Color transforms for concave device gamuts

A method for building color transforms for color imaging devices having color gamuts with one or more concave surface regions, comprising:

• a) forming a device model that relates device control signals for a color imaging device to corresponding device-independent color values in a device-independent color space;
• b) forming a device color gamut that represents the set of colors in the device-independent color space that are producible by the color imaging device, wherein the device color gamut has one or more concave surface regions;
• c) forming a convex color gamut by fitting a convex hull to the device color gamut;
• d) forming an expanded device model that relates device control signals for the color imaging device to expanded device-independent color values in the device-independent color space, such that the expanded device-independent color values fill the convex color gamut, wherein the formation of the expanded device model includes:
• i) determining the relative position of a device-independent color value within the device color gamut;
• and
• ii) determining an expanded device-independent color value within the three-dimensionally convex color gamut responsive to the relative position of the device-independent color value within the device color gamut;
• and
• e) building a color transform that relates input device-independent color values to corresponding device control signals for the color imaging device using the expanded device model.