CMOS Image Sensor Black Level Correction for Skip-Reading Shading
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Solution Overview
Problem
CMOS image sensors face challenges in correcting vertical shading steps when performing skip-reading, leading to unfinished corrections and image quality issues due to large offset steps between before and after skipping areas.
Innovation Solution
An imaging apparatus with a two-dimensional matrix of pixels, including aperture and light-shielded areas, features a reading unit, selection unit, correction unit, and control unit that corrects black levels based on reference signals from light-shielded areas to address signal level steps during non-sequential row selection, effectively suppressing vertical shading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If skip-reading is performed to reduce reading time and improve frame rate, then productivity is improved, but manufacturing precision deteriorates due to offset steps in vertical shading correction
Solution Approach 1:
The patent applies preliminary action by performing black level correction using optical black pixels before the actual image reading process. The correction values calculated from optical black pixels are used to compensate for vertical shading effects in subsequent image data, ensuring that even when skip-reading is performed, the black level correction is already in place and offset steps are minimized.
Solution Approach 2:
The patent uses optical black pixels as an intermediary element between the light-shielded region and the effective pixel region. These optical black pixels serve as a reference to measure and correct vertical shading effects, acting as a mediator that enables accurate black level correction even when non-sequential reading is performed, thus resolving the contradiction between speed and precision.
2Speed
If clamping operation is performed at large gain for high speed correction, then speed is improved, but manufacturing precision deteriorates due to overshooting and unfinished corrections
Solution Approach 1:
The patent implements periodic action by performing black level correction at multiple stages: first using optical black pixels before image reading, then using actual image data after reading. This multi-stage periodic correction approach allows the system to achieve both speed (through pre-correction) and precision (through post-correction refinement), avoiding the overshooting problem of single-stage high-gain clamping.
Solution Approach 2:
The patent applies preliminary action by performing initial black level correction using optical black pixels before the main image reading and processing. This pre-correction establishes a baseline that prevents the need for aggressive high-gain clamping during real-time processing, thereby achieving both speed and accuracy without overshooting.
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
The solution allows for suitable correction of signal level steps, ensuring improved image quality by accurately adjusting black levels and reducing vertical shading, even in high ISO sensitivity conditions.
Implementation Method 1
a plurality of pixels each outputting a signal based on a charge generated by photoelectric conversion
Data Source
AI summary
An imaging apparatus, which includes an imaging device having a plurality of image sensors, is configured to receive light incident on the imaging device, obtain an output voltage based the received light, and generate an image based on the output voltage. The plurality of image sensors have an aperture pixel region that accumulates and outputs the charges generated based on the incident light and a shielded optical black region. The imaging device performs a skipping operation for arbitrarily and non-sequentially selecting a read row. By performing an offset correction of a step amount produced during the non-sequential reading due to the skip operation, the step resulting from the skip reading can be corrected.