CMOS Image Sensor Blooming Reduction via Staggered Exposure
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Solution Overview
Problem
Solid-state image sensors have limited dynamic range and suffer from blooming issues, which result in poor capture of both bright and dark subjects and distortion of brightness due to charge overflow, respectively.
Innovation Solution
The implementation of a CMOS image sensor with a pixel array configured in rows for varying exposure periods, utilizing a timing and control circuit to manage exposure and readout sequences, and including column-select and row-select circuits to reduce blooming by selectively enabling output from each row and column, thereby improving dynamic range and reducing blooming effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a single exposure time is used for all pixels, then the device structure is simple, but the dynamic range is limited and cannot capture both bright and dark subjects simultaneously
Solution Approach 1:
The pixel array is segmented into multiple rows, where different rows have different exposure times. Specifically, even rows and odd rows are assigned different integration periods, allowing the sensor to capture both bright and dark subjects simultaneously by combining data from rows with different exposure characteristics.
Solution Approach 2:
Different regions of the pixel array (specifically different rows) are assigned different exposure times based on local requirements. This allows certain rows to be optimized for bright subjects while other rows are optimized for dark subjects, with the final image combining these locally optimized captures.
2Illumination intensity
If a long exposure time is used to capture dark subjects, then dark subjects are captured clearly, but bright subjects lose contrast and become bright spots
Solution Approach 1:
The pixel array is divided into rows with different exposure times. Even rows use a first integration period optimized for dark subjects, while odd rows use a second integration period optimized for bright subjects. This segmentation allows each row type to capture its optimized subject range without the other's drawbacks.
Solution Approach 2:
The integration time parameter is changed across different rows of the pixel array. By varying the exposure time parameter from row to row (even vs odd rows), the system can capture both dark and bright subjects with appropriate exposure levels, then combine these measurements to produce a final image with preserved contrast across all brightness levels.
3Illumination intensity
If a short exposure time is used to capture bright subjects, then bright subjects are captured clearly, but dark subjects blend into the dark background and disappear
Solution Approach 1:
The pixel array is segmented into even and odd rows with different exposure times. Odd rows use a shorter integration period suitable for bright subjects, while even rows use a longer integration period suitable for dark subjects. This ensures dark subjects remain visible in the final composite image while bright subjects maintain their detail.
Solution Approach 2:
The integration time parameter is varied across different rows to match the brightness requirements of different subject regions. By changing the exposure parameter from row to row, the system captures both bright and dark subjects with appropriate exposure, preventing dark subjects from disappearing against the dark background.
4Measurement precision
If no blooming reduction mechanism is used, then the device structure is simple, but charge overflow distorts brightness and reduces spatial resolution
Solution Approach 1:
The pixel array is segmented into alternating rows with different exposure times. This segmentation inherently reduces blooming because the staggered readout timing prevents simultaneous charge overflow from adjacent rows, and the different integration periods mean that not all pixels reach saturation at the same time.
Solution Approach 2:
The system performs preliminary differentiation of exposure times across rows before charge overflow can occur. By having even and odd rows at different integration stages, the system prevents the conditions that lead to blooming (simultaneous saturation of adjacent pixels) before they happen, rather than needing additional active blooming suppression circuitry.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the dynamic range of the image sensor by allowing clear capture of both dark and bright subjects while minimizing blooming, resulting in improved image quality with reduced distortion and increased spatial resolution.
Implementation Method 1
each photoelectric device records intensity or brightness of an incident light by converting optical energy into accumulated electrical charges
Data Source
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AI summary
A CMOS image sensor having blooming reduction mechanisms is disclosed. The image sensor can include a plurality of pixels arranged in rows and a timing and control circuit in electrical communication with the plurality of pixels. The timing and control circuit includes a readout module configured for outputting a first row of pixels exposed for a first exposure period, outputting a second row of pixels exposed for the first exposure period after outputting the first row of pixels, and thereafter outputting a third row of pixels exposed for a second exposure period different than the first exposure period, the third row of pixels being between the first and second rows of pixels.