Electronic camera capable of detecting defective pixel

Details Electronic camera capable of detecting defective pixel Electronic camera capable of detecting defective pixel

1998-03-18

2004-01-27

Vu, Ngoc-Yen (Department: 2612)

Television

Camera, system and detail

Combined image signal generator and general image signal...

C348S280000, C348S349000

Reexamination Certificate

active

06683643

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a technology which detects, in an electronic camera equipped with a solid image pickup element, a defective pixel of the solid image pickup element, and corrects output signals from the defective pixel.
A solid image pickup element equipped in an electronic camera has a function to convert, with many pixels arranged two-dimensionally, optical images of a subject formed on the pixel into an amount of electric charges (electric signals), and to output them. Among these pixels, incidentally, there can be some pixels which can not output normal signals due to the defects (pixel defects) based on dust adhesion and crystal defects. These pixel defects are represented by both a white flaw wherein signals in which excessive signal components are added to output signals which are supposed to be outputted in accordance with luminance of a subject are outputted accidentally to make an image to be whitish, and a black flaw wherein signals in which certain signal components are subtracted from output signals which are supposed to be outputted in accordance with luminance of a subject are outputted accidentally to make an image to be blackish.
When there are caused much pixel defects, it is apprehended that image quality is deteriorated badly, when reproducing images which are picked up by the use of the solid image pickup element having that pixel defects. On the other hand, with regard to the solid image pickup element having therein at least hundreds of thousands of pixels or more which has recently come to be used, it is actually difficult to manufacture the solid image pickup element which is free from pixel defects. It is therefore required to use the solid image pickup element on the assumption that pixel defects to a certain extent always exist.
There has already been developed an electronic camera which is equipped with a correction circuit which corrects, through post-processing, the electric signals outputted from the pixel having pixel defects to improve image quality, based on the assumption mentioned above. The electronic camera stated above employs a method wherein a pixel having pixel defects (defect pixel) in the solid image pickup element is detected by the use of a pixel defect inspecting instrument on the occasion of factory shipments of the electronic camera, and a position thereof is stored in a ROM accompanying the electronic camera, for example, as information, whereby signals outputted from the defect pixel are corrected properly in the case of actual photographing.
However, it was found that the white flaw stated above is sometimes increased in accordance with aging deterioration or environmental conditions where the solid image pickup element is used, because it is a pixel defect based on a crystal defect. For example, the white flaw tends to be increased when the temperature surrounding the solid image pickup element is raised, or when the exposure time is long. In such a case, another defect pixel is caused at a position which is different from the position of the defect pixel detected under a prescribed condition on the occasion of factory shipments, which sometimes makes it impossible to correct sufficiently. Therefore, it is also possible to consider a method wherein exposure for a long time or exposure at high temperature is conducted to obtain defect pixel information, and signals from the defect pixel are always corrected based on the aforesaid information.
However, the white flaw caused by the exposure for a long time is one which is not caused by exposure for a short time, and it is not preferable to conduct correction processing at all times with regard to the white flaw, because the correction processing delays the processing time. Further, since the pixel causing a white flaw under exposure for a long time can function as a normal pixel in the course of ordinary photographing, it is apprehended that correction for the normal output signals from that pixel may rather deteriorate image quality.
In particular, a digital camera is in a tendency that the number of pixels of a solid image pickup element is increased for improvement of image quality, and this tendency of increase of the number of pixels has created a tendency that the number of defect pixels is naturally increased and the number of occurrence of another white flaw caused by aging change is increased in proportion to the increase of the number of pixels. Therefore, in a digital camera having many pixels of the solid image pickup element, the defect pixel stated above matters much especially, and a technology to cope with aging change of the defect pixel in the market place has been desired.
SUMMARY OF THE INVENTION
The invention has been achieved in view of the problems stated above, and its object is to provide an electronic camera which can cope with aging changees of defective pixels of a solid image pickup element and can detect the defect pixels accurately. Further object of the invention is to provide an electronic camera which can properly correct white flaws the number of which depends on a length of time of exposure, a pixel signal correcting method and a recording medium.
The objects mentioned above can be attained by the structures or methods described in each item below.
Item 1
An electronic camera equipped with a solid image pickup element wherein an image for detecting pixel defects is subjected to image pickup, and image data of each pixel of the solid image pickup element obtained through the image pickup is compared with reference image data respectively to detect defect pixels in the solid image pickup element.
In the structure mentioned above, an image suitable for detecting pixel defects is photographed for image pickup by an electronic camera, and image data of each pixel of the solid image pickup element obtained through the image pickup are compared with image data representing a reference to detect defect pixels for each image pickup of the image for detecting pixel defects.
Item 2
The image data representing a reference is assumed to be the value stored in advance.
In the structure, the reference image data for judging whether image data are normal or abnormal in accordance with the image for detecting pixel defects are stored in advance, and image data obtained through image pickup of the image for detecting pixel defects are compared with the reference image data for each pixel, whereby the image data are judged whether they are normal or abnormal for each pixel.
Item 3
The reference image data are operated based on image data in a prescribed area which includes a targeted pixel.
In the aforesaid structure, a defect pixel is detected by judging whether or not the targeted pixel is outputting image data which are on the same level as in the normal pixel, with the image data around the targeted pixel which are assumed to be image data obtained by the normal pixel.
Item 4
Color filters respectively for plural different colors are provided on the solid image pickup element, and the reference image data stated above are represented by a mean value of image data of the pixel on which a color filter having the same color as in the targeted pixel in the prescribed area is provided.
According to the aforesaid structure, in an electronic camera having the structure wherein each pixel is provided with each of color filters respectively for R, G and B and image pickup for a color image is conducted, a mean value of image data of the pixel which is located around the targeted pixel for judging the defect pixel and is provided with a filter having the same color as in the targeted pixel is calculated as image data in the normal pixel, and this calculated value is compared with image data of the targeted pixel to judge whether the image data of the targeted pixel are normal or abnormal.
Item 5
A prescribed area including the targeted pixel is assumed to be a prescribed area in which the targeted pixel is centered.
In the structure stated above, a mean value of image data of the pixel which is provided with a filter havi

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