Image Sensor Sub-Pixel Resolution for High-Dynamic-Range Imaging
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Solution Overview
Problem
Conventional imaging systems struggle to capture high-dynamic-range images effectively, often losing highlight and shadow detail due to limitations in spatial resolution and motion artifacts caused by alternating exposure times in Bayer mosaic patterns.
Innovation Solution
The implementation of an image sensor with sub-pixel resolution capabilities, utilizing multiple photodiodes with shared charge storage nodes and varying exposure times, allows for improved capture and processing of image signals, enabling better retention of detail in both bright and dark areas of images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If alternating pairs of rows of pixels capture short and long exposure images, then high-dynamic-range imaging is achieved, but spatial resolution is limited and motion artifacts are generated
Solution Approach 1:
Each pixel is divided into multiple photodiodes (e.g., first, second, third, and fourth photodiodes) that can independently capture light at different exposure levels. This segmentation allows simultaneous capture of short and long exposure data within the same pixel location, eliminating the need to alternate rows and preserving spatial resolution while achieving HDR imaging capability
Solution Approach 2:
The patent adds a temporal dimension to the spatial pixel array by enabling multiple photodiodes within each pixel to operate at different exposure levels. This transforms the conventional 2D spatial sampling into a 3D space-time sampling structure, allowing HDR information to be captured without sacrificing spatial resolution
2Adaptability or versatility
If alternating pairs of rows of pixels capture short and long exposure images, then high-dynamic-range imaging is achieved, but motion artifacts are generated
Solution Approach 1:
By segmenting each pixel into multiple photodiodes with different exposure capabilities, the system captures short and long exposure images simultaneously at the same spatial location. This eliminates temporal separation between exposure types, preventing motion artifacts while maintaining HDR capability
Solution Approach 2:
The multiple photodiodes are pre-configured within each pixel to capture different exposure levels during the same exposure window. This preliminary arrangement ensures that both short and long exposure data are collected before any motion occurs, preventing motion-induced inconsistencies
3Device complexity
If a single photodiode is used per pixel, then device complexity is reduced, but sub-pixel resolution capabilities are lost
Solution Approach 1:
Multiple photodiodes within each pixel share common circuitry including charge storage nodes, readout circuitry, and control signals. This merging approach allows the system to achieve sub-pixel resolution capabilities while minimizing the increase in device complexity through resource sharing
Solution Approach 2:
The shared circuitry and structures serve multiple functions: they support both standard full-resolution mode and HDR mode, and enable both short and long exposure capture. This multi-functionality reduces the need for separate dedicated circuits for each photodiode, limiting the complexity increase
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the spatial resolution and reduces motion artifacts in high-dynamic-range imaging, allowing for more accurate representation of scenes with high contrast by capturing images with different exposure levels across sub-pixels.
Implementation Method 1
The image pixels contain a single photodiode for generating charge in response to image light
Data Source
AI summary
An image sensor may include an array of photodiodes and readout circuitry. A group of adjacent photodiodes in the array may be covered with a first color filter element that transmits a first color light and an additional group of adjacent photodiodes may be covered with a second color filter element that transmits a second color light. The group of photodiodes may share a floating diffusion node. The array may be operable in a low resolution mode in which the readout circuitry reads out image signals corresponding to a sum of charges generated by the group of photodiodes and in a high resolution mode in which the readout circuitry reads out image signals corresponding to charges generated by each of the photodiodes from the shared floating diffusion node. The photodiodes in the group may capture charge using different integration times for generating high-dynamic-range images.