CCD Vertical Scan Streak Removal via Overscan Subtraction
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Solution Overview
Problem
Charge-coupled device (CCD) imaging sensors experience vertical scan streaks due to light leakage during readout, which existing methods struggle to accurately correct without affecting frame rate and response time.
Innovation Solution
The method involves subtracting an overscan row from each row of an image to correct for smear, using either a zero-second exposure reference image or averaging multiple overscan rows to match the smear pattern, allowing for accurate correction of scan streaks in interline, full-frame, and frame-transfer CCDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If light leakage during readout is allowed to occur in interline or frame-transfer CCDs, then continuous illumination with close to 100% duty cycle is achieved, but vertical scan streaks are generated in the read-out image
Solution Approach 1:
The patent segments the CCD array into active imaging rows and overscan rows. The overscan rows are specifically designed to capture only the smear pattern without image content, allowing separate measurement and subsequent subtraction of the smear effect from the final image, thus resolving the contradiction between continuous illumination and streak-free imaging
Solution Approach 2:
The patent introduces an intermediary overscan region that acts as a mediator between the harmful light leakage and the final image. This intermediary region captures the smear pattern caused by light leakage during readout, which then serves as a reference for correcting the main image, allowing continuous illumination without streaks in the final output
2Object-generated harmful factors
If digital post-processing is used to correct streaking, then streak removal is achieved, but the correction is inaccurate due to inability to distinguish vertical features from streaks
Solution Approach 1:
The patent extracts the smear pattern measurement from the main imaging process by using dedicated overscan rows that contain only smear information without vertical image features. This extracted smear reference is then used for correction, solving the accuracy problem by providing a pure measurement of the streaking effect separate from the image content
Solution Approach 2:
The patent adds a spatial dimension to the correction process by incorporating overscan rows beyond the active imaging area. This additional dimension provides pure smear information that is mathematically combined with the main image data, enabling accurate separation of streaks from vertical features through dimensional analysis
3Loss of time
If conventional full-frame CCDs are operated without a shutter at high frame rates, then fast response time is achieved, but large smear is added to the image during scanning
Solution Approach 1:
The patent performs preliminary measurement of the smear pattern during the readout process itself using overscan rows, before the main image is fully processed. This preliminary smear characterization allows for subsequent correction of the high-speed captured image, enabling fast response times while removing the smear that inevitably occurs during rapid scanning
Data Source
AI summary
Methods are disclosed for correcting vertical line streaks in an interline or full-frame CCD. The method includes the step of subtracting an overscan row from each row of a previous image or from each row of a next image, such that each row of the final image contains the same readout smear effect and such that readout overscan rows contain the same smear information as each row of the final image. The method is also described for use with frame transfer CCDs.