Vertical CCD White Line Defect Correction via Dark Current Subtraction
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Solution Overview
Problem
Existing image defect correction methods fail to effectively reduce the prominence of white lines caused by point defects in vertical CCDs without significantly reducing image resolution, especially in imaging apparatuses that require high-speed signal processing.
Innovation Solution
An image defect correction apparatus and method that records the X address of correction-target vertical lines with point defects, calculates correction values based on luminance signals from both the correction-target and non-correction-target vertical lines, and adjusts luminance signals accordingly to minimize the visibility of white lines while maintaining resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional image defect correction methods replace pixel data of white points with surrounding pixel data, then white points become invisible, but this method cannot be applied to white lines from vertical CCD defects as it substantially reduces resolution
Solution Approach 1:
The patent segments the correction process by identifying and recording the specific X address of the defective vertical line, then applying correction only to that specific segment rather than to the entire image. This allows localized correction without affecting the resolution of other areas.
Solution Approach 2:
The patent applies different correction strategies to different parts of the image: for vertical lines from vertical CCD defects, it uses dark current subtraction based on transfer stop period characteristics; for other defects, it may use surrounding pixel replacement. This localized quality approach ensures resolution is maintained in non-defective areas.
2Productivity
If the number of vertical CCDs with point defects is increased to improve yield rate, then production cost decreases, but the prominence of white lines on displayed images increases
Solution Approach 1:
The patent converts the harmful effect of point defects in vertical CCDs into a measurable characteristic (dark current during transfer stop period). By measuring and subtracting this dark current, the system can correct the white line defects, allowing defective CCDs to be used without compromising image quality.
Solution Approach 2:
The patent implements a feedback mechanism where the system measures the actual dark current produced by each vertical CCD during the transfer stop period, then uses this measured value to calculate and apply the appropriate correction. This feedback loop ensures accurate correction tailored to each specific defect.
3Object-affected harmful factors
If luminance signals are corrected by replacing with surrounding pixel data, then white points are corrected, but the correction becomes noticeable and resolution deteriorates as the number of corrected pixels increases
Solution Approach 1:
The patent segments the correction approach by distinguishing between different types of defects (point defects vs. vertical line defects) and applying appropriate correction methods to each segment, preventing the need for extensive pixel replacement that would reduce resolution.
Solution Approach 2:
The patent changes the correction parameter from spatial replacement (using surrounding pixels) to temporal subtraction (removing dark current component). This parameter change allows correction without introducing the artifacts and resolution loss associated with spatial interpolation.
Data Source
AI summary
An image defect correction apparatus that processes luminance signals output from two-dimensionally arranged light-sensitive elements via a plurality of vertical charge coupled devices and a horizontal charge coupled device in a predetermined order, outputs image information, and includes: a recording unit that records therein an X address for identifying a correction-target vertical line of pixels corresponding to a vertical charge coupled device in which a point defect exists; a correction value calculating unit that calculates a correction value from values of (i) a luminance signal corresponding to at least one pixel at a predetermined position on the correction-target vertical line identified by the X address and (ii) a luminance signal corresponding to at least one pixel at a predetermined position on another vertical line; and a correcting unit that corrects values of luminance signals corresponding to the correction-target vertical line, based on the calculated correction value.