Gamut Mapping with Saturation Intent and Cusp Point Shear
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Solution Overview
Problem
Current gamut mapping methods often result in dull colors when rendering colors from a large gamut to a smaller gamut, particularly noticeable in printing business graphics, where vivid colors are desired, due to the lack of effective saturation control in appearance spaces like JCh.
Innovation Solution
The use of primary cusp points, lightness compression toward cusp point lightness, and chroma expansion techniques in gamut mapping, which involve determining and interpolating cusp points between primary and secondary hues, applying shear mapping, and adjusting chroma values to enhance saturation and smoothness of color transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional gamut mapping methods are used to render colors from a large gamut to a smaller gamut, then color accuracy is maintained, but color saturation is lost resulting in dull colors
Solution Approach 1:
The gamut mapping process is segmented into distinct operations: identifying primary cusp points in both source and destination gamuts, performing shear mapping to align these cusp points, and then applying chroma expansion. This segmentation allows independent optimization of color accuracy (through cusp point alignment) and color vividness (through chroma expansion), resolving the contradiction between maintaining accuracy while improving saturation.
Solution Approach 2:
The invention changes the chroma parameter of colors in the destination gamut by applying chroma expansion after the initial gamut mapping. This parameter change increases saturation and vividness without compromising the color accuracy established by the cusp point alignment, thereby resolving the contradiction between accuracy and vividness.
2Ease of manufacture
If saturation is enhanced in gamut mapping, then color vividness improves, but smoothness of color transitions may deteriorate
Solution Approach 1:
The shear mapping operation is performed as a preliminary action before chroma expansion. This preliminary alignment of primary cusp points establishes a stable geometric framework that ensures smooth color transitions. Subsequent chroma expansion then enhances vividness within this stable framework, preventing transition artifacts.
Solution Approach 2:
Chroma expansion is applied locally to colors based on their position in the gamut space. The expansion factor varies depending on the local properties of the destination gamut at each color's location, ensuring that saturation enhancement maintains smooth transitions in gradient areas while maximizing vividness in saturated regions.
Data Source
AI summary
Techniques for use in gamut mapping processes are presented, including a method for mapping cusp points using hue wheels to obtain a source relative hue angle, and interpolating a lightness value at the source point hue. A maximum chroma value is determined at the source hue and the interpolated lightness, thus defining a source primary cusp point. A primary cusp point for a second color gamut is similarly obtained, and the source primary cusp point is mapped to the destination primary cusp point using a shear mapping technique. Another technique includes performing lightness compression by applying a chroma dependency factor and either a first or second factor, depending on a comparison of a lightness values of a destination point and a second point. Another technique involves performing chroma expansion by comparing chroma extents of source and destination points, and adjusting the chroma of the destination point based on the comparison.