Pixel Array Exposure Control for High-Dynamic-Range Imaging
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Solution Overview
Problem
Consumer electronics cameras struggle to capture high-dynamic range images effectively, as standard exposure settings often result in either overexposure or underexposure of scenes with varying luminosity, such as a person and a sunny background, due to a single optimized exposure time.
Innovation Solution
A method and exposure controller that determine exposure levels for a pixel array by storing pixel values, calculating global and local statistics, assigning scale factors, and adjusting exposure configurations to capture images with varying exposure levels, allowing for refined exposure settings for different regions of the image sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single optimized exposure time is used for the entire pixel array, then the exposure for the majority of the scene is optimized, but regions with varying luminosity (such as bright backgrounds or dark foreground objects) become overexposed or underexposed
Solution Approach 1:
The pixel array is divided into multiple distinct regions, each assigned a different exposure level from a set of available exposure levels. This segmentation allows different parts of the image to be captured at different exposure settings, enabling proper exposure across regions with varying luminosity while maintaining a single capture operation.
Solution Approach 2:
Different regions of the pixel array are assigned different exposure levels based on their local luminosity characteristics. Bright regions receive lower exposure levels to prevent overexposure, while dark regions receive higher exposure levels to prevent underexposure, creating locally optimized exposure quality across the entire image.
2Reliability
If multiple images with different exposure settings are captured and combined, then high-dynamic range coverage is improved, but the capture time and processing complexity increase significantly
Solution Approach 1:
Multiple pixel arrays with different exposure levels are combined within a single captured image to create a high-dynamic range image. This merging approach achieves HDR coverage in one capture operation rather than requiring multiple sequential captures, significantly reducing capture time and eliminating motion artifacts between shots.
Solution Approach 2:
The system pre-configures multiple pixel arrays with different exposure levels before capture, allowing the image sensor to simultaneously capture multiple exposure settings in a single operation. This preliminary configuration eliminates the need for sequential captures and post-alignment processing.
3Reliability
If the image sensor captures multiple exposure levels simultaneously, then dynamic range coverage is improved, but the device complexity and processing requirements increase
Solution Approach 1:
The image sensor is designed with multi-functional capability to simultaneously capture multiple exposure levels across different regions of the pixel array. This universal sensor configuration allows a single device to perform both standard single-exposure imaging and high-dynamic range imaging without requiring separate specialized sensors.
Data Source
AI summary
A method for determining exposure levels of an image-sensor pixel array includes (a) storing a first plurality of pixel values representing a first captured image, captured with the image sensor in an applied exposure configuration, each distinct region of the pixel array having a respective first exposure level, (b) determining pixel-value global statistics, (c) estimating, from the global statistics, a global pixel value of the first captured image, (d) determining, for each distinct region, a respective local statistics of the first pixel values, (e) assigning, to each distinct region, a respective scale factor based on the local statistics of the distinct region, (f) determining a refined exposure configuration including, for each distinct region, a second exposure level proportional to a product of its respective first exposure level and its respective scale factor, and (g) capturing second pixel values with the image sensor configured in the refined exposure configuration.