Exposure Time Controller for Video Camera Auto-Exposure
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Video cameras, especially those used for surveillance, face slow autoexposure convergence in variable lighting conditions, leading to image quality issues and potential operational disruptions due to exposure artifacts, particularly when connected to rate-controlled video encoders.
Innovation Solution
An exposure time controller that records and estimates ET values, identifies the most frequent ones, and assigns them to the video camera's ET variable to rapidly and stably adjust to new lighting conditions, bypassing the setpoint-restoring AE algorithm and temporarily disabling rate control when necessary to suppress oscillations and artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the AE control loop uses continuous incrementing and decrementing of the exposure time variable, then the algorithm maintains stability, but the convergence speed becomes slow
Solution Approach 1:
The patent applies dynamics by making the AE control system adaptive - it automatically adjusts the step size of exposure time adjustments based on the current state. When exposure mismatch is large, larger steps are taken; when接近 target, smaller steps are used. This dynamic adjustment resolves the contradiction by allowing fast convergence initially while maintaining stability near the target.
Solution Approach 2:
The patent changes the parameter of step size dynamically during operation. Instead of fixed small increments/decrements, the system varies the adjustment magnitude based on exposure mismatch magnitude and convergence progress, enabling both rapid initial response and stable final convergence.
2Adaptability or versatility
If the AE algorithm operates in variable lighting conditions, then it can adapt to different scenes, but oscillations and artifacts occur during convergence
Solution Approach 1:
The patent uses feedback mechanisms where the system continuously monitors exposure mismatch and adjusts subsequent steps based on previous performance. The adaptive step size is determined by feedback from the magnitude and persistence of exposure errors, allowing the system to handle variable lighting while suppressing oscillations through informed adjustment decisions.
3Loss of energy
If rate-controlled video encoder is used, then data compression is improved, but exposure artifacts are exacerbated and convergence time is prolonged
Solution Approach 1:
The patent applies preliminary action by performing exposure time adjustments more aggressively before the encoder processes the video stream. By reducing exposure mismatch earlier through adaptive large-step adjustments, the system prevents the generation of excessive exposure artifacts that would otherwise require heavy compression and prolong convergence.
4Speed
If the AE control loop responds fast to lighting changes, then convergence speed improves, but oscillations and instability increase
Solution Approach 1:
The patent makes the control system dynamic by adjusting the aggressiveness of responses based on real-time conditions. Fast response is applied when needed (large exposure mismatch), while stability is maintained when接近 target (small adjustments). This dynamic control resolves the speed-stability tradeoff.
Solution Approach 2:
The system changes the control parameter (step size) dynamically - using larger changes for fast initial response to lighting changes, then transitioning to smaller changes for stable convergence, thereby achieving both speed and stability at different stages of the process.
Data Source
AI summary
An exposure time controller for controlling an exposure time (ET) variable of a video camera, which is associated with an auto-exposure algorithm configured to reduce an exposure mismatch (ΔE) by incrementing and decrementing the ET variable, which comprises: a memory for recording ET values applied while the video camera is imaging a scene and the algorithm is active; and processing circuitry configured to: determine that the exposure mismatch exceeds a threshold while the video camera is imaging the scene; estimate a distribution of the recorded ET values; based on the estimated distribution, identify multiple relatively most frequent ET values; and, in reaction to determining that the exposure mismatch exceeds the threshold, assign one of the identified ET values to the ET variable.