Intra-Operative Camera Focal Length Estimation Without Calibration
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Solution Overview
Problem
Standard operating room cameras lack calibrated optical characteristics, such as focal length, necessitating time-consuming calibration processes, which are undesirable for applications requiring three-dimensional information derivation from two-dimensional images.
Innovation Solution
A computer-implemented method to intra-operatively determine the focal length of an uncalibrated camera by specifying an initial value, calculating a change factor, and adjusting the viewing direction in a pre-operative image, allowing the use of uncalibrated camera data for tracking applications without hardware modifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If standard operating room cameras are used without calibration, then the camera can be used immediately for recording, but the optical characteristics (focal length) remain unknown and cannot be used for three-dimensional information derivation
Solution Approach 1:
The system performs self-calibration by automatically determining the focal length using the camera's own image data of the tracking system. The computer processes images captured by the camera, detects tracking markers, and calculates the focal length without requiring external calibration equipment or manual intervention, enabling the camera to calibrate itself during operation
Solution Approach 2:
The system changes the state of the camera from uncalibrated to calibrated by dynamically determining and updating the focal length parameter. The computer calculates the focal length based on detected marker positions and image data, then uses this parameter for subsequent three-dimensional reconstructions and tracking applications
2Measurement precision
If traditional calibration procedures are performed to determine focal length, then accurate optical characteristics are obtained, but the process is time-consuming and interrupts surgical procedures
Solution Approach 1:
The system performs calibration actions continuously in the background during surgical procedures rather than requiring a separate calibration phase. The computer constantly processes camera images, detects tracking markers, and updates the focal length parameter as needed, preparing calibration data preliminarily without interrupting the main surgical workflow
Solution Approach 2:
The calibration process continues uninterrupted throughout the surgical procedure. The system maintains continuous image processing, marker detection, and focal length calculation, ensuring that accurate optical characteristics are always available for three-dimensional reconstruction without stopping or slowing down the surgical operation
3Measurement precision
If calibration equipment and procedures are used, then accurate focal length data is obtained, but the device complexity and hardware requirements increase
Solution Approach 1:
The system extracts the calibration function from external calibration equipment and integrates it into the existing camera and computer system. By using the camera's own image data and built-in tracking markers, the patent eliminates the need for separate calibration devices, reducing hardware complexity while maintaining measurement precision
Solution Approach 2:
The camera system serves multiple functions: it records surgical procedures, tracks surgical instruments through detected markers, and simultaneously performs self-calibration to determine optical characteristics. This multi-functionality eliminates the need for dedicated calibration equipment, reducing overall system complexity
Data Source
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AI summary
A computer-implemented method of determining a focal length of a camera (12) and/or of adjusting a viewing direction in a graphical representation of a pre-operative image of at least a part of a patient is provided. The method comprises providing uncalibrated camera data of a camera (12), wherein the uncalibrated camera data comprise an image of at least a part of a tracking system (22; S1); specifying an initial value of a focal length of the camera (12; S2); specifying a working distance value of a distance between the camera (12) and the at least part of the tracking system (22; S3); calculating a distance value of the distance between the camera (12) and the at least part of the tracking system (22) based on the uncalibrated camera data and based on the specified initial value of the focal length of the camera (S4); calculating a change factor based on the specified working distance value and the calculated distance value (S5); and calculating an adapted value of the focal length of the camera (12) based on the initial value of the focal length and based on the change factor (S6).