JP5747846B2 - Chart inspection method, inspection apparatus, and image sensor for shading correction of image sensor using defocus - Google Patents

Description

The present invention relates to an inspection method, an inspection apparatus, and an image sensor for detecting foreign matter and scratches on a shading correction chart of an image sensor.

In an image sensor used in an apparatus that optically reads a document, a black reference value when a light source is turned off and a white reference value when a light source is turned on are based on a reading value of a white chart called a shading correction chart. A process for normalizing the sensitivity characteristics of the sensor chip is performed. However, if a foreign object or a flaw occurs on the shading correction chart, an error occurs in the white reference value, and the black and white correction cannot be performed correctly. Therefore, it is necessary to detect the foreign object or the flaw. For this reason, the method shown in Patent Document 1 is used as a method for detecting dust and scratches on the shading correction chart.

That is, as shown in Patent Document 1, after scanning a test chart in which a black band and a gray band of a predetermined density are printed in the center, and when scan data is taken into inspection software, a black band of a scanned image, And gray strips are extracted. The line average value X (i), matrix average value Y (i), matrix average value Y (i), and standard deviation σ of each line average value X (i) in the i-th column are calculated for each of the extracted black and gray bands, and X It is sequentially determined whether (i) is in a relationship of Y (i) −4σ <X (i) <Y (i) + 4σ. A method is disclosed in which i is stored as a pixel having an abnormality in shading data when X (i) is not in the above-mentioned range.

JP 2007-267078 A

However, in the shading data inspection method disclosed in Patent Document 1, the non-defective range of X (i) is defined as Y (i) ± 4σ (X (i) is the average value in the sub-scanning direction of the target pixel, and Y (i) is Since the average value of 8 pixels around the pixel of interest, σ is the standard deviation of each line average value X (i)), there are the following problems.
1) When the image sensor is composed of a plurality of sensor chips, if there is a large difference in output luminance between sensor chips due to the influence of the sensitivity difference between the sensor chips, the above-mentioned σ becomes large. It is difficult to determine whether or not the shading data is appropriate.
2) When the image sensor is composed of a plurality of sensor chips, if there is a large difference in output luminance between the sensor chips due to the sensitivity difference of the sensor chips, Y (i) and X Since the difference of (i) becomes large, it is difficult to judge good / bad.

The present invention has been made to solve the above problems, and even if there are foreign objects or scratches generated on the shading correction chart, these foreign objects or scratches can be detected efficiently and reliably. An object of the present invention is to provide an image sensor shading correction chart inspection method, an inspection apparatus, and an image sensor capable of determining a defect and generating an appropriate white reference value.

In order to solve the above-described problem, the image sensor shading correction chart inspection method of the present invention uses an image sensor and the shading correction chart data imaged at a regular distance and the shading correction image data defocused and imaged. Using the chart data, the difference data of the same pixel is generated, and the generated difference data of the same pixel is subjected to threshold processing, thereby detecting the occurrence of foreign matter or scratches on the shading correction chart.

The image sensor shading correction chart inspection apparatus according to the present invention includes a shading correction chart, moving means for changing an imaging distance between the image sensor and the shading correction chart, and shading correction read by the image sensor. Means for analyzing pixel data of the chart, and means for storing adjustment information of each pixel of the image sensor in a memory of the image sensor,
Shading correction is performed by generating difference data for the same pixel using the shading correction chart data imaged at a regular distance and the shading correction chart data imaged after defocusing, and thresholding the difference data for the same pixel. If foreign matter or scratches are detected on the correction chart and it is determined that there are no foreign matter or scratches, the shading correction chart data captured at a regular distance is stored in the image sensor memory as a white reference value. If it is determined that the shading correction chart is present, it is determined that the shading correction chart is abnormal, and the captured shading correction chart data is discarded.

Furthermore, the image sensor of the present invention generates difference data of the same pixel using the data of the shading correction chart imaged at a normal distance and the data of the shading correction chart imaged after defocusing, and generates the data The difference data of the same pixel is thresholded to detect the occurrence of foreign matter or scratches on the shading correction chart, and when it is determined that there is no foreign matter or scratches, the captured shading correction chart data is used as a white reference. An image sensor created using a shading correction chart inspection device as a value, and having a memory storing a white reference value for each pixel determined by the shading correction chart inspection device of the image sensor is there.

According to the present invention, when the white reference value used for shading correction by the image sensor is generated, the presence or absence of foreign matter or scratches attached to the surface of the shading correction chart can be detected, and it can be determined that there is no foreign matter or scratches. The captured shading correction chart data is held as a white reference value. If it is determined that there is a foreign object or a flaw, the shading correction chart data is abnormal, the captured shading correction chart data is discarded, and an appropriate There is an effect that shading correction can be performed.

The front view of the structural example of the inspection apparatus in Embodiment 1 of this invention is shown. The side view of the structural example of the test | inspection apparatus in Embodiment 1 of this invention is shown. It is a figure which shows an example of the chart layout in Embodiment 1 of this invention. It is a figure which shows an example of the connection structure of the apparatus used for the test | inspection apparatus in Embodiment 1 of this invention. It is a figure which shows operation | movement of the inspection apparatus in Embodiment 1 of this invention. It is explanatory drawing which shows the detection method of the damage | wound on a chart by the defocus in Embodiment 1 of this invention, and dust.

An image sensor shading correction chart inspection method, an image sensor shading correction chart inspection apparatus, and an image sensor according to embodiments of the present invention will be described below with reference to FIGS.

Embodiment 1 FIG.
FIG. 1 shows a front view of a configuration example of the inspection apparatus of the present invention, and FIG. 2 shows a side view of the configuration example of the inspection apparatus.
In FIG. 1, an image sensor 1 to be inspected is a one-dimensional sensor. In order to perform an adjustment test on the optical characteristics of the image sensor 1, illumination light is irradiated onto the chart 2 and reflected light is input.
In order to capture a two-dimensional image with the image sensor 1, the chart drive unit 3 is used to move the relative position of the chart 2 in the sub-scanning direction of the image sensor 1. Further, the image sensor 1 is installed on the inspection table 7 and is fixed to the image sensor installation table by the sensor fixing unit 8 so that the position of the image sensor is not shifted on the inspection table during the adjustment test. Further, the moving means 6 is used to change the distance between the image sensor 1 and the chart 2 in the optical axis direction of the image sensor 1 to adjust the focus. The apparatus cover 9 has a function of blocking ambient light from being input to the image sensor 1 and protecting an operator from the apparatus operating unit.

FIG. 3 shows a chart layout of the present invention.
A chart 2 used for a plurality of adjustment tests is installed on the chart driving means 3. Here, the plurality of adjustment tests means brightness adjustment, color variation adjustment, brightness test, color variation test, and the like (the same applies hereinafter). In FIG. 3, each chart (shown by charts 2 (i) and (i = 1 to n) in the figure) has a length that covers the size of the image sensor 1 in the main scanning direction, and is in the sub-scanning direction. It is the length that can capture multiple lines while moving to. The length in the sub-scanning direction is determined by the number of lines that need to be captured in the adjustment test, the capture speed of the image sensor 1, and the movement speed of the chart driving means 3. The moving speed of the chart driving means 3 is often set to a speed at which the size of one pixel output from the image sensor 1 is the same in the main scanning direction and the sub scanning direction. The size of one pixel on the chart in the main scanning direction (usually about several tens of μm to several hundreds of μm) is uniquely determined by the pixel size of the image sensor (in this application, the same size as the one pixel). In accordance with the main pixel size, the chart driving unit 3 is set to move in the sub-scanning direction by the size of one pixel in the main scanning direction during the time when the image sensor 1 captures an image of one line in the sub-scanning direction. .

FIG. 4 shows a device connection configuration of the present invention.
The video data 13 output from the image sensor 1 is fetched into the memory 12 via the relay board 10 and the fetching means 4, and the video data 13 fetched using the analyzing means 5 is processed. The relay board 10 also relays the control signal 14 to the image sensor 1.
In this system, the entire device is controlled mainly by the overall control unit 11, and video data is output from the image sensor 1 by sending a control signal 14 to the image sensor 1 via the relay board 10. . The overall control unit 11 is configured by a device such as a personal computer, for example.

The image sensor 1 held on the inspection table 8 takes in the video data of the chart 2 by moving the chart driving means 3. The captured video data 13 is transferred to the capturing means 4 via the relay board 10 and stored in the memory 12. The capturing unit 4 is configured by a device such as a frame grabber, and the video data 13 is converted into a standardized video signal such as CameraLink inside the relay substrate 10 and is captured by the capturing unit 4. By converting the signal by the relay board 10, it is possible to capture the video data by the capturing unit 4 regardless of the specifications of the video data 13 from the image sensor 1. The analysis unit 5 uses the video data 13 stored in the memory 12 to perform normalization of the brightness of the image sensor itself and an adjustment test for color variation.

FIG. 5 shows the operation of the apparatus of the present invention.
FIG. 5A shows an initial state of operation. A sensor fixing unit 8 is installed on the inspection table 7, and the inspection table 7 is installed at a position away from the chart 2 on the chart driving unit 3 by moving means (not shown). Similarly to the above, the apparatus cover 9 blocks the disturbance light from being input to the image sensor 1.
FIG. 5B is a diagram illustrating a state in which the image sensor 1 is installed on the inspection table 7.
FIG. 5C is a diagram showing a fixed state of the image sensor 1. The sensor fixing unit 8 is lowered and the main body of the image sensor 1 is fixed to the inspection table 7. This is because there is a possibility that the position shift of the image sensor 1 on the inspection table 7 may occur by moving the image sensor 1 in the adjustment test. The arrow indicates the moving direction of the sensor fixing part.
FIG. 5D is a diagram illustrating an imaging state of the image sensor 1. The inspection table 7 is lowered by moving means (not shown), and the position of the chart 2 is set to the focal position of the image sensor 1. In this state, video data is captured from the image sensor 1 via a relay board (not shown) in synchronization with the movement of the chart 2 using the chart driving means 3. The moving direction of the inspection table is shown.

Here, FIG. 6 shows an operation when a foreign object or a flaw is attached on the shading correction chart (one of the charts in FIG. 3 corresponds to the shading correction chart). That is, the shading correction chart mentioned here is a part of the chart 2 described above, and the chart 2 includes various adjustments (color adjustment, black and white adjustment, etc.) and tests (color adjustment test) in addition to the shading correction chart. Etc.) are installed.

  Video data captured by the image sensor 1 has a variation in video data called shading caused by variations in filter transmittance of the image sensor, variations in the amount of light due to the imaging lens, variations in illumination intensity of the illumination system, and the like. . However, ideally, the video data output from each pixel of the image sensor needs to be constant when a surface with little variation in white reflectance, that is, when a shading correction chart is captured. Therefore, the video data when the shading correction chart is imaged is the white reference value, the video data when the illumination light is turned off and the image is captured without reflection from the imaging surface is the black reference value, and the white reference value and the black By performing shading correction that normalizes the video data captured between the reference values, luminance variation for each pixel of the image sensor is reduced.

However, if the above-mentioned shading correction chart has foreign matter attached or scratched, the reflectance of the chart varies, and an error occurs in the acquired white reference value. For this reason, normalization processing cannot be performed correctly, and thereafter, image data corresponding to foreign matter or scratched parts on the shading correction chart in reading of all image data includes errors at the time of normalization. Value. For this reason, it is necessary to detect foreign matter and scratches on the shading correction chart.

The luminance distribution when defocusing is performed with a solid line (curve indicated by A in the figure) when the shading correction chart is imaged at a normal distance, that is, in a focused state in FIG. Is indicated by a broken line (curve indicated by B in the figure). On the shading correction chart, a portion considered to be attached or scratched as indicated by C is imaged, and a black point C is obtained.
FIG. 6B shows a graph in which the difference values between the solid line (A) and the broken line (B) acquired in FIG. 6A are plotted.

In FIG. 6B, the difference value is large at a place where dust or scratches are considered to be attached (the place indicated by C in the figure), and the difference value is small at other places. The difference value D of each pixel where there is no dust adhesion or scratch can be defined by the output variation of the image sensor or the fluctuation of the reflectance of the shading correction chart. For this reason, a threshold value (not shown) is set to be defined as 0 (zero), for example, and the presence or absence of dust or scratches on the shading correction chart is determined by detecting a portion below this threshold value. I can do it.

In addition, when dust or scratches are attached to the image sensor, the amount of light input to the image sensor is blocked regardless of the image pickup location of the shading correction chart, and as shown in C in FIG. A luminance difference occurs in the main scanning direction, but no luminance difference occurs in the sub scanning direction. Thereby, in FIG. 6B, it is possible to determine only dust and scratches on the shading correction chart. That is, A can be distinguished from dust and scratches on the shading correction chart as indicating a defect related to the image sensor.

If it can be determined that there is no dust or scratches on the shading correction chart, the captured luminance distribution is stored in the image sensor memory as a white reference value, and used for normalization processing of the subsequent captured image, resulting in uniform whiteness. It is possible to output a surface (a uniform reflection surface free from dust and scratches) at a constant luminance level. If it is determined that there is a foreign object or a flaw, it is determined that the shading correction chart is abnormal, the captured shading correction chart data is discarded, and abnormal shading correction is not performed, that is, proper shading correction is possible.

DESCRIPTION OF SYMBOLS 1 Image sensor, 2 chart, 3 chart drive means, 4 acquisition means, 5 analysis means, 6 moving means, 7 inspection stand, 8 sensor fixing | fixed part, 9 apparatus cover, 10 relay board, 11 whole control part, 12 memory, 13 video data, 14 control signals.

Claims (3)

Using the image sensor, the data of the shading correction chart imaged at a normal distance and the data of the shading correction chart imaged after defocusing are used to generate difference data of the same pixel, and the generated same pixel An image sensor shading correction chart inspection method that uses defocusing to detect the occurrence of foreign matter or scratches on a shading correction chart by thresholding difference data. A shading correction chart, a moving means for changing an imaging distance between the image sensor and the shading correction chart, a means for analyzing pixel data of the shading correction chart read by the image sensor, and each pixel of the image sensor Means for storing the adjustment information in the memory of the image sensor,
Shading correction is performed by generating difference data for the same pixel using the shading correction chart data imaged at a regular distance and the shading correction chart data imaged after defocusing, and thresholding the difference data for the same pixel. Detecting foreign matter and scratches on the correction chart, and if it is determined that there is no foreign matter or scratches, the shading correction chart data captured at a regular distance is stored as a white reference value in the memory of the image sensor. Chart inspection device for shading correction of image sensor using defocus. Using the data of the shading correction chart imaged at a regular distance and the data of the shading correction chart imaged after defocusing, the difference data of the same pixel is generated, and the generated difference data of the same pixel is thresholded. By detecting the occurrence of foreign matter or scratches on the shading correction chart and determining that there are no foreign matter or scratches, the shading correction chart inspection device that uses the captured shading correction chart data as a white reference value An image sensor comprising: a memory in which a white reference value for each pixel determined by a shading correction chart inspection device of the image sensor is stored.

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