Clamping Method for Imaging Device Black Signal Stability
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Solution Overview
Problem
Existing imaging devices face challenges in maintaining stable image signals due to variations in black signal levels caused by changes in storage time, leading to noise and shading issues.
Innovation Solution
A clamping method that uses shielded pixel regions to calculate and stabilize reference values, adjusting the optical black signal level by subtracting reference values and adding target values, while also incorporating clamp correction to maintain consistent black signal levels across frames.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional clamping methods are used to handle dark current, then vertical shading is reduced, but random noise influence and variations in black signal level remain when storage time changes
Solution Approach 1:
The imaging device pixel array is divided into three distinct regions: effective pixel region for image capture, first shielded pixel region for pre-storage reference signals, and second shielded pixel region for post-storage reference signals. This segmentation allows independent measurement and correction of black signal levels at different storage time points, resolving the contradiction between shading reduction and signal stability.
Solution Approach 2:
The first shielded pixel region captures reference signals before the effective pixel region undergoes photoelectric conversion and storage. This preliminary action establishes a baseline black signal level that accounts for dark current characteristics at the start of the storage period, enabling correction of storage time-induced variations.
Solution Approach 3:
The system calculates first and second reference values from shielded pixel regions, compares them against target values, and performs clamping corrections by adding or subtracting difference values. This feedback mechanism continuously adjusts the black signal level to maintain stability despite storage time changes.
2Measurement precision
If storage time is increased to improve image quality, then signal-to-noise ratio improves, but black signal level variations and random noise increase
Solution Approach 1:
Reference signals are captured at predetermined timing (before and after effective pixel storage) to establish baseline black signal levels. This preliminary action enables subsequent correction of storage time-induced variations without compromising the benefits of extended storage time for improved signal-to-noise ratio.
Solution Approach 2:
The system dynamically adjusts clamping parameters (first reference value RA(n) and second reference value RB(n)) based on measured black signal levels at different storage time points. This parameter adaptation allows the system to maintain black signal level consistency while utilizing extended storage times for improved image quality.
3Adaptability or versatility
If frame rate is changed to adapt to different imaging scenarios, then imaging versatility improves, but black signal level stability deteriorates
Solution Approach 1:
The clamping system dynamically adjusts reference values and correction amounts based on the actual storage time corresponding to the current frame rate. By calculating reference values at predetermined timing relative to each frame's storage period, the system adapts to varying frame rates while maintaining black signal level stability through real-time clamping corrections.
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
The method effectively reduces noise and maintains stable image signals even with changes in storage time, ensuring consistent black signal levels and improved imaging performance.
Implementation Method 1
image pickup elements arranged in a matrix pattern and having photoelectric conversion function
Data Source
AI summary
An imaging device includes an effective pixel region outputting an effective pixel signal, a first shielded pixel region outputting a shielded pixel signal before the effective pixel signal is output, and a second shielded pixel region outputting a shielded pixel signal after the effective pixel signal has been output. In the device, in a steady state, frame clamping is performed using a clamping reference value generated from the pixel signals of the second shielded pixel region. A frame in a transition state in which the optical black signal level of the imaging device changes is subjected to frame clamping using a clamping reference value generated from the pixel signals of the first shielded pixel region.