Vehicle Camera Exposure Control for PWM Light Flicker
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Solution Overview
Problem
Streaming video images captured by cameras of amplitude-modulated light sources, such as PWM LED headlamps and tail-lamps, often result in a flickering effect due to unsynchronized exposure times and frame rates, causing inconsistent representation of light sources in image data, which is perceivable as flicker when displayed.
Innovation Solution
An image processing unit adjusts the exposure time of the camera to match a multiple of the modulation frequency of the amplitude-modulated light sources, mitigating the flickering effect by ensuring consistent representation of light sources in video images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the camera exposure time is set to capture video frames at a standard frame rate, then the video playback is smooth and continuous, but the captured light sources appear to flicker due to unsynchronized exposure with the PWM modulation frequency
Solution Approach 1:
The patent changes the exposure time parameter of the camera to be a multiple of the PWM modulation period. This parameter adjustment synchronizes the camera exposure with the light source modulation, ensuring that each captured frame integrates the same proportion of the PWM cycle, thereby eliminating flicker while preserving standard video frame rates
Solution Approach 2:
The patent applies periodic action by setting the exposure time to match integer multiples of the PWM modulation period. This creates a synchronized periodic relationship between the camera exposure cycles and the light source modulation cycles, ensuring consistent light intensity representation across all video frames without flicker
2Stability of the object's composition
If the exposure time is adjusted to eliminate flicker by matching PWM frequency, then light sources appear stable in video, but the system requires complex frequency detection and dynamic exposure adjustment
Solution Approach 1:
The patent implements feedback by detecting the PWM modulation frequency from captured video frames and using this information to dynamically adjust the camera exposure time. The system continuously monitors light source behavior, identifies flicker patterns, and modifies exposure settings accordingly to maintain stable light source representation
Solution Approach 2:
The patent applies preliminary action by first detecting and analyzing the PWM modulation frequency before finalizing the exposure time setting. The system performs frequency detection and calculation in advance, then configures the optimal exposure time as an integer multiple of the detected period, preparing the system to eliminate flicker before video capture begins
3Illumination intensity
If the exposure time is increased to capture more light, then image brightness improves, but the flicker effect becomes more pronounced due to longer exposure windows capturing varying light intensities
Solution Approach 1:
The patent changes the exposure time parameter to specific values that are integer multiples of the PWM modulation period. This parameter selection allows the system to maintain longer exposure times for improved brightness while ensuring that each exposure window captures a complete number of PWM cycles, thereby preventing flicker artifacts
Data Source
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AI summary
An image capture system is provided for a vehicle equipped with a display for displaying streamed video images of a scene proximate the vehicle. The image capture system includes a camera for capturing video images of the scene proximate the vehicle at a selected exposure time and streaming the video images, and an image processing unit for receiving the streamed video images, processing the streamed video images and supplying the streamed video images to the display. The image processing unit is configured to detect amplitude-modulated light sources in the streamed video images, and adjust the exposure time of the camera to match a multiple of a modulation frequency of the amplitude-modulated light sources decreasing a flicker intensity of the amplitude-modulated light sources in the streamed video images supplied to the display.