Gamut mapping using hue-preserving color space

A system for applying gamut mapping to an input digital image having input color values represented in an input color space, the input color values having an associated input color gamut, to produce an output digital image having output color values represented in an output color space, the output color values having an associated output color gamut, comprising:

• a data processing system;
• and
• a memory system communicatively connected to the data processing system and storing:
• a gamut mapping color transform which embodies the operations of:
• i) transforming input color values from the input device independent color space to linear RGB color values for a linear RGB color space, wherein the linear RGB color space has three color channels, each color channel having an associated color primary;
• ii) transforming the linear RGB color values to determine nonlinear RGB color values by applying a one-dimensional nonlinear transformation to each the linear RGB color values;
• iii) applying a 3×3 matrix transformation to the nonlinear RGB values to an opponent color space having opponent color values;
• iv) applying a gamut mapping function to map opponent color values within the input color gamut to produce modified opponent color values within the output color gamut;
• and
• v) transforming the modified opponent color values to produce the output color values in the output color space;
• and
• instructions configured to cause the data processing system to apply the gamut mapping color transform to the input color values of the input digital image to produce output color values for the output digital image;
• wherein the color primaries are defined such that the sides of a corresponding color gamut triangle, when plotted on a CIE chromaticity diagram, are substantially tangential to a spectrum locus curve defining a human visual system color gamut, and such that the opponent color space has desirable hue preserving characteristics.

A method for applying gamut mapping to an input digital image having input color values represented in an input color space, the input color values having an associated input color gamut, to produce an output digital image having output color values represented in an output color space, the output color values having an associated output color gamut, comprising:

• a) defining a gamut mapping color transform which embodies the operations of
• i) transforming input color values from the input device independent color space to linear RGB color values for a linear RGB color space, wherein the linear RGB color space has three color channels, each color channel having an associated color primary;
• ii) transforming the linear RGB color values to determine nonlinear RGB color values by applying a one-dimensional nonlinear transformation to each the linear RGB color values;
• iii) applying a 3×3 matrix transformation to the nonlinear RGB values to an opponent color space having opponent color values;
• iv) applying a gamut mapping function to map opponent color values within the input color gamut to produce modified opponent color values within the output color gamut;
• and
• v) transforming the modified opponent color values to produce the output color values in the output color space;
• and
• b) using a processor to apply the gamut mapping color transform to the input color values of the input digital image to produce output color values for the output digital image;
• wherein the color primaries are defined such that the sides of a corresponding color gamut triangle, when plotted on a CIE chromaticity diagram, contain substantially all of a real world surface color gamut, and such that the opponent color space has desirable hue preserving characteristics.