Imaging Device Calibration via Off-Squareness Correction
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Solution Overview
Problem
Existing imaging device calibration techniques suffer from systematic measurement errors due to the assumption of a tilted axis, which introduces scale-size-distortion bias and geometry/location biases in 3D scanning and telemetry, especially when the lens axis is off-square with the image plane.
Innovation Solution
A method and system that define a true scale plane orthogonal to the line of sight and an image plane off-squareness relative to the line of sight, using 3D coordinate systems to accurately correct for assembly tolerances and distortions, including geometric and chromatic distortions, through perspective correction and homography transformations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the tilted axis assumption is used for calibration, then the calibration process can be simplified, but systematic measurement errors and scale-size-distortion bias are introduced
Solution Approach 1:
The patent extracts and removes the tilted axis assumption from the calibration model, separating the ideal orthogonal case from the actual off-squareness error. By taking out this simplifying assumption, the patent eliminates the source of systematic bias while maintaining practical calibration capabilities through separate parameter estimation for focal length and off-squareness angles.
Solution Approach 2:
Instead of assuming the image plane is tilted relative to the line of sight (traditional approach), the patent inverts the model by assuming the line of sight is off-square relative to the image plane. This inversion allows the use of standard pinhole camera models while accounting for assembly tolerances through dedicated off-squareness parameters.
2Ease of manufacture
If the tilted axis assumption is used, then calibration can proceed with standard models, but geometry and location bias of 3D objects is introduced in reconstruction
Solution Approach 1:
The patent segments the calibration parameters into distinct components: focal length, image center, and off-squareness angles. This segmentation allows each parameter to be estimated independently, preventing the coupling of errors that occurs in traditional tilted axis models where all parameters are interdependent and biased together.
Solution Approach 2:
The patent introduces an intermediary coordinate system that bridges the ideal pinhole model and the actual off-square image plane. This intermediary framework allows standard pinhole projection equations to be used while incorporating off-squareness corrections, maintaining ease of implementation without sacrificing accuracy.
3Productivity
If standard calibration techniques are used, then the process is simpler, but focal length and image center measurements are biased
Solution Approach 1:
The patent performs preliminary action by separately estimating the off-squareness angles before finalizing the focal length and image center parameters. This preliminary estimation of the off-squareness error allows subsequent calibration steps to proceed without the bias that would otherwise contaminate all parameter estimates, improving overall measurement precision while maintaining efficiency.
Data Source
AI summary
The invention relates to a camera modeling and calibration system and method using a new set of variables to compensate for imperfections in line of sight axis squareness with camera plane and which increases accuracy in measuring distortion introduced by image curvature caused by geometric and chromatic lens distortion and wherein the camera image plane is represented from a full 3D perspective projection.