Auto Exposure Control for Mobile Videoconferencing
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Solution Overview
Problem
Handheld and mobile videoconferencing applications face challenges in capturing visually appealing images in varying lighting conditions due to the limitations of auto exposure methods, which often result in video oscillations and poor quality video streams.
Innovation Solution
Implementing a small, centered exposure metering region with a center-weighted metering weighting matrix, a large AE stability region, and a fast AE convergence speed to dynamically adjust exposure parameters, allowing for visually pleasing images and efficient video encoding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If auto exposure algorithms adjust exposure parameter values frequently to adapt to rapidly changing lighting conditions, then the ability to capture visually appealing images in variable lighting is improved, but video oscillations occur causing visually jarring effects
Solution Approach 1:
The patent applies dynamics by making the AE stability region adaptive rather than fixed. The stability region dynamically adjusts its size and position based on scene characteristics and lighting conditions, allowing the system to be more stable in uniform lighting while remaining adaptable in rapidly changing conditions. This resolves the contradiction by enabling the system to optimize both stability and adaptability according to real-time requirements.
Solution Approach 2:
The patent changes the parameter of AE stability region characteristics (size, position, shape) based on scene analysis. By modifying these parameters dynamically, the system can expand the stability region to reduce oscillations in stable scenes while contracting it to allow faster adaptation in changing lighting conditions, thus resolving the contradiction between stability and adaptability.
2Stability of the object's composition
If exposure parameter values are adjusted gradually to reduce video oscillations, then video stability is improved, but the video encoder makes inaccurate temporal predictions resulting in poor quality video streams
Solution Approach 1:
The patent makes the AE response dynamic by adjusting the stability region characteristics based on scene conditions. In scenes where gradual adjustment is beneficial, the system expands the stability region to allow slower convergence. In scenes requiring faster response, the system contracts the stability region to enable more aggressive parameter changes, thus maintaining both stability and encoding accuracy.
Solution Approach 2:
The patent implements feedback mechanisms where the AE system continuously monitors scene characteristics and adjusts exposure parameters with hysteresis-based decision making. This feedback approach allows the system to make informed decisions about when to adjust parameters and when to maintain stability, improving temporal prediction accuracy while preserving video stability.
3Measurement precision
If a small, centered exposure metering region is used with a center-weighted metering weighting matrix, then focus on the subject of interest is improved, but the ability to handle varying lighting conditions across the entire scene is reduced
Solution Approach 1:
The patent applies local quality by using a center-weighted metering weighting matrix that concentrates measurement sensitivity on the centered subject region. This allows precise exposure control for the subject while the overall AE stability region considers broader scene characteristics, thus maintaining both subject accuracy and scene adaptability.
Solution Approach 2:
The patent segments the metering function into two parts: a small centered region with high weighting for subject focus, and a larger AE stability region that considers overall scene lighting. This segmentation allows the system to simultaneously optimize for subject exposure accuracy and overall scene adaptability.
4Stability of the object's composition
If a large AE stability region is used to maintain stable exposure in high contrast scenes, then exposure stability is improved, but the AE convergence speed decreases
Solution Approach 1:
The patent makes the AE stability region dynamic by adjusting its size and characteristics based on scene conditions. In high contrast scenes requiring stability, the system expands the stability region. In scenes requiring fast convergence, the system contracts the stability region, thus resolving the contradiction between stability and convergence speed through adaptive parameter adjustment.
Data Source
AI summary
Systems, methods, and a computer readable medium for performing auto exposure (AE) techniques that are beneficial in variable lighting conditions—and particularly applicable to handheld and/or mobile videoconferencing applications—are disclosed herein. Handheld and/or mobile videoconferencing applications—unlike their fixed camera counterparts—are often exposed to a wide variety of rapidly changing lighting and scene conditions, and thus face a difficult trade-off between adjusting exposure parameter values too frequently or not frequently enough. In personal electronic devices executing such handheld and/or mobile videoconferencing applications, it may be desirable to: use a small, centered, and center-weighted exposure metering region; set a relatively low brightness target value; and adjust the camera's exposure parameter values according to a distance-dependent convergence speed function. The use of such techniques, in conjunction with a relatively large stability region, may also improve the quality of a video encoder's temporal predictions—and thus video quality—in videoconferencing applications.