Image Sensor Flicker Noise Compensation via Optimum Light Model
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Solution Overview
Problem
Conventional digital cameras face challenges in capturing images under varying light sources due to flicker noise caused by non-integer multiple exposure times relative to the power source frequency, which can differ by country and is inconvenient to set, especially when exposure times are less than the light source period.
Innovation Solution
An image capture device with an image sensor, analysis unit, and compensation unit that determines an optimum light model and generates compensation gains to adjust image signals from rows of a pixel array, minimizing differences and compensating for flicker noise regardless of light source frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the exposure time is set to be an integer multiple of the light source period to remove flicker noise, then flicker noise is reduced, but the user convenience deteriorates due to the need to manually adjust exposure time according to different power frequencies
Solution Approach 1:
The system automatically determines the light source period by analyzing the image signal itself, eliminating the need for manual user input. The analysis unit extracts the period information from the captured image data, and the control unit automatically adjusts the exposure time accordingly, making the system self-configure without user intervention.
Solution Approach 2:
The exposure time parameter is dynamically adjusted based on the detected light source period. The control unit changes the exposure time from a fixed value to a variable value that adapts to different power frequencies (50Hz, 60Hz, etc.), allowing the system to maintain optimal settings across different regions without manual reconfiguration.
2Illumination intensity
If the exposure time is reduced to capture bright light sources, then the ability to capture bright scenes improves, but the exposure time can no longer be set as an integer multiple of the light source period, causing flicker noise
Solution Approach 1:
The exposure time is changed from a static fixed value to a dynamic parameter that adapts to the detected light source period. The control unit adjusts the exposure time based on real-time analysis of the image signal, allowing the system to capture bright scenes while maintaining flicker-free images by synchronizing exposure with the actual light source frequency.
3Reliability
If the image sensor circuit exposes pixels sequentially row-by-row, then the concern over leakage current is addressed, but flicker noise occurs when exposure time is not an integer multiple of the light source period
Solution Approach 1:
The system implements a feedback loop where the analysis unit continuously monitors the image signal to detect the light source period, and the control unit uses this information to adjust the exposure time. This closed-loop feedback mechanism ensures that the exposure time remains synchronized with the light source frequency, eliminating flicker noise while maintaining the benefits of sequential pixel exposure.
Data Source
AI summary
An image capture device can include an analysis unit that can be configured to determine a refined light model that models a light source based on first and second image signals sampled with first and second exposure times, respectively, and corresponding to first and second rows of pixels. A compensation unit can be coupled to the analysis unit, and can be configured to generate an output image signal by compensating the first and second image signals and the second image signal using compensation gains associated with the refined light model.