JP2007060561A - Method and apparatus for inspecting pixel defect of solid-state imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately and surely detect a defective pixel in a solid-state imaging device. <P>SOLUTION: A pixel defect inspecting apparatus 3 comprises a light source 6, an optical lens 7, a timing generator 8, a signal processing part 9, a system controller 10, an arithmetic circuit 11, a memory 12, and an interface part 13. Image data outputted from a solid-state imaging device 2 driven by the timing generator 8 are signal-processed by the signal processing part 9 and stored in the memory 12. Image data read from the memory 12 are averaged by the arithmetic circuit 11, a ratio of luminance levels before and after averaging is calculated, and a defective pixel is detected from a value of the ratio. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inspection method and an inspection apparatus for inspecting a pixel defect of a solid-state imaging device.

  2. Description of the Related Art In recent years, digital cameras that convert a captured image captured using an image sensor such as a CCD into digital image data and record it on a recording medium such as a built-in memory or a memory card have become widespread. Usually, the solid-state imaging device is formed on a semiconductor substrate such as a silicon wafer. A solid-state imaging device such as a CCD or CMOS has millions of photosensitive parts arranged on a semiconductor substrate, and external light is incident on these photosensitive parts through a lens. The photosensitive part to which the external light is incident outputs a signal charge, and image data is formed by the signal charge.

  Such a solid-state imaging device may include a light receiving device that does not output a signal charge even when external light is incident, and a light receiving device that generates an abnormally large dark current without incident light. A defective pixel having a defective light receiving element appears as a black spot or a white spot when image data is displayed.

Therefore, conventionally, a method and an inspection apparatus for inspecting a defective pixel of a solid-state imaging device are known. For example, in the inspection method described in Patent Document 1, first, image data is read and white point pixels are extracted. In this white point pixel extraction processing, the image data is averaged, and white point pixel data is extracted by taking a difference between the original image data and the averaged image data.
JP 2004-56395 A

  Incidentally, some solid-state imaging devices have a configuration in which a light receiving element having a feature of a high luminance portion and a light receiving element having a feature of a low luminance portion are mixed. In the case of such a solid-state imaging device, when a defective pixel is detected by the inspection method described in Patent Document 1, the light-receiving device in the low-luminance portion has a small pixel level value. The value of the difference between the image data and the average processed image data also becomes small. Therefore, with such a difference value, even if detection is performed by comparison with a predetermined threshold value, it is very difficult to extract a defective pixel with a light-receiving element in a low-luminance portion, and detection accuracy is low.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a pixel defect inspection method and inspection apparatus capable of accurately and reliably detecting defective pixels of a solid-state imaging device.

  In order to achieve the above object, in the inspection method according to claim 1, in the inspection method for inspecting a pixel defect of a solid-state imaging device in which a plurality of pixels each including a light-receiving element that photoelectrically converts incident light are arranged, the solid-state imaging device The step of obtaining the image data captured by the step, the step of averaging the image data, and the ratio of the luminance level at each pixel of the image data before the averaging process to the luminance level at each pixel of the image data after the processing The method includes a step of calculating, and a step of detecting a defective pixel from the ratio of the calculated luminance levels.

  The inspection apparatus according to claim 2, wherein in the inspection apparatus for inspecting a pixel defect of a solid-state imaging device in which a plurality of pixels each including a light-receiving element that photoelectrically converts incident light is arranged, the solid-state imaging device is exposed to receive the light. An exposure unit that outputs an imaging signal from the element, an average processing unit that averages image data output from the solid-state imaging element, a luminance level in each pixel of the image data, and an average process performed by the average processing unit It is characterized by comprising detection means for calculating a ratio of each pixel of the image data to the luminance level and detecting a defective pixel from this ratio.

  In the solid-state imaging device inspection method and inspection apparatus according to the present invention, after averaging the image data output from the solid-state imaging device, the luminance level in each pixel of the image data before the average processing and each pixel of the processed image data Since the ratio of the brightness level to the brightness level is calculated and the defective pixel is detected from this ratio, the defective pixel of the solid-state imaging device can be detected accurately and reliably.

  A pixel defect inspection apparatus to which the first embodiment of the present invention is applied will be described below with reference to the drawings. As shown in FIG. 1, the pixel defect inspection apparatus 3 includes a light source 6, an optical lens 7, a timing generator 8, a signal processing unit 9, a system controller 10, an arithmetic circuit (average processing means) (detection circuit). 11, a memory 12, and an interface unit 13. The timing generator 8 and the image signal processing unit 9 are connected to the solid-state imaging device 2 to be inspected.

  In the present invention, an image sensor such as a CCD or CMOS is used as the solid-state imaging device 2 to be inspected. In the solid-state imaging device 2, a large number of light receiving elements are generally arranged in a matrix or honeycomb shape, and a microlens layer for condensing external light is provided so as to cover the light receiving elements.

  The light source 6 and the optical lens 7 constitute exposure means for exposing the solid-state imaging device 2 and outputting an imaging signal from the light receiving device. The light emitted from the light source 6 passes through the optical lens 7 and enters the solid-state imaging device 2. In the present embodiment, the light source 6 and the optical lens 7 are configured so that light incident on the solid-state imaging device 2 becomes parallel light.

  The timing generator 8 is connected to the system controller 10 and generates a timing signal (clock pulse) under the control of the system controller 10. The solid-state imaging device 2 is driven by a timing signal input from the timing generator 8.

  The analog signal output from the solid-state imaging device 2 is input to the signal processing unit 9. The signal processing unit 9 amplifies the output from the solid-state imaging device 2 and converts it into digital image data. The image data digitally converted by the storage unit signal processing unit 9 is temporarily stored in a predetermined area of the memory 12.

  An arithmetic circuit (average processing means) (detection circuit) 11 reads image data from the memory 12 and performs a defective pixel extraction process. The details of this defective pixel extraction process will be described in the inspection process described later. The interface unit 13 inputs information to the system controller 10 and displays a pixel defect inspection status and inspection results.

  Below, the pixel defect inspection of the solid-state image sensor 2 by the pixel defect inspection apparatus 3 will be described. FIG. 2 is a flowchart showing a sequence of the inspection apparatus when this pixel defect inspection is performed. When performing this pixel defect inspection, first, in step S1, the solid-state imaging device 2 driven by the timing generator 7 captures an image, and the image data output from the solid-state imaging device 2 is stored in the memory 12. An image 20 shown in FIG. 3 shows an example of an image acquired from the solid-state imaging device 2.

  In step S2, an image is read from the memory 12 and averaged. As this average process, for example, a moving average process is performed. As shown in FIG. 4, the moving average processing is performed by setting the luminance level of each pixel P (x, y) constituting the image 20 within a predetermined area (for example, a 3 × 3 pixel area) centered on the pixel. This is a process of replacing with the average value of the luminance level. Note that the average processing of image data applied to the present embodiment is not limited to moving average processing.

  5A is a waveform showing the distribution of luminance levels on the line 20a (horizontal line along the X direction in FIG. 3) in the image 20, and FIG. 5B shows the line 20a after the average processing. It is a waveform which shows distribution of the upper luminance level. Note that some solid-state imaging devices are configured by mixing a light-receiving element with a high luminance part and a light-receiving element with a low luminance part. In the solid-state imaging element 2 of the present embodiment, as shown in FIG. Further, the distribution is such that the luminance level near the center is high and the luminance level in the peripheral portion is low. The reason why the luminance level is distributed as described above is that the microlens of each pixel constituting the solid-state imaging device 2 is different in the direction near the center and the peripheral portion, that is, the microlens near the center is the imaging surface of the solid-state imaging device 2 The center of the optical axis is set along the direction perpendicular to the optical axis, and the center of the optical axis is set so that the peripheral part is inclined with respect to the direction perpendicular to the imaging surface. When the solid-state imaging device 2 is irradiated with parallel light from 6, external light is incident on the light receiving element with high light collection efficiency in the vicinity of the center, but the light collection efficiency is low in the peripheral portion.

After the averaging process in step S2, in step S3, the luminance level G ₁ (see FIG. 5A) at each pixel (x, y) of the image 20 before the averaging process and each pixel (x, y after the averaging process). The ratio G ₂ / G ₁ with the luminance level G ₂ (see FIG. 5B) is calculated. FIG. 6 is a waveform showing the distribution of the ratio G ₂ / G ₁ on the line 20a.

In step S4, the value of the ratio G ₂ / G ₁ that exceeds a predetermined threshold value L is determined that the corresponding pixel P (x, y) is a defective pixel. In step S5, the inspection result of the detected defective pixel is stored in the memory 12, and various information including the inspection result is displayed by the interface unit 13. The sequence of steps S1 to S5 can be executed as a computer program for controlling the inspection apparatus.

Thus, since the ratio G ₂ / G ₁ of the luminance level in each pixel before and after the average processing is calculated, a calculated value that does not change from the high luminance portion near the center even in the low luminance portion in the peripheral portion. Distribution. Therefore, since the sensitivity for detecting defective pixels is improved, pixel defect inspection can be performed with high accuracy.

If the luminance level G ₁ at each pixel (x, y) before the average processing and the luminance level G ₂ at each pixel (x, y) after the average processing are calculated as in the conventional inspection method. In this case, the distribution is as shown in the waveform of FIG. In the distribution when this difference is taken, the value of the difference is large in the central high-brightness part, so that the defective pixel can be detected with high sensitivity, but the noise amount itself of the defective pixel is small in the peripheral low-brightness part. Since the value of the difference becomes smaller, the defective pixel may not be detected. Therefore, in the inspection method that takes such a difference value, the accuracy of the pixel defect inspection is lowered, but this is not the case in the present invention.

  The pixel defect inspection result data detected by the pixel defect inspection apparatus 3 of the above embodiment is used when, for example, the solid-state image sensor 2 is incorporated in a digital camera or the like. This is used in image processing for interpolating pixel defects when they appear in the image data picked up in (1).

It is a block diagram which shows the electrical constitution of the pixel defect inspection apparatus to which this invention is applied. It is a flowchart which shows a sequence when performing a pixel defect inspection. It is explanatory drawing which shows an example of the captured image when performing an image defect inspection. It is explanatory drawing which shows an example of the average process of an image. It is the distribution map of the luminance level on one horizontal line segment of an image, and the distribution map after an average process. FIG. 6 is a distribution diagram when a ratio between a luminance level before average processing and a luminance level after average processing is calculated. It is a distribution map at the time of taking the difference of the luminance level before an average process, and the luminance level after an average process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 Solid-state image sensor 3 Pixel defect inspection apparatus 6 Light source 7 Optical lens 10 System controller 11 Arithmetic circuit (average processing means) (detection circuit)

Claims (2)

In an inspection method for inspecting a pixel defect of a solid-state imaging device in which a large number of pixels each composed of a light receiving element that photoelectrically converts incident light are arranged,
A step of acquiring image data captured by the solid-state imaging device, a step of averaging the image data, a luminance level in each pixel of the image data before the average processing, and a luminance level in each pixel of the image data after the processing; And a step of detecting a defective pixel from the calculated luminance level ratio. In an inspection apparatus for inspecting a pixel defect of a solid-state imaging device in which a large number of pixels each composed of a light receiving element that photoelectrically converts incident light are arranged,
An exposure unit that exposes the solid-state image sensor and outputs an image pickup signal from the light-receiving element; an average processing unit that averages image data output from the solid-state image sensor; and a luminance level in each pixel of the image data; An inspection apparatus comprising: detection means for calculating a ratio of each pixel of the image data averaged by the average processing means to a luminance level, and detecting a defective pixel from the ratio.

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