Selection of samples for spanning a spectral gamut

A method of spectral gamut mapping a color value in a color space for a device having a spectral gamut, the method comprising:

• executing an off-line phase and an on-line phase by one or more computers;
• wherein the off-line phase comprises:
• establishing a first crude spanning set of samples for spanning the spectral gamut by specifying one or more corresponding device values in a device color space;
• refining the first crude spanning set by processing a plurality of new samples in a predetermined order, wherein the processing includes, for each new sample, determining if the new sample does or does not differ in an objective function value by more than a predetermined threshold from all samples in the first crude spanning set, and modifying the first crude spanning set by adding the new sample to the first crude spanning set if the new sample differs in the objective function value by more than the predetermined threshold from all samples in the first crude spanning set;
• designating the resulting first crude spanning set as a spanning set of samples for spanning the spectral gamut;
• obtaining a spectral reflectance array for each sample in the spanning set;
• generating a colorimetric value for each sample in the spanning set by transforming the spectral reflectance array corresponding to the sample under a reference illuminant, wherein the colorimetric value includes a lightness in a lightness dimension, a chroma in a chroma dimension and a hue in a hue dimension;
• and
• subdividing the spanning set of samples into subdivisions based on the lightness, the chroma and the hue of the samples such that the number of samples in each subdivision is limited by a predetermined number;
• wherein the on-line phase comprises:
• accepting the color value in the color space;
• converting the color value into a colorimetric value under the reference illuminant, wherein the converted colorimetric value includes a lightness in the lightness dimension, a chroma in the chroma dimension and a hue in the hue dimension;
• identifying subdivisions of the spanning set of samples which fall within a tolerance of the converted colorimetric value by using the lightness, the chroma and the hue of the converted colorimetric value;
• and
• searching the samples within the identified subdivisions so as to find a sample that matches acceptably to the accepted color value relative to an on-line objective function.

A color management apparatus comprising:

• a computer-readable memory constructed to store computer-executable process steps;
• and
• a processor constructed to execute the computer-executable process steps stored in the memory;
• wherein the process steps stored in the memory cause the processor to determine a spectral gamut of a device during an off-line phase by constructing plural subdivisions of a spanning set of samples which span the spectral gamut, and includes computer-executable process steps to:
• establish a first crude spanning set of samples by specifying one or more corresponding device values in a device color space;
• refine the first crude spanning set by processing a plurality of new samples in a predetermined order, wherein the processing includes, for each new sample, determining if the new sample does or does not differ in an objective function value by more than a predetermined threshold from all samples in the first crude spanning set, and modifying the first crude spanning set by adding the new sample to the first crude spanning set if the new sample differs in the objective function value by more than the predetermined threshold from all samples in the first crude spanning set;
• designate the resulting first crude spanning set as the spanning set of samples;
• obtain a spectral reflectance array for each sample in the spanning set;
• generate a colorimetric value for each sample in the spanning set by transforming the spectral reflectance array corresponding to the sample under a reference illuminant, wherein the colorimetric value includes a lightness in a lightness dimension, a chroma in a chroma dimension and a hue in a hue dimension;
• and
• subdivide the spanning set of samples into subdivisions based on the lightness, the chroma and the hue of the samples such that the number of samples in each subdivision is limited by a predetermined number,
• whereby in an on-line phase of spectral gamut mapping, subdivisions are identified that contain samples that are candidates for an acceptable match to an input color value which is given in the on-line phase.

A non-transitory computer-readable memory medium on which are stored computer-executable process steps for causing a computer to determine a spectral gamut of a device during an off-line phase by constructing plural subdivisions of a spanning set of samples which span the spectral gamut, the process steps comprising:

• establishing a first crude spanning set of samples by specifying one or more corresponding device values in a device color space;
• refining the first crude spanning set by processing a plurality of new samples in a predetermined order, wherein the processing includes, for each new sample, determining if the new sample does or does not differ in an objective function value by more than a predetermined threshold from all samples in the first crude spanning set, and modifying the first crude spanning set by adding the new sample to the first crude spanning set if the new sample differs in the objective function value by more than the predetermined threshold from all samples in the first crude spanning set;
• designating the resulting first crude spanning set as the spanning set of samples;
• obtaining a spectral reflectance array for each sample in the spanning set;
• generating a colorimetric value for each sample in the spanning set by transforming the spectral reflectance array corresponding to the sample under a reference illuminant, wherein the colorimetric value includes a lightness in a lightness dimension, a chroma in a chroma dimension and a hue in a hue dimension;
• and
• subdividing the spanning set of samples into subdivisions based on the lightness, the chroma and the hue of the samples such that the number of samples in each subdivision is limited by a predetermined number,
• whereby in an on-line phase of spectral gamut mapping, subdivisions are identified that contain samples that are candidates for an acceptable match to an input color value which is given in the on-line phase.