JP2002176653A - Pixel defect detecting method and electronic camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pixel defect detection method that can properly detect pixel defects, while taking characteristics of pixels into account, and to provide an electronic camera adopting the method. SOLUTION: In the electronic camera employing a CCD 1 provided with RGB filters, an exposure time is set to obtain a proper luminous quantity for each color immediately prior to saturation, by taking into account pixel sensitivity difference of green, red, and blue colors, so that these pixels saturated are discriminated, based on output signals from the CCD 1 obtained by setting each exposure time, thereby detecting pixel defects with higher accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pixel defect detection method for detecting a pixel defect in a solid-state image sensor and an electronic camera using the same.

[0002]

2. Description of the Related Art A solid-state imaging device provided in an electronic camera converts an optical image of a subject formed on a pixel into a charge (electric signal) by using a large number of pixels arranged two-dimensionally and outputs the charge. It has the function to do. By the way, some of such pixels may not be able to output a normal signal because they have a defect (pixel defect) based on dust adhesion, crystal defect or the like. For such a pixel defect, a signal that is obtained by adding an extra signal component to an output signal that should be output in accordance with the luminance of the subject is output, resulting in a white flaw that makes an image whitish, There is a black flaw that outputs a signal obtained by subtracting a certain signal component from an output signal that should be output in accordance with the luminance, thereby making an image blackish.

[0003] When many pixel defects occur, when an image captured using such a solid-state imaging device is reproduced, the image quality may be significantly reduced. On the other hand, since a solid-state imaging device that has recently been used has at least several hundred thousand pixels, it can be said that it is actually difficult to manufacture a solid-state imaging device having no pixel defect. Therefore, it is required to use a solid-state imaging device on the assumption that a certain degree of pixel defect always exists.

[0004] On the basis of such a premise, an electronic camera which has a correction circuit for correcting an electric signal output from a pixel having a pixel defect by post-processing to improve the image quality has already been developed. According to such an electronic camera, a pixel having a pixel defect (defective pixel) of the solid-state imaging device is detected by using a pixel defect inspection device at the time of shipment from a factory, and its position is stored as information in, for example, a ROM attached to the electronic camera. By storing the information, an output signal from the defective pixel is appropriately corrected at the time of actual imaging.

[0005]

By the way, when a black defect is detected, a uniform light amount immediately before the pixel is saturated is given to each pixel, and if only a pixel signal below the threshold value can be output,
Such an image is regarded as a defect. Here, the solid-state imaging device is provided with a color filter for each pixel, and light passing through the color filter is incident on each pixel. However, since pixels have different sensitivities for each color of incident light (for each wavelength of light),
Even if the amount of light is the same, for example, a pixel that receives light that has passed through a green (G) filter is immediately before saturation,
Pixels that have received light that has passed through the
It can also occur that it is about / 3. Therefore, in the pixel defect inspection by one exposure, a defective pixel can be appropriately detected for the G signal, but there is a problem that the pixel defect cannot be detected for the B signal. Such a defect is B
Since a large amount of exposure for obtaining a signal cannot be obtained, a normal B
The difference between the pixel output and the threshold value for defective pixel determination becomes small, and the accuracy in comparison with the threshold value is not so good. For example, a slight variation in the pixel output based on a factor other than the defective pixel, such as noise in the pixel output, may cause the output of the normal pixel to fall below the threshold while the output of the defective pixel also exceeds the threshold. It is.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and provides a defective pixel detection method capable of detecting an appropriate pixel defect in consideration of pixel characteristics and an electronic camera using the same. The purpose is to provide.

[0007]

In order to achieve the above object, a first aspect of the present invention provides a pixel defect detecting method, comprising: a plurality of color filters, at least one of which has a different color; In a pixel defect detection method for a solid-state imaging device including a combination of a plurality of pixels that receive light, a defect of the pixel is determined based on an output signal of the solid-state imaging device obtained by performing imaging a plurality of times at different exposure times. It is characterized by doing.

According to a second aspect of the present invention, there is provided a pixel defect detecting method comprising a combination of a plurality of color filters, at least one of which is a different color, and a plurality of pixels each receiving light passing through the color filters. In the pixel defect detection method of the above, the light receiving surface of the solid-state imaging device, light received through an optical member having a characteristic that the light transmittance changes depending on the wavelength, the output signal of the solid-state imaging device obtained thereby, A defect of the pixel is determined based on the determination.

[0009]

According to a first aspect of the present invention, there is provided a pixel defect detecting method including a combination of a plurality of color filters, at least one of which is a different color, and a plurality of pixels each receiving light passing through the color filters. In the pixel defect detection method, the defect of the pixel is determined based on an output signal of the solid-state imaging device obtained by performing imaging a plurality of times at different exposure times. In consideration of the fact that the pixel sensitivity differs for each color of green, red, and blue, an exposure time is set for each color so that an appropriate amount of light is obtained immediately before saturation, and imaging is performed a plurality of times with the set exposure time. As a result, in each of the output signals of the solid-state imaging device obtained therefrom, a pixel below the threshold can be determined as a defective pixel, and more accurate pixel defect detection can be performed. It made.

That is, it is preferable that the exposure time is determined by the characteristics of the pixel.

According to a second aspect of the present invention, there is provided a pixel defect detecting method comprising a combination of a plurality of color filters, at least one of which is a different color, and a plurality of pixels each receiving light passing through the color filters. In the pixel defect detection method of the above, the light receiving surface of the solid-state imaging device, light received through an optical member having a characteristic that the light transmittance changes depending on the wavelength, the output signal of the solid-state imaging device obtained thereby, Since the pixel defect is determined on the basis of, for example, in the case of a solid-state imaging device having an RGB filter, the exposure time is the same in consideration of the fact that the pixel sensitivity is different for each of green, red, and blue colors. Also, if light is applied to the solid-state imaging device via an optical member whose light transmittance changes according to the wavelength so that an appropriate amount of light immediately before saturation is obtained for each color, Can be determined that the pixel is a defective pixel below the threshold value in the output signal more resulting solid-state imaging device, it is possible to more accurate pixel defect detection in a short time.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a digital still camera as an electronic camera to which the pixel defect detection method according to the present embodiment can be applied. In FIG. 1, a CCD (Charge Co.) as a solid-state imaging device is used.
The coupled device image sensor 1 performs a so-called photoelectric conversion that converts an optical image of a subject formed on the pixel into an electric signal (generates a charge), that is, performs a so-called photoelectric conversion. To generate a CCD
1 circuit. The CCD 1 outputs an analog electric signal based on the transfer pulse generated by the drive circuit 2.

A CDS (correlated double sampling) circuit 3 is a circuit for reducing noise, and is driven based on a driving pulse output from the driving circuit 2. The A / D conversion circuit 4 converts an input analog signal into a digital signal and outputs the digital signal. In the A / D conversion circuit 4 according to the present embodiment, it is assumed that the higher the intensity of the light incident on the pixels on the CCD 1, the larger the value of the light is converted to a digital signal. Image data for each pixel of the CCD 1 obtained through the A / D conversion circuit 4 is temporarily
It is stored in the image memory 5.

The image data stored in the image memory 5 is subjected to various types of image processing by the CPU 6 and is finally stored in a recording unit 7 composed of a recording medium such as a memory card or a magneto-optical disk.

Here, various types of image processing include processing for correcting image data of defective pixels of the CCD 1. As described later, the CPU 6 detects a defective pixel, and stores the position information (coordinates) of the defective pixel in a memory 9 provided in the control circuit 8, and corrects the image data of the defective pixel. In the processing, such position information is read out from the memory 9 to perform correction. still,
Various data used for detecting a defective pixel are also stored in the memory 9.

The liquid crystal display device 10 displays a captured image, necessary operation information, and the like. On the front surface of the CCD 1, there are provided a lens 11 for forming an image of light from a subject on a pixel, and an aperture 12 for adjusting the amount of incident light.

Further, a distance measuring means (not shown) to the subject is provided, and the control circuit 8 drives the lens driving circuit 14 to move the lens 11 to a focus position by a signal from the distance measuring means. It has become. Further, a power switch 15 and a mode switch 16 (mode selection means) for selecting a detection mode for detecting a pixel defect are provided, and a signal based on the operation of the switch is input to the control circuit 8. Has become. On the other hand, the timer 17
Are connected to the control circuit 8. Timer 17 is a CCD
The exposure time at the time of imaging 1 is detected, and a signal corresponding to the exposure time is output to the control circuit 8. The diffusion plate 21 is used for performing exposure with a uniform light amount when detecting a black flaw, and is not used for actual imaging.

FIG. 2 is a diagram schematically showing an arrangement of colors of a color filter provided in the CCD 1. As shown in FIG.

Next, detection of a black defect as a defective pixel will be described. Here, according to the characteristics of the CCD 1 in advance,
The first light amount immediately before saturation of the pixel that has received the light that has passed through the G filter, the second light amount immediately before saturation of the pixel that has received the light that has passed the R filter, and the light that has passed through the B filter The third light amount immediately before saturation of the received pixel is detected in advance.

At the time of assembling, for example, the diffusion plate 21 is inserted between the lens 12 and the CCD 1 so that a uniform amount of light is
When the power switch 15 is turned on in a state where the mode switch 16 is turned on after the light is input to the control circuit 8, the switch signal is input to the control circuit 8, and the control circuit 8
The aperture 12 (light amount adjusting means) is controlled to be fully opened by this, and in this state, an image for one screen is taken at an exposure time at which the first light amount reaches the CCD 1. CCD by such imaging
The output from 1 is stored in the image memory 5. Subsequently, an image for one screen is taken at an exposure time at which the second light amount reaches the CCD 1. The output from the CCD 1 by such imaging is stored in the image memory 5. Finally, C
In the exposure time at which the third light amount reaches CD1, 1
The imaging for the screen is performed. The output from the CCD 1 by such imaging is stored in the image memory 5. The CPU 6 compares the threshold value (reference data) for black defect determination stored in the memory 9 in advance with the image data of each pixel, that is, the output signal, and determines that a pixel below the threshold value is defective. Can be. The coordinates of the defective pixel are stored in the non-volatile memory 9, and at the time of actual imaging, a signal from the pixel is replaced with a signal calculated by a known image processing, thereby forming a high-quality image. It is possible to obtain.

As described above, according to the present embodiment, in consideration of the characteristics of pixels having different sensitivities for each color of incident light, pixel defects are detected using an optimal light amount for each color, thereby achieving higher accuracy. Pixel defects can be detected well.

A modification of the embodiment will be described.
An optical member 20 is arranged on the subject side of the taking lens 11. The optical member 20 depends on the wavelength of the light passing therethrough.
For example, the transmittance of the G component of light, the transmittance of the R component of light, and the transmittance of the B component of light can be changed to 1/3, 1/2, and 1 (for example, But not limited to this).
In the state where such an optical member 20 is disposed, the amount of light reaching the pixel for each color changes according to the sensitivity of the pixel even during the same exposure time. As a result, data for determining pixel defects of all pixels can be obtained, so that the inspection time can be reduced.

As described above, the present invention has been described with reference to the embodiments. However, the present invention should not be construed as being limited to the above embodiments, and it is needless to say that modifications and improvements can be made as appropriate. is there. For example, color filters are RGB
Instead of the type, a YMC type may be used.

[0024]

According to the electronic camera of the present invention, it is possible to provide a defective pixel detection method capable of detecting an appropriate pixel defect in consideration of pixel characteristics and an electronic camera using the same.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a digital still camera as an electronic camera.

FIG. 2 is a diagram schematically illustrating a color arrangement of a color filter.

[Explanation of symbols]

 Reference Signs List 1 CCD 2 drive circuit 3 CDS circuit 4 A / D conversion circuit 5 image memory 6 CPU 7 storage unit 8 control circuit 9 memory 10 liquid crystal display device 11 lens 12 aperture 13 temperature sensor 14 lens drive circuit 15 power switch 16 mode switch 17 Timer 20 Optical member 21 Diffusion plate

Claims (4)

[Claims] 1. A pixel defect detection method for a solid-state imaging device, comprising: a combination of a plurality of color filters, at least one of which is a different color, and a plurality of pixels each receiving light passing through the color filters. A pixel defect detection method based on an output signal of the solid-state imaging device obtained by performing image capturing a plurality of times. 2. The method according to claim 1, wherein the exposure time is determined by characteristics of the pixel. 3. A pixel defect detection method for a solid-state imaging device including a combination of a plurality of color filters, at least one of which is a different color, and a plurality of pixels each receiving light passing through the color filters. On the light-receiving surface of the element, receive light through an optical member having a characteristic that the light transmittance changes according to the wavelength,
A pixel defect detection method, wherein a defect of the pixel is determined based on an output signal of the solid-state imaging device obtained thereby. 4. An electronic camera storing defective pixels detected by using the pixel defect detection method according to claim 1.