JP3391163B2 - Circular container inner surface inspection device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention inspects the inner surface of a circular container such as a beer can conveyed by a conveyor,
The present invention relates to a circular container inner surface inspection device as an image processing device for detecting deformation, foreign matter, dust, scratches, etc. of a container. In the drawings, the same reference numerals denote the same or corresponding parts.

[0002]

2. Description of the Related Art FIG. 2 is an explanatory view of a high-intensity part when an aluminum can container for beer is observed from above, as an example. FIG. 2A is an upper surface (image) view of the can container and FIG. ) Is a side sectional view. 102 is a container, 101 is this container 10
A ring-shaped illuminator that illuminates 2 from above, 103 is a high-intensity part at the mouth, and 104 is a high-intensity part at the bottom. By thus irradiating the inner surface of the container 102 with light rays by using the ring illuminator 101, the mouth portion and the bottom portion of the inner surface of the container 10 are respectively irradiated.
High-luminance portions such as 3,104 occur. This is particularly noticeable when the inner surface of the container has a metallic luster such as a can.

FIG. 3B is a top view image of the container 102 (see FIG.
It shows the density change on the scanning line Q-Q1 with respect to (A)), but is classified into five regions W1 to W5 according to the characteristics of the density change. The first region W1 is the mouth high-intensity part 10
3, the second region W2 is the middle upper part of the side surface of the container where the change in concentration is relatively small, and the third region W3 is darker than the other regions because the light rays from the illumination 101 described in FIG. It is the lower part of the side surface, the fourth region W4 is the bottom high-intensity part 104, and the fifth region W5 is the bottom.

Conventionally, windows are provided in the respective areas W1 to W5, and a threshold value for detecting a defect of black stain (black spot) or white stain (white spot) is set according to the optical characteristics of the regions. Was. As a method of detecting such a minute defect, for example, an 8-bit multi-value grayscale image signal obtained by A / D converting an analog video signal (analog grayscale image signal) obtained by scanning a target image. There is known a method of binarizing the signal with a predetermined threshold value, a differentiation method of differentiating the video signal to extract a defect signal, and the like. In the case of this differentiation method, a differential signal is also generated in the contour portion of the outer shape of the object, but either one of the positive direction pulse and the negative direction pulse is generated by the differentiation in the contour portion, while the positive direction pulse is generated in the minute defect portion. The defect can be extracted by utilizing the fact that the negative pulses are generated at the same time.

That is, a value P (i, j) at a target point (coordinate values X = i, Y = j) of a signal P (X, Y) obtained by differentiating an analog grayscale image signal based on raster scanning,
The value P (i-α, at a point separated by a predetermined minute pixel number α, β from the point of interest on the X-direction scanning line, respectively.
j) and P (i + β, j),

[0006]

## EQU00001 ## P (i, j) -P (i-.alpha., J)> TH1 ... (1) P (i + .beta., J) -P (i, j)> TH1 ... (2) (however, If TH1 is a predetermined threshold value (positive value) and there is a relation of the above equations (1) and (2), the binarization function value PD (i, j) for defect detection at this focus point = The point of interest is 1 as a black level defective point, and in other cases, PD (i, j) = 0 is set as the point of normality.

Next, a conventional method for detecting the depression of the side surface of the container will be described. FIG. 3C shows the density on the scanning line Q′-Q1 ′ passing through the recess 105 when the recess 105 is formed on the side surface of the container as shown in the top image of the container 102 (FIG. 3A). Show changes. FIG. 4 is FIG. 3 (B)
The determination thresholds THP1 to THP4 are assigned corresponding to the respective window areas (W1 to W5). Since the threshold value THP3 is common to the windows W3 and W4, there are four areas in FIG.

FIG. 5 shows the absolute value of the difference between the density values of FIG. The depression 105 is detected as a defective pixel because the density change amount caused by the difference is larger than the threshold value THP2. The defect determination at this time is performed by the following equation (3).

[0009]

## EQU00002 ## | P (i, j) -P (i-.alpha., J) |> THPn (3) where P (i, j): Point of interest on the scanning line (coordinate value X = i, Y)
= Pixel density at j), P (i-α, j): Pixel density at a point distant from the point of interest on the X-direction scanning line by a small number of pixels α, THPn: Region of the point of interest (number is n Yes) decision threshold.

FIG. 6 is a hardware block diagram for detecting a defective pixel according to the equation (3). The inspection image in the frame memory 1 is radially read from the radiation address generator 4, and the FIFO 21 is used in the above equation. The image data is delayed by an amount corresponding to the number α of pixels of
The difference value between (i, j) and P (i-α, j) is obtained, and the absolute value conversion circuit 25 sets the difference value as an absolute value, and the comparator 2
The defective pixel is compared with the threshold value at 6 and the defective pixel is output as a binarized output. The counter 27 expresses the distance from the container center in the scanning direction, and supplies the judgment threshold value THPn of each window region to the comparator 26 by the threshold value table 23.

[0011]

The recess 10 in FIG. 4 is to be solved.
No. 5 occurred in the region where the concentration change was relatively small even on the inner surface of the container, and the judgment threshold value THP2 in the recess 105 portion in FIG. 5 can be set to a smaller value than in other regions. . However, when the container recess 105 occurs at a position lower than this position, the determination threshold value becomes a region of THP3, which is a region where the concentration change is originally large, and therefore the sensitivity of the recess detection is considerable. There was a problem that it decreased to.

Further, FIG. 7 shows an example of a high-intensity portion on the inner surface of a circular container having a projecting portion at the bottom. As shown in FIG. 7 (B), the bottom surface of the container is molded to form a projecting portion 102a. In the case where the bottom surface of the container is reflected, the reflection of the bottom surface of the container becomes more complicated than that of the case where the processing of the bottom surface of the container is simple, and the plurality of bottom high brightness portions 10
4-1, 104-2 appear, the density change becomes more complicated, and there is a problem that the threshold value that can be set as the THP3 is inevitably lower in sensitivity.

Therefore, according to the present invention, as described above, the height of the container, which has been difficult to detect in the past, occurs midway from the bottom of the container, that is, the inner surface of the circular container for inspecting the recess on the lower side of the container with high accuracy. The challenge is to provide.

[0014]

In order to solve the above-mentioned problems, the apparatus for inspecting the inner surface of a circular container according to claim 1 has a ring-shaped illuminating means (ring illuminator 101) coaxial with an axisymmetric circular container (102). After illuminating the inner surface side of this circular container via the camera, the illumination surface of this circular container is imaged from this axial direction via a TV camera, and the image is obtained by scanning an imaging screen containing concentric images of the imaged circular container. The multi-value grayscale image signal (PO) as an A / D conversion signal of the grayscale image signal is stored in the frame memory (301) as image data on the screen corresponding to the imaging screen, and (image edge detection circuit 314, The center position (O) of the circular container on the screen of the image data of this frame memory is detected (via the position shift amount determination circuit 315), and (radiation address generator 3
The inner surface of the circular container for detecting a defect in the circular container by scanning the image data of this screen a plurality of times along the radial scanning line passing through the center of the circular container, changing the angle of the radial scanning line each time. The inspection apparatus is a minimum density value within a predetermined width section (reference pixel search section d2) at a predetermined distance (d1) counted from the center position of the circular container on the radial scanning line by the number of pixels. Pixels are detected and set as reference pixels (Pk), and a predetermined distance (d3, d) on the radial scanning line is counted from the reference pixels.
5, etc.) and for each of a plurality of measurement sections (first, second measurement sections, etc.) having a predetermined width (d4, d6, etc.), the reference pixel of the density value of each pixel in the measurement section. Image density integrated value (S1,
S2), and when the difference (| S1−S2 |) between the image density integration values between adjacent measurement sections exceeds a predetermined allowable amount, it is determined that the container has a dent defect (defect detection). A circuit 312 and a defect detection determination circuit 313) are provided.

According to a second aspect of the present invention, in the inspection apparatus according to the first aspect, the permissible amount can be variably selected according to the angle of the radial scanning line. Further, in the inspection apparatus according to claim 3, in the inspection apparatus according to claim 1 or 2, the distance counted by the number of pixels from the center position of the circular container of each pixel used for the determination on the radial scanning line is It should be corrected according to the angle of the scanning line.

The principle of the present invention will now be described. FIG. 1 is a diagram showing the principle of the present invention. FIG. 1 is a diagram showing a change in shading of an image corresponding to the enlarged portion M of FIG. 4 for a container having a bottom shape as shown in FIG. 7, and (A) to (F) show the order of processing according to the present invention. Show. That is, in (A), the section d2 is positioned (reference pixel search section is set) based on the calculated distance d1 from the container center O, and in (B), the pixel of the lowest density value in the section d2 ( (Reference pixel)
Calculate Pk. Next, in (C), the reference pixel Pk
The first measurement section d4 is set by the distance d3 from
In (D), the difference between the density value of each pixel in the first measurement section d4 and the density value of the reference pixel Pk is integrated in this measurement section to calculate the image density integration value S1 of the first measurement section. To do. Next, in (E), the distance d from the reference pixel Pk
5, the second measurement section d adjacent to the first measurement section d4
6 is set, and in (F), the image density integration value S2 is calculated by integrating the difference between the density value of each pixel in the second measurement section d6 and the density value of the reference pixel Pk.

After that, similarly, if necessary, the adjacent measurement sections are sequentially set and the image density integration value is calculated up to the n-th measurement section (here, the (n-1) th measurement section and the nth measurement section are respectively calculated. The image grayscale integration values are S _n-1 and S _n ). afterwards,
Amount of difference in the image density integral value between adjacent measurement sections |
S1-S2 |, ···, | S n-1 -S n | is calculated and
The presence or absence of defects is determined by comparing with the allowable difference amount.

It should be noted that the parameters for setting the measurement sections such as d3 to d6 at the time of initial setting are usually required to be set so that the image density integral values are almost equal between the adjacent measurement sections.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the present invention will be described. FIG. 8 is a block diagram showing a configuration of a main part of the circular container inner surface inspection apparatus according to the present invention. PO in the figure
Is a grayscale image signal obtained by A / D converting a video signal obtained by raster scanning a screen of a TV camera (not shown), and 301 is a multivalued grayscale image signal PO to which a multivalued screen is input. Frame memory to store as data, 3
Reference numeral 03 is a raster address generator for generating a raster address for this frame memory.

Reference numeral 304 denotes a radial address generator for generating an address for the frame memory 301 for radial image scanning, and reference numeral 302 stores a ring-shaped mask pattern for each window as shown in FIG. 3B. Window memory, 305 is this window memory 30
2 is a raster address generator for generating a raster address similarly to the generator 303, and 306 is a radial address generator for similarly generating an address for radial scanning with respect to the window memory 302 similarly to the generator 304. And these generators 303, 305, 304, 30
It is possible to switch the generation of the raster address and the radial address by switching the switch between No.

A window gate circuit 307 masks the multi-value grayscale signal PO or the image signal 301a read from the frame memory 301 with the mask pattern data from the window memory 302, and the image signal PO only in the designated window area. Alternatively, it is a circuit which allows the image signal 301 a read from the frame memory 301 to pass.

Image edge detection circuits 308 and 314 are
It has a function to detect the edge of the image, specifically the outer edge (outer peripheral point) and inner edge (inner peripheral point) of the ring-shaped high-intensity part. In this case, the input image signal is used to detect the position of the target image and The image is binarized with a predetermined threshold value for the circularity inspection, and the coordinates of the rising point and the falling point of the binarized signal are stored in the internal memory as image edges. Reference numeral 309 denotes a circuit for inspecting the circularity of the coordinate values of the outer peripheral points or the inner peripheral points detected by the image edge detecting circuit 308.

An image edge detection circuit 314 is provided for displaying a window at a correct position 315 with respect to the target image.
Is a circuit for detecting the deviation between the center position of the actual target image detected by inputting the latest multi-value grayscale image signal PO and the center position of the preset window. 31
0 inputs the image signal 301a read from the frame memory 301 by the raster scanning of the frame memory 301 through the window gate circuit 307, and the defect detection circuit 311 for detecting a defective pixel such as a black dot detects this. It is a defect detection determination circuit that aggregates defective pixels and determines a defect.

Reference numeral 312 denotes a frame memory 30 as described later.
The image signal 301a read from the frame memory 301 by the radial scan of 1 is transmitted to the window gate circuit 30.
A defect detection circuit 313 for inputting via 7 to detect a defective pixel having a dent is a defect detection determination circuit for totaling the detected defective pixels to determine a defect. Also, 31
Reference numeral 9 is a circuit for inputting the judgment results of the circularity judgment circuit 309 and the defect detection judgment circuits 311 and 313 to make a comprehensive judgment,
Reference numeral 320 denotes an output circuit that outputs a pass / fail according to the output determination signal of this comprehensive determination circuit 319.

In FIG. 8, the inspection image is inputted from the multi-value grayscale image signal PO and stored in the frame memory 301, and the window gate circuit 307 masks the outside of the region of interest of the image to the image edge detection circuit 314. Supplied. The pattern of the attention area of the image is preset in the window memory 302. The image edge detection circuit 314 fixes the input multi-value grayscale image signal PO 2
Quantize, and 0 → 1 or 1 → in one scanning line of the binarized signal
Change point coordinates of 0 (referred to as an image edge point) are detected and stored, and similarly, an image edge point is detected and stored for each scanning line. This image edge point information is sent to the position shift amount determination circuit 315, where the position shift within the screen of the circular container to be inspected is calculated.

FIG. 9 shows one method for determining the position of the circular container. In FIG. 9, the upper edge inspection area 21 is shown.
1 and the left edge inspection area 212 are set in a portion corresponding to the mouth high brightness portion (103 in FIG. 2) of the circular container. The image in which the mouth high-intensity part is binarized corresponds to the fixed binary image 210 of the container in FIG. 9. The inspection area 21
In 1 and 212, the image edge is detected as shown by the dotted line in FIG. 9, the position reference point 213 which is the intersection thereof is determined, and the processing coordinate system of this container is determined. As a result, the position of the container on the screen is determined, and the coordinates of the center of the container can be the coordinates to which the fixed offset amount from the position reference point 213 is added.

FIG. 10 is a view showing another method for determining the container position. As shown in FIG.
04, an upper edge inspection area 112 and a left edge inspection area 113 are set, and a position reference point 114 is calculated as shown in FIG.
It can be calculated as coordinates obtained by adding a fixed offset amount to 14.

When the calculation of the container center is completed in this way, the raster address generator 3 is added to the frame memory 301.
03, the scanning coordinates are sent, and the multi-value grayscale image signal corresponding to the coordinates is sent by the window gate circuit 307 to the image edge detection circuit 308 while being limited to only the region of interest. By similar processing, the image edge point coordinates are output to the circularity determination circuit 309. Here, it goes without saying that the image edge detection circuits 308 and 314 have different thresholds when binarizing the image because the shade of the image of interest is different.

The circularity determination circuit 309 determines from the edge point coordinates of the outermost shape of the container how close the circular container is to a perfect circle, and mainly inspects the deformation and dent of the container mouth, and the determination result Is output to the comprehensive determination circuit 319. The defect detection circuit 310 outputs the binary image data obtained by the conventional differential binarization method when the inner surface of the circular container is raster-scanned to the defect detection determination circuit 311 as a defective pixel signal. The number of pixels of the binary image data is counted, and if the number of pixels exceeds a preset allowable amount, a defective signal is output to the comprehensive determination circuit 319.

Next, the core part of the present invention will be described. With respect to the frame memory 301 of FIG. 8, a radiation address with the center of the container as the scanning center is generated by the radiation address generator 304, and the multi-value grayscale image signal of the pixel corresponding to the coordinates is sent to the window gate circuit 307. On the other hand, if necessary, the pattern in the window memory 302 limits the image signal of only the region of interest and outputs the image signal to the defect detection circuit 312.

The defect detection circuit 312 temporarily stores the radiation address and the image data corresponding to the radiation address. FIG. 11 shows an example of image data based on such one scan,
The figure (A) shows the density cross section of the image on this scanning line, and the figure (B) is a table showing the relationship between the radiation address X and the image data of the shaded area in the figure (A). Three
Image data is stored in 12 as such a table. In the following, since the concentration cross section is symmetrical with respect to the center of the container, only the shaded portion of FIG. 11A will be described. However, in the present invention, the remaining half (non-shaded portion) of FIG. 11A is also described. It goes without saying that the same inspection is performed.

The defect detection circuit 312 has a built-in CPU,
The determination according to the present invention is performed based on the table of FIG. 11B. In the present embodiment, the measurement section for calculating the image density integral value is set to two sections, and the measurement section is determined by d in FIG.
It is assumed that the parameters 1 to d6 have already been given. The CPU makes a determination according to the following procedure.

In the table of FIG. 11B, the address d1
The pointer of the process is advanced to the position indicated by (that is, the distance from the container center O to the start point of the reference pixel search section, which is counted in the number of pixels). The address and the density value of the pixel (reference pixel) Pk at the lowest density point from the position of the address d1 until counting d2 (that is, the reference pixel search section) are stored.

After the pointer is once placed at the position of the reference pixel Pk, the pointer is advanced by d3 and the density value of the reference pixel Pk is calculated from the density value of each pixel in the period for counting d4 from that point (that is, the first measurement section). Add the result of subtracting,
The sum is calculated and used as the image density integration value S1 of the first measurement section. The result of subtracting the density value of the reference pixel Pk from the density value of each pixel in the period for counting d6 from that point (that is, the second measurement section) after the pointer is once placed on the reference pixel Pk portion Is added and the sum is calculated,
The image density integration value S2 in the second measurement section is used.

.Vertline.S1-S2.vertline. Is calculated as .DELTA.S. If ΔS does not exceed the preset allowable amount, it is regarded as good,
The other cases are considered defective. The quality of is output to the defect detection determination circuit 313. Reference numeral 105 in FIG. 12 is an example of the recess of the container, and FIG. 13 shows the concentration cross section. When the product is non-defective, the image density integration values S1 and S2 in the first measurement section and the second measurement section are substantially equal to each other, but if the container has a recess 105, S1 and S2.
13 are S1 'and S2' in FIG. 13, respectively. As shown in FIG. 12, the reflection condition of the light rays in the bottom high-intensity portion changes, and the density in the S1 'area including the bottom high-intensity portion 104 tends to decrease. , The area is set with the lowest density point Pk as a reference, and the vicinity of the lowest density point is the S1 ′ area, and therefore S
In the 2'region, the density does not change or tends to increase due to reflection, so that the difference ΔS between the image density integral values of the first measurement section and the second measurement section becomes large, which is a defect.

In the defect detection determination circuit 313 of FIG. 8, the defect detection frequency of each radial scan is determined by the defect detection circuit 3.
When the number of detection times exceeds 12, the output is judged to be defective and is output to the comprehensive judgment circuit 319. In the comprehensive judgment circuit 319, each judgment circuit 30 in the preceding stage is
If the determination results of 9, 311 and 313 are all good, a good signal is output; otherwise, a bad signal is output circuit 32.
Output to outside the device via 0.

When the sections for calculating the image density integrated value are sequentially provided up to the n-th section, the image density of each of the third, fourth, ..., (n-1), and n-th measurement sections. If the integrated values are S3, S4, ..., S _n-1 and S _n , respectively, in the present invention, the difference between the image density integrated values of the adjacent measurement sections, that is, | S2-S3 |, | S3-S4 | , ・ ・ ・, | S _n-1
-S _n | is taken as ΔS, and this ΔS is compared with the set allowable value. If ΔS does not exceed the set allowable value, it is judged as good, and otherwise it is judged as defective.

Since each pixel is square, the pixel resolution of the radial address varies depending on the radial scanning angle. For example, when scanning in the 45 ° direction, when scanning horizontally or vertically. Compared with √2 times. Therefore, if the threshold value for ΔS and the parameters for determining the sections of d1 to d6 are normalized according to the scanning angle, the defect can be detected with higher accuracy.

[0039]

According to the present invention, an image of the inner surface of a circular container is radially scanned from the center of the circular container, and a pixel having the minimum density value is detected within a section designated by the distance from the center of the container to obtain a reference. An image density integration value is calculated as the sum of the density differences between the pixel density of each of a plurality of measurement sections specified by the distance from the reference pixel and the density of the reference pixel, and the image density integration between adjacent measurement sections is performed. It is determined whether there is a dent defect in the container by checking whether the difference between the values exceeds a predetermined allowable value. Even if the mark is applied, it is possible to determine the dent defect at the bottom of the container with high accuracy.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of the principle of an inspection method according to the present invention.

FIG. 2 is a diagram showing an example of a high-intensity part on the inner surface of a circular container.

FIG. 3 is an explanatory diagram of a change in concentration on a radial scanning line on the inner surface of a circular container and window division.

FIG. 4 is a diagram showing an example of setting a density distribution on a radial scanning line and a binarization threshold value.

FIG. 5 is a diagram showing an example of comparison between a density difference value on a radial scanning line and a binarization threshold value.

FIG. 6 is a block diagram of a conventional inspection device.

FIG. 7 is a diagram showing an example of a high-intensity portion on the inner surface of a circular container having a protrusion on the bottom.

FIG. 8 is a block diagram showing a main configuration of an inspection apparatus as an embodiment of the present invention.

FIG. 9 is a diagram showing an example of position detection processing of a circular container.

FIG. 10 is a diagram showing another example of position detection processing for a circular container.

FIG. 11 is a diagram showing a table of image data at the time of radial scanning as one embodiment of the present invention.

FIG. 12 is a diagram showing an example of changes in a high-intensity part at the bottom of a circular container having a recess.

FIG. 13 is a diagram showing an example of a difference in the image grayscale integration value according to the present invention depending on the presence or absence of a depression.

[Explanation of symbols]

O container center Pk reference pixel d1 Distance from container center to reference pixel search section d2 reference pixel search section d3 Distance from the reference pixel to the first measurement section d4 1st measurement section d5 Distance from the reference pixel to the second measurement section d6 Second measurement section S1, S1 'Image density integration value of the first measurement section S2, S2 'Image density integration value of the second measurement section 101 ring illuminator 102 containers 103 mouth high brightness part 104, 104-1, 104-2 Bottom high brightness part 105 dent W1-W5 windows 110 Bottom part 111 Bottom low brightness part 112 Upper edge inspection area 113 Left edge inspection area 114 position reference point 210 Fixed Binary Image of Container 211 Upper edge inspection area 212 Left edge inspection area 213 Position reference point PO multi-value grayscale image signal 301 frame memory 302 window memory 303 Raster address generator 304 Radiation Address Generator 305 Raster address generator 306 Radiation address generator 307 Window gate circuit 308 Image edge detection circuit 309 Circularity judgment circuit 310 Defect detection circuit (raster) 311 Defect Detection Judgment Circuit 312 Defect detection circuit (radiation) 313 Defect detection judgment circuit 314 Image edge detection circuit 315 Position shift amount determination circuit 319 Comprehensive judgment circuit 320 output circuit

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-6-94645 (JP, A) JP-A-6-160289 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 21/84-21/958

Claims (3)

(57) [Claims] 1. An inner surface side of this circular container is illuminated through a ring-shaped illuminating means coaxial with an axially symmetric circular container, and an illumination surface of this circular container is imaged from this axial direction through a TV camera, and this imaging is performed. A multi-value grayscale image signal as an A / D conversion signal of a grayscale image signal obtained by scanning an imaging screen including concentric circular images of a circular container is stored in a frame memory as image data on the screen corresponding to the imaging screen. While storing, the center position of the circular container on the screen of the image data of this frame memory is detected, and the angle of the radial scanning line is changed multiple times along the radial scanning line passing through the center of this circular container. A circular container inner surface inspection device that scans the image data on this screen to detect defects in the circular container, which is counted in advance from the center position of the circular container on this radial scanning line by the number of pixels. A pixel having the minimum density value is detected within a predetermined width section at a predetermined distance and is used as a reference pixel. Similarly, the pixel on the radial scanning line is counted from the reference pixel at a predetermined distance. Then, for each of a plurality of measurement sections having a predetermined width, the image density integral value obtained by summing the difference between the density value of each pixel in the measurement section and the density value of the reference pixel is calculated, and adjacent measurement sections are When the difference between the image grayscale integration values of is greater than a predetermined allowable amount,
An apparatus for inspecting an inner surface of a circular container, comprising means for determining that the container has a dent defect. 2. The inspection apparatus according to claim 1, wherein the allowable amount can be variably selected according to an angle of the radial scanning line. 3. The inspection apparatus according to claim 1, wherein the distance counted by the number of pixels from the center position of the circular container of each pixel used for the determination on the radial scanning line is the angle of the radial scanning line. The inner surface of the circular container is inspected according to the above.