JPH0630413A - Image binarization circuit - Google Patents

Abstract

PURPOSE:To improve the detection performance of a foreign matter in a free part and to properly identify the free part, a center land and a conductive part in an image binarization circuit for inspecting the wiring pattern of a printed wire board. CONSTITUTION:An area identifying means 21 outputs binarization data obtained by comparing the brightness of an image with a 1st threshold. A threshold setting means 22 sets up a 2nd threshold which is the sane value as the 1st threshold in an area other than the 1st area and sets up the 2nd threshold corresponding to the minimum measured length obtained by radially measuring a length from an optical point in the 1st area up to the end part of the 1st area in the 1st area. A comparing means 23 outputs binarization data obtained by comparing the brightness of the image with the 2nd threshold.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image binarization circuit,
In particular, it relates to an image binarization circuit for inspecting a wiring pattern of a printed wiring board.

When inspecting a wiring pattern of a printed wiring board, an image of the wiring pattern obtained by a video camera or the like is used.
Binarization is performed to facilitate the processing. The binarization circuit that performs this binarization is required to have high performance for detecting foreign matter on the wiring pattern.

[0003]

2. Description of the Related Art FIG. 7 shows an example of a wiring pattern of a printed wiring board to be inspected. As shown in FIG. 7, the printed wiring board 1
Is a conductor portion 2, and is provided with a central land 4 and a donut-shaped air space portion 3 (a portion having no conductor).
Further, under the central land 4, conductors for electrically connecting to other layers are provided. (Not shown).

In the visual inspection of this wiring pattern, an image of the wiring pattern is taken from above the printed wiring board 1 by illuminating from below the printed wiring board 1 with a video camera, and this image is binarized by an image binarization circuit. The conductor 2, the airspace 3, the central land 4, and the bright foreign matter 6 in the airspace are identified from the converted image data.

FIG. 8 is an explanatory diagram of threshold values in a conventional image binarization circuit for pattern inspection. When the printed wiring board 1 is illuminated from below, the alternate long and short dash line ii in FIG.
The brightness of the image on the line is as shown by the solid line in FIG. The conductor portion 2 and the central land 4 have the lowest luminance, and the air space portion 3 has the highest luminance. In addition, since the conductor is provided below the central land 4 for electrical connection with other layers, the area around the central land 4 of the air space portion 3 has a higher brightness than the portion of the air space portion 3 having the highest brightness. There is a low-brightness, mid-brightness portion 5.

In order to distinguish the conductor portion 2, the central land 4 and the air space portion 3, the image data of the wiring pattern may be binarized using the threshold value 7 in FIG. However, with this threshold value 7, the bright foreign matter 6 in the air space cannot be detected.

Therefore, conventionally, a dynamic binarization method has been used in which a neighborhood average of the brightness of an image is obtained and a threshold value is determined from this. In the example of FIG. 8, the threshold value 8 as shown by the chain double-dashed line in FIG. 8 is determined.

[0008]

However, in the conventional dynamic binarization method in which the neighborhood average of the brightness of the image is obtained and the threshold value is determined from this, the air space part 3 of the inspection object as shown in FIG. There was a problem that the level of the threshold value 8 did not change much both inside and outside, and the detection rate of the foreign matter 6 in the air space was insufficient.

The present invention has been made in view of the above points, and is a binary image that has a high foreign matter detection performance in the air space portion and can properly identify the air space portion, the central land, and the conductor portion. It is an object of the present invention to provide a conversion circuit.

[0010]

The invention according to claim 1 is the first
Area 3 and the second area 4 surrounded by the first area 3, the brightness of the image in one area is higher than the first threshold value and the brightness of the image in the other area is the first. In an image binarization circuit for binarizing an image lower than a threshold value, a region identification means 21 for outputting binarized data obtained by comparing the brightness of the image with a first threshold value, and a first Except for the region 3 of, the second threshold having the same value as the first threshold is set, and the first threshold is set.
In the area 3 of No. 2, the second distance, which is a value corresponding to the minimum measurement value obtained by radially measuring the distance from an arbitrary point of the first area 3 to the end of the first area 3. A threshold value setting means 22 for setting a threshold value and a comparison means 23 for outputting binarized data obtained by comparing the brightness of the image with a second threshold value are provided.

According to a second aspect of the invention, the first region 3 and the first region 3 are provided.
There is a second region 4 surrounded by the region 3 and a third region 2 surrounding the first region 3, and the brightness of the image in the first region 3 and the first threshold value are high and low. The relationship is different from the relationship between the brightness of the images in the second area 4 and the third area 2 and the first threshold value, and the second area 4 in the first area 3 is different.
In the image binarization circuit for binarizing an image having a portion 5 having an intermediate luminance between the first threshold and the luminance of the image of the first region 3 around, the threshold setting means 22 The minimum length measurement value and the length measurement direction of the minimum length measurement value and the adjacent length measurement values of two directions are compared, and the predetermined value is added to the length measurement value of the two directions where the minimum length measurement value is adjacent. When the value exceeds the value, the second threshold value is determined by the first function which is the function of the minimum length measurement value, and the minimum length measurement value is the predetermined value added to the length measurement values in the two adjacent directions. When the value is less than or equal to the value, the second threshold value is determined by the second function that is the function of the minimum length measurement value.

According to a third aspect of the present invention, the first and second functions are piecewise linear functions.

According to a fourth aspect of the invention, the first and second functions are logistic functions.

[0014]

According to the first aspect of the invention, in the first region, the second threshold value is set according to the minimum distance from an arbitrary point of the first region to the end of the first region. , A second threshold value that is appropriate for identifying foreign matter in the first region is set.

According to the second aspect of the present invention, the first function or the second function that determines the threshold value depending on which of the second region and the third region is closer to an arbitrary point in the first region. Select a function and set a second threshold of appropriate value.

According to the third aspect of the invention, it is possible to easily set the second threshold value having an appropriate value in the first area.

According to a fourth aspect of the invention, the second area in the first area is
Smooth the change in the threshold of. Therefore, it is possible to set the second threshold value to a more appropriate value.

[0018]

2 is a block diagram of a wiring pattern inspection apparatus to which the present invention is applied. The printed wiring board 1 to be inspected is shown in FIG.
The wiring pattern shown in FIG. As shown in FIG. 2, the printed wiring board 1 to be inspected is illuminated from below with an illumination light source 11, and an image of the wiring pattern is taken from above the printed wiring board 1 with a video camera 12. This image is the image input circuit 13
Is A / D converted in step S4 and stored in the image memory 14 as grayscale image data.

An image binarization circuit 1 which is an embodiment of the present invention.
5, the grayscale image data of the image memory 14 is output as binarized data for identifying the conductor portion 2, the airspace portion 3, the foreign matter 6 in the airspace portion, and the binarized data is output. Memorized in. The central processing unit (CPU) 17 compares the obtained binary image data with the data of the non-defective wiring pattern to determine whether the wiring pattern of the printed wiring board 1 to be inspected is good or bad.

FIG. 3 shows a block diagram of an embodiment of the present invention.
FIG. 4 is an explanatory diagram of the threshold value in this embodiment. Figure 3
In the image binarization circuit, the comparison circuit 31 which is the area identifying means 21 has a fixed threshold value S which is a first threshold value.
L1 and the grayscale image data of the wiring pattern are compared and binary data is output.

As shown in FIG. 4, the threshold value SL1 enables identification of the air space portion 3 which is the first area, the central land 4 which is the second area, and the conductor portion 2 which is the third area. . Therefore, this binarized data is binarized data for identifying the air space portion 3, the central land 4, and the conductor portion 2.

The threshold setting means 22 comprises a length measuring circuit 34 and a threshold determining circuit 35. As will be described later, the length measurement circuit 34 includes, in the air space portion 3, an end portion of the air space portion 3 from an arbitrary point of the air space portion 3, that is, a boundary between the air space portion 3 and the conductor portion 2, or a space between the air space portion 3 and the central land 4. Radially measure the distance to the boundary, and output the minimum measured value.

The threshold value determination circuit 35 outputs SL2 which is the second threshold value. In the air space section 3, a threshold value SL having a value corresponding to the minimum length measurement value output from the length measurement circuit 34.
2 is output, and the threshold value SL2 having the same value as the threshold value SL1 is output except for the air space section 3.

The comparison circuit 36, which is the comparison means 23, compares the threshold value SL2 output from the threshold value determination circuit 35 with the grayscale image data and outputs the binarized data. This 2
Based on the binarized data, it is possible to identify the air space portion 3, the conductor portion 2, the central land 4, and the foreign matter 6 in the air space portion 3 in the grayscale image data.

Next, the operation of this embodiment will be described.
First, the length measurement circuit 34 holds the binarized data obtained by the comparison circuit 31 for identifying the air space portion 3, the central land 4, and the conductor portion 2. A portion having a value lower than the threshold SL1 is referred to as a logic 0 after binarization (hereinafter referred to as "0"), and a portion having a value higher than the threshold SL1 is referred to as a logic 1 after binarization (hereinafter referred to as "1"). Then, the air space portion 3 becomes "1", and the central land 4 and the conductor portion 2 become "0".

Next, regarding the grayscale data of the wiring pattern, the air region 3, the conductor portion 2, the central land 4,
And binarization processing for identifying the foreign matter 6 in the airspace portion 3 is performed. Here, the binarization processing on the alternate long and short dash line i-i in FIG. 7 will be described.

If the point to be binarized is located on the conductor portion 2 on the alternate long and short dash line i or on the central land 4 (the output of the comparison circuit 31 is "0"), the threshold value is determined. Circuit 35
Outputs a threshold value SL2 having the same value as the threshold value SL1. Therefore, the comparison circuit 36 outputs "0". Therefore, the conductor portion 2 or the portion of the central land 4 becomes "0" by the binarization process.

Next, the point to be binarized is the one-dot chain line i-
The case where the data is in the air space section 3 on i (the output of the comparison circuit 31 is “1”) will be described. In this case, the threshold value SL2 is set according to the position of the point at which the binarization process is performed, and the binarization process is thereby performed.

In the length measurement circuit 34, the distance from the point where the binarization processing is performed to the boundary with the central land 4 or the boundary with the conductor portion 2 at the end of the air space portion 3 is shown in FIG. As described above, the length is measured in 16 directions radially, and the length measurement result is output.
The minimum length measurement value at this time is LC, the length measurement value in the direction adjacent to the length measurement direction of LC is LR, and the length measurement value in the direction adjacent to the length measurement direction of LC is counterclockwise. LL.

In the threshold value determining circuit 35, the LC, L
The center land 4 is the point where binarization processing is performed using R and LL.
And the conductor portion 2 are judged to be closer to each other, and a first function or a second function for determining the threshold value SL2 is selected according to the result of the judgment, and the threshold value SL2 is selected according to the selected function. To decide.

When the following conditions are satisfied, it is determined that the point where the binarization processing is performed is close to the central land 4.

In LL> LC + α and LR> LC + α −−−− α, the point of performing the binarization processing is that the central land 4 and the conductor portion 2 are
So that you can correctly determine which of
Set to an appropriate value. When the condition of is satisfied,
The value of the threshold value SL2 is determined by the following equation which is the first function.

SL2 = SL1 + β (LC-W) ----- where β is the slope coefficient of the threshold value SL2, and is the slope of the brightness of the intermediate brightness part 5 around the land 4 shown in FIG. Equal value. Further, W is a fixed value smaller than the size of the airspace portion 3, and SL2 is set to an appropriate value.

However, when LC <W, SL2 = SL1
And when SL2> SLMAX, SL2 = SLMAX
And The relationship between LC and SL2 thus obtained is shown in FIG. This function is a piecewise linear function. Threshold SL
2 can be easily calculated by this piecewise linear function.

On the other hand, when the condition is not satisfied, it is determined that the point where the binarization processing is performed is close to the conductor portion 2, and the second
The threshold value SL2 is determined by the following equation that is a function of

SL2 = SL1 + γ (LC-W) ----- where γ is the slope coefficient of the threshold value SL2, and is set to a value equal to the brightness slope near the boundary with the conductor portion 2 shown in FIG. . However, when LC <W, SL2 = SL1 and S
When L2> SLMAX, SL2 = SLMAX.
As shown in FIG. 4, the slope of the brightness near the boundary with the conductor portion 2 is larger than the slope of the brightness of the portion 5 having the intermediate brightness, and therefore, there is a relation of γ> β. The threshold value SL2 can be easily calculated by this zonal linear function.

As described above, in the threshold value determining circuit 35, when the point to be binarized is close to the central land 4, the threshold value SL2 is determined by the equation which is the first function. When the point where the binarization processing is performed is close to the conductor portion 2, the threshold value SL2 is determined by the equation that is the second function.

The threshold value SL2 determined by the threshold value determining circuit 35 is shown by a chain line in FIG. As shown in FIG. 4, the threshold value SL2 is a value smaller than the brightness of the grayscale image data by a predetermined value in a portion where the distance from the end of the air space portion 3 is W or more, and the line of the brightness of the grayscale image data. Are set parallel to each other. In addition, the distance from the end of the airspace 3 is W
In the inside portion, the same value as the threshold value SL1 is set.

Therefore, the normal pattern portion of the air space portion 3 becomes "1" by the binarization by the comparison circuit 36. On the other hand, the brightness of the foreign matter 6 in the air space 3 is determined by the set threshold value SL.
Since it becomes lower than 2, by the binarization by the comparison circuit 36,
It becomes "0". Therefore, the foreign matter 6 in the air space part 3 is not
Can be correctly identified as a part of the normal pattern of.

As described above, in the present embodiment, the first function or the second function for determining the threshold value SL2 is selected according to the position in the air space 3, and the threshold value SL having an appropriate value is selected.
Since it is possible to set 2, it is possible to detect foreign matter in the air space portion 3 with a high probability, and it is possible to properly identify the air space portion 3, the central land 4, and the conductor portion 2.

The function for determining the threshold SL2 is
The logistic function shown in FIG. 6 (B) and the following equation can be used instead of the piecewise linear function shown in FIG. 6 (A).

Y = C · (1 / (1 + exp ((− x + A) · B))) −−− In this case, the change of the threshold value SL2 becomes smooth,
The threshold value SL2 can be set to a more appropriate value.

[0043]

As described above, according to the first aspect of the invention, the second value of the value suitable for identifying the foreign matter in the first area is set.
Since the threshold value can be set, the foreign matter in the first region can be detected with high probability, and the first region and the second region can be properly discriminated. With the features of.

According to the second aspect of the present invention, the first function or the second function for determining the threshold value is selected in accordance with the position in the first area, and the second function having an appropriate value is selected. Since the threshold value can be set, foreign matter in the first area can be detected with high probability, and the first area, the second area, and the third area can be properly identified. it can.

According to the third aspect of the invention, it is possible to easily set the appropriate second threshold value in the first region.

According to the fourth aspect of the invention, since the change of the second threshold value in the first region can be smoothed, the second threshold value should be set to a more appropriate value. You can

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a configuration diagram of an inspection apparatus to which the present invention is applied.

FIG. 3 is a configuration diagram of an embodiment of the present invention.

FIG. 4 is an explanatory diagram of threshold values in the present embodiment.

FIG. 5 is an explanatory diagram of a length measuring method in a length measuring circuit.

FIG. 6 is an explanatory diagram of a function that determines a threshold value.

FIG. 7 is a diagram showing an example of a printed wiring board to be inspected.

FIG. 8 is an explanatory diagram of threshold values in a conventional circuit.

[Explanation of symbols]

 1 Printed Wiring Board 2 Conductor Part 3 Air Region Part 4 Central Land 5 Part of Intermediate Luminance 11 Illumination Light Source 12 Video Camera 13 Image Input Circuit 14 Image Memory 15 Image Binarization Circuit 16 Binary Image Memory 17 Central Processing Unit (CPU) 21 area identifying means 22 threshold setting means 23 comparing means 31 comparing circuit 34 length measuring circuit 35 threshold determining circuit 36 comparing circuit

Claims (4)

[Claims] 1. The brightness of the image in one of the first area (3) and the second area (4) surrounded by the first area (3) is a first threshold value. In an image binarization circuit for binarizing an image having a higher image brightness in the other region than the first threshold value, the image brightness is obtained by comparing the image brightness with the first threshold value. Area identification means (21) for outputting binarized data and a second threshold value which is the same value as the first threshold value except for the first area 3 is set. In the area (3), the distance from an arbitrary point of the first area (3) to the end of the first area (3) is measured in a radial direction, and the minimum length measurement value is obtained. Threshold setting means (22) for setting a second threshold value which is a value, and comparison means (22) for outputting binarized data obtained by comparing the luminance of the image with the second threshold value. 23) and An image binarization circuit characterized by: 2. A first region (3), a second region (4) surrounded by the first region (3), and a third region (which surrounds the first region (3) ( 2) and the relationship between the brightness of the image in the first area (3) and the first threshold is higher or lower than that of the second area (4) and the third area (2). Unlike the relationship between the image brightness and the first threshold value,
A portion of the first area (3) having an intermediate brightness between the first threshold value and the brightness of the image of the first area (3) around the second area (4). In the image binarization circuit for binarizing an image with (5), the threshold value setting means (22) is adjacent to the minimum length measurement value and the length measurement direction of the minimum length measurement value. If the minimum length measurement value exceeds the value obtained by adding a predetermined value to the adjacent length measurement values in the two directions, the first length measurement function that is the function of the minimum length measurement value is compared. The second threshold value is determined by a function, and when the minimum length measurement value is less than or equal to the value obtained by adding a predetermined value to the length measurement values in the two adjacent directions, the second length measurement function is the minimum length measurement value. 2. The image binarization circuit according to claim 1, wherein the second threshold value is determined by a function of. 3. The image binarization circuit according to claim 2, wherein the first and second functions are piecewise linear functions. 4. The image binarization circuit according to claim 2, wherein the first and second functions are logistic functions.