# US 6,724,500 B1 · Piecewise color transformation by gamut partitioning > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 6,724,500 B1 - Document ID: US6724500B1 - Status: Granted - Kind: B1 - Application number: 09/450,799 - Filed: 1999-11-29 - Granted: 2004-04-20 - Earliest claimed: 1999-11-29 - Assignees: Xerox Corporation - Inventors: Charles M. Hains; Robert R. Buckley - Web page: https://patentgrep.com/patent/US6724500B1 ## CPC - H04N 1/6055: {using test pattern analysis} - H04N 1/6019: {using look-up tables (H04N1/6025 takes precedence)} - H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION ## Abstract A method for selecting CMY coordinates for printing a desired source color represented in an source color-space includes the step of obtaining coordinates for the printer gamut in the source color-space and then dividing the printer gamut into a plurality of tetrahedra, one of which contains the desired source color. This particular tetrahedron, referred to as the source-bearing tetrahedron, is identified and transformed into a target-bearing tetrahedron in the CMY color space. The target-bearing tetrahedron contains the CMY coordinates of the desired color. The specific color within the target-bearing tetrahedron is identified by obtaining barycentric coordinates for the source color relative to the source-bearing tetrahedron and identifying that color in the target-bearing tetrahedron that has the same barycenric coordinates. The CMY coordinates for that color can then be provided to a printer to print the desired source color. ## Claims ### Claim 1 A color correction system for identifying a target color from a printer gamut in a subtractive color-space that corresponds to a source color in a source color-space, said system comprising: a gamut transformation module adapted to convert said printer gamut into an equivalent gamut in said source color-space, said equivalent gamut having a plurality of non-overlapping constituent volumes, said constituent volumes sharing a common boundary point; a volume finder having access to said plurality of constituent volumes and to said source color, said volume finder adapted to identify a source-bearing volume from said plurality of constituent volumes; a volume mapper for matching a target-bearing volume in said printer gamut in said subtractive color-space with said source-bearing volume in said equivalent gamut in said source color space; and a coordinate mapper for determining a target color in said target-bearing volume that corresponds to said source color in said source-bearing volume. ### Claim 2 (depends on 1) The system of claim 1 wherein said gamut transformation module comprises a gamut cleaver adapted to partition said equivalent gamut into said plurality of non-overlapping constituent volumes. ### Claim 3 (depends on 2) The system of claim 2 wherein said gamut cleaver comprises partitioning means for partitioning said equivalent gamut into a plurality of tetrahedra, each of said tetrahedra having a common vertex interior to said equivalent gamut. ### Claim 4 (depends on 3) The system of claim 3 wherein said gamut cleaver comprises selection means for selecting said common vertex to be on a neutral axis in said equivalent gamut. ### Claim 5 (depends on 3) The system of claim 3 wherein said partitioning means comprises means for selecting the number of tetrahedra to be at least twelve. ### Claim 6 (depends on 3) The system of claim 3 wherein said partitioning means comprises means for selecting the number of tetrahedra to be at least twenty-four. ### Claim 7 (depends on 1) The system of claim 1 wherein said gamut transformation module comprises a calorimeter configured to view a print sample having a plurality of test patches imprinted thereon. ### Claim 8 A color correction system for identifying a target color from a printer gamut in a subtractive color-space that corresponds to a source color in a source color-space, said system comprising: a gamut transformation module adapted to convert said printer gamut into an equivalent gamut in said source color-space, said equivalent gamut having a plurality of non-overlapping constituent volumes, said constituent volumes sharing a common boundary point; a volume finder having access to said plurality of constituent volumes and to said source color, said volume finder adapted to identify a source-bearing volume from said plurality of constituent volumes; a volume mapper for matching a target-bearing volume in said printer gamut in said subtractive color-space with said source-bearing volume in said equivalent gamut in said source color space; and a coordinate mapper, which comprises barycentric mapping means for determining barycentric coordinates of said source color relative to said source-bearing volume for determining a target color in said target-bearing volume that corresponds to said source color in said source-bearing volume. ### Claim 9 (depends on 8) The system of claim 8 wherein said coordinate mapper further comprises means for identifying a point in said target volume having barycentric coordinates relative to said target volume that are equivalent to said barycentric coordinates of said source color relative to said source-bearing volume. ### Claim 10 A color correction system for identifying a target color from a printer gamut in a subtractive color-space that corresponds to a source color in a source color-space, said system comprising: a gamut transformation module adapted to convert said printer gamut into an equivalent gamut in said source color-space, said equivalent gamut having a plurality of non-overlapping constituent volumes, said constituent volumes sharing a common boundary point; a volume finder having access to said plurality of constituent volumes and to said source color, said volume finder adapted to identify a source-bearing volume from said plurality of constituent volumes; a volume mapper for matching a target-bearing volume in said printer gamut in said subtractive color-space with said source-bearing volume in said equivalent gamut in said source color space; and a coordinate mapper for determining a target color in said target-bearing volume that corresponds to said source color in said source-bearing volume, which comprises a gamut compressor for generating a compressed printer-gamut, said gamut comprising: print selection means defining a ray extending between said common boundary point and said target color; and compression means for translating said target color toward said common boundary point along said ray. ### Claim 11 (depends on 10) The system of claim 10 wherein said compression means comprises compression function means for determining a distance through which said target color is to be translated along said ray, said distance being dependent on a separation between said common boundary point and said source color. ### Claim 12 (depends on 11) The system of claim 11 wherein said compression function means comprises means for evaluating a fourth-degree polynomial mapping function. ### Claim 13 A method for identifying a target color from a printer gamut in a subtractive color-space that corresponds to a source color in a source color-space, said method comprising the steps of: transforming said printer gamut into an equivalent gamut in said source color-space; said equivalent gamut having a plurality of non-overlapping constituent volumes, said constituent volumes sharing a common boundary point; identifying a source-bearing volume from said plurality of constituent volumes; matching a target-bearing volume in said printer gamut in said subtractive color-space with said source-bearing volume in said equivalent gamut in said source color-space; and determining a target color in said target-bearing volume that corresponds to said source color in said source-bearing volume. ### Claim 14 (depends on 13) The method of claim 13 wherein said transforming step comprises the step of partitioning said equivalent gamut into a plurality of tetrahedra, each of said tetrahedra having a common vertex interior to said equivalent gamut. ### Claim 15 (depends on 14) The method of claim 14 further comprising the step of selecting said common vertex to be on a neutral axis in said equivalent gamut. ### Claim 16 (depends on 14) The method of claim 14 wherein said partitioning step comprises the step of selecting the number of tetrahedra to be at least twelve. ### Claim 17 (depends on 14) The method of claim 14 wherein said partitioning step comprises the step of selecting the number of tetrahedra to be at least 24. ### Claim 18 (depends on 13) The method of claim 13 wherein the step of transforming said printer gamut comprises the step of performing a colorimetric measurement of a print sample having a plurality of test patches imprinted thereon. ### Claim 19 A method for identifying a target color from a printer gamut in a subtractive color-space that corresponds to a source color in a source color-space, said method comprising the steps of: transforming said printer gamut into an equivalent gamut in said source color-space; said equivalent gamut having a plurality of non-overlapping constituent volumes, said constituent volumes sharing a common boundary point; identifying a source-bearing volume from said plurality of constituent volumes; matching a target-bearing volume in said printer gamut in said subtractive color-space with said source-bearing volume in said equivalent gamut in said source color-space; and determining a target color in said target-bearing volume that corresponds to said source color in said source-bearing volume by determining barycentric coordinates of said source color relative to said source-bearing volume. ### Claim 20 (depends on 19) The method of claim 19 wherein said step of determining said target color comprises the step of identifying a point in said target volume having barycentric coordinates relative to said target volume that are equivalent to said barycentric coordinates of said source color relative to said source-bearing volume. ### Claim 21 A method for identifying a target color from a printer gamut in a subtractive color-space that corresponds to a source color in a source color-space, said method comprising the steps of; transforming said printer gamut into an equivalent gamut in said source color-space; said equivalent gamut having a plurality of non-overlapping constituent volumes, said constituent volumes sharing a common boundary point; identifying a source-bearing volume from said plurality of constituent volumes; matching a target-bearing volume in said printer gamut in said subtractive color-space with said source-bearing volume in said equivalent gamut in said source color-space; and determining a target color in said target-bearing volume that corresponds to said source color in said source-bearing volume by defining a ray extending between said common boundary point and said target color, and translating said target color toward said common boundary point along said ray. ### Claim 22 (depends on 21) The method of claim 21 further comprising the step of determining, on the basis of a separation between said common boundary point and said source color, a distance through which said target color is to be translated along said ray. ### Claim 23 (depends on 22) The method of claim 22 wherein said distance determining step comprises the step of evaluating a fourth-degree polynomial mapping function.