Stereo Camera Rolling Shutter Synchronization
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Solution Overview
Problem
Camera-based driver assistance systems face challenges in accurately determining object distances, especially with rolling shutter image sensors, which introduce synchronization issues in stereo image processing, particularly in asymmetric configurations with different fields of view, leading to inaccuracies in object distance measurements.
Innovation Solution
The system employs two image capture devices with rolling shutters, where the timing control parameters such as line scan rates, horizontal and vertical blanking periods, and pixel delays are adjusted to synchronize the acquisition of image frames, even when the cameras have different fields of view, ensuring that overlapping regions are captured during the same period, thereby overcoming synchronization challenges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If both wide FOV and narrow FOV cameras acquire images at similar line scan rates, then the imaging system can maintain consistent frame acquisition speed, but the image scan lines in the overlapping field of view area will lack synchronization, leading to inaccurate object distance measurements
Solution Approach 1:
The patent adjusts the line scan rate parameter of the narrow FOV camera to be different from the wide FOV camera. Specifically, the narrow FOV camera operates at a higher line scan rate so that its image scan lines are synchronized with the corresponding scan lines of the wide FOV camera in the overlapping field of view area, thereby enabling accurate stereo correspondence and object distance measurement while maintaining efficient frame acquisition
Solution Approach 2:
The system dynamically adjusts the timing parameters of the rolling shutter based on the camera configuration and field of view overlap. By making the line scan rates adaptive rather than fixed, the system optimizes both the acquisition speed and the synchronization accuracy for asymmetric stereo setups
2Area of stationary object
If the narrow FOV camera overlaps with only a portion of the wide FOV camera's field of view, then the asymmetric configuration can provide extended coverage, but the acquired image scan lines in the overlap area will lack synchronization, introducing difficulties in determining image point correspondence
Solution Approach 1:
The patent changes the line scan rate parameter of the narrow FOV camera to achieve synchronization of image scan lines in the overlapping region. This parameter adjustment ensures that corresponding scan lines from both cameras are captured at the same time, making it possible to accurately detect image point correspondence and calculate stereo disparity for reliable depth measurement
Solution Approach 2:
The system performs preliminary timing configuration of the rolling shutters before image acquisition. By pre-calculating and setting the appropriate line scan rates based on the known field of view overlap geometry, the system ensures that synchronization is already established when imaging begins, eliminating the need for post-processing correction and simplifying the correspondence detection process
Data Source
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AI summary
An imaging system for a vehicle may include a first image capture device having a first field of view and configured to acquire a first image relative to a scene associated with the vehicle, the first image being acquired as a first series of image scan lines captured using a rolling shutter. The imaging system may also include a second image capture device having a second field of view different from the first field of view and that at least partially overlaps the first field of view, the second image capture device being configured to acquire a second image relative to the scene associated with the vehicle, the second image being acquired as a second series of image scan lines captured using a rolling shutter. As a result of overlap between the first field of view and the second field of view, a first overlap portion of the first image corresponds with a second overlap portion of the second image. The first image capture device has a first scan rate associated with acquisition of the first series of image scan lines that is different from a second scan rate associated with acquisition of the second series of image scan lines, such that the first image capture device acquires the first overlap portion of the first image over a period of time during which the second overlap portion of the second image is acquired.