Imaging Device Dark Level Determination via Sealed Pixels
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Solution Overview
Problem
Direct measurement of the dark level of an imaging device is often not feasible due to limitations and changes over time, making previously determined dark levels invalid.
Innovation Solution
A method involving calibration by collecting readings from regular and sealed pixels over varying integration times and number of lines, using equations to determine and update the dark level, including linear correlations and logarithmic fitting to account for changes in integration time and number of lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct measurement of dark level is performed, then measurement accuracy is improved, but measurement feasibility deteriorates due to limitations and changes over time
Solution Approach 1:
The patent introduces sealed pixels as intermediary elements that are not affected by light but exhibit similar temporal and environmental variations to regular pixels. By measuring the dark level through the sealed pixels' response characteristics rather than direct measurement of regular pixels, the system achieves accurate dark level determination while avoiding the limitations of direct measurement methods
Solution Approach 2:
The patent creates a copy of the dark level behavior through sealed pixels that mimic the temporal and environmental response of regular pixels without being affected by light. The sealed pixels serve as a replica system that captures the same drift and variation patterns, allowing indirect determination of dark level characteristics without the complications of direct measurement
2Loss of time
If dark level is determined previously and stored, then measurement time is reduced, but reliability deteriorates due to changes over time
Solution Approach 1:
The patent implements a feedback mechanism where the sealed pixels continuously monitor changes in dark level characteristics over time. By comparing current sealed pixel responses with previously stored calibration data, the system can detect drift and determine whether previous dark level measurements remain valid, allowing for dynamic updates only when necessary
Solution Approach 2:
The patent performs preliminary characterization of temporal and environmental effects using sealed pixels during calibration phases. This preliminary action establishes baseline drift patterns and response characteristics that enable prediction of when dark level measurements will become invalid, allowing the system to proactively update before reliability deteriorates
3Adaptability or versatility
If calibration is performed for all integration times and number of lines, then adaptability is improved, but device complexity increases
Solution Approach 1:
The patent exploits the observation that sealed pixel response characteristics follow predictable patterns with respect to integration time and number of lines. By establishing mathematical relationships between these parameters and the sealed pixel responses, the system can generalize from a limited set of calibration measurements to cover all possible operating conditions without requiring exhaustive calibration for each parameter combination
4Measurement precision
If readings are collected from all pixels, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The patent extracts the essential dark level characterization information from a small subset of sealed pixels rather than collecting readings from all pixels. By selecting specific sealed pixels that exhibit representative behavior, the system obtains sufficient calibration data with minimal measurement time while maintaining adequate precision through the sealed pixels' stable and representative response characteristics
Data Source
AI summary
A method of characterizing an imaging device includes calibrating the imaging device by collecting readings for regular pixels and at least one sealed pixel of the imaging device over one or more periods of time for a sequence of integration time (T) and a plurality of number of lines (NOL) when no light enters the imaging device, obtaining a dark level (DL) by averaging the readings for the regular pixels over the respective period of time and the number of the regular pixels, and obtaining P by averaging the readings of the at least one sealed pixel over the respective period of time and the number of the at least one sealed pixel. A relation between DL and P is determined for each T and NOL using an equation: DL=A*P+Offset. A current value of DL is determined by using a current value of P and the equation.