Double Charge Storage Pixel Structure for HDR Ghosting Reduction
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Solution Overview
Problem
High dynamic range (HDR) imaging in CMOS image sensors often results in fuzzy or phantom effects when capturing moving objects due to the limitations of the global shutter mode, particularly the absence of image capture between integration phases leading to incomplete exposure of photons.
Innovation Solution
The method involves accumulating electrical charges during two distinct periods and transferring them to separate storage regions before combining the images, allowing for the acquisition of two images with different exposure times, which are then alternately transferred to a common reading node for processing, thereby reducing the ghosting effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If global shutter mode is used to capture two successive images for HDR, then uniform exposure time and accurate image content are achieved, but waiting time between integration phases causes incomplete photon exposure and ghosting effects
Solution Approach 1:
The pixel circuit is segmented into two independent photosensitive regions (first and second photodiodes) that can accumulate charges simultaneously during different integration periods. This segmentation allows the first image to be captured during the first integration phase while the second image is captured during the second integration phase, eliminating the waiting time between phases and preventing ghosting effects.
2Adaptability or versatility
If two successive images are captured with different integration times for HDR, then dynamic range is increased, but ghosting effects occur on moving objects
Solution Approach 1:
The first image is captured and stored in the first storage region during the first integration phase before the second integration phase begins. This preliminary capture and storage action allows the second image to be captured during the second integration phase without any waiting time, ensuring that moving objects are continuously exposed and ghosting effects are eliminated while maintaining HDR capability.
3Adaptability or versatility
If charges are transferred to a common reading node from separate storage regions, then two images with different exposure times are acquired, but circuit complexity increases
Solution Approach 1:
Two separate storage regions (first and second storage regions) are merged into a single common reading node. This merging allows both images captured during different integration phases to be read out through the same node, simplifying the circuit architecture while maintaining HDR capability. The common reading node processes charges from both storage regions without requiring separate reading circuits for each image.
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 image quality by eliminating the waiting time between integration phases, reducing the occurrence of fuzziness or phantom effects in HDR mode, especially when capturing scenes with moving objects, by ensuring complete exposure and accurate detail capture in both light and dark areas.
Implementation Method 1
Each pixel includes a photosensitive area, generally a photodiode, configured to accumulate electrical charges as a function of the light that it receives
Data Source
AI summary
A method of acquisition of an image may include accumulating electrical charges by a photosensitive element of a pixel circuit of an image sensor during a first period, transferring the electrical charges accumulated during the first period to a first electrical charge storage region of the pixel circuit, and at the end of the transfer of the electrical charges, accumulating the electrical charges by the photosensitive element during a second period. The method may further include transferring the electrical charges accumulated during the second period to a second electrical charge storage region of the pixel circuit, successively transferring the electrical charges stored in the first and second storage regions to a common reading node of the pixel circuit, acquiring two images from electrical charges transferred to the reading node from the first and second storage regions, respectively, and combining the two images acquired into a resultant image.