Event-Based Camera Exposure Control for PWM Flicker Reduction
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Solution Overview
Problem
Conventional frame-based cameras incorrectly interpret PWM-modulated brightness signals from flickering light sources, leading to erroneous signal detection and potentially hazardous autonomous decision-making in vehicles.
Innovation Solution
An event-based camera system adjusts pixel parameters, such as exposure time and digital accumulation, to mitigate flickering by altering the imaging behavior of pixels in regions with flickering light sources, reducing the generation of events and extending exposure duration to minimize flicker perception.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional frame-based cameras capture images at equidistant instances of time, then the camera operation is simple and consistent, but PWM-modulated brightness signals are incorrectly interpreted as flickering or erroneous signals
Solution Approach 1:
The patent applies dynamics by making the exposure time adaptive rather than fixed. The camera system dynamically adjusts exposure time based on detected flicker frequency, transitioning from static equidistant capture to dynamic variable-interval capture. This allows the system to synchronize with PWM-modulated light sources and correctly interpret brightness signals without erroneous flicker detection.
Solution Approach 2:
The patent changes the exposure time parameter from a fixed value to a variable value that adapts to different flicker frequencies. By modifying this key parameter based on detected signal characteristics, the system resolves the contradiction between simple operation and reliable signal detection, as the parameter adjustment is performed automatically through algorithmic processing.
2Reliability
If the exposure time is prolonged to mitigate flicker perception, then the sensitivity to flickering light sources is reduced, but the temporal resolution of the camera is degraded
Solution Approach 1:
The system dynamically adjusts exposure time based on the detected flicker frequency rather than using a fixed prolonged exposure time. This allows the camera to maintain high temporal resolution when flicker is absent or use longer exposure only when needed for flicker mitigation, thus resolving the contradiction between reliability and speed.
Solution Approach 2:
The patent employs periodic action by synchronizing the exposure intervals with the detected PWM frequency of the light source. By aligning the camera's capture rhythm with the light modulation period, the system achieves both flicker mitigation and maintained temporal resolution, as the periodic sampling captures complete PWM cycles rather than partial ones.
3Reliability
If different pixel parameters are assigned to different regions of the image, then flicker mitigation is improved in specific regions, but the device complexity increases
Solution Approach 1:
The patent applies local quality by assigning different exposure time parameters to different spatial regions of the image based on flicker detection. Regions containing PWM-modulated light sources receive customized exposure settings optimized for flicker mitigation, while other regions maintain standard settings. This localized approach improves flicker mitigation effectiveness without unnecessarily complicating the entire system.
Solution Approach 2:
The system segments the image into regions with different flicker characteristics and applies appropriate pixel parameters to each segment. By dividing the image processing into region-specific operations, the patent manages complexity through modular region handling rather than uniform complex processing across the entire image.
4Measurement precision
If the camera operates with updated pixel parameters to mitigate flicker, then the accuracy of image processing is improved, but the processing time and complexity increase
Solution Approach 1:
The patent performs preliminary flicker detection and parameter optimization before final image processing. By detecting PWM frequencies and determining optimal exposure times in advance, the system prepares the appropriate pixel parameters beforehand, reducing the computational burden during actual image processing and minimizing processing time loss.
Solution Approach 2:
The system employs feedback by continuously monitoring the detected flicker signals and adjusting pixel parameters accordingly. This closed-loop approach optimizes image processing accuracy by adapting parameters based on real-time conditions while minimizing processing time through efficient feedback-based parameter selection rather than exhaustive optimization.
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 reduces the perception of flickering light sources, enhancing the accuracy of image processing and improving the reliability of autonomous vehicle decision-making by minimizing erroneous signal detection.
Implementation Method 1
each pixel typically comprises a photodetector (e.g., a photodiode) converting light to, e.g., charge
Data Source
Figure 1~4
AI summary
The invention relates to a method for mitigating flickering lights in a scene of interest imaged by an event-based camera (7), wherein the event-based camera (7) comprises a plurality of pixels, wherein an imaging behaviour of the plurality of pixels is influenced by a set of pixel parameters comprising at least one exposure time parameter and/or at least one digital accumulation parameter, and wherein the method comprises the following steps: 1) operating (1) the event-based camera (7) having an assignment of first values to the set of pixel parameters, said operating (1) providing a plurality of events (2) generated by the event-based camera (7);2) reconstructing (3) an image based on at least the generated plurality of events (2), 3) determining (4) at least one region in the reconstructed image, said determined at least one region corresponding to at least one spatial region in the scene of interest comprising at least one flickering light source (8,9) active during the operating of the event-based camera (7), 4) determining (5) a subset of pixel parameters of the set of pixel parameters, which subset of pixel parameters influences imaging behaviour of pixels in the determined at least one region, assigning (5) second values for the determined subset of pixel parameters, which second values are determined to mitigate flicker in the pixels of the determined at least one region, and updating (5) the first values assigned to the subset of pixel parameters with the second values, and 5) further operating (6) the event- based camera (7) with the updated set of pixel parameters. The invention also relates to an assembly and to a vehicle comprising said assembly.