Image Sensor Dark Current Calibration via Pre-captured Shading Data
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Solution Overview
Problem
Existing image sensors face challenges in accurately calibrating and correcting dark current noise due to temperature inconsistencies and variations in exposure time and gain, leading to non-uniform image shading and reduced signal-to-noise ratio.
Innovation Solution
The implementation of sentinel Dark Shading Correction (DSC) marks stored on the image sensors, which involves configuring the sensor into multiple states to capture dark images, determining and storing dark current distributions, and using these distributions to offset dark current noise in real-time imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If cooling systems are used to reduce dark current, then dark current noise is reduced, but temperature consistency across the sensor deteriorates
Solution Approach 1:
The system performs preliminary calibration by capturing dark images at multiple temperature points before actual imaging. These pre-captured dark images are stored and later used to compensate for temperature variations, eliminating the need for active cooling during operation and avoiding temperature consistency issues.
Solution Approach 2:
The system changes the temperature parameter deliberately during calibration by capturing dark images at different temperature conditions. Multiple dark images corresponding to different temperature ranges are stored, and the appropriate image is selected or interpolated based on the current sensor temperature, thereby adapting to temperature variations without requiring active thermal management.
2Measurement precision
If multiple sensor states are configured for calibration, then dark current correction accuracy is improved, but device complexity increases
Solution Approach 1:
The calibration process is segmented into discrete sensor states based on combinations of exposure time and gain settings. Each state captures a specific dark image, and the system selectively applies the appropriate calibration data based on current operating conditions, making the complex multi-parameter calibration manageable through state discretization.
Solution Approach 2:
The system dynamically selects which pre-captured dark image to apply based on the current sensor temperature and operating parameters. Instead of using a fixed calibration, the system adapts by choosing or interpolating between multiple stored dark images, making the calibration process flexible and accurate across varying conditions without requiring real-time complex computations.
3Adaptability or versatility
If dark images are captured at multiple exposure times and gains, then correction adaptability is improved, but data processing complexity increases
Solution Approach 1:
The system performs preliminary captures of dark images at various combinations of exposure times and gain settings, storing these results for later use. This pre-computation approach eliminates the need for complex real-time processing during actual imaging, as the system simply retrieves or interpolates from the pre-stored calibration data matching current operating conditions.
Data Source
AI summary
This application describes methods and systems for dark shading calibration and correction. An example method may include configuring an image sensor into a plurality of sensor states to capture a plurality of dark images, determining a dark current distribution on each of the plurality of dark images captured by the image sensor to obtain a plurality of dark current distributions respectively corresponding to the plurality of sensor states, storing the plurality of dark current distributions in a memory associated with the image sensor, capturing an image by the image sensor at a first sensor state, determining a first dark current distribution for the first sensor state of the image sensor based on the plurality of dark current distributions stored in the memory, and offsetting dark current noise on the image based on the first dark current distribution for the first sensor state of the image sensor.