Ink reduction method

A method for forming a color transform for a color printing device having a plurality of colorant channels, each having an associated colorant control value, comprising:

• determining a device characterization transform that relates colorant control values to device-independent color values;
• defining a tone scale adjustment function having one or more tone scale adjustment parameters;
• defining a merit function including a tone scale reproduction accuracy term which is responsive to the tone scale adjustment function and a gamut shape term which is responsive to a color gamut shape;
• defining an initial total colorant load limit;
• determining an initial color gamut shape responsive to the device characterization transform and the initial total colorant load limit;
• determining an initial merit function value corresponding to an initial set of tone scale adjustment parameters and the initial total colorant load limit;
• using a data processor to determine modified set of tone scale adjustment parameters and a modified total colorant load limit that provides an improved merit function value relative to the initial merit function value, wherein the improved merit function value is determined responsive to a modified tone scale adjustment function corresponding to the modified set of tone scale adjustment parameters and a modified color gamut shape corresponding to the modified total colorant load limit;
• and
• determining a color transform for transforming input color values for an input digital image to colorant control values for the color printing device responsive to the modified set of tone scale adjustment parameters and the modified total colorant load limit;
• wherein the modified set of tone scale adjustment parameters and the modified total colorant load limit are determined subject to a constraint that an average total colorant load is no more than a predefined threshold for a set of printed colors produced by applying the color transform to a predefined distribution of input colors.