Imaging Device Dark Shading Correction via Pixel Signal Subtraction
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Solution Overview
Problem
Existing imaging devices fail to effectively address dark shading caused by dark current accumulation in photodiodes during charge accumulation, especially when analog gain is increased, leading to noticeable irregularities in images.
Innovation Solution
The imaging device incorporates a control unit to manage signal output from pixel units, including a correction unit that generates pixel signals by subtracting a correction amount from the first signal, which is a product of the second signal's intensity and a predetermined coefficient, to account for dark current and circuit noise components, and employs light-blocking pixels to isolate noise components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If analog gain is increased to improve signal strength, then signal-to-noise ratio improves, but dark shading irregularities become more noticeable
Solution Approach 1:
The patent applies preliminary action by performing shading correction before final image output. The correction unit pre-calculates and applies correction values based on dark current characteristics measured during manufacturing, so that when analog gain is increased, the dark shading irregularities have already been compensated, preventing them from becoming noticeable in the final image.
Solution Approach 2:
The patent uses parameter changes by adjusting the correction coefficient based on the charge accumulation period. The correction unit stores multiple correction coefficients corresponding to different accumulation times, and selects the appropriate coefficient to match the current imaging conditions, thereby dynamically compensating for dark current effects across varying gain settings.
2Reliability
If charge accumulation period is extended to improve light sensitivity, then signal intensity increases, but dark current accumulation increases causing more irregularities
Solution Approach 1:
The patent measures and stores correction data during manufacturing for various charge accumulation periods. When imaging with extended accumulation times, the correction unit retrieves the pre-measured correction coefficients that specifically account for dark current accumulation at those durations, enabling accurate compensation without requiring real-time measurement.
Solution Approach 2:
The correction unit implements feedback by continuously monitoring the actual charge accumulation period and selecting the appropriate correction coefficient from stored values. This feedback mechanism ensures that the correction applied always matches the actual imaging conditions, maintaining image uniformity across varying accumulation periods.
3Measurement precision
If correction processing is applied to reduce dark shading, then image uniformity improves, but processing complexity increases
Solution Approach 1:
The patent performs complex correction coefficient measurements during the manufacturing process, storing the results in a lookup table. During actual imaging operations, the correction unit simply retrieves and applies the appropriate pre-calculated coefficients, converting a complex real-time calculation problem into a simple table-lookup operation that maintains image uniformity without adding processing complexity.
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 significantly reduces dark shading irregularities by accurately correcting pixel signals, improving image quality even at higher analog gains and varying charge accumulation periods, and allows for effective noise component separation and correction.
Implementation Method 1
Each of the plurality of pixel units includes a photoelectric conversion unit
Data Source
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AI summary
An imaging device includes pixel units, a control unit, and a correction unit. The control unit causes each pixel unit to output first and second signal. The first signal is a potential of a floating diffusion held when the charge accumulated in a photoelectric conversion unit is transferred upon a transfer switch being closed. The second signal is a potential of the floating diffusion held when a reset switch is closed with the transfer switch being open. The correction unit generates, with respect to the first and second signals output by each pixel unit, the pixel signal by subtracting a correction amount from a signal intensity of the first signal. The correction amount is a product of a signal intensity of the second signal and a coefficient determined in advance in accordance with a position of each pixel unit.