Camera Response Function Calibration for Non-Uniform Illumination
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Solution Overview
Problem
Current camera radiometric calibration methods are inadequate for medical endoscopes due to non-linear light relationships and specific illumination challenges, such as near-light sources and varying vignetting, which affect image quality and require complex calibration procedures that are not easily applicable in minimally invasive procedures.
Innovation Solution
A method for estimating the camera response function and color mapping using a single calibration image under generic illumination, which segments regions of different albedos to normalize irradiance and derive a vignetting model without assuming light source shape or conditions, allowing for fast and robust calibration suitable for medical endoscopes and other generic setups.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional CRF estimation methods are used, then they assume far light sources or punctual isotropic illumination, but medical endoscopes have near-light sources with non-uniform illumination patterns that these methods cannot handle
Solution Approach 1:
The patent changes the fundamental parameters of the illumination model by not assuming any specific light source configuration (far field, punctual, isotropic). Instead, it works with the actual near-light source configuration having non-uniform illumination patterns, deriving CRF estimation methods that are valid for generic illumination conditions without requiring parameter changes to match idealized models.
Solution Approach 2:
The patent creates a universal CRF estimation method that works across different illumination conditions (near-light sources, non-uniform patterns, various geometries) by formulating a general approach that does not depend on specific illumination assumptions. This single method can handle multiple lighting scenarios that previously required different specialized approaches.
2Measurement precision
If complex calibration procedures are implemented to achieve accurate radiometric calibration, then measurement precision improves, but device complexity and user intervention requirements increase
Solution Approach 1:
The patent implements self-service calibration by enabling the camera system to automatically characterize its own response function using images captured during normal operation. The system performs self-calibration without requiring external calibration devices, complex procedures, or extensive user intervention, making the process simple and integrated into the workflow.
Solution Approach 2:
The patent performs preliminary characterization of the illumination pattern and vignetting effects during the calibration phase, storing these parameters for later use. This preliminary action allows the system to compensate for non-uniform illumination and vignetting in real-time operation, achieving accurate radiometric calibration without repeating complex procedures during actual use.
3Measurement precision
If multiple calibration images under controlled conditions are acquired, then CRF estimation accuracy improves, but calibration time and user intervention increase
Solution Approach 1:
The patent enables a single calibration image to serve multiple purposes: characterizing the illumination pattern, estimating vignetting, and deriving the camera response function. This multi-functional approach extracts maximum information from minimal data, achieving accurate CRF estimation without requiring multiple images under different controlled conditions.
Solution Approach 2:
The patent skips the traditional multi-step calibration process requiring multiple images and controlled conditions by directly estimating CRF from a single image captured under the actual operating conditions. This rushes through the calibration process efficiently while maintaining accuracy through sophisticated algorithms that handle the complexity in one step.
4Manufacturing precision
If vignetting compensation is applied to improve image quality, then image quality improves, but the complexity of the imaging system increases
Solution Approach 1:
The patent implements self-service vignetting compensation by automatically characterizing the vignetting pattern during calibration and applying compensation in real-time operation. The system performs this correction autonomously without requiring manual intervention or complex hardware modifications, achieving improved image quality through software-based solutions.
Solution Approach 2:
The patent performs preliminary characterization of the vignetting pattern during the calibration phase, storing the vignetting map for later use. This preliminary action allows the system to compensate for vignetting effects in real-time operation by applying pre-computed correction factors, avoiding the need for complex real-time calculations during actual imaging.
Data Source
Figure 1A~1B
Figure 1C
Figure 2A~2B
AI summary
Methods and systems for describing a camera radiometrically, in terms of camera response function and vignetting, and in terms of color, suitable for non-uniform illumination set-ups. It estimates the camera response function and the camera color mapping from a single image of a generic scene with two albedos. With a second same-pose image with a different intensity of the near-light the vignetting is also estimated. The camera response function calibration involves the segmentation of the two albedos, the definition of the system of equations based on the assumption that can be made about the image formation process, and the actual estimation. For the modelling the vignetting there are three steps: computing the albedo-normalized irradiance, finding points of equal vignetting, when needed, and estimation.