Auto Exposure Control for CMOS Imagers
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Solution Overview
Problem
Existing automatic exposure and gain control algorithms in CMOS imagers often result in oscillations, leading to suboptimal image quality due to failure in converging desired and actual exposure and gain settings.
Innovation Solution
Implementing an automatic exposure control method that adjusts exposure based on current measured luminance and dynamically modifiable target luminance levels, using statistics such as current luminance, saturated luminance, and saturation thresholds to prevent oscillations and ensure optimal image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional automatic exposure control algorithms are used to adjust exposure settings, then exposure control is achieved, but oscillations occur and convergence to optimal settings is failed
Solution Approach 1:
The patent applies dynamics by making the target luminance level adjustable and modifiable during operation. The system dynamically adapts the target luminance based on scene analysis and historical data, allowing the exposure control to respond flexibly to changing conditions without oscillating. This dynamic adjustment capability enables the system to converge to optimal settings by learning from past performance and modifying targets accordingly.
Solution Approach 2:
The patent implements feedback mechanisms by continuously monitoring actual luminance measurements and comparing them against target luminance levels. The system uses this feedback to adjust exposure settings and to modify target luminance levels based on whether the feedback indicates over-exposure or under-exposure trends. This closed-loop feedback system prevents oscillations by making informed, stable adjustments rather than reactive corrections.
2Illumination intensity
If exposure settings are adjusted to prevent under-exposure, then brightness is improved, but over-exposure occurs
Solution Approach 1:
The patent applies partial or excessive action by intentionally setting target luminance levels that may appear slightly conservative initially, then gradually adjusting them based on feedback. Rather than aggressively pushing for maximum brightness, the system uses moderate adjustments that prevent over-exposure while steadily improving image brightness. This approach accepts some initial conservatism to avoid the harmful effect of over-exposure.
Solution Approach 2:
The patent uses parameter changes by dynamically modifying the target luminance parameter based on scene characteristics and historical exposure outcomes. The system changes this key parameter to balance brightness improvement against over-exposure risk, adjusting it upward when under-exposure is detected and downward when over-exposure risk increases. This adaptive parameter adjustment maintains exposure accuracy while improving overall image brightness.
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 stabilizes image exposure, preventing oscillations and ensuring optimal image quality by dynamically adjusting target luminance and exposure settings, thereby maintaining a balance between preventing over and under-exposure.
Implementation Method 1
Each pixel cell includes a photosensor, for example, a photogate, photoconductor or a photodiode overlying a substrate for accumulating photo-generated charge in the underlying portion of the substrate
Data Source
AI summary
An apparatus and method for performing automatic exposure control based on current measured luminance of an image and dynamic/modifiable target luminance levels. Exposure adjustments and/or adjustments to the dynamic/modifiable target luminance windows are based on the measured luminance and threshold settings to improve image quality while avoiding oscillations and other problems typically associated with automatic exposure.