Image Sensor Pixel Subarray Segmentation for Dynamic Range
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Solution Overview
Problem
Conventional digital imaging systems struggle to capture high-dynamic range images effectively, as they often require a single exposure value optimized for either bright or dark areas, leading to under-exposure or over-exposure issues, especially when capturing scenes with significant luminosity variations, resulting in low signal-to-noise ratios or saturation.
Innovation Solution
The implementation of an image sensor with a pixel array that includes multiple exposure values, where each rectangular pixel-subarray has a rescue pixel set to an intermediate exposure value, and contiguous pixels are set to different exposure values, allowing for spatially varying exposure settings across the pixel array to capture high-dynamic range images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single exposure value is used for the entire pixel array, then the device complexity is reduced, but the image quality deteriorates due to under-exposure or over-exposure in different scene regions
Solution Approach 1:
The pixel array is divided into multiple pixel-subarrays, each capable of independent exposure control. This segmentation allows different exposure values to be applied to different regions of the scene, resolving the contradiction between simple device structure and high image quality by enabling localized exposure optimization without requiring complex per-pixel control.
Solution Approach 2:
Different exposure values are assigned to different pixel-subarrays based on local scene requirements. Bright regions use shorter exposure times while dark regions use longer exposure times, allowing each local area to be optimally exposed. This local quality approach maintains relatively simple device architecture while achieving high overall image quality through spatially varying exposure settings.
2Manufacturing precision
If spatially varying exposure settings are implemented across the pixel array, then image quality is improved, but the device complexity increases due to multiple memory elements and pixel configurations
Solution Approach 1:
The pixel array is organized into rectangular pixel-subarrays with specific internal structures (first, second, and third pluralities of contiguous pixels connected to different memory elements). This segmentation provides the necessary exposure variation capability while maintaining a systematic, manageable structure that balances functionality with device complexity.
Solution Approach 2:
Each pixel-subarray is designed to be multi-functional, capable of capturing images at multiple exposure levels simultaneously. The structured arrangement of pixels and memory elements allows the same hardware configuration to serve multiple exposure purposes, reducing overall device complexity while maintaining high image quality through spatially varying exposures.
3Reliability
If a single exposure value optimized for bright areas is used, then saturation is avoided in bright regions, but under-exposure and low signal-to-noise ratios occur in dark regions
Solution Approach 1:
Different exposure values are assigned to different pixel-subarrays based on local luminosity requirements. Bright scene regions are captured by pixel-subarrays with shorter exposure times to avoid saturation, while dark regions are captured by pixel-subarrays with longer exposure times to ensure adequate signal strength. This local quality approach eliminates under-exposure and noise in dark regions while preventing saturation in bright regions, significantly improving exposure accuracy across the entire image.
4Reliability
If a single exposure value optimized for dark areas is used, then adequate exposure is achieved in dark regions, but over-exposure and saturation occur in bright regions
Solution Approach 1:
The pixel array is configured with multiple pixel-subarrays that have different exposure settings tailored to local scene characteristics. Dark regions are imaged by pixel-subarrays with longer exposure times to ensure adequate brightness, while bright regions are imaged by pixel-subarrays with shorter exposure times to prevent saturation. This local quality strategy achieves reliable exposure accuracy across the entire dynamic range by matching exposure settings to local luminosity conditions.
Data Source
AI summary
An image sensor includes a pixel array, and a first, second, and an intermediate memory-element. The memory-elements store, respectively, a first, second, and an intermediate exposure value. The pixel array includes pixel-subarrays each including a rescue pixel and a first, second, and third plurality of contiguous pixels. Each of the first plurality of pixels is connected to the first memory-element and spans diagonally-opposite corners of the pixel-subarray. Each of the second plurality of pixels is connected to the second memory-element and located on a first side of the first plurality of pixels. Each of the third plurality of pixels is connected to the second memory-element and located on a second side of the first plurality of pixels. The rescue-pixel is connected to the intermediate memory-element and is (i) located on one of the first side and the second side and/or (ii) adjacent to one of the first plurality of pixels.