time is shorter. It is. However, the lighting device (reference number 4 in Fig. 7)
If the brightness of the object (reference) changes over time, or if the reflectance of the object itself changes depending on the solid state, the image signal from the camera will naturally change as well. If you try to binarize this at a fixed level, the object image will be significantly distorted, and as a result, the big problem is that the object will be considered a defective product even though it is normal. have.

Note that when there is one piece of image information, for example, the video signal is converted into a digital quantity of a predetermined number of bits, the grayscale information is stored in a pixel-by-pixel memory, and this information is continuously outputted to perform the required information processing. There is also a method of determining the optimal level. However, this method has the problem that not only the circuit configuration becomes enormous, but also the processing time for determining the threshold value becomes long.

Therefore, the present invention provides a stable and highly accurate binarization method that is economical in that it takes a short processing time, and that does not cause erroneous judgments due to variations in brightness of a lighting device or the type of object. The purpose is to

[Means for solving problems]

two-dimensional imaging means for capturing a still image of a moving object; window generation means for generating at least one window of a predetermined size at a predetermined position of the captured image; and shading of an area extracted through the window. A binarization level determining means for detecting the level and determining a binarization level according to the gray level is provided.

[Effect]

The two-dimensional imaging means takes out at least two still images that follow each other based on a predetermined time, and the window generation means generates a window at a predetermined position of the still image temporally, and the binarization level is determined. By checking the shading level within the window area using a means, determining the optimum binarization level from this shading level, and binarizing the temporally later still image using this binarization level, it is possible to easily and To determine an optimum binarization level with an inexpensive configuration and without wasting time.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention. In the same figure, 11 is a low pass filter (LPF), 12 is a peak hold circuit (PH circuit),
13 is an analog/digital (A/D) conversion circuit, 14 is an arithmetic circuit, 15 is a comparison level selection circuit, 16 is a digital/analog (D/A) conversion circuit, 17 is a binary output control circuit, and 18 is a PH level. 19 is a standard value output circuit; 21 is a window generation circuit; 22 is a scanning point coordinate generation circuit;
3 is a window setting value storage circuit, 24 is a PH reset circuit, 25 is a reset timing circuit, 26
27 is an effective screen control circuit, 27 is a camera drive synchronization circuit, and the other parts are the same as in FIG.

Therefore, as in the case of FIG. 7, the object 1 is conveyed by the belt conveyor 2 so as to come within the field of view of the television camera 3. The television camera 3 used here includes, for example, as shown in FIG. 2, an image sensor 31, an image processing and image sensor drive circuit 32, a lens 33, a rotating disk 34, a motor 35,
A rotation control circuit 36, a case 37, etc. are used. A rotating disk 34 having an aperture slit at a predetermined position on the circumference is arranged between the lens 33 and the image sensor 31, and this rotating disk 34
By rotating the lens with a motor 35, a kind of focal plane type shutter effect is produced. The rotation control circuit 36 controls the rotation of the motor so that the exposure operation by this disk is always performed in conjunction with every vertical blanking period V _BLK of the television camera.

Although the above device has a shutter function, a strobe light can be used instead as shown in FIG. 2A. Note that FIG. 2A is a schematic diagram showing an example of the strobe method. That is, strobe 41,
It consists of a strobe firing circuit 42 and a strobe firing control circuit 43, and by introducing the V _BLK signal and the position sensor (see reference numeral 5 in Fig. 1) output into the control circuit 43, the signal
The strobe 41 is ignited via the ignition circuit 42 by V _BLK .

Therefore, in the case of a television camera with a shutter, for example, by constructing it as shown in FIG. 2 and using the illumination device 4 as shown in FIG.
In the case of a strobe type, for example, a plurality of image signals can be obtained by configuring as shown in FIG. 2A.

The image signal from the television camera 3 obtained in this manner is applied to an analog amplifier 7 of the image processing device, where it is amplified to an appropriate level. The signal from amplifier 7 is input to binarization circuit 8 and low-pass filter 11. The LPF 11 cuts noise and small image signals (high frequency) of one to several pixels from the image signal of the television camera 3.
Only image signals below the intermediate frequency are extracted. This is provided in order to avoid malfunctions based on noise or local false image signals caused by objects (eg, caused by halation, etc.). this
The output of the LPF 11 is led to a peak hold circuit (PH circuit) 12, which holds the peak value of the image signal at a predetermined timing. The operation timing of the PH circuit 12 is controlled by the output from the hold window generation circuit 21. In other words,
The PH circuit 12 operates only within the window area, and its hold value is determined by the PH reset circuit 24 and the PH
The reset timing circuit 25 erases the data at a predetermined timing. Window generation circuit 21
The method generates a two-dimensional area of a predetermined size as a window at a predetermined position in a preset screen, and the window area is formed by generating a window signal for each scanning line.

The scanning point coordinate generation circuit 22 knows the y-coordinate at the current scanning point by counting the number of horizontal scanning lines from the television camera 3, and also calculates the y-coordinate at the current scanning point by counting the number of horizontal scanning lines from the television camera 3.
By counting the reference clock (6MHz), the x coordinate on the current horizontal scanning line is known, and based on this, the x and y coordinate signals at the time of scanning are output for each scanning. Therefore, if the window area information is set and stored in the setting value storage circuit 23 in advance, by comparing this with the x, y coordinate position information from the scanning point coordinate generation circuit 22, the window generation circuit 31 A predetermined window area can be set via .

Here, the window generation and peak hold functions will be explained in more detail. Third
The figure is a reference diagram showing relative position changes on the screen due to movement of the object, and FIG. 4 is a time chart mainly for explaining the peak hold operation.

Since the shutter performs an exposure operation every vertical blanking period V _BLK and performs a light shielding operation outside this period, the start time of the period V _BLK is t _i-2 , t _i-1 , t _i
Considering this, the relationship between the object and the window at each time is shown, for example, as shown in FIG. 3, A, B, and C. Here, 1 is the object, W is the window,
P represents the field of view (screen) of the television camera, and V _i-2 , V _i-1 and V _i represent the object images at each time point, respectively.

Now, assuming that the above-mentioned times are shown as shown in FIG. 4A, the position sensor output will be obtained immediately before time t _i , as shown in FIG. 4B. The control circuit 26 generates a binarized output effective screen signal as shown in _FIG . On the other hand, the image signal from the television camera 3 is given to the PH circuit 12 via the amplifier 7 and the LPF 11, but at this time, the window generation circuit 21 outputs all the window signals except during the generation period of the effective screen signal. As a result, the peak hold operation is performed every high (H) level period shown in FIG.
Therefore, the PH circuit 12 holds the peak value of the low frequency signal from the television camera 3 until a reset signal is applied. The PH circuit reset signal is output for each V _BLK signal other than the V _BLK signal for which an effective screen signal is formed, as shown in FIG. 2, to reset the PH circuit 12. Therefore, in the case shown in FIG. 3 or 4, the output of the PH circuit 12 becomes substantially zero because the object has not reached the window position at time t _i-2 ; At time t _i-1 , the object has reached the window position, so
The PH circuit 12 holds the peak value of the output corresponding to the window area among the outputs of the LPF circuit 11 regarding the density information of the object as _VH as shown in the figure. Note that this value V _H is reset by a reset signal output at time t _{i +1} . Also, if there is an object image at time t _i+1 ,
The peak value is held as V _H ' in the same figure.

In other words, the peak value of a predetermined area can be known from the image information just before the position sensor output is obtained (t _i-1 in this case), so the appropriate binarization level can be determined based on this. If this is done, it will be possible to binarize the image information immediately after the sensor output is obtained (t _i in this case) at the determined binarization level, and then perform inspection based on the binarized image thus extracted. , the processing time for binarization is shortened and the accuracy of inspection or discrimination is improved.

Next, a method of determining the binarization level from the peak value obtained in this way will be explained.

First, image the standard object at the standard position,
Adjust the binarization threshold so that an appropriate binary image is obtained, find the appropriate binarization threshold L _S and the corresponding peak hold value V _HS of the PH circuit 12,
These are stored in the arithmetic circuit 14 as reference values. Next, the same operation is performed on the object to be inspected, and the peak hold value, which is the grayscale information in the window area of the image immediately before judgment V _i-1, is obtained.
Find V _HX . In this way, _from the relative relationship of the peak hold values, the binarization threshold candidate L _X of the object to _be inspected can be set as L _X = V _H An appropriate binarization threshold value can be determined by performing the calculation in the above equation. At this time, this also applies to the peak hold value V _HX itself.
Check whether it is within the range of 0.5V _HS ~ 1.5V _HS ,
We are trying to judge its appropriateness. The PH level discrimination circuit 18 makes this judgment.
If V _HX is within the above range (Y), the comparison level selection circuit 15 selects the output _L given as a threshold. On the other hand, if V _HX is outside the above range (N), the selection circuit 15 operates to select the output from the standard value output circuit 19. Note that the standard value output circuit 19 is
Normally, L _S is output as the standard value. In other words, the reason for doing this is that when V _HX is abnormal, it is dangerous to use the binarization threshold calculated by calculation.
This is because it is considered safer to adopt the standard value _VHS .

The binary level signal determined in this way is
It becomes one input of the binarization circuit 8 via the A conversion circuit 16. The image signal at time i is input to the other side of the binarization circuit 8, and this image signal is binarized using the binarization level from the D/A conversion circuit 16. At this time, the control circuit 26 generates the above-mentioned effective screen signal and supplies it to the binary output control circuit 17, so that the circuit 17 only uses the binary image information effective for inspection and discrimination out of the output from the binary conversion circuit. Control is performed to output . The arithmetic control unit 9 executes predetermined image processing using the binary image information obtained in this way, and inspects and discriminates the object.

The above has mainly explained the operation when a television camera with a shutter is used, but the same applies to the strobe type, and the time chart in that case is shown in FIG. The difference from Fig. 4 is that the strobe firing timing is as shown in Fig. 5 (g), and the operation of each part is shifted one screen later based on the position sensor output, but both are basic. Since this is not a fundamental difference, a detailed explanation will be omitted. However, since the time shift of one screen is a constant value, it is necessary to take this into consideration and shift the set position of the position sensor by that amount.

In addition, in the above, the binarization circuit is assumed to be one channel,
One window was set for this, but in order to deal with the shading of the object, the binarization circuit was made to have multiple channels, correspondingly multiple windows were set up, and each was binarized. It is also possible to control the threshold values individually. Of course, a plurality of windows can be set for one binarization circuit. Note that FIG. 6 shows an example in which two windows are set, and W ₁ and W ₂ are the windows. Furthermore, regarding the image signal within the window,
Although the peak value is used, the average value of the gradation information may also be used. Further, the shape of the window is not limited to a rectangle, but can be any shape.

〔Effect of the invention〕

According to this invention, two temporally adjacent image signals are extracted, a binarization level is determined from the temporally previous image signal, and the temporally subsequent image signal is binarized. Therefore, even if the reflectance of the object changes individually, the binarization threshold is selected according to this change, so stable and highly accurate judgment is always possible. The same applies to changes in the illuminance of the device. Furthermore, since a moving object is converted into a still image, a clear image without image blurring can be obtained, which improves the accuracy of inspection or discrimination. Furthermore, since the present invention does not require a high-speed A/D conversion circuit, a memory circuit, a huge amount of processing circuits, etc., it is possible to provide this type of device easily and inexpensively. Further, the present invention utilizes information immediately preceding image information to be determined, and
Since this method uses something that has conventionally been overlooked as a waste, the processing time does not substantially increase, and therefore high-speed performance equivalent to that of the conventional method is guaranteed. Further, in determining the binarization threshold, a certain limit is set on the grayscale value of the image, so it is possible to avoid malfunctions due to unexpected objects or the like.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing an embodiment of this invention;
Figure 2A is a configuration diagram showing a specific example of a television camera with shutter, Figure 2A is a schematic diagram showing a strobe system, Figure 3
The figure is a reference diagram showing the relative position change on the screen due to the movement of the object, Figure 4 is a time chart mainly for explaining the peak hold operation of Figure 1,
FIG. 5 is a time chart for explaining the operation using the strobe method, FIG. 6 is a reference diagram showing an example of setting two windows, FIG. 7 is a configuration diagram showing a conventional example of an inspection/discrimination device, and FIG. FIG. 8 is a time chart for explaining the operation of FIG. 7. Code explanation, 1...Object, 2...Conveyor, 3
...TV camera, 4...Lighting device, 5...Position sensor, 6...Image processing device, 7...Amplifier, 8
... Binarization circuit, 9 ... Calculation determination unit, 10 ... Timing control circuit, 11 ... Low pass filter (LPF), 12 ... Peak hold circuit (PH circuit), 13 ... A/D conversion circuit, 14...Arithmetic circuit, 15...Comparison level selection circuit, 16...D/
A conversion circuit, 17... Binary output control circuit, 18...
...PH level discrimination circuit, 19...Standard value output circuit, 21...Window generation circuit, 22...Scanning point coordinate generation circuit, 23...Window setting value storage circuit, 24...PH reset circuit, 25...Reset Timing circuit, 26... Effective screen control circuit, 27... Camera drive synchronization circuit, 31... Imaging device, 32... Video processing and drive circuit, 33...
... Lens, 34 ... Rotating disk, 35 ... Motor,
36... Rotation control circuit, 37... Case, 41...
...Strobe, 42...Strobe firing circuit, 43...
...Strobe firing control circuit, 91...Memory, 92
... Feature extraction circuit, 93 ... Arithmetic processing unit, 94
...Position detection/correction circuit, 95...Setting circuit, P
... TV camera field of view, W, W ₁ , W ₂ ... window.

Claims (1)

[Scope of Claims] 1. Image extracting means that includes a two-dimensional imaging device that images a moving object and extracts a still image of the object, and a window generator that generates at least one window with a predetermined shape at a predetermined position of the image. and binarization level determining means that includes at least a detection unit that detects the gray level of the image within the window area and determines a binarization level according to the gray level, The extraction means extracts at least two consecutive still images with a predetermined time as a reference, the window generation means generates a window at a predetermined position of the temporally previous image, and the binarization level determination means generates a window area. An image binarization method characterized in that a binarization level is determined from the gray level of the image, and a temporally subsequent image is binarized using the determined binarization level. 2. In the image binarization method according to claim 1, the image signal for determining the binarization level is extracted by applying a low-pass filter to the output from the image extraction means. Image binarization method. 3. In the image binarization method according to claim 1 or 2, when the gray level of the image detected by the detection unit exceeds a predetermined range, a separately provided standard value is set. An image binarization method characterized by employing a binarization level.