Colorimetric Mapping Using Reference Image Calibration
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Solution Overview
Problem
Existing digital camera systems achieve lower perceptual color reproduction accuracy due to the interpolation of pre-calibrated color space transforms when capturing images under illuminations not represented by the two factory-calibrated illuminations, as these interpolations do not accurately account for arbitrary lighting conditions.
Innovation Solution
A method and system for colorimetric mapping that involves obtaining a digital reference image, determining a color-balance matrix by minimizing errors between colorimetric values and pixel values, and applying a color-space transformation matrix to transform the image sensor's color space to a perceptual color space, using a trained Bayesian classifier and a Macbeth Color rendition chart for calibration, allowing for improved color correction under arbitrary illuminations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If two pre-calibrated color space transforms are used for factory calibration, then device complexity is reduced and ease of manufacture is improved, but color reproduction accuracy deteriorates under arbitrary illuminations
Solution Approach 1:
The system performs preliminary calibration by capturing a reference image of a color chart under the actual illumination conditions before processing the main scene. This preliminary action allows the system to compute illumination-specific color correction matrices that are then applied to subsequent images, resolving the contradiction between ease of manufacture and color accuracy under arbitrary illuminations.
Solution Approach 2:
The system dynamically changes color correction parameters based on the captured reference image. By computing a color-balance matrix and color-space transformation matrix from the reference image under actual illumination, the system adapts the color correction parameters to match the specific lighting conditions, thereby maintaining high color reproduction accuracy without requiring multiple pre-calibrated transforms for every possible illumination.
2Adaptability or versatility
If linear interpolation is used to blend two pre-calibrated color space transforms, then adaptability to different illuminations is improved, but color reproduction accuracy deteriorates
Solution Approach 1:
The system performs self-calibration by automatically capturing a reference image under the current illumination conditions and computing the appropriate color correction matrices. This self-service approach eliminates the need for linear interpolation between pre-calibrated transforms, as the system generates its own illumination-specific correction parameters, thereby maintaining both adaptability and high color reproduction accuracy.
Solution Approach 2:
The system uses feedback from the captured reference image to dynamically adjust color correction parameters. By comparing the reference image colors with known reference values and iteratively optimizing the color-balance and transformation matrices, the system achieves accurate color reproduction under arbitrary illuminations without relying on inaccurate linear interpolation methods.
Data Source
AI summary
Computer-based systems, methods and computer program products for colorimetric mapping are provided. In one embodiment of the method, the method includes obtaining a digital reference image, including: illuminating a known reference source with an arbitrary illumination; and determining an observed illumination by receiving light signals from the reference source at an image sensor; determining a color-balance matrix by minimizing an error between colorimetric values of the digital reference image and color corrected pixel values; applying the color-balance matrix to the digital reference image to produce a color-corrected image; determining a color-space transformation matrix that transforms a color space of the image sensor to a perceptual color space; generating a transformed image by applying the color-space transformation matrix to the color corrected image; and outputting the transformed image.