Canon Information Systems, Inc.

Brigitte Ruetz

Gesualdo Alesii

Timothy I Kohler

A method and apparatus for constructing a color printer table. Printable colors in CIELAB space are transformed to Munsell space and color mapping functions are derived which map Munsell space coordinates into primary color coordinates CMY of the printer. A Munsell printer gamut is determined by selecting points in Munsell space where the color mapping functions result within the printable primary color range. All discrete points of an extended gamut in CIELAB space are mapped into the Munsell space. The extended gamut comprises colors inside the printer gamut as well as colors outside the printer gamut, such as colors typically found in a color monitor. Primary color values are inserted into the color printer table by taking the mapped CIELAB points and applying the color mapping functions to the mapped CIELAB points that lie inside the Munsell printer gamut, and applying gamut mapping to the mapped CIELAB points in Munsell space that lie outside the Munsell printer gamut. Since the gamut mapping takes place in Munsell space, the hue is exactly preserved by simply preserving the hue angle.

Color printing method and apparatus using gamut mapping in Munsell space

A method and apparatus for building and using tables which determine the colors to be printed from a device independent color coordinate system. Two tables are built: the first is a printer table for colors in the printer gamut as well as for colors in a typical color monitor gamut, and the second is a border table for colors outside the printer table. The printer table is constructed from a mathematically smooth mapping function for mapping from the device independent coordinate system (such as CIELAB space) to the printer coordinate system, and the mathematically smooth mapping function is determined based on a measurement of the printable colors in the device independent coordinate system. The border table is constructed so as to preserve the hue of unprintable colors but to increase saturation so as to achieve a more natural looking result. Transition colors are added to the printer table outside the printer gamut, smoothing the transition from the edge of the printer gamut to the border table. In use, either the printer table or the border table is selected based on whether the desired color in the device independent coordinate system is within the printer table or outside the printer table.

Method and apparatus for printing high fidelity color reproductions of

Method and apparatus for color printing according to a printer table in which the hue angle of the colors in the printer table are warped so as to compensate for the Abney effect. A color printer gamut edge is first determined through printer gamut measurement, and color primary values within the printer gamut and outside the printer gamut are calculated and inserted into the printer table. If desired, a border table may be provided for colors outside the printer table. The hue angles for the printer table and the border table are then warped, for example, by stretching some ranges of hue angles and by compressing other ranges of hue angles, so that out-of-gamut colors are printed with a hue that is perceived to be the same as the hue of the desired color.

Color printing method and apparatus which compensates for Abney effect

Method and apparatus for color printing according to a printer table having high color smoothness for out-of-gamut colors. A color printer gamut edge is first determined and color primary values for colors within the printer gamut are calculated and inserted into the printer table. For transition colors, namely those colors outside the printer gamut edge but still within the printer table, color primary values are calculated by selecting a color from the printer gamut edge at a point which lies at a constant angle from the transition color in question. The same constant angle is used for each and every one of the transition colors. A border table is provided for colors outside of the printer table; the color primary values for the border table are selected in the same manner as for the transition colors. According to the invention, it is possible to provide smooth color transitions for out-of-gamut colors, and in particular it is possible to provide monotonically increasing lightness in both the printer table and the border table and thereby avoid undesirable bands of darker colors within lighter colors.

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San Bruno, CA, United States of America

Brigitte Ruetz