CCD Residual Signal Reduction via Dynamic Flush Timing
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Solution Overview
Problem
Digital cameras with full frame CCD sensors face challenges in continuous capture mode due to residual signals from trapped charge, which cannot be effectively eliminated by mechanical shutters or dark current subtraction, leading to artifacts in images, especially under varying light conditions.
Innovation Solution
A method to automatically adjust the flush time based on the exposure information of the previous image capture, using a light meter to estimate the optimal flush time for the next image, thereby reducing residual signals by correlating light intensity and exposure time with predefined thresholds and lookup tables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mechanical shutter is used to clear charge before exposure, then dark current is removed, but the shutter cannot eliminate residual signal from trapped charge and causes delay in continuous capture mode
Solution Approach 1:
The patent performs a preliminary flush operation before each exposure to clear trapped charge from the CCD. By estimating the residual signal level from the previous image's exposure parameters and performing a targeted flush, the system removes residual signals proactively before they contaminate the next image, eliminating the need for lengthy mechanical shutter operations.
Solution Approach 2:
The patent replaces the mechanical shutter system with an electronic flush mechanism. Instead of using a mechanical shutter to clear charge, the system uses electronic control to initiate a flush operation that clears trapped charge from the CCD through controlled charge transfer and clearing operations, eliminating mechanical moving parts and associated delays.
2Reliability
If flush time is extended to reduce residual signal, then residual signal is reduced, but capture speed decreases
Solution Approach 1:
The patent dynamically adjusts the flush time based on the actual residual signal level estimated from the previous image's exposure parameters. Rather than using a fixed, conservative flush time, the system calculates the optimal flush duration needed to reduce residual signals below a threshold, allowing shorter flush times when residual signals are low and maintaining capture speed.
Solution Approach 2:
The patent changes the flush time parameter dynamically based on exposure conditions. By monitoring the previous image's exposure time and peak light intensity, the system adjusts the flush time parameter to match the actual residual signal level, optimizing the balance between residual signal reduction and capture speed.
3Measurement precision
If exposure time is increased to capture more light, then image quality improves, but residual signal from trapped charge increases
Solution Approach 1:
The patent uses feedback from the previous image's exposure parameters (exposure time and peak light intensity) to estimate the residual signal level and adjust the flush time accordingly. This feedback loop allows the system to compensate for increased residual signals from longer exposures by performing more thorough flush operations, maintaining image quality without excessive residual contamination.
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
Substantially reduces residual signals in subsequent images while minimizing delays between captures, maintaining high image quality and enabling continuous capture modes without user-perceptible slowdowns.
Implementation Method 1
The sensor captures light during exposure and converts photons to electrical charge, namely electrons.
Data Source
AI summary
A method for reducing residual signal from a first image from appearing in a second image, the method includes the steps of capturing the first image on an image sensor having a known exposure that includes exposure time and a peak light intensity; estimating a flush time for the second image based on the known exposure in capturing the first image; and capturing the second image using the estimated flush time for substantially reducing the residual signal.