JP2821044B2 - Setting method and setting device for binarization threshold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for setting a threshold for binarizing an image to be processed, which is used, for example, in a wiring pattern inspection of a printed circuit board.

[0002]

2. Description of the Related Art In image processing, a process of binarizing a grayscale image (multi-valued image) having a gradation value is a typical method of extracting an object in an image from a background. In this binarization process, a method of determining an appropriate binarization threshold is particularly important. Many methods have been proposed for determining the binarization threshold. For example, a method is employed in which the number of pixels included in the grayscale image is obtained as a frequency distribution for each gradation value, and the gradation value that minimizes the frequency is determined as a binarization threshold.

FIG. 8 (a) shows an example thereof.
In the inspection of a wiring pattern of a printed circuit board, the intensity of light reflected from the board is converted into a signal having an 8-bit gradation value, and the frequency distribution for the gradation value of the pixel is examined (histogram). Mountain occurring on the high side of the gradation value indicates the presence of a high wiring pattern reflection strength, low mountain occurring on the side is low reflection intensity through holes (through holes) 及
And the presence of a substrate . And when it is desired wiring pattern to obtain a binarized data small tone value T ₁ of the frequency of the reflected intensity is employed as a binarization threshold.

[0004]

However, as will be described later, since the wiring pattern inspection is performed using light transmitted through the through holes of the substrate, the substrate is mounted on a transparent stage such as glass. Are often inspected. In such a case, light may be reflected by the stage not only from the substrate, but also at a portion where the substrate is not mounted, or through a through hole of the substrate.

[0005] The reflection by this stage generates reflected light of a certain intensity, although not as much as that of the wiring pattern. Therefore, as shown in FIG. 8B, a mountain which is parasitic on the curve of FIG. 8A is observed. (The broken line shows the curve of FIG. 8A). Then gradation value frequency is less reflective intensity T _2, and the larger than the gradation value T ₁ to be originally set as the binarization threshold, to optimize the binary image of the wiring pattern on the substrate There was a problem that it was not possible.

The present invention has been made to solve the above problem, and eliminates the influence of light reflected by a stage on a histogram at a portion where a substrate is not mounted or through a through hole. It is an object of the present invention to obtain a method and an apparatus for setting a binarization threshold that can obtain an optimal binarization threshold.

[0007]

According to the present invention, there is provided a method for setting a binarization threshold value comprising the steps of: (a) having first and second main surfaces and a through hole, having a relatively low reflectance, and providing a light shielding property; A substrate having a pattern having a relatively high reflectance on the first main surface, the substrate being placed on a stage, and (b)
By optically reading the substrate, of the first main surface and the stage, the substrate is not placed.
Board signal showing the area and the image of the through hole ,
Obtaining a Hall signal indicating the image of the serial area and the through hole. And (c) the area and the front of the substrate signal.
Serial image of the through-hole to obtain a correction signal Lima disk treated by the Hall signal, the first from; (d) the correction signal
A histogram relating to the reflection intensity of the main surface is created, and (e)
Based on the shape of the histogram ,
A binarization threshold for identifying the pattern by the value conversion is set.

Preferably, the stage is translucent, and in (b), (b-1) irradiating the first main surface with first light from a first light source; -2) The above territory
Receiving reflected light of the first light reflected by the stage through the area and the through hole and by the first main surface; and (b-3) intensity of the reflected light. Is converted into an electric signal to obtain the substrate signal. On the other hand, (b-4) second
Irradiating the second main surface with the second light from the light source of (b-
5) receiving the transmitted light of the second light transmitted through the through hole or the region, and (b-6) converting the intensity of the transmitted light into an electric signal to obtain the hole signal.

Alternatively, in the above (b), (b-7)
Light is irradiated to the first main surface from the light source, (b-8) wherein
The stage through the area and the through-hole,
Was by receiving the reflected light reflected by the first major surface to obtain the substrate signal into an electric signal the intensity of the reflected light (b-9). (B-10) The hall signal is obtained by discriminating the substrate signal with a threshold value.

Preferably, in the above (c),
(C-1) binarizing the hall signal to obtain a binarized hall signal designating the through hole and the area;
2) The portion corresponding to the through-hole and the area specified by the binarized Hall signal in the substrate signal is set to a predetermined value to obtain the correction signal.

More preferably, prior to (c-1), (c-3) two-dimensionally expanding the hole signal to obtain a hole image, and (c-4) expanding the hole image. To get an enlarged hall image. And (c-
5) A signal corresponding to the enlarged hall image is used as the hall signal again.

[0012] setting device binarization threshold according to the present invention comprises a stage for mounting a substrate having a through hole and a pattern thereon, reading means for reading said substrate to optically obtained by said reading means the substrate and the vinegar
An image of a region that is not placed in the substrate of stage, the through hole and the substrate signal by converting said region into respective electrical signals, and converting means for obtaining a Hall signal, the <br/> substrate signal The image of the area and the through hole
Calculating means for obtaining a serial correction signal Lima disk treated by the Hall signal, a histogram creating means for creating a histogram from said correction signal, based on the shape of the histogram
Te, and a threshold setting means for setting a binarization threshold to identify the pattern by binarizing the substrate signal.

[0013]

According to the present invention, a corrected image is generated by masking a substrate image with a hole image.

By creating a histogram using this corrected image, it is possible to obtain a binarization threshold almost equal to the case where there is no light reflected from the stage.

[0015]

【Example】

A. FIG. 2 is a schematic diagram of an optical wiring pattern reading device 100 used in an embodiment of the present invention.

The reading device 100 includes a substrate 2 to be inspected.
0 is placed translucency of stage 15, the red LED11
A first light source 110 comprising infrared rays L,
An ED 120 (second light source), a lens system 140, a cold mirror 150, an image sensor 161 for reflected light, and an image sensor 162 for transmitted light are provided.

Since the stage 15 moves in two directions perpendicular to each other in a plane parallel to the stage 15, the entire upper surface of the substrate 20 placed thereon can be read.

Light emitted from the first light source 110 is reflected by the wiring pattern 22 and the base material 21 formed on the first main surface of the substrate 20 and reaches the cold mirror 150 through the lens system 140. The cold mirror 150 transmits infrared light but does not transmit red light .
The light reflected on the main surface side is further reflected by the cold mirror 150, and is used as the reflected light LR as the reflected light image sensor 1.
Enter 61. The reflected light image sensor 161 has the reflected light L
Converting the intensity of the R in the substrate signal PS ₀ is an electrical signal.

Meanwhile, light emitted from <br/> second light source 120 located at the second main surface side of the substrate 20 passes through the back surface 15 a or al surface 15 b of the stage 15 comprises a substrate 20 The lens system 1 is inserted through a through hole 25 (through hole) or from an area (not shown) where the substrate 20 is not mounted.
Reaches 40. This light is infrared light.
The transmitted light 50 passes through the transmitted light LT and enters the transmitted light image sensor 162. The transmitted light image sensor 162 includes:
The intensity of the transmitted light LT is converted into a Hall signal HS which is an electrical signal.
Convert to ₀ . The board signal PS ₀ and the hole signal HS ₀ are used for detecting the wiring pattern 22 and the through hole 25, respectively.

B. FIG. 1 shows a pattern 2 used in an embodiment of the present invention.
FIG. 3 is a block diagram of a value processing unit 200; The pattern binarization processing unit 200 generates a signal PIS obtained by binarizing the image of the substrate using an optimal binarization threshold based on the substrate signal PS ₀ and the hall signal HS ₀ obtained from the reading device 100. I do. The signal PIS is thereafter subjected to a pattern break inspection or the like depending on the purpose.

The A / D converter 210 and 220 respectively substrate signal PS _0, and a Hall signal HS ₀ converted A / D, digitize substrate is a digital signal having a tone value of the example 8 bits (= 256) A signal PS and a digitized hall signal HS are obtained.

The substrate signal PS is supplied to the mask processing units 230 and 2
It is sent to the value conversion circuit 270. In the binarization circuit 270,
The signal PIS is generated by binarizing the substrate signal PS with an optimal binarization threshold T obtained as described later.

The hall signal HS is sent to a binarization processing unit 240.
And a binarized Hall signal HIS is obtained.
You. This signal HIS is sent to the mask processing unit 230,
Of the image PI created by the substrate signal PSERulePart H
(See Fig. 3)And distinguished from non-hole area NHI do. Base
Board signal PSChihoRulePart HThe part corresponding to
, A correction signal CS is obtained.
Is sent to the histogram creation unit 250.

The histogram creating section 250 creates a histogram G by plotting the frequency of pixels for each gradation value from the correction signal CS. The binarization threshold setting unit 260 obtains, for example, a gradation value T at which the frequency becomes the minimum based on the histogram G, and sets it as a binarization threshold.

Hereinafter, the operation of the processing units 230 and 240 will be described in more detail. First, the binarization processing unit 240 binarizes the Hall signal HS with a certain threshold TH _h. A region having a value greater than the threshold TH _h is determined that the hole portion H, to determine the other portions to be non-hole portions NH (hole portion H is not only part corresponding to the through hole 25, the substrate The area on the stage on which 20 is not placed is also included.) FIG. 3 shows the relationship between the Hall signal HS read on the line AA ′ and the substrate 20. Generally, when the through hole 25 is formed in the printed circuit board 20, the hole signal HS has an inclination at the edge portion E due to light reflection on the inner wall thereof. As a result, as shown in FIG. 3, the hole portion H does not always correspond exactly to the through hole 25, and is slightly smaller. Improvements to cope with such circumstances will be described later.

FIG. 4 shows the relationship between the substrate signal PS and the substrate 20.
This is shown in the same manner as FIG. Through hole 25
Corresponding to the position, there is a reflection signal RF resulting from the reflection of light by the stage described in the related art. Such a reflection signal RF is applied to the stage surface 1 for the first light source.
5b and the back surface 15a, the stage 15
This occurs in an area where there is no light shielding above, that is, an area determined to be the hole H. Therefore,
The place of interest is Hall H or non-Hall NH
Is a signal HIS having information on whether the reflected signal R
The region where F occurs can be masked.

More specifically, for example, in the mask processing section 230, the logical product of the substrate signal PS and the inverted signal of the Hall signal HIS may be obtained. In such a case, the mask processing unit 230 can be configured only by including the AND circuit 231 as shown in FIG. Of the correction signal CS,
The value of the signal corresponding to the hole portion H is “0”, and a signal indicating the wiring pattern 22 with the influence of the reflection signal RF suppressed can be obtained.

In the correction signal CS, the value of the signal corresponding to the hole H is not limited to "0", but takes another value that makes it easy to determine the binarization threshold T from the histogram G generated later. You can also do so. In this case, a predetermined value (corresponding to the gradation value) is output only when the hall signal HIS is "1" (corresponding to the hall portion H),
When it is “0” (corresponding to the non-hole portion NH), the mask processing section 230 can be configured using a multiplexer that outputs the substrate signal PS.

C. Generation of Histogram and Setting of Binarization Threshold FIG. 6 shows a histogram G of the reflection intensity when the value of the correction signal CS at the hole H is set to T ₃ . Such a histogram G is obtained by counting the frequency distribution of the reflection intensity for each gradation value. Since the gradation value at the hole H is set to T ₃ , the histogram G has the gradation value T
₃ has a peak, but if the gradation value T ₃ is kept sufficiently small, the shape of the histogram in the vicinity of the gradation value T ₁ will not be affected, and therefore the ideal shape as shown in FIG. A tone value T ₁ ′ (FIG. 6) which is almost equal to the tone value (binary threshold value) T ₁ set for a histogram having a simple shape is set as a binary threshold value for identifying a pattern . Can be.

D. Modifications (1) As described in “B. Generation of Corrected Image”, the hole H may be set smaller than the actual through-hole 25, and the reflection signal R near the edge E shown in FIG.
When F is large, it cannot be masked, which causes a problem. In order to cope with this, the processing in the mask processing section 230 may be performed after the image (hole image) HI of the hole H is enlarged.

Specifically, the binarized Hall signal HI
S is once expanded two-dimensionally using a shift register to obtain a hole image HI, and then subjected to an enlargement process to generate an enlarged hole image. The corresponding enlarged hole signal is transmitted to the mask processing unit 230. I just need to provide.

In this case, the enlarged hole image is enlarged so as to cover at least the area occupied by the actual through hole 25. Even if the enlarged hole image slightly covers a part of the area corresponding to the pattern, the effect of the present invention can be obtained. Is not compromised. As the binarization threshold value, a gradation value having a low frequency of reflection intensity in the histogram G is selected.
Reflection intensity is high as, also its power is large area somewhat reduces, also peaks is somewhat higher shown in the gradation value T ₃ in FIG. 6, is little effect on the setting of the binarization threshold Because there is no.

(2) The present invention does not necessarily require the second light source, and the effect can be obtained only with the first light source.

As shown in FIG. 7, two threshold values TH ₁ and TH ₂ are set in the substrate signal PS, and a region giving a value less than the threshold value TH ₂ among the regions giving a value not less than the threshold value TH ₁ is a hole portion H. Therefore, the binarized Hall signal HIS can be obtained without using the second light source. This may be used for processing in the mask processing unit 230.

Alternatively, the substrate signal PS is temporarily binarized to obtain a binarized signal, a circular area is searched for in an image (pattern image) PI obtained by two-dimensionally developing the signal, and the area is defined as a hole H May be obtained as
Such an exploration method is disclosed in, for example, Japanese Patent Application Laid-Open No. 63-15374 by the present applicant. After that, the binarization threshold may be determined again and the substrate signal PS may be binarized again.

[0036]

As described above, according to the method for setting the binarization threshold value of the present invention, the hall signal masks the substrate signal to generate a correction signal, and the first signal is generated based on the correction signal.
A histogram relating to the reflection intensity of the main surface is created. Then, since a binarization threshold for identifying a pattern is set from the histogram, when binarizing the image of the first main surface of the substrate on which the pattern is provided, the binarization threshold is set from an area where the substrate is not placed or through the area. The effect of light reflected by the stage through the hole can be eliminated.

Further, according to the binarization threshold setting device of the present invention, the above-described binarization threshold setting method can be executed.

[Brief description of the drawings]

FIG. 1 is a block diagram of a pattern binarization processing unit 200 used in one embodiment of the present invention.

FIG. 2 is a schematic view of an optical wiring pattern reader 100 used in one embodiment of the present invention.

FIG. 3 is a diagram illustrating a relationship between a hall signal HS and a through hole 25;

FIG. 4 is a diagram showing a relationship between a substrate signal PS and a reflected signal RF due to reflection from a stage.

FIG. 5 is a circuit diagram showing a configuration of a mask processing unit 230.

FIG. 6 is a diagram showing a histogram G;

FIG. 7 is an explanatory view showing another embodiment of the present invention.

FIG. 8 is an explanatory diagram showing a conventional technique.

[Explanation of symbols]

Reference Signs List 15 stage 20 printed circuit board 22 wiring pattern 25 through hole (through hole) 110 first light source 120 second light source 210, 220 A / D conversion unit 230 mask processing unit 240 binarization processing unit 250 histogram creation unit 260 binary Digitized threshold value setting unit PS ₀ substrate signal PS digitized substrate signal PI pattern image HS ₀ hall signal HS digitized hall signal HIS binarized hall signal HI hall image CS correction signal G histogram T binarization threshold

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ identification code FI H04N 1/403 H04N 1/40 103A (58) Fields investigated (Int.Cl. ⁶ , DB name) G06T 7/00 G06T 1 / 00 G06T 5/00 H04N 1/40 G01B 11/00 G01N 21/88

Claims (6)

(57) [Claims] (A) a substrate having first and second main surfaces and a through hole, having a relatively low reflectance, and having a light-shielding property, and further having a relatively light-reflecting surface on the first main surface; Placing a substrate having a pattern with a high rate on a stage; and (b) optically reading the substrate to place the substrate on the first main surface and the stage.
A substrate signal showing an image of non region and the through-hole, a step of obtaining a Hall signal indicating the image of the previous SL area and the through hole, of the region and the through-hole of the (c) the substrate signal I
Obtaining a correction signal was Lima disk treated by the Hall signal image, (d) a step of creating a histogram of reflection intensity of the first major surface from said correction signal, the shape of (e) the histogram based on the identifying binary to the pattern of the substrate signal, setting the binarization threshold comprising a step of setting a binarization threshold, the. 2. The method according to claim 1, wherein said stage is translucent, and said step (b) comprises the steps of: (b-1) placing a first light source on said first main surface from a first light source; Irradiating light; and (b-2) the stay through the region and the through hole.
Receiving the reflected light of the first light reflected by the first main surface by the laser beam; and (b-3) converting the intensity of the reflected light into an electric signal to obtain the substrate signal. (B-4) irradiating the second main surface with second light from a second light source; and (b-5) transmitting the second light through the through hole or the region. (B-6) a step of converting the intensity of the transmitted light into an electric signal to obtain the Hall signal; 3. A method according to claim 1 wherein step (b) includes the step of irradiating light to the first major surface from (b-7) light source, (b-8) the region and the The stay through the through hole
By di, and the step of receiving the reflected light reflected by the first major surface, and a step of obtaining the substrate signal into an electric signal the intensity of the reflected light (b-9), (b- And 10) obtaining the Hall signal by discriminating the substrate signal with a predetermined threshold value. 4. The method according to claim 1, wherein the step (c) comprises: (c-1) binarizing the hall signal to obtain a binarized hall signal designating the through hole and the area. (C-2) obtaining the correction signal by setting a portion of the substrate signal corresponding to the through hole and the region specified by the binarized hole signal to a predetermined value; A method for setting a binarization threshold comprising: 5. The method according to claim 4, wherein in the step (c), prior to the step (c-1), (c-3) developing the hole signal two-dimensionally to form a hole image. (C-4) a step of enlarging the hole image to obtain an enlarged hole image; and (c-5) a step of newly converting a signal corresponding to the enlarged hole image into the hole signal. How to set the binarization threshold. 6. A stage on which a substrate having a through hole and a pattern is mounted, reading means for optically reading the substrate, the substrate and the stay obtained by the reading means.
An image of a region that is not placed in the substrate of di, the through hole and the front Symbol area and the substrate signal into an electric signal, respectively, and converting means for obtaining a Hall signal, among the substrate signal the Image of area and through hole
Calculating means for obtaining a correction signal Lima disk treated by the Hall signal, the histogram creating means for creating a histogram from the correction signal, from the histogram, the binarizes the substrate signal
Binarization threshold setting device comprising a threshold value setting means for setting a binarization threshold to identify the pattern.