Camera Calibration Device Using Linear Model for Wide-Angle Lenses
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Solution Overview
Problem
Conventional camera calibration methods face challenges with nonlinear models, leading to issues such as convergence to incorrect minimum values and lengthy optimization processes due to the assumption that all backprojection lines intersect at the optical center, which is not accurate, especially with wide-angle lenses experiencing significant pupil aberration.
Innovation Solution
A calibration device and method that use a linear camera model to express image-formation relationships, allowing for precise parameter calculation by treating two-dimensional world coordinates as functions of one coordinate value and pixel coordinates, thereby avoiding repeated optimization and improving calculation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a nonlinear camera model is used for calibration, then measurement precision is improved, but calculation time increases and convergence to correct minimum values cannot be guaranteed
Solution Approach 1:
The patent segments the calibration problem into two parts: first determining the optical center separately, then using it to simplify the camera model parameter optimization. This segmentation allows the complex nonlinear optimization to be broken down into more manageable steps that converge faster and more reliably.
Solution Approach 2:
The patent performs preliminary determination of the optical center before proceeding with camera parameter calibration. This preliminary action provides a fixed reference point that simplifies subsequent calculations and ensures the optimization process starts from a known correct position, preventing convergence to incorrect minimum values.
2Device complexity
If conventional camera calibration assuming all backprojection lines intersect at the optical center is used, then device complexity is reduced, but measurement precision deteriorates for wide-angle lenses with pupil aberration
Solution Approach 1:
The patent applies local quality by treating the optical center determination as a special local property that is determined separately and then used to guide the global camera parameter calibration. This allows the model to account for pupil aberration effects locally at the optical center while maintaining overall model manageability.
Solution Approach 2:
The patent introduces the optical center as an intermediary element that mediates between the complex reality of pupil aberration and the simplified camera model. By determining the optical center first and using it as a reference, the patent creates a bridge that allows accurate calibration without requiring the full complexity of pupil aberration modeling throughout the entire system.
3Measurement precision
If repeated optimization is performed to obtain camera parameters, then measurement precision is improved, but productivity decreases
Solution Approach 1:
The patent performs the preliminary determination of the optical center before camera parameter optimization, which eliminates the need for repeated optimization cycles. This preliminary action provides a stable foundation that allows camera parameters to be determined in a single optimization pass, significantly improving calibration speed while maintaining precision.
Solution Approach 2:
The patent inverts the conventional calibration approach by determining the optical center first (rather than trying to determine all parameters simultaneously through repeated optimization). This inversion of the calibration sequence reduces the computational burden and eliminates the need for multiple optimization iterations, thereby improving productivity.
Data Source
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AI summary
An object is to quickly obtain precise camera parameters. A calibration device 1 of the present invention is a calibration device 1 for an optical device 2 including a two-dimensional image conversion element having a plurality of pixels and an optical system that forms an image-formation relationship between the image conversion element and the three-dimensional world coordinate space. The calibration device 1 includes: a calibration-data acquisition unit 8 that acquires calibration data representing the correspondence between two-dimensional pixel coordinates in the image conversion element and three-dimensional world coordinates in the world coordinate space; and a parameter calculating unit 7 that calculates parameters of a camera model by applying, to the calibration data acquired by the calibration-data acquisition unit 8, a camera model in which two coordinate values of the three-dimensional world coordinates are expressed as functions of the other one coordinate value of the world coordinates and the two coordinate values of the two-dimensional pixel coordinates.