JP2002290994A - Foreign matter inspection method and apparatus for small camera module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect foreign matters stuck on the surface of a lens or an image pickup device in an inspection process in the production process of an image pickup device incorporated with lens or a small camera module. SOLUTION: This method is provided with a step for detecting a maximum luminance position by comparing luminance from a horizontal line scan starting position to an ending position concerning image information for arbitrary one horizontal line while using the foreign material inspecting device provided with a miniaturized camera module 1, a light source 5, an image memory 6 and an arithmetic circuit 7, a step for finding a luminance difference between adjacent pixels from the horizontal line scan starting position to the maximum luminance position, a step for finding a luminance difference between adjacent pixels from the horizontal line scan ending position to the maximum luminance position, and a step for deciding a compare pixel as a defect when a difference Yj-Yi between luminance Yi of a reference pixel and luminance Yj of the compare pixel is negative and lower than a decision value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a CCD or a CMOS.
In the manufacturing process of a lens-integrated image sensor in which a dedicated lens is attached to a solid-state image sensor such as an image sensor, and a small camera module in which the lens-integrated image sensor is mounted on a substrate together with a signal processing circuit, it adheres to the lens and the image sensor surface The present invention relates to a foreign matter inspection method and a foreign matter inspection device for a small camera module used for detecting a foreign matter.

[0002]

2. Description of the Related Art Although the purpose of the present invention is different from that of the present invention, an apparatus for correcting a defect of a solid-state image pickup device is disclosed in, for example, Japanese Patent Laid-Open No. 7-2.
Japanese Patent No. 3297 (a defect detection device for a solid-state imaging device, Sony Corporation) discloses a technique similar to the present invention. This technique is used when the luminance difference between the test pixel and the adjacent upper, lower, left and right pixels is larger than the determination value, and when the edge determination result of the pixel has no tendency to increase in the peripheral pixel signal and is isolated, the test pixel Is determined as a defect. The determination value of the luminance difference is variable according to the signal level of the AGC amplifier.

[0003] In Japanese Patent Application Laid-Open No. 2000-180377 (Defect / Foreign Substance Inspection System, Sharp Corporation), an image (M) obtained by performing a maximum value filtering process on an inspection image (I) and a minimum value filtering process are performed. Is performed, and each image is compared with the inspection image (I), and a pixel whose density is higher than the maximum value filter image (M) and a pixel whose density is lower than the minimum value filter pixel (m) are determined as defects. Has been extracted.

Japanese Patent Application Laid-Open No. 9-105618 discloses a technique for inspecting minute defects on a CD printing surface (method and apparatus for inspecting defects on a smooth surface of an object, and methods and devices for measuring roughness of an object surface). In)), the absolute value of the difference (luminance difference) between the previously input normal image and the inspection image is calculated, the area of the extracted defect candidate is measured, and the non-defective item is determined.

In literatures (basic techniques of image processing <Introduction to Techniques>, Technical Review Company, co-authored by Hasegawa / Nakayama / Yokoi / Koshimizu), an image is evaluated by dividing it into regions in which the gray value can be regarded as uniform (constant). Is described. When evaluating an image in which the gray level changes at a specific location in a normal state,
An application to a technique of dividing an area having a uniform gray value in advance and evaluating each area is generally performed.
For example, the inspection image can be divided into lattice windows, and an appropriate determination value can be set for each window to determine pass / fail. As the determination value at this time, a luminance histogram in the window is taken, and the most existing gray value can be used.

[0006]

The above prior art is
This is similar to the present invention in that a difference in luminance between adjacent pixels is used for defect detection. However, if the luminance difference between adjacent pixels is simply taken in the horizontal line direction for an image in which the luminance of the peripheral portion is reduced due to the lens characteristics, the following problem occurs. Even in a normal state, since the difference in luminance between adjacent pixels differs in the increase and decrease (sign) on the left and right with the center of the lens having the highest luminance as the center, the defect can be uniquely determined by the change in difference (sign). Can not. Further, even if a defect is determined based on the absolute value of the difference, it is not possible to distinguish between a white point (a place with high luminance) and a foreign substance (a place with low luminance). Further, when there is a foreign substance over several pixels, the edge part of the foreign substance can be detected, but it cannot be detected because there is no difference in a part other than the edge, so that accurate determination cannot be performed.

The above-mentioned prior art is an effective technique for detecting a foreign substance because a noise component of an image can be reduced by filtering and a defective portion can be emphasized. However, since the equipment constituting the pipeline processing unit is expensive, using a plurality of units in the inspection process deteriorates cost performance.

The above prior art employs a method of preparing a non-defective reference image (normal image) in advance and detecting a defect based on a difference from an inspection image. However, since the center of the lens does not always correspond to the center of the image due to assembly variations, the portion where the luminance drops greatly varies in the peripheral portion. Therefore, the reference image cannot detect a change in luminance in the peripheral portion of the inspection image, and determines a non-defective product as defective.

In the above prior art, when a grid-like area division is performed, it is not possible to detect a brightness change that changes in a circular shape from the center of the lens, and a brightness difference occurs in a grid around the image. In addition, a good product is determined to be defective. This can be alleviated by increasing the number of divided areas, but the size of the foreign matter that can be detected is reduced. It is also conceivable to divide the area in a circular shape, but it is difficult to uniquely determine an area in which the gray value is uniform because of variations in products. Further, it is conceivable that the regions having the same characteristics are merged to make a comprehensive judgment, but the processing time is long, which is not suitable for mass production.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems of the prior art. In an inspection process in a manufacturing process of a lens-integrated image pickup device or a small camera module, the present invention is applied to a surface of a lens or an image pickup device. It is an object of the present invention to provide a foreign matter inspection method and a foreign matter inspection device for a small camera module that can accurately detect foreign matter.

[0011]

SUMMARY OF THE INVENTION A foreign object inspection method for a small camera module according to the present invention comprises a lens-integrated solid-state imaging device for imaging light condensed by a lens, and a pixel signal supplied from the solid-state imaging device. In the manufacturing process of a small camera module having a signal processing circuit for converting information, a light source for irradiating the small camera module with uniform light to inspect foreign matter adhering to the surface of a lens or an image sensor, and a signal processing circuit Using a foreign matter inspection device including an image memory for storing image information to be output and an arithmetic circuit for performing arithmetic processing on the image information stored in the image memory to calculate arbitrary image information, an arbitrary horizontal direction is used. For one line of image information, the luminance from the scanning start position to the scanning end position of the horizontal line is sequentially compared to detect the position of the maximum luminance. And taking a difference in luminance between adjacent pixels in the direction from the horizontal line scanning start position to the position of maximum luminance. Taking a difference in luminance, and in the difference in luminance between the adjacent pixels, the difference Yj-Yi between the luminance Yi of the reference pixel and the luminance Yj of the comparison pixel closer to the maximum luminance position than the reference pixel is a negative value. And determining whether the comparison pixel is defective if the value is equal to or less than the determination value, thereby achieving the above object.

According to the above method, even when there is a drop in the amount of peripheral light due to the lens characteristics, it is possible to uniquely determine a pixel having a low luminance (dark) as a foreign substance based on a difference between adjacent pixels. Each of the above means can be realized by controlling an arithmetic circuit and a memory by software.

In the step of detecting the position of the maximum luminance, when the luminances of the horizontal line from the scanning start position to the scanning end position are sequentially compared, pixels having a luminance exceeding a reference value may be excluded from the inspection target. Good.

According to the above-described method, the position of the maximum luminance is stably extracted except for the white point (a part having high luminance due to a pixel defect) included in the image information, and the foreign matter and the white point are distinguished in the inspection. It becomes possible.

In the step of judging a defect, if there is a pixel judged to be defective before that, the luminance Yj of the comparison pixel is changed to the luminance Yi of the reference pixel at the time of the defect judgment.
Until the above luminance value is obtained, all the comparison pixels may be determined to be defective.

According to the above method, it is possible to accurately detect a foreign substance over several pixels.

In the step of judging the defect, when the luminance Y2 of the comparative pixel is less than a predetermined reference value, the comparative pixel is judged to be defective, and the luminance Yj of the comparative pixel is determined.
Until the brightness value becomes equal to or more than the reference value, all the comparison pixels may be determined to be defective.

According to the above-mentioned method, it is possible to determine a defect of a foreign substance extending over several pixels at a scanning start position or a scanning end position of a horizontal line.

In the step of judging the defect, an offset may be added to the judgment value.

According to the above method, it is possible to stably detect a foreign substance without determining a non-defective product in consideration of a noise component included in image information.

According to the present invention, there is provided a foreign object inspection apparatus for a small camera module, comprising: a solid-state imaging device for imaging light condensed by a lens; a signal processing circuit for converting a pixel signal supplied from the solid-state imaging device into image information. In a manufacturing process of a small camera module provided with a light source for irradiating uniform light to the small camera module, a light source that irradiates the small camera module with uniform light, and a signal processing circuit. An image memory for storing the image information to be output, and an arithmetic circuit for performing arithmetic processing on the image information stored in the image memory to calculate arbitrary image information. Means for detecting the position of the maximum luminance by sequentially comparing the luminance from the scanning start position to the scanning end position of the horizontal line; Means for taking the difference in luminance between adjacent pixels in the direction from the start position to the position of maximum luminance; means for taking the difference in luminance between adjacent pixels in the direction from the scanning end position of the horizontal line to the position of maximum luminance; In the difference in luminance between the adjacent pixels, Yj-Yi of the luminance Y1 of the reference pixel and the luminance Y2 of the comparative pixel closer to the maximum luminance position than the reference pixel.
Means for determining that the comparison pixel is defective when the value of the reference pixel is a negative value and is equal to or less than the determination value, thereby achieving the above object.

According to the above configuration, it is possible to accurately detect foreign matter adhering to the surface of the lens or the imaging element in the inspection step in the manufacturing process of the lens-integrated imaging element or the small camera module.

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a photograph showing an example of a compact camera module to which the present invention is applied. FIG. 1 (a) shows its front surface and FIG. 1 (b) shows its back surface. In this small camera module 1, a lens 2 is integrated with a solid-state imaging device 3,
A lens-integrated solid-state image sensor that generates pixel signals by receiving light condensed by the lens 2 with the solid-state image sensor 3 and a signal processing circuit 4 that converts pixel signals from the solid-state image sensor 3 into image information Have been.

FIG. 2 is a view for explaining the configuration of a foreign matter inspection device for a small camera module according to an embodiment of the present invention. This device accumulates a light source 5 for irradiating uniform light (for example, a halogen light / inverter type fluorescent lamp using a DC power supply) and image information (including pixel luminance information) output from the signal processing circuit 4. And an arithmetic circuit 7 for arithmetically processing and processing image information stored in the image memory 6 to calculate arbitrary image information. Light from the light source 5 is incident on the entire angle of view. First, the small camera module 1 is arranged. According to this configuration example, since the image memory 6 and the arithmetic circuit 7 can be realized by commercially available PCs and I / O boards, the cost performance is excellent.

FIG. 3 shows image information (a photograph taken by the small camera module 1) output from the signal processing circuit 4 of the small camera module 1 when the light source 5 is a subject. Here, the foreign matter 8 is located around the center of the image information.
Can be confirmed. An object of the present invention is to detect such foreign matter in an inspection process in a manufacturing process.

FIG. 4 shows a luminance waveform 12 on the horizontal line 9 of the image information shown in FIG. In this figure, the vertical axis indicates luminance (unit IRE: the reference level of black used when evaluating an analog output signal is 7.5 IRE), and the horizontal axis indicates the horizontal line position. The luminance waveform 12 indicates a drop in peripheral luminance due to the lens characteristics, and the luminance level is lower at the horizontal line scanning start position 10 and the horizontal line scanning end position 11 than at the center of the lens. Further, the foreign substance 8 has a luminance waveform 12
This appears as a drop in the brightness of several pixels above. The present invention is intended to accurately extract image information of the foreign substance 8 based on the luminance waveform 12.

Hereinafter, a foreign matter inspection method for a small camera module according to an embodiment of the present invention will be described with reference to the flowchart of FIG. First, in a process 100, image information for one screen output from the signal processing circuit 4 of the small camera module 1 is stored in the image memory 6. The processing described hereinafter is performed by the arithmetic circuit 7 on the image information stored in the image memory 6.

Next, in process 101, the arithmetic circuit 7
Performs a process of extracting the position 15 having the maximum luminance in the first one of the horizontal lines. Regarding this processing 101,
This will be described in detail with reference to FIG. First, the luminance level of the pixel at the horizontal line scanning start position 10 is used as a reference. Next, the luminance of the pixels is sequentially compared up to the horizontal line scanning end position 11, and when a high luminance portion is detected, the process of exchanging the reference of the luminance level is repeated, and the position 15 of the maximum luminance is repeated.
Is extracted.

When the luminances of the horizontal line from the scanning start position to the scanning end position are sequentially compared, it is confirmed that the luminance of the compared pixel does not exceed the reference value 14.
If the luminance of the pixel exceeds the reference value, the pixel is excluded as a white point 13 and is excluded from the inspection target. Although this white spot 13 is a pixel defect, it is not subjected to a correction process as described in, for example, Japanese Patent Application Laid-Open No. Hei 7-232297 at the time of shipment of the small camera module. It is necessary to exclude in inspection. Further, since the reference value 14 for detecting the white point 13 differs depending on the conversion level (pixel signal → image information) of the signal processing circuit 4, it is necessary to measure and determine the luminance of the white point 13 for each product. .

Next, in a process 102, a pixel at the horizontal line scanning start position 10 is set as a reference pixel with respect to the horizontal line to be inspected, and a pixel next to the reference pixel (on the side closer to the maximum luminance position) is set as a comparison pixel. Initialize. At this time,
The luminance of the reference pixel (the pixel at the horizontal scanning start position 10) is compared with the reference values 14 and 20, and the suitability as the reference pixel is evaluated. That is, if the value exceeds the reference value 14, it is excluded as a white point 13, and if the value is less than the reference value 20, it is determined to be defective. If it is determined that the pixel is not appropriate, the next pixel (on the side closer to the maximum luminance position) is set as a candidate for a reference pixel.
The same evaluation is repeated.

Next, in process 103, the inspection circuit 7
Confirms that the luminance of the comparison pixel is equal to or greater than the reference value 20. If the value is less than the reference value 20, the process 104
In, the comparison pixel is determined to be defective (NG), and the comparison pixel is set as the next pixel without changing the reference pixel. Then, all the comparison pixels are determined to be defective until the luminance of the comparison pixel becomes equal to or higher than the reference value.

These processes will be described with reference to FIG. When there is a foreign substance having a size of several pixels at the horizontal line scanning start position 10, the luminance waveform 12 is as shown in FIG. In this case, since there is no luminance difference between the horizontal line scanning start position 10 and several pixels, the pass / fail judgment using only the difference results in a non-defective product. For this reason, it is necessary to determine the reference value 20 and make a pass / fail judgment. Note that the reference value 20 is determined for each product in consideration of a drop in luminance in the peripheral portion due to lens characteristics.

Next, in process 105, the difference between the luminance of the reference pixel and the luminance of the comparative pixel (the luminance of the comparative pixel minus the luminance of the reference pixel) is obtained and compared with the judgment value. If the difference exceeds the determination value, in process 106, the current comparison pixel is determined to be defective while the luminance of the reference pixel is maintained, and the comparison pixel is set as the next pixel. Then, in the process 107,
Until a luminance value equal to or higher than the luminance of the held reference pixel is obtained,
The process of determining that all the comparison pixels are defective is repeated. In addition,
Since the luminance level changes when the conversion level of the signal processing circuit 4 changes, it is preferable that the determination value be determined for each product. However, a reference for matching the output level of the signal processing circuit 4 is provided (for example, a standard defined by the standard). By taking an image of the subject and using the white, black, and mid-range output levels as adjustment standards), it is considered that the determination value does not significantly change.

These processes will be described with reference to FIG. 8, on the luminance waveform 12 shown in FIG. 9 is an enlarged view of the frame 16 portion including the foreign substance 8, Y _n in FIG.
ＹY _{n +9} is the luminance of each sampled pixel. In the difference between adjacent pixels in the process 105, _{Yn +} is first determined to be defective. Thereafter, in processing 106 and processing 107, the luminance level 17 of Y _{n + 2} becomes the luminance of the reference pixel, and the comparison pixels Y _{n + 4} and Y _{n + 5} whose luminance values are lower than the luminance of the reference pixel are determined to be defective. judge. Thereby, Y _{n + 3}
Even when there is no difference in luminance between adjacent pixels as in the case of the? -Type _{Yn + 5} , it can be determined as defective.

Further, in the process 105, an offset (offset) is added to the judgment value in order to allow a noise component included in the image information. This is because, as shown in FIG. 8, there are variations in the luminance levels of the actual signals Y _{n to} Y _{n + 9} , and it is necessary to allow this variation in the determination. The offset 18 is determined in consideration of the noise amount for each product.

Next, in a process 108, it is confirmed whether or not the inspection of one horizontal line has been completed. If the inspection has been completed, the process proceeds to a process 110, and if not completed, the process proceeds to a process 109.

In step 109, the current comparison pixel is set as a reference pixel, and the comparison pixel is set as the next pixel. At this time, when the comparison pixel is at the maximum luminance position 15 on the horizontal line, the scanning direction is switched. That is, the pixel at the horizontal line scanning end position 11 is set as a reference pixel, and the pixel before the reference pixel (on the side closer to the maximum luminance position) is initialized as a comparison pixel. Thereafter, the reference pixel and the comparison pixel shift from the horizontal line scanning end position 11 to the position 15 of the maximum luminance. Therefore, as shown in FIG. 9, inspection of one horizontal line is performed in the direction from the horizontal line scanning start position 10 to the maximum luminance position 15 and in the direction from the horizontal line end start position 11 to the maximum luminance position 15. Will be.
This is because the difference between adjacent pixels is calculated in the direction in which the luminance is maximum, and when the difference is small (when the difference is negative), the foreign matter 8 is present. This is because it is possible to uniquely determine a white point in the case of (+).

In the process 110, it is confirmed whether or not the inspection for each horizontal line has been performed for the entire screen. If the scanning of the entire screen is not completed, the process 11
In step 1, a horizontal line is extracted next, and the process returns to step 101. When the scanning of the entire screen is completed, the inspection is ended in a process 112.

Although the embodiments of the present invention have been described above, the present invention is not limited to the details described in the above embodiments, and various modifications may be made without departing from the technical spirit of the present invention. It goes without saying that it is possible.

[0041]

As described in detail above, according to the first and sixth aspects of the present invention, in the inspection process in the manufacturing process of the lens-integrated imaging device and the small camera module, the peripheral light amount due to the lens characteristics In this case, foreign substances adhering to the surface of the lens or the image sensor can be detected with high accuracy.

According to the second aspect of the present invention,
Except for the white point included in the image information, the position of the maximum luminance can be stably extracted, and the foreign matter and the white point can be distinguished in the inspection.

According to the third aspect of the present invention,
Foreign matter over several pixels can be accurately detected.

According to the fourth aspect of the present invention,
Defects can be determined for a foreign substance extending over several pixels at the scanning start position or scanning end position of the horizontal line.

Further, according to the present invention, in consideration of a noise component included in image information, it is possible to stably detect a foreign substance without determining a non-defective product as defective.

[Brief description of the drawings]

FIG. 1 is a photograph showing an example of a compact camera module to which the present invention is applied, where (a) shows the front surface and (b) shows the back surface.

FIG. 2 is a diagram illustrating a configuration of a foreign object inspection device for a small camera module according to an embodiment of the present invention.

FIG. 3 is a photograph taken by a small camera module using a light source as a subject.

FIG. 4 is a diagram showing a luminance waveform on a horizontal line of the captured photograph shown in FIG. 3;

FIG. 5 is a flowchart for explaining a foreign matter inspection method for a small camera module according to an embodiment of the present invention.

FIG. 6 is a diagram for describing a process of extracting a maximum luminance position of one horizontal line.

FIG. 7 is a diagram showing a luminance waveform of a foreign substance at a horizontal line scanning start position.

FIG. 8 is an enlarged view of a foreign substance on a luminance waveform.

FIG. 9 is a diagram illustrating a horizontal line scanning direction in the foreign substance inspection.

FIG. 10 is a diagram showing variations in an actual luminance waveform.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Small camera module 2 Lens 3 Solid-state image sensor 4 Signal processing circuit 5 Light source 6 Image memory 7 Arithmetic circuit 8 Foreign matter (Foreign matter on luminance waveform) 9 Horizontal line 10 Horizontal line scanning start position 11 Horizontal line scanning end position 12 Brightness waveform 13 White point 14 Reference value (luminance level for white point detection) 15 Maximum luminance position of horizontal line 16 Frame 17 Reference pixel luminance level 18 Offset (allowable level of noise component) 19 Foreign matter (scanning start position and end of horizontal line) Foreign matter at position) 20 Reference value (brightness level for foreign matter detection at scanning start position and end position of horizontal line)

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 2G051 AA73 AA90 AB01 CA03 CA04 EA08 EB01 5B057 AA01 BA02 BA15 CA02 CA08 CA12 CA16 CC02 CE20 CH08 CH11 DA03 DA07 DA08 DB02 DB05 DB09 5C061 BB01 BB05 CC09

Claims (6)

[Claims] 1. A compact camera module comprising: a lens-integrated solid-state imaging device that captures light condensed by a lens; and a signal processing circuit that converts pixel signals supplied from the solid-state imaging device into image information. In the process, a light source for irradiating a uniform light to a small camera module to inspect a lens or a foreign substance adhering to a surface of an imaging device;
Using a foreign matter inspection device including an image memory that stores image information output from the signal processing circuit, and an arithmetic circuit that performs arithmetic processing on the image information stored in the image memory to calculate arbitrary image information Detecting the position of the maximum luminance by sequentially comparing the luminance from the scanning start position to the scanning end position of one horizontal line of image information, and detecting the maximum luminance from the scanning start position of the horizontal line. Taking the difference in brightness between adjacent pixels in the direction of the brightness position; taking the difference in brightness between adjacent pixels in the direction of the position of maximum brightness from the horizontal line scanning end position; , The luminance Y of the reference pixel
determining the comparison pixel as defective if the difference Yj−Yi between i and the luminance Yj of the comparison pixel closer to the maximum luminance position than the reference pixel is a negative value and equal to or smaller than the determination value. Inspection method for small camera module. 2. In the step of detecting the position of the maximum luminance, when the luminances of the horizontal line from the scanning start position to the scanning end position are sequentially compared, pixels having a luminance exceeding a reference value are excluded from the inspection target. The method for inspecting foreign matter of a small camera module according to claim 1. 3. The step of determining a defect,
If there is a pixel determined to be defective before that, the luminance Yj of the comparison pixel is set to the luminance Y of the reference pixel at the time of the defect determination.
3. The foreign matter inspection method for a small camera module according to claim 1, wherein all the comparison pixels are determined to be defective until the luminance value becomes i or more. 4. In the step of determining a defect,
When the luminance Y2 of the comparative pixel is less than a predetermined reference value, the comparative pixel is determined to be defective, and the luminance Y of the comparative pixel is determined.
4. The foreign matter inspection method for a small camera module according to claim 1, wherein all the comparison pixels are determined to be defective until j becomes a luminance value equal to or greater than the reference value. 5. In the step of determining a defect,
4. The method according to claim 1, further comprising: adding an offset to the determination value. 6. A manufacturing process of a small camera module comprising: a solid-state imaging device for imaging light condensed by a lens; and a signal processing circuit for converting a pixel signal supplied from the solid-state imaging device into image information. A light source for irradiating a uniform light to a small camera module; and an image memory for storing image information output from the signal processing circuit. And an arithmetic circuit for performing arithmetic processing on the image information stored in the image memory to calculate arbitrary image information. For one horizontal line of image information, a horizontal line scanning start position to a horizontal line scanning end position The means for detecting the position of the maximum luminance by sequentially comparing the luminances up to the horizontal line from the scanning start position of the horizontal line to the position of the maximum luminance position Means for taking the difference in luminance between the elements; means for taking the difference in luminance between adjacent pixels in the direction from the scanning end position of the horizontal line to the position of the maximum luminance; Brightness Y
Means for judging the comparison pixel as defective when the difference Y2-Y1 between 1 and the luminance Y2 of the comparison pixel closer to the maximum luminance position than the reference pixel is a negative value and equal to or smaller than the judgment value. A foreign object inspection device for a small camera module equipped with: