Generation of hue slice table for gamut mapping

A method of extracting a hue slice from a hue slice look-up table for a color management system, wherein colors are represented in a color appearance space, comprising the steps of:

• receiving a request for extraction of a hue slice from the look-up table at a given hue angle;
• determining whether a hue slice exists in the look-up table at the given hue angle, or at a hue angle within a threshold angular amount of the given hue angle;
• in a case where it is determined in the determining step that a hue slice does exist in the table, extracting the hue slice from the look-up table;
• and
• in a case where it is determined in the determining step that a hue slice does not exist in the table, performing the steps of:
• obtaining, from the look-up table, two hue slices at hue angles that adjoin the given hue angle;
• performing a linear interpolation process between hue slice points of the two adjoining hue slices so as to generate hue slice points at the given hue angle for the new hue slice, wherein the linear interpolation process comprises the steps of:
• a) obtaining hue point lists of the two adjoining hue slices, which contain hue points represented by two-dimensional coordinates;
• b) defining a first point-pair comprising a first point in each list and defining a first line segment connecting each point of the first point-pair;
• c) determining a point on the first line segment that is located proportionally along the first line segment with respect to the given hue angle and the hue angles of the two adjoining hue slices, thereby defining a first point of the new hue slice, and adding the determined point to a list of points for the new hue slice;
• d) determining a next point-pair to be used for defining a next line segment, the next point pair being determined by computing a distance between (1) an endpoint of an immediately preceding determined line segment for the first hue slice and a next hue slice point in the list of points for the second hue slice, and (2) an endpoint of the immediately preceding determined line segment for the second hue slice and a next hue slice point in the list of points for the first hue slice, wherein a smaller one of the two computed distances defines the next point pair;
• e) defining the line segment connecting the two points of the next point-pair;
• f) determining a point on the next line segment that is located proportionally along the next line segment with respect to the given hue angle and the hue angles of the two adjoining hue slices, thereby defining a next point of the new hue slice;
• g) adding the determined next point to the list of points for the new hue slice;
• and
• h) repeating steps d) through g) until no more points are left in the point lists of the first and second hue slices, wherein the resulting list of points for the new hue slice defines the new hue slice at the given hue angle;
• and
• i) extracting the new slice at the given hue angle.

A computer readable medium having encoded thereon a table representing a color gamut for a device for use in a color management system, wherein colors are represented in a color appearance space, comprising:

• data representing a collection of hue slices through a boundary surface of the color gamut,
• wherein the collection of hue slices comprises entries for vertex point hue slices obtained at each vertex point on the boundary surface of the color gamut, and entries obtained for additional hue slices between adjoining vertex point hue slices, where a number of the additional hue slices is determined such that there is no more than a specified angular difference between each hue slice,
• wherein, each hue slice is represented by a hue value and a collection of hue slice points each containing a lightness value and a chroma value, and
• wherein the hue slice points of each hue slice are ordered in the table based on an angular altitude of each point, the angular altitude of each point being determined between a lightness axis of the color gamut and a vector projected from a reference point on the lightness axis to the hue slice point.