Dual Camera Calibration Using Segmented Circular Rings
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Solution Overview
Problem
Calibrating a dual camera system with a fixed focus camera is challenging due to its far focus position, requiring large calibration charts that occupy significant space and are affected by gravity, and traditional methods like checkerboard patterns struggle with unfocused images near the focal point.
Innovation Solution
A calibration method using a chart with multiple circular rings and a disk, where edge detection and binarization are performed to detect inner and outer edges, fit centers and radii, and index features to align the cameras based on matching image features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large calibration chart is used to cover the full field of view of a fixed focus camera, then the calibration precision is improved, but the space occupation increases and the chart is affected by gravity
Solution Approach 1:
The calibration chart is segmented into multiple circular rings with discrete geometric outlines instead of a single large checkerboard pattern. This segmentation allows the chart to be smaller while providing sufficient calibration features across the field of view, reducing both space occupation and gravitational effects.
Solution Approach 2:
The invention transitions from using intersection points (2D grid intersections) to using circular ring centers and radii (concentric circular patterns). This dimensional change in the geometric features allows for more efficient space utilization while maintaining calibration precision, as the circular patterns provide robust feature points without requiring a large extended chart area.
2Ease of manufacture
If traditional checkerboard patterns are used for calibration, then the calibration process is simple, but the method struggles with unfocused images near the focal point of fixed focus cameras
Solution Approach 1:
The calibration method changes the geometric parameters from rectangular grid intersections to circular ring centers and radii. This parameter change makes the calibration features more robust to focus variations, as circular patterns maintain their geometric integrity and detectability even when slightly out of focus, unlike sharp corner intersections that become ambiguous.
Solution Approach 2:
The patent employs binarization to convert grayscale images to binary (black and white) representations, enhancing the contrast and detectability of the circular ring features. This binary transformation ensures that the calibration features remain clearly distinguishable regardless of focus variations, improving reliability near the focal point while maintaining process simplicity.
3Length of stationary object
If the calibration chart is placed at an extended length from the cameras, then the full field of view is covered, but the space occupation increases
Solution Approach 1:
By segmenting the calibration information into multiple concentric circular rings with distinct geometric outlines, the system can achieve comprehensive field of view coverage with a smaller, more compact chart placed at a shorter distance, reducing the overall space occupation in the calibration setup.
Solution Approach 2:
The calibration chart uses nested concentric circular rings where smaller rings are contained within larger ones. This nesting arrangement allows multiple calibration features to be packed into a compact area, enabling full field of view calibration with a smaller chart at a reduced distance from the cameras.
Data Source
AI summary
A method of calibration of a dual camera system, including, providing a chart of a plurality of circular rings and at least one disk, imaging the chart with a first camera to provide a first chart image and a second camera to provide a second chart image, performing edge detection of the first and second chart image on the plurality of circular rings and the at least one disk, determining the relative position of the plurality of circular rings to the at least one disk, matching the relative positions of the plurality of circular rings of the first chart image and the second chart image and aligning the first camera and the second camera based on the matching of the first chart image to the second chart image.