Circular Fisheye Camera Array Rectification via Equirectangular Warping
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Solution Overview
Problem
Current techniques are inadequate for high-quality and efficient calibration and rectification of images from circular camera arrays equipped with ultra-wide field of view fisheye lenses, which are essential for generating omnidirectional light field content.
Innovation Solution
The method involves iteratively determining feature point correspondences and warping functions between equirectangular images to align feature points horizontally and eliminate vertical disparities, using an alternating pair-wise approach to reduce image distortion and preserve depth information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If current rectification techniques based on epipolar geometry are applied to planar camera arrays, then corresponding pixels can be horizontally or vertically aligned, but these techniques are not suitable for circular camera arrays with ultra-wide field of view fisheye lenses
Solution Approach 1:
The patent transforms the rectification problem from the original fisheye image coordinate system to an equirectangular projection coordinate system. This parameter transformation allows the application of standard rectification techniques to circular camera arrays by changing the mathematical representation of image coordinates, thereby achieving both adaptability to circular arrays and maintaining rectification quality through established epipolar geometry methods
Solution Approach 2:
The patent utilizes the spherical nature of fisheye lens projections by converting images to equirectangular projection, which represents spherical geometry in a rectangular format. This approach respects the curved field of view characteristics of ultra-wide angle lenses while enabling systematic rectification through coordinate transformation, making the technique suitable for circular camera arrays
2Manufacturing precision
If rectification transformation is applied to align optical axes of all cameras, then corresponding pixels become horizontally or vertically aligned, but vertical disparities remain in circular camera arrays
Solution Approach 1:
The patent addresses vertical disparities by introducing a second rectification step that operates in the vertical dimension. After initial horizontal alignment through epipolar geometry, the method applies additional vertical shift corrections based on the specific geometry of circular camera arrays, thereby eliminating residual vertical disparities while maintaining horizontal alignment precision
Solution Approach 2:
The patent employs an iterative refinement process where feature point correspondences are detected between rectified images, and the detected disparities provide feedback for adjusting the rectification parameters. This feedback loop continues until vertical disparities are minimized, achieving both precise pixel alignment and elimination of harmful vertical shifts
3Ease of manufacture
If standard rectification methods are used on fisheye images, then processing can be simplified, but image distortion is not reduced and depth information may be lost
Solution Approach 1:
The patent applies preliminary coordinate transformation to convert fisheye projections to equirectangular projections before rectification. This preliminary action straightens the distorted geometry of fisheye images, creating a more uniform coordinate system that simplifies subsequent rectification operations while simultaneously reducing image distortion and preserving depth relationships in the transformed space
Data Source
AI summary
Techniques related to image rectification for fisheye images are discussed. Such techniques may include iteratively determining warpings for equirectangular images corresponding to the fisheye images using alternating feature mappings between neighboring ones of the equirectangular images until mean vertical disparities between the features are reduced below a threshold, and warping the equirectangular images to rectified equirectangular images.