Color Lookup Table Generation Minimizing Interpolation Errors
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Solution Overview
Problem
Existing color lookup table (LUT) generation methods result in higher interpolation errors, particularly for off-grid colors located in areas of high curvature near the gamut boundary, due to the direct estimation of grid point correspondences and subsequent interpolation.
Innovation Solution
A novel method that computes grid point values using a least mean square error solution, considering off-grid point errors, by defining vectors and matrices to minimize total interpolation error energy, and weighting color accuracy for different colors, thereby generating an optimized LUT that reduces errors across the entire color space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct estimation of grid point correspondences is used with standard interpolation methods, then the LUT generation process is simple, but interpolation errors increase significantly for off-grid colors in high curvature areas near the gamut boundary
Solution Approach 1:
The patent changes the parameters used in LUT generation by formulating an optimization problem that minimizes total interpolation error energy. Instead of directly estimating grid point correspondences and accepting interpolation errors, the method computes optimal grid point values by solving a minimization problem that considers off-grid point errors, thereby improving color conversion accuracy particularly in high curvature areas
Solution Approach 2:
The patent creates an optimized copy of the traditional LUT generation approach by formulating a new objective function that copies the essential elements (grid points, interpolation) but adds an optimization layer to minimize total error energy, producing a more accurate LUT without completely redesigning the interpolation mechanism
2Productivity
If standard interpolation methods are used for off-grid colors, then the LUT can be generated quickly, but errors are higher particularly near the gamut boundary
Solution Approach 1:
The patent applies preliminary action by pre-computing optimal grid point values that minimize total interpolation error energy before actual color conversions are performed. This optimization is done once during LUT generation, allowing subsequent conversions to use these pre-optimized values, thereby achieving both speed and accuracy
3Ease of manufacture
If grid point values are directly estimated without optimization, then the process is straightforward, but off-grid point errors are not minimized
Solution Approach 1:
The patent implements feedback by formulating an optimization problem where the total interpolation error energy is calculated based on off-grid point errors, and this error information feeds back into the grid point value computation. The grid points are adjusted based on this feedback to minimize overall error, creating an iterative refinement process that improves off-grid color accuracy
Data Source
AI summary
What is disclosed is a novel system and method for generating a color lookup table (LUT) that minimizes interpolation errors over the entire color space, including the off-grid colors. The present method for LUT optimization considers off-grid point errors in assigning entries to the LUT. As described herein further, grid point values are computed that provide a least mean square error solution for the entire printer gamut volume. The present method dramatically reduces errors near the gamut boundary and can be used for populating nodes of any LUT that will be linearly interpolated, not only a table mapping from L*a*b* to CMYK.