Color appearance space to CMYK mapping

• US 7,505,625 B2
• Filed: 10/07/2005
• Issued: 03/17/2009
• Est. Priority Date: 05/06/2004
• Status: Expired due to Fees

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Haikin, John
• Primary Examiner(s): Chen; Wenpeng
• Application Number:
  US11/245,244
• Publication Number:
  US 20060033970A1
• Time in Patent Office: 1,257 Days
• Field of Search: 382/167, 358/518, 358/3.23
• US Class Current: 382/167
• CPC Class Codes: G06K 15/02 using printers
• CPC Class Codes: G06K 2215/0094 Colour printing
• CPC Class Codes: H04N 1/6025 using look-up tables

Abstract

Color management which converts internal color appearance space color values to CMYK device values. CMY values are interpolated from a plurality of CMY to color appearance space lookup tables, wherein each CMY table is associated with a specific value of K. A target internal color value is received and one of the plurality of CMY lookup tables is selected based on a lightness value and neutrality of the target internal color value. A CMY value is interpolated from the selected lookup table and the target internal color value. The interpolated CMY value together with the associated K value from the selected table is provided as the converted CMYK color value. Advantageously, the conversion effects control over the output K value in a color appearance space to CMYK conversion. Accordingly, both neutral and non-neutral colors can be reproduced with better accuracy and higher quality.

Claims

1. A color management method for converting color values to CMYK color values, wherein the method utilizes a color transform that converts CMYK color values to appearance space color values, the color transform being arranged as a plurality of three-dimensional CMY space to appearance space lookup tables, each indexed to a different K value, the method comprising using a processor to perform the steps of:

receiving a target appearance space color value;

determining neutrality of the target appearance space color value;

selecting one of the plurality of CMY lookup tables that contains the target appearance space color value based on the determined neutrality of the target appearance space color value;

obtaining the K value indexed to the selected one lookup table;

interpolating a CMY value from the selected one lookup table and the target appearance space color value;

providing the interpolated CMY value and the indexed K value obtained from the selected one table as the converted CMYK color value.

2. A color management method according to claim 1, wherein the selection step further includes the steps of:

selecting the CMY lookup table indexed with the largest value of K which contains the target appearance space color value in the case that the target appearance space color value is determined to be neutral; and

selecting the CMY lookup table indexed with the smallest value of K which contains the target appearance space color value in the case that the target appearance space color value is determined to be non-neutral.

3. A color management method according to claim 2, wherein the target appearance space color value is determined to be non-neutral if its value is greater than a predetermined distance from the neutral axis, and

wherein the target appearance space color value is determined to be neutral if its value is less than a predetermined distance from the neutral axis.

4. Computer-executable process steps encoded on a computer readable memory medium, said computer-executable process steps being executable by a computer to convert color values to CMYK color values, wherein the process steps utilize a color transform that converts CMYK color values to appearance space color values, the color transform being arranged as a plurality of three-dimensional CMY space to appearance space lookup tables, each indexed to a different K value, said computer-executable process steps comprising process steps executable to perform a method according to any of claims 1 to 3.