JPH1114501A - Method and apparatus for inspecting image sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to judge only the presence of refuse, flaws, etc., which exert a bad influence on focus detection by detecting the presence of foreign matters on a photodetecting unit, on the basis of outputs of an image sensor when tradiated with a parallel beam, and when irradiated with a diffused beam. SOLUTION: A beam from a light source Lp is changed into a parallel beam PB by a lens Ls and strikes an image sensor IS. When a diffusing board WB is inserted between this lens Ls and the image sensor IS, a diffused beam DB strikes the image sensor IS. If a part of the parallel beam is scattered by refuse, etc., the light quantity of a pixel just below it lowers extremely and its output reflects both sensitivity nonuniformity and the presence of refuse, flaws, etc. On the other hand, if a part of the diffused beam is scattered by refuse, etc., a light quantity incident on a pixel just below it is not different from other pixels, and its output reflects the sensitivity nonuniformity but does not reflect the presence of the refuse, flaws, etc. Accordingly, if both pixel outputs are subtracted a waveform owing to the refuse etc., remains, but a waveform owing to the sensitivity nonuniformity is canceled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for inspecting an image sensor which outputs an image signal corresponding to an intensity distribution of irradiated light.

[0002]

2. Description of the Related Art Heretofore, in an image sensor array in which a plurality of photoelectric conversion elements are arranged, there is a variation in sensitivity among the plurality of photoelectric conversion elements. This is called sensitivity non-uniformity. If arithmetic processing is performed based on the pixel output obtained in a state in which the variation is included, the accuracy of focus detection may be degraded or false focusing may be caused. Therefore, sensitivity non-uniformity correction is performed. In this correction, first, an output of the image sensor array ISA corresponding to a subject having uniform luminance is obtained in a state where the optical system of a known focus detection device as shown in FIG. 6 is provided. The plurality of photoelectric conversion element rows of the image sensor array ISA are called row A and row B, respectively. FIG. 7A shows an output example of column A of the image sensor array ISA in that case. Originally, the output of the image sensor that received a light beam from a subject having uniform luminance should have a horizontal waveform as shown in FIG. 7 (2). However, due to variations in the sensitivity of each element, small irregularities and large central depressions occur in the output waveform. The reason why the output of the pixels at both ends is reduced and the entire output waveform has a mountain shape is due to a decrease in the amount of light around the lens. Therefore, a correction coefficient for converting the output waveform shown in FIG. 7A into the output waveform shown in FIG.

The correction coefficient Hi of the i-th pixel is obtained by the following equation.

[0004]

## EQU00001 ## Hi = AVE (a1..an) / ai (1) i = 1. . . n where AVE (a1 ... an) is the average value of the outputs from a1 to an. When the correction is performed, each pixel output ai is multiplied by the corresponding correction coefficient Hi, and all the pixel outputs become AVE (a1... An), and the output waveform shown in FIG.

The same applies to the B column of the image sensor array ISA. However, if the variation in sensitivity is too large, it cannot be corrected naturally. For example, when there is a pixel having extremely higher sensitivity than other pixels, if the light beam incident on the pixel is bright, the output is saturated before the other pixels, and accurate correction cannot be performed. When there is a pixel having extremely low sensitivity, the resolution of the pixel is deteriorated. Therefore, it is preferable not to use an image sensor array having a large variation in sensitivity.

Therefore, it is determined whether the sensitivity nonuniformity of the image sensor array is good or bad. The determination method is based on, for example, whether the difference between the maximum value of the correction coefficient Hi and 1 and (Hi-1) are equal to or smaller than a predetermined threshold value. However, when the correction coefficient Hi is measured by using the focus detection optical system, the correction coefficient Hi becomes a correction coefficient Hi including aberration of the focus detection optical system. The measurement of the correction coefficient Hi is performed under an optical system having no or negligible aberration.

FIG. 5 is a diagram showing an image sensor. The image sensor shown in FIG. 5A includes a base B having columns A and B of an image sensor array ISA and peripheral circuits (not shown) for driving the image sensor ISA.
S and package PKG that holds and protects this base BS
And a glass plate SG for sealing the upper surface of the package PKG. Further, for the package PKG, ceramic or the like is used to improve heat radiation efficiency. FIG. 5 (2)
The image sensor shown in FIG. 5 has the entire base BS covered with a transparent resin package TPKG instead of the package PKG made of ceramic or the like shown in FIG. 5A or the glass plate SG. By doing so, there is an advantage that the image sensor can be manufactured at low cost.

[0008] In the above prior art, the glass plate SG
Alternatively, the transparent resin package TPKG forms a light receiving unit.

[0009]

If the sealing glass plate or the transparent resin package has dust or scratches, the output of the image sensor array is also affected. In a state where a focus detection optical system of a known phase difference detection method as shown in FIG. 6 is provided, for example, when dust is enclosed near the surface of a resinous package, an image receiving a light flux of uniform luminance is received. Figure 8 shows the output of the sensor array.
As shown in the figure, the shadow of dust is projected. At first glance, this output waveform is similar to the output of the image sensor array in which the sensitivity non-uniformity occurs.

However, if there is dust or scratches, the following problems occur. In the case of a subject having a black solid white line as shown in FIG. 9A, the desired output of the image sensor array is the output shown in FIG. The output before the correction is as shown in FIG. 10A, and the amount of light incident on the pixel ap due to dust or scratches is reduced.
Output SDW also becomes smaller. Further, since scattered light due to dust or scratches enters the pixel aq which is originally a black area, that is, an area where the output is small, the output DFSD of the pixel aq
W increases. Even if the output as shown in FIG. 10A is corrected by the correction coefficient calculated by the above equation 1, the output becomes as shown in FIG.
The DW is corrected, but the output DFSDW of the pixel aq is not corrected. Therefore, a desired output as shown in FIG. 9B cannot be obtained. That is, a false contrast due to dust, scratches, or the like is formed in the pixel aq, and the focus adjustment state of the photographing lens 100 is determined based on the false contrast by a known calculation process, which may cause false focusing. Will be higher.

As described above, the output of an image sensor array in which dust or scratches are present near the surface of the resin package is similar to the output of an image sensor array with poor sensitivity nonuniformity, but has good sensitivity nonuniformity. Even if the output is determined to be good in the defect determination, the sensitivity nonuniformity correction cannot correct the scattered light due to dust or scratches. In order to judge an image sensor array having such dust or scratches as defective, a method of reducing the threshold value for good / bad determination of non-uniform sensitivity may be considered. Even if the image sensor array can be corrected by the non-uniformity correction, it is determined to be defective, and the yield is deteriorated.

Accordingly, the present invention provides an image sensor in which the output corresponding to a subject having uniform luminance varies from pixel to pixel, and the determination of good / bad sensitivity non-uniformity is made stricter than necessary to reduce the yield of the image sensor. An object of the present invention is to determine only the presence or absence of dust, scratches, and the like that adversely affect the focus detection operation without deteriorating.

[0013]

SUMMARY OF THE INVENTION In order to solve such a problem, the present invention is directed to an image sensor IS that outputs an image signal corresponding to a light intensity distribution. Based on the first output when the light beam PB is irradiated and the second output when the image sensor IS is irradiated with the diffused light beam DB having uniform illuminance, a foreign matter is formed on the light receiving portion of the image sensor IS. Is to check for the existence of

According to a second aspect of the present invention, an image sensor IS
The presence of a foreign substance on the light receiving unit is determined by the first output, which is the output of each pixel of the image sensor IS, and the second output, which is the output of each pixel of the image sensor IS. In this case, the inspection is performed based on the output difference. According to a third aspect of the present invention, there is provided a light source device capable of selectively irradiating a parallel light beam PB and a diffuse light beam DB with uniform illuminance, and a light receiving unit of an image sensor IS for outputting an image signal corresponding to a light intensity distribution. Inspection means for inspecting whether a foreign substance is present.

According to a fourth aspect of the present invention, the inspection means includes a first output when the image sensor IS is irradiated with the parallel light flux PB having a uniform illuminance, and a uniform illuminance with respect to the image sensor IS. When the diffused light beam DB is irradiated
Is used to check whether a foreign substance exists on the light receiving portion of the image sensor IS based on the output of the image sensor IS.

According to a fifth aspect of the present invention, there is provided the image processing apparatus according to claim 1, wherein said first output is an image sensor IS output for each pixel, and said second output is an image sensor IS output for each pixel. Is to check whether or not a foreign substance exists on the light receiving portion of the image sensor IS based on the output difference at.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing an embodiment of the present invention. The light from the light source Lp is the lens L
Due to s, the light becomes parallel light PB and enters the image sensor IS. When the diffusion plate WB is inserted between the lens Ls and the image sensor IS, the parallel light PB becomes the diffusion light DB and enters the image sensor IS. In either case, the illuminance is made uniform on the image sensor IS.

FIG. 2A is a schematic diagram showing how parallel light PB is incident on the image sensor array ISA. The parallel light PB indicated by the solid arrow is uniformly incident on the pixels a1 to an of the image sensor array ISA, but part of the parallel light PB is scattered by the dust TR, so that the amount of light incident on the pixel ap immediately below the dust TR is Extremely low. Then, a part of the scattered light SB due to the dust TR enters the pixel aq. The pixel ax is assumed to have lower sensitivity than the other pixels. The output of the image sensor array ISA in this case is as shown in FIG. The output of the pixel ap is smaller than other pixels because the incident light is small and the pixel ax has low sensitivity. Further FIG.
The output of the pixel aq where the scattered light SB shown in (2) is incident is:
Unlike the output as shown in FIG. 10 (2), the light amount of the light beam directly incident on the pixel aq is large. That is, pixel a
The output of q itself is large. Therefore, even if the scattered light SB, which is a small amount of light with respect to the amount of the light beam directly entering, is added to the pixel aq, it is negligibly small.
The output of the pixel aq is approximately the same as the output of the other pixels. When the light flux from the subject having uniform brightness is irradiated onto the image sensor array ISA in the form of the parallel light PB, the output reflects both the sensitivity non-uniformity and the presence / absence of dust TR and scratches.

FIG. 3A is a schematic diagram showing a state where the diffused light DB enters the image sensor array ISA. The parallel light PB is diffused by the diffusion plate WB, and the diffused light DB is transmitted from each pixel a1 to a of the image sensor array ISA.
n. Part of the light is further scattered by the dust TR, but the amount of light incident on the pixel ap immediately below the dust TR is not different from other pixels. The output of the image sensor array ISA in this case is as shown in FIG. Since the pixel ax has low sensitivity, the output is also smaller than the other pixels. However, the pixel ap has the same amount of incident light as the other pixels, so that the output is naturally the same as the other pixels, and the shadow of dust as shown in FIG. 2B disappears. Irradiating the luminous flux from the subject with uniform luminance in this way reflects the sensitivity non-uniformity,
The presence or absence of dust TR or scratches is not reflected.

FIG. 4 shows output waveforms obtained by subtracting the corresponding pixel outputs shown in FIG. 2 (2) from the pixel outputs shown in FIG. 3 (2). The concave waveform due to the dust TR remains, but the concave waveform due to the non-uniform sensitivity is canceled and disappears. In this way, it is possible to determine whether the unevenness appearing in the output of the image sensor array is due to non-uniformity in sensitivity or due to dust, scratches, or the like.

For example, in an image sensor inspection process, first, an output as shown in FIG. 3 (2) is measured by irradiating a diffused light DB, and based on the output, good / bad determination of sensitivity non-uniformity is performed. Do. If the correction coefficient calculated by the above equation 1 is equal to or smaller than the predetermined threshold value, a good decision is made, and only the image sensor which has received this good decision is irradiated with the parallel light PB as shown in FIG. The output may be measured, and the output waveform shown in FIG. 4 may be determined to determine the presence or absence of dust or flaws.

When measuring the outputs shown in FIGS. 2 (2) and 3 (2), the outputs may be averaged a plurality of times in order to avoid the influence of random noise. If the output of the image sensor adversely affects the focus detection operation due to dust or scratches, the image sensor is not used. Here, a description will be given of the use of an image sensor that is determined as good for both the sensitivity nonuniformity and the presence / absence of dust, scratches, and the like in a focus detection device of a camera.

FIG. 6 is a diagram showing an optical system of a focus detection device of a known phase difference detection system. The light beam incident from the exit pupil region 101 of the photographing lens 100 includes a bandpass filter 700, a field mask 200, a field lens 300,
The light passes through the aperture opening 401 and the re-imaging lens 501, and forms an image on the A column of the image sensor array ISA. Similarly, a light beam incident from the exit pupil region 102 of the photographing lens 100 includes a bandpass filter 700, a field mask 200,
The image sensor array ISA passes through the field lens 300, the aperture 402, and the re-imaging lens 502.
Is formed on the B column. This image sensor array IS
The focus adjustment state of the photographing lens 100 can be determined by performing a known calculation process on the output signal of A. The image sensor having the image sensor array ISA used here is an image sensor that is determined to be good in both the sensitivity non-uniformity and the presence / absence of dust or scratches. As described above, since the image sensor in which the output of the image sensor array ISA is not lost due to dust or scratches is used for the focus detection device, more accurate focus detection can be performed.

In the embodiment of the present invention, the corresponding pixel output shown in FIG. 2 (2) is subtracted from the pixel output shown in FIG. 3 (2). However, the present invention is not limited to this. The corresponding pixel output shown in FIG. 3 (2) may be subtracted from the pixel output shown in 2 (2). Further, although the focus detection device of the camera has been described in the embodiment of the present invention, the present invention is not limited to this.
The present invention is also effective for inspection of image sensors used in other fields such as for video and scanner.

In the embodiment of the present invention, the parallel light PB represents a parallel light flux, the diffused light DB represents a diffused light flux, and the dust TR
Scratches, scratches, etc. constitute foreign substances.

[0026]

As described above, according to the present invention, it is possible to determine an image sensor whose output varies from pixel to pixel due to dust or scratches regardless of sensitivity non-uniformity. Sensors can be eliminated. Further, in an image sensor in which the output corresponding to a subject having uniform luminance varies from pixel to pixel, it is not necessary to make the determination of good / bad sensitivity nonuniformity unnecessarily strict, thereby lowering the yield of the image sensor.

Further, by using an image sensor having an accurate output for the focus detection device, the accuracy of focus detection can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic diagram in the case where parallel light is irradiated.

FIG. 3 is a schematic diagram when irradiation with diffused light is performed.

FIG. 4 is an output diagram obtained by subtracting the output of FIG. 2 from the output of FIG. 3;

FIG. 5 is a diagram illustrating a configuration of an image sensor.

FIG. 6 is a diagram illustrating an optical system and an image sensor array of a focus detection device using a phase difference detection method.

FIG. 7 is a diagram illustrating sensitivity non-uniformity.

FIG. 8 is a diagram for explaining the influence of dust and scratches on the focus detection operation.

FIG. 9 is a diagram for explaining the influence of dust and scratches on the focus detection operation.

FIG. 10 is a diagram for explaining the influence of dust and scratches on the focus detection operation.

[Explanation of symbols]

 Lp light source Ls lens WB diffuser PB parallel light DB diffused light IS image sensor ISA image sensor array

Claims (5)

[Claims] 1. A first output when a parallel luminous flux of uniform illuminance is irradiated to an image sensor that outputs an image signal corresponding to a light intensity distribution, and a first output of uniform illuminance to the image sensor. A method for inspecting an image sensor, comprising: inspecting whether a foreign substance is present on a light receiving portion of the image sensor based on a second output when the diffused light beam is irradiated. 2. The image sensor inspection method according to claim 1, wherein the presence of a foreign substance on a light receiving portion of the image sensor includes an output for each pixel of the image sensor, which is the first output. An inspection method for an image sensor, wherein the inspection is performed based on an output difference at each pixel from an output of each pixel of the image sensor as the second output. 3. A light source device capable of selectively irradiating a parallel light beam and a diffuse light beam with uniform illuminance, and a foreign object present on a light receiving portion of an image sensor for outputting an image signal corresponding to a light intensity distribution. An inspection device for an image sensor, comprising: inspection means for inspecting whether or not the image sensor is present. 4. The image sensor inspection apparatus according to claim 3, wherein the inspection unit outputs a first output when the image sensor is irradiated with a parallel light beam having a uniform illuminance, and the image sensor. And a second output in the case of irradiating a diffused light beam with uniform illuminance with respect to the image sensor. Inspection equipment. 5. The image sensor inspection device according to claim 4, wherein the inspection unit is an output for each pixel of the image sensor that is the first output, and the second output is the second output. An inspection apparatus for an image sensor, comprising: inspecting whether a foreign substance is present on a light receiving portion of the image sensor based on an output difference of each pixel from an output of each pixel of the image sensor.