Gamut mapping utilizing cusp points and three-dimensional boundary surfaces

A method of performing gamut-mapping of a source point for a source device to a destination point of a destination device in a perceptually linear color space, comprising the steps of:

• obtaining the source point for a source image;
• determining tristimulus values for the source point and converting the tristimulus values to device-independent color appearance space values;
• obtaining a source hue wheel and a destination hue wheel each respectively comprising known hue angles for each of primary and secondary color components of their respective gamuts;
• determining a source hue angle of the source point in the source hue wheel, and determining a source relative position of the source point in the source hue wheel between the nearest primary color and the nearest secondary color;
• determining, in the destination hue wheel, a corresponding relative position between the primary and secondary color corresponding to the nearest primary and secondary in the source hue wheel, the determined relative position in the destination hue wheel resulting in a destination hue angle;
• obtaining a source cusp point representing a maximum chroma value on a source gamut boundary surface at the source hue angle, and obtaining a destination cusp point representing a maximum chroma value on a destination gamut boundary surface at the destination hue angle;
• performing a cusp mapping process to map the source cusp point to the destination cusp point;
• if after the cusp mapping process, the source point lies outside of the destination gamut boundary surface, mapping the source point to the destination gamut boundary surface;
• and
• converting results of the mapping process from device-independent color appearance space values to tristimulus values, and converting the converted tristimulus values to a color space of the destination device.

Computer-executable process steps stored on a computer-readable medium, the process steps for performing gamut-mapping of a source point for a source device to a destination point of a destination device in a perceptually linear color space, comprising the steps of:

• separating the source point into primary color components;
• determining tristimulus values for each of the separated primary color components, and converting the tristimulus values for each primary color component into respective device-independent color appearance space values;
• for each primary color component, performing a mapping process comprising the steps of:
• determining a source hue angle and a destination hue angle for the source image;
• obtaining a source cusp point representing a maximum chroma value on a source gamut boundary surface at the source hue angle, and obtaining a destination cusp point representing a maximum chroma value on a destination gamut boundary surface at the destination hue angle;
• performing a cusp mapping process to map the source cusp point to the destination cusp point;
• and
• if after the cusp mapping process, the source point lies outside of the destination gamut boundary surface, mapping the source point to the destination gamut boundary surface;
• converting results of the mapping process for each respective primary color component from device-independent color appearance space values to tristimulus values;
• summing respective tristimulus values for each primary color component to obtain a resultant tristimulus values;
• and
• converting the resultant tristimulus values to a color space of the destination device to obtain a destination image.

Computer-executable process steps stored on a computer-readable medium, the process steps for performing gamut-mapping of a source point for a source device to a destination point for a destination device in a perceptually linear color space, comprising the steps of:

• obtaining the source point for a source image;
• determining tristimulus values for the source point and converting the tristimulus values to device-independent color appearance space values;
• obtaining a source hue wheel and a destination hue wheel each respectively comprising known hue angles for each of primary and secondary color components of their respective gamuts;
• determining a source hue angle of the source point in the source hue wheel, and determining a source relative position of the source point in the source hue wheel between the nearest primary color and the nearest secondary color;
• determining, in the destination hue wheel, a corresponding relative position between the primary and secondary color corresponding to the nearest primary and secondary in the source hue wheel, the determined relative position in the destination hue wheel resulting in a destination hue angle;
• obtaining a source cusp point representing a maximum chroma value on a source gamut boundary surface at the source hue angle, and obtaining a destination cusp point representing a maximum chroma value on a destination gamut boundary surface at the destination hue angle;
• performing a cusp mapping process to map the source cusp point to the destination cusp point;
• if after the cusp mapping process, the source point lies outside of the destination gamut boundary surface, mapping the source point to the destination gamut boundary surface;
• and
• converting results of the mapping process from device-independent color appearance space values to tristimulus values, and converting the converted tristimulus values to a color space of the destination device.

An apparatus for performing gamut-mapping of a source point for a source device to a destination point for a destination device in a perceptually linear color space, comprising:

• a processor for executing computer-executable process steps;
• and
• a memory that stores computer-executable process step, comprising the steps of:
• separating the source point into primary color components;
• determining tristimulus values for each of the separated primary color components, and converting the tristimulus values for each primary color component into respective device-independent color appearance space values;
• for each primary color component, performing a mapping process comprising the steps of:
• determining a source hue angle and a destination hue angle for the source image;
• obtaining a source cusp point representing a maximum chroma value on a source gamut boundary surface at the source hue angle, and obtaining a destination cusp point representing a maximum chroma value on a destination gamut boundary surface at the destination hue angle;
• performing a cusp mapping process to map the source cusp point to the destination cusp point;
• and
• if after the cusp mapping process, the source point lies outside of the destination gamut boundary surface, mapping the source point to the destination gamut boundary surface;
• converting results of the mapping process for each respective primary color component from device-independent color appearance space values to tristimulus values;
• summing respective tristimulus values for each primary color component to obtain a resultant tristimulus values;
• and
• converting the resultant tristimulus values to a color space of the destination device to obtain a destination image.

An apparatus for performing gamut-mapping of a source point for a source device to a destination point for a destination device in a perceptually linear color space, comprising:

• a processor for executing computer-executable process steps;
• and
• a memory that stores computer-executable process steps, comprising the steps of:
• obtaining the source point for a source image;
• determining tristimulus values for the source point and converting the tristimulus values to device-independent color appearance space values;
• obtaining a source hue wheel and a destination hue wheel each respectively comprising known hue angles for each of primary and secondary color components of their respective gamuts;
• determining a source hue angle of the source point in the source hue wheel, and determining a source relative position of the source point in the source hue wheel between the nearest primary color and the nearest secondary color;
• determining, in the destination hue wheel, a corresponding relative position between the primary and secondary color corresponding to the nearest primary and secondary in the source hue wheel, the determined relative position in the destination hue wheel resulting in a destination hue angle;
• obtaining a source cusp point representing a maximum chroma value on a source gamut boundary surface at the source hue angle, and obtaining a destination cusp point representing a maximum chroma value on a destination gamut boundary surface at the destination hue angle;
• performing a cusp mapping process to map the source cusp point to the destination cusp point;
• if after the cusp mapping process, the source point lies outside of the destination gamut boundary surface, mapping the source point to the destination gamut boundary surface;
• and
• converting results of the mapping process from device-independent color appearance space values to tristimulus values, and converting the converted tristimulus values to a color space of the destination device.