JP2005309651A - Shading processor and shading processing method for imaging element and imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform a precise shading inspection and correction further matched to human visual characteristics. <P>SOLUTION: This shading processor comprises a first detection means detecting the change rate of image data in a predetermined measuring area set within the image data; a second detection means dividing the measuring area to a plurality of areas in a case that the change rate detected by the first detection means is determined to be larger than a predetermined value, and detecting the change rate of the image data for each of the divided measuring areas; and an arithmetic means determining a shading correction value based on the detection results detected by the first and second detection means. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to shading inspection and shading correction of an image sensor and an imaging apparatus.

  The image sensor is formed from a large number of pixels, but due to manufacturing, each pixel has uneven aperture, uneven etching, uneven filter staining, etc., and it is difficult to have uniform light receiving characteristics on the entire light receiving surface of the image sensor. It is. This can cause problems with luminance shading or color shading.

  Conventionally, as a method for inspecting such luminance shading and color shading, the entire light-receiving surface is divided into blocks of x × y, and the maximum value and minimum value of luminance or color difference data between each area are obtained, and (maximum value−minimum value). Value) There was a method for judging good and defective products based on the data size. As another method for inspecting luminance shading or color shading, there is a method in which a test operator performs a visual evaluation by visual comparison with a reference image to judge a non-defective product or a defective product.

Further, as a first method of correcting luminance shading and color shading, there is a method of performing correction of luminance shading or color shading by having correction data for each pixel of an image captured by an imaging apparatus. As a second method, an image captured by the imaging device is divided into a plurality of regions, the distance from the center of the imaging surface of the target pixel is obtained, and luminance shading or color shading correction is performed according to the distance information. There was a way. (For example, Reference 1)
JP 2003-348604 A

  Divide the entire light-receiving surface into blocks (xxy), determine the maximum and minimum values of luminance or color difference data between each area, and determine whether the product is good or defective based on the size of (maximum value-minimum value) data. Since the method does not take into account the degree of change in luminance or color difference signal, for example, the case where the luminance or color changes sharply, it often does not match human visual characteristics. Further, in the method in which the test operator performs the visual inspection, when the same operator performs the inspection for a long time, the inspection result may vary. In addition, if the test operator changes, there will be a difference in individual inspection.

  Further, in the first method of luminance shading or color shading correction, an image captured by the imaging device can be corrected for each pixel, so that correction with very high accuracy is possible. However, since it is necessary to have correction data for each pixel, a large-capacity correction memory is required. For example, if the correction data necessary for the image data of 2048 pixels in the horizontal direction and 1536 pixels in the vertical direction has 8 bits for each color, that is, 3 × 8 = 24 bits for R, G, B, 2048 × 1536 × 24 = Approximately 75.5 Mbits of correction data is required. Further, when there are a plurality of zoom and aperture parameters, an enormous amount of correction data memory that is several times or several tens of times larger than 75.5 Mbits is required. In the second method, the correction data memory can be reduced because the entire screen is divided. However, when linearly interpolating each area, correction error does not occur if the luminance or color changes linearly with respect to the luminance or color of the subject, but if the luminance or color changes sharply, the correction error Will occur depending on the degree of steepness.

  In order to achieve the above object, a first detection means for detecting a change rate of image data in a predetermined measurement region set in image data, and a change rate detected by the first detection means from a predetermined value A second detection unit that divides the measurement region into a plurality of regions and detects a change rate of the image data for each of the divided plurality of measurement regions; The present invention provides a shading processing apparatus characterized by comprising an arithmetic means for obtaining a shading correction value based on a detection result detected from the second detection means. The shading processing apparatus stores a shading correction value for each of a plurality of divided areas, and the change rate of the image data is smaller than the predetermined value in an area where the change rate of the image data is larger than the predetermined value. A storage means for storing a shading correction value for each area by setting the number of area divisions larger than the area, and a correction for correcting image data using the shading correction value stored in the storage means. There is provided a shading processing apparatus characterized by comprising means.

  Also, a first detection step for detecting a change rate of image data in a predetermined measurement region set in the image data, and a change rate detected in the first detection step is determined to be larger than a predetermined value. In this case, a second detection step of dividing the measurement region into a plurality of regions and detecting a change rate of the image data for each of the plurality of divided measurement regions, and the first and second detection steps And a calculation step for obtaining a shading correction value based on the detection result detected from the above. The shading correction method stores a shading correction value for each of a plurality of divided areas, and the change rate of the image data is smaller than the predetermined value for an area where the change rate of the image data is larger than the predetermined value. A storage step of storing a shading correction value for each region by setting the number of divisions of the region larger than that of the region, and a correction for correcting the image data using the shading correction value stored in the storage step There is provided a shading processing method characterized by comprising steps.

  According to the present invention, it is possible to perform a highly accurate shading inspection that matches a human visual characteristic. In addition, shading correction with less correction error can be performed with the minimum necessary memory capacity.

(Example 1)
Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the luminance or color shading processing apparatus of the present embodiment. FIG. 2 is a diagram illustrating a measurement region of image data according to the present embodiment. FIG. 3 is a flowchart of the luminance or color shading inspection of this embodiment.

  First, the function of each part in FIG. 1 will be described. Reference numeral 10 denotes a light source that generates light of a uniform surface on an inspection target, and reference numeral 20 denotes an imaging device that is an inspection target for luminance or color shading. In this embodiment, the image pickup apparatus is a digital still camera 20, and the internal functions are described in detail. Reference numeral 22 denotes an image pickup element (CCD 22 in this embodiment) that converts light into an electrical signal, and 21 denotes light from the light source 10. A lens for focusing on the CCD 22, 23 an A / D conversion circuit for converting an analog video signal output from the CCD 22 into a digital signal, 24 an image memory for storing digitally converted image data, and 25 for controlling the imaging device The control means (CPU 25 in this embodiment) and 26 are composed of a communication circuit for transmitting image data to the outside. Reference numeral 30 denotes a luminance or color shading processing device for inspecting the digital still camera 20. The internal functions are described in detail. 31 is a communication circuit for capturing image data of the digital still camera 20, and 32 is image data captured by the communication circuit 31. , 33 is a change rate calculating means for quantifying the change rate of luminance or color shading of the image data (detection means for detecting the change rate in claims 1 to 7), and 34 is a numerical value. Determining means 35 for judging pass (non-defective) / fail (defective), 35 is a control means for controlling the change rate calculating means 33 and the judging means 34. In this embodiment, 33, 34, and 35 are software on the CPU 36. Each function is realized.

  Next, the flow of the color shading inspection embodiment of the present invention will be described with reference to the flowchart of FIG. First, with the digital still camera 20 to be inspected, light of a uniform surface of the light source 10 (light having a predetermined luminance value set in advance) is photographed with white balance adjusted at the center (S102). As described above, the light of the uniform surface is converted into a digital signal through the lens 21, CCD 22, and A / D converter 23, then recorded in the image memory, and finally through the communication circuits 26 and 31, the image of the processing device 30. It is recorded as image data in the memory 32 (S103). Next, the luminance or color shading change rate of the image data is digitized. In this embodiment, the change rate of the color shading is divided into m × n screens as shown in FIG. 2, here 5 × 5 = 25. An example of dividing and digitizing will be described.

  First, an average value of color difference signals is obtained for each area (S104). The average value of the color difference signal can express the average degree of coloring in each area. For example, when obtaining the average value of the color difference signals in the x1y1 area, the average value of the color difference signals is obtained from all the pixels in the x1y1 area or thinned pixels. When the image obtained in S103 is JPEG and uses Cr and Cb as color difference signals, an average value Cr (ave) of x1y1 area Cr and an average value Cb (ave) of Cb are calculated. Next, the determination means 34 determines whether the average value Cr (ave) of Cr and the average value Cb (ave) of Cb in each area satisfy a preset standard value (S105).

In this example, Cr (ave) <Cr (ave standard)
Cb (ave) <Cb (ave standard)
Is satisfied in all areas, the inspection of this item is passed, and the process proceeds to S106. If the standard value cannot be satisfied even in one of all the areas, it is determined that the degree of coloring is high, and the inspection is determined to be unacceptable (S109). If it passes in S105, then the standard deviation of the color difference signal is obtained for each area (S106). The standard deviation of the color difference signal can express the color change rate in each area. For example, as shown in FIG. 4, in the case where the color suddenly changes from green to magenta in the x1y3, x2y4, and x3y5 areas, the distribution of Cr shown in FIG. The axis represents the color distribution, and the vertical axis represents the number n of pixels of each color). On the other hand, since the distribution shown in FIG. 6 is obtained in an area where the color change is small, the color distribution is increased in the case of a distribution in which the standard deviation becomes higher when comparing FIGS. It can be seen that the rate of change is large. For example, when obtaining the standard deviation of the color difference signal in the x1y2 area, the standard deviation of the color difference signal is obtained from all the pixels in the x1y2 area or pixels thinned out. When the image obtained in S103 is JPEG and Cr and Cb are used as color difference signals, the standard deviation Cr (stdev) of the x1y1 area Cr and the standard deviation Cb (stdev) of Cb are calculated. Next, the determination means 34 determines whether the standard deviation Cr (stdev) of Cr and the standard deviation Cb (stdev) of Cb in each area satisfy a preset standard value (S107).

In this embodiment, Cr (stdev) <Cr (stdev standard)
Cb (stdev) <Cb (stdev standard)
If all the areas are satisfied, the inspection is finally accepted (S108). If the standard value is not satisfied even in one area in all the areas, it is determined that the color change rate is large, and the inspection is rejected. Determination is made (S109).

  In this embodiment, the communication circuits 26 and 31 are used to inspect the image after it is transmitted and received. In this embodiment, it is determined whether it is acceptable or not based on the inspection result. However, the imaging device 20 and the processing device 30 are integrated, and the inspection is performed by the above method at times other than normal imaging. The image data may be corrected and output based on the inspection result.

  Further, in the present embodiment, the flow of the color shading inspection embodiment has been described with reference to the flowchart of FIG. 3, but in the case of the luminance shading inspection, the average value of the luminance values of the respective areas is calculated and the average of the areas is calculated. The standard value is compared with the standard value, and if it is above the reference value, the test is rejected. If the standard value is below the standard value, the standard deviation of the brightness value is calculated and the standard deviation of each area is compared with the standard value. The pass / fail judgment is performed. In other words, the luminance signal and the color signal can be subjected to the same procedure, and shading determination suitable for each imaging device or imaging element can be performed.

(Example 2)
An embodiment of a correction coefficient calculation method for color shading correction according to the present invention will be described with reference to the drawings. FIG. 7 shows an image pickup apparatus according to the present embodiment, which is a block diagram showing a configuration of a digital still camera. FIG. 8 is a flowchart of a color shading correction coefficient calculation method according to the present embodiment, and FIG. 10 is a diagram in which the image data illustrated in FIG. 2 described in the first embodiment is subdivided into areas having a high color change rate.

  First, the function of each part in FIG. 7 will be described. A light source 10 generates light with a uniform surface. Reference numeral 20 denotes an imaging apparatus, which is a digital still camera in this embodiment. The internal function will be described in detail. Reference numeral 22 denotes an image sensor for converting light into an electrical signal, in this embodiment a CCD, 21 a lens for condensing light from the light source 10 onto the CCD 22, and 23 an analog image output from the CCD 22. A / D conversion circuit for converting a signal into a digital video signal; 24, an image memory for storing digitally converted image data; 25, a control means for controlling the imaging device; 33, a change in luminance or color shading of the image data In the present embodiment, 25 and 33 realize the respective functions with the firmware on the CPU 37.

Next, the flow of the embodiment of the present invention will be described using the flowchart of FIG. First, light of a uniform surface of the light source 10 is photographed with the digital still camera 20 with white balance adjusted at the center (S202). As described above, the light of the uniform surface is converted into a digital signal through the lens 21, the CCD 22, and the A / D converter 23, and finally recorded in the image memory 21 (S203). Next, the standard deviation of the color difference signal is obtained for each area with respect to the 25-divided image (FIG. 2) described in the first embodiment. As described above in the first embodiment, the standard deviation of the color difference signal can represent the color change rate in each area. For example, when the standard deviation of the color difference signal in the x1y2 area is obtained, the standard deviation of the color difference signal is obtained from all the pixels in the x1y2 area or thinned pixels. When the image obtained in S203 is JPEG and Cr and Cb are used as color difference signals, the standard deviation Cr (stdev) of the x1y1 area Cr and the standard deviation Cb (stdev) of Cb are calculated (S204). Next, in this embodiment, the square root of the sum of squares of the standard deviation Cr (stdev) of Cr and the standard deviation Cb (stdev) of Cb in each area is calculated (S205).
C = √ (Cr ^ 2 + Cb ^ 2)

The above calculation is performed for all areas, and Cmax of the area having the highest color change rate is extracted (S206). Finally, a shading correction coefficient corresponding to Cmax is determined. In this embodiment, C _100% at the time of complete correction, that is, 100% correction is set in advance,
Cmax / C _100% where Cmax / C _100% <= 1
Is set as a shading correction coefficient (S207).

  Although the color shading correction has been described in the present embodiment, this procedure can be applied to the luminance shading correction as in the first embodiment.

  If shading correction is performed using the shading correction coefficient obtained in this embodiment, the area is divided and corrected for each area, and the luminance or color change rate in each area is numerically corrected. Since the coefficient is obtained, it is possible to perform highly accurate shading correction that matches the human visual characteristics when the luminance and color change sharply. Further, shading correction with a small correction error can be performed with the minimum necessary memory capacity.

The flow of color shading correction in the digital still camera of this embodiment will be described with reference to the flowchart of FIG. First, light of a uniform surface of the light source 10 is photographed by adjusting the white balance at the center with the digital still camera 20 (S302). As described above, the light of the uniform surface is converted into a digital signal through the lens 21, the CCD 22, and the A / D converter 23, and finally recorded in the image memory 24 (S303). Next, the standard deviation of the color difference signal is obtained for each of the 25 divided areas. As described above in the first embodiment, the standard deviation of the color difference signal can express the color change rate in each area. For example, when obtaining the standard deviation of the color difference signal in the x1y2 area, the standard deviation of the color difference signal is obtained from all the pixels in the x1y2 area or pixels thinned out. When the image obtained in S303 is JPEG and uses Cr and Cb as color difference signals, the standard deviation Cr (stdev) of the x1y1 area Cr and the standard deviation Cb (stdev) of Cb are calculated (S304). Next, in this embodiment, the square root of the sum of squares of the standard deviation Cr (stdev) of Cr and the standard deviation Cb (stdev) of Cb in each area is calculated (S305).
C _xnyn = √ (Cr ^ 2 + Cb ^ 2)

Next, it is determined whether C _xnyn calculated in S305 exceeds a preset reference value (S306). When the reference value is not exceeded, it is determined that the color change rate of the image is smaller than the reference value, and correction is performed based on predetermined 25-division shading correction coefficient data. If it exceeds the reference value, it is determined that the color change rate is larger than the reference value, and the measurement area of the image data is subdivided into the area as shown in FIG. 10 (S307). Here, it is determined that the color change rate greatly exceeds the reference value in each of the areas x1y3, x2y4, and x3y5, and in this embodiment, the area is divided into four. 34-division image data to which the subdivided area is added is calculated, and correction is performed using the 34-division shading correction coefficient data and correction data obtained by linear interpolation. As described above, when it is determined that the rate of change exceeds the reference value, the shading correction error caused by the steep color change can be minimized by further dividing and correcting the image area. Further, since only necessary portions can be subdivided, correction data can be reduced (S308).

  In the second embodiment, the change rate is obtained for each region, and the shading correction is performed by dividing the region if necessary. However, if necessary, the region is divided and the change rate for each region is calculated. The correction value may be stored in the storage unit in advance, and shading correction may be performed based on the correction value stored in advance.

It is a block diagram which shows the structure of the brightness | luminance or color shading processing apparatus of the Example of this invention. It is a figure showing the measurement area | region of the image data by the Example of this invention. 4 is a flowchart of luminance or color shading inspection according to an embodiment of the present invention. It is the figure which represented the image data by the Example of this invention for every area. It is a figure showing distribution of Cr in the x1y3, x2y4, x3y5 area of FIG. 4 of the Example of this invention. It is a figure showing distribution of Cr of the area with a small color change in the image data by the Example of this invention. 1 is a block diagram illustrating a configuration of an imaging apparatus according to an embodiment of the present invention, here, a digital still camera. 4 is a flowchart of a method for calculating a color shading correction coefficient according to an embodiment of the present invention. 10 is a flowchart showing a flow of an embodiment of a color shading correction method of Embodiment 3 in the digital still camera described in Embodiment 2; FIG. 3 is a diagram in which the image data in FIG. 2 is subdivided into areas with a high color change rate.

Explanation of symbols

10 Light source 20 Digital still camera 21 Lens 22 CCD
23 A / D conversion circuit 24 Image memory 25 Control means 26 Communication circuit 30 Color unevenness, color shading processing device 31 Communication circuit 32 Image memory 33 Change rate calculation means 34 Determination means 35 Control means

Claims (10)

First detecting means for detecting a rate of change of image data in a predetermined measurement region set in the image data;
If it is determined that the rate of change detected by the first detection means is greater than a predetermined value, the measurement area is divided into a plurality of areas, and the image data of the image data is divided into a plurality of divided measurement areas. A second detection means for detecting the rate of change;
A shading processing apparatus comprising: an arithmetic unit that obtains a shading correction value based on the detection results detected by the first and second detection units.   The shading processing apparatus according to claim 1, further comprising a correcting unit that corrects the image data based on a shading correction value obtained by the calculating unit.   The shading processing apparatus according to claim 1, wherein the first detection unit detects an average value of image data in the predetermined measurement region.   The second detection means is characterized in that a change rate of the image data is detected by obtaining a standard deviation of the image data from a plurality of pixels in the measurement region. Item 4. The shading processing device according to any one of Items 3 to 3.   The rate of change of image data detected by the first and second detection means is a rate of change of luminance in the measurement region or a rate of change of color in the measurement region. The shading processing apparatus according to claim 4. A shading processing device that stores a shading correction value for each of a plurality of divided areas,
For areas where the rate of change of image data is greater than a predetermined value, set the number of area divisions larger than areas where the rate of change of image data is less than a predetermined value, and store shading correction values for each area. Storage means for
A shading processing apparatus comprising correction means for correcting image data using a shading correction value stored in the storage means.   The shading processing apparatus according to any one of claims 1 to 6, wherein the shading correction value is a correction ratio when the image data is subjected to shading correction. A lens that forms an image on the image sensor;
An A / D converter for A / D converting a signal from the image sensor;
8. The shading processing apparatus according to claim 2, further comprising camera signal processing means for performing camera signal processing on the signal output from the A / D converter. A first detection step of detecting a change rate of image data in a predetermined measurement region set in the image data;
If it is determined that the rate of change detected in the first detection step is greater than a predetermined value, the measurement area is divided into a plurality of areas, and the image data is divided into a plurality of divided measurement areas. A second detection step for detecting the rate of change;
A shading processing method comprising: a calculation step of obtaining a shading correction value based on the detection results detected from the first and second detection steps. A shading processing method for storing a shading correction value for each of a plurality of divided areas,
For areas where the rate of change of image data is greater than a predetermined value, set the number of area divisions larger than areas where the rate of change of image data is less than a predetermined value, and store shading correction values for each area. A storage process to
A shading processing method comprising: a correction step of correcting image data using the shading correction value stored in the storage step.

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