Thick Lens Calibration for Complex Camera Systems
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Solution Overview
Problem
High-end cameras with complex lenses cannot be effectively calibrated using the pinhole model, as their lens systems move to focus at different distances, leading to inaccuracies in image projection and depth estimation in applications like stereo and structure from motion.
Innovation Solution
A method for calibrating complex camera devices by determining the distances between nodal points and the image sensor using a checkerboard pattern, calculating magnification factors, and fitting linear curves to compensate for different lens settings, allowing for precise calibration of sensor distances and nodal point distances across various depths of field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a pinhole or thin lens model is used for calibration, then the calibration process is simple, but the calibration accuracy is poor for complex lens systems
Solution Approach 1:
The patent transitions from a simple pinhole model to a thick lens model by introducing additional parameters including two nodal points (first and second nodal points), multiple focal lengths, and variable sensor distances. This parameter expansion enables accurate representation of complex lens systems while maintaining calibration feasibility through systematic measurement approaches
Solution Approach 2:
The patent introduces a checkerboard pattern as an intermediary calibration object that facilitates measurement of the complex lens parameters. The checkerboard provides known geometric features that can be detected and used to calculate magnification factors, which in turn reveal the nodal point positions and sensor distances through the established mathematical relationships
2Adaptability or versatility
If lens settings are changed to focus at different distances, then the adaptability is improved, but the sensor distance varies making calibration difficult
Solution Approach 1:
The patent establishes predetermined mathematical relationships between lens parameters before actual calibration occurs. The thick lens model with its defined nodal points and focal length relationships provides a framework that guides the calibration process, allowing systematic determination of parameters through sequential measurements rather than attempting to solve the complex system simultaneously
Solution Approach 2:
The patent uses magnification factor calculations as feedback to determine nodal point positions and sensor distances. By measuring the magnification of known objects at different depths of field and iteratively applying the thick lens model equations, the calibration process converges on accurate parameter values that account for varying lens settings
3Measurement precision
If nodal point distance differs from sensor distance, then the projection accuracy is improved, but the inversion calculation becomes complex
Solution Approach 1:
The patent segments the projection calculation into two distinct components: the forward projection from object space to image space using the thick lens model with nodal points, and the inverse projection from image coordinates to 3D space. This segmentation allows each transformation to be optimized independently, with the nodal point distances providing accurate geometric relationships for both directions
Data Source
AI summary
The thick lens calibration method enables better calibration of complex camera devices such as devices with thick lens systems. The thick lens calibration method includes a two step process of calibrating using the distance between a second nodal point and an image sensor, and calibrating using the distance between the first and second nodal point.