Scene-Aware Auto-Exposure Control Reducing Lighting Flicker
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Solution Overview
Problem
Modern digital cameras face challenges in accurately determining scene lighting, leading to false low-light identification and exposure adjustments that can result in lighting flicker, especially when combined with video encoding, due to the difficulty in distinguishing between true lighting changes and scene composition changes.
Innovation Solution
A scene-aware auto-exposure control process that stabilizes exposure settings by using a Modified Adjusted Luminance (MAL) metric to suppress exposure adjustments during stable lighting conditions, reducing lighting and color flicker by comparing successive frames and only restoring auto-exposure when significant changes are detected.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If auto-exposure control continuously adjusts exposure time based on scene luminance, then scenes with insufficient light are brightened, but scenes with many low luminance objects are falsely identified as low-light scenes causing unnecessary exposure adjustments
Solution Approach 1:
The patent introduces a scene complexity metric as an intermediary parameter to assess whether a scene contains many low luminance objects. This metric acts as a mediator between the raw luminance measurement and the exposure control decision, preventing false low-light identification by considering the distribution and variety of objects in the scene before triggering exposure adjustments
Solution Approach 2:
The patent changes the parameter used for exposure control from simple average luminance to a composite metric that incorporates scene complexity assessment. By transforming the control parameter to include object detection and scene analysis, the system achieves more accurate light amount determination that distinguishes between truly dark scenes and scenes with many low luminance objects
2Illumination intensity
If auto-exposure control adjusts exposure frequently to respond to lighting changes, then poor illumination is corrected, but lighting flicker appears in the captured images
Solution Approach 1:
The patent implements periodic assessment of scene changes by comparing the current scene complexity metric with historical metrics from previous frames. Instead of reacting to every luminance change, the system periodically evaluates whether changes exceed a threshold and persist for a specified number of frames, creating a stable response pattern that prevents flicker while maintaining responsiveness to genuine lighting changes
Solution Approach 2:
The patent performs preliminary scene complexity assessment and change detection before triggering exposure adjustments. By evaluating multiple frames in advance and determining whether changes are significant and persistent, the system prepares the exposure control decision in advance, preventing reactive adjustments that would cause flicker
3Illumination intensity
If auto-exposure control responds quickly to lighting changes, then illumination quality is maintained, but encoding efficiency is greatly impacted by quick changes in scene lighting
Solution Approach 1:
The scene complexity metric serves as an intermediary that filters and stabilizes the control signal sent to the video encoder. By assessing scene complexity and change persistence before allowing exposure adjustments, the system reduces the frequency of encoding parameter changes, thereby maintaining illumination quality while improving encoding efficiency
Solution Approach 2:
The patent transforms the exposure control parameter from continuously variable to discretely adjusted based on scene complexity thresholds. This parameter transformation reduces the number of exposure adjustment events, which directly reduces encoding complexity and improves video encoding efficiency while maintaining adequate illumination quality
Data Source
AI summary
A scene-aware auto-exposure control process stabilizes changes in a camera's auto-exposure settings so as to reduce lighting and color flicker during image capture operations. A metric, referred to as the Modified Adjusted Luminance (MAL) metric, is defined to remain relatively constant as long as the lighting of the scene being captured remains relatively constant. Thus, scene changes such as an object moving into, out of, or around in a scene do not significantly affect the MAL metric's value and do not, therefore, trigger an exposure adjustment. Once the MAL metric indicates a scene's lighting is stable, the camera's auto-exposure operation may be suppressed. As long as incoming frames indicate a stable lighting condition (based on the MAL metric), auto-exposure operation may remain suppressed. When incoming frames result in a substantially different MAL over a specified number of frames, auto-exposure operation may be restored.