Image Sensor Rolling Flicker Adjustment via Frame Rate Sync
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Solution Overview
Problem
Image sensors experience rolling flicker issues due to mismatched frame rates with ambient light frequency variations, caused by clock frequency shifts from environmental changes, leading to degraded motion detection accuracy.
Innovation Solution
An image sensor that adjusts its frame rate to match the ambient light oscillation frequency by modifying the blank time interval between image frames, using a processor to calculate and compare bright-dark distribution patterns, and incorporating dummy pixel rows to extend the frame period, thereby eliminating rolling flickers without correcting the clock frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the frame rate is fixed based on clock frequency, then the image sensor operates with a stable timing structure, but rolling flickers appear when the frame rate does not match the ambient light intensity variation frequency
Solution Approach 1:
The patent applies dynamics by making the frame rate adjustable rather than fixed. The system dynamically changes the frame rate to match the ambient light intensity variation frequency, allowing the image sensor to adapt to different lighting conditions and eliminate rolling flickers while maintaining reliable operation
Solution Approach 2:
The patent changes the frame rate parameter based on detected ambient light frequency. By measuring the intensity variation frequency of ambient light and adjusting the frame rate accordingly, the system resolves the contradiction between fixed timing stability and flicker elimination
2Measurement precision
If the clock frequency is corrected using temperature compensation, then the frame rate can match ambient light frequency, but the device complexity increases due to additional compensation circuits
Solution Approach 1:
The patent uses feedback by measuring the actual frame rate and comparing it with the expected frame rate based on ambient light frequency. The system detects the intensity variation frequency of ambient light and adjusts the frame rate accordingly, achieving accurate frame rate matching without complex temperature compensation circuits
Solution Approach 2:
The system performs self-adjustment by automatically detecting ambient light frequency and modifying its own frame rate. This self-service approach eliminates the need for external temperature compensation circuits while maintaining measurement precision
3Measurement precision
If dummy pixel rows are added to extend the frame period, then the frame rate can be adjusted to match ambient light frequency, but the area of the pixel array increases
Solution Approach 1:
The patent extracts the frame rate adjustment function from the physical pixel array structure. Instead of adding dummy pixel rows to the array, the system achieves frame rate matching through processing and timing adjustments in the signal processing pipeline, thereby maintaining measurement precision without increasing pixel array area
Data Source
AI summary
There is provided an image sensor for exposing a plurality of pixel rows within a frame period using a rolling shutter. The image sensor includes a processor for calculating bright-dark distribution patterns of image frames. The processor further adjusts the frame period to be substantially identical to a predetermined period by changing a total number of exposed line times within the frame period when a difference between the bright-dark distribution patterns of two image frames is larger than a predetermined threshold.