Dual Conversion Gain Pixel Array for Single-Exposure HDR Imaging
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Solution Overview
Problem
Standard image sensors have a limited dynamic range, which cannot capture the full luminance range of natural scenes, requiring multiple exposures to achieve high dynamic range (HDR) images, resulting in decreased overall image resolution and issues like ghosting and light flickering.
Innovation Solution
A color pixel array that reads out pixels with dual conversion gain, allowing both high and low conversion gain values to be captured in a single exposure, eliminating the need for multiple exposures and reducing ghosting and flickering by outputting pixel values with different conversion gains using a single integration time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If multiple exposures are used to capture HDR images, then dynamic range is improved, but image resolution is degraded
Solution Approach 1:
The pixel array is divided into first and second pixel arrays, where each pixel type is optimized for specific exposure conditions. The first pixel array captures short exposure images for bright regions, while the second pixel array captures long exposure images for dark regions, allowing full resolution HDR without merging multiple exposures of the same pixels
Solution Approach 2:
The system dynamically assigns different pixel types to different exposure times based on scene requirements. During operation, the image sensor adapts by selecting which pixel array to read out based on the desired exposure duration, enabling flexible dynamic range adjustment without fixed hardware constraints
2Illumination intensity
If multiple exposures are used to capture HDR images, then dynamic range is improved, but image artifacts increase
Solution Approach 1:
By segmenting the pixel array into specialized first and second pixel arrays, the system eliminates the need to merge multiple exposures from the same pixels. Each pixel type is dedicated to specific exposure conditions, preventing misalignment artifacts like ghosting and flickering that occur when combining multiple exposures
Solution Approach 2:
The system creates separate image data copies from different pixel arrays for different exposure times, rather than attempting to merge multiple exposures from the same pixel array. This copying approach preserves full resolution and eliminates artifacts by using dedicated pixels for each exposure condition
3Illumination intensity
If a single image sensor captures multiple exposures, then HDR capability is improved, but device complexity increases
Solution Approach 1:
The pixel array is segmented into first and second pixel arrays with different exposure characteristics, allowing the system to achieve HDR capability through spatial division rather than temporal multiple exposures. This reduces device complexity by eliminating the need for complex timing control and image merging algorithms
Solution Approach 2:
The image sensor achieves multi-functionality by incorporating both first and second pixel arrays that can operate independently or together. The same sensor hardware provides both short exposure and long exposure capabilities simultaneously, eliminating the need for separate sensors or complex mechanical switching mechanisms
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
Enables the capture of both bright and dark objects simultaneously in a single frame, increasing dynamic range without the resolution loss and image artifacts associated with multiple exposures, thereby achieving HDR imaging without ghosting or light flickering.
Implementation Method 1
a photodetector PD coupled to a transfer transistor TT
Data Source
AI summary
A method of reading out a pixel includes resetting a photodetector of the pixel. Light incident on the photodetector is then integrated for a single exposure of a single image capture. A floating diffusion node of the pixel is then reset. The floating diffusion is set to low conversion gain and a low conversion gain reset signal is sampled from the floating diffusion node. The floating diffusion is set to high conversion gain and a high conversion gain reset signal is sampled from the floating diffusion node. Charge carriers are transferred from the photodetector to the floating diffusion node and a high conversion image signal is then sampled from the floating diffusion node. The floating diffusion is set to low conversion gain. Charge carriers are transferred again from the photodetector to the floating diffusion node and a low conversion image signal is sampled from the floating diffusion node.