Colour image processing

Claim 5

The method as defined in claim 2, wherein said input color data is RGB color data, and wherein said output color data is CMY color data.

Claim 6

The method as defined in Claim 3, wherein said intermediate color space is a uniform color space.

Claim 7

The method as defined in claim 3, wherein calibrating said first calibration comprises the steps of: measuring colorimetrically a plurality of color patches to obtain a set of device independent color input values corresponding to said patches; measuring with said input device said patches to obtain a set of device dependent color input values corresponding to said patches; correlating said device independent and said device dependent color input values for said patches; interpolating other device independent color input values from said set to correspond to input not represented by said patches; and creating from said device independent and said device dependent color input values an input lookup table mapping said input RGB color data to said intermediate color space data.

Claim 8

The method as defined in claim 5, wherein said intermediate color space defines an input gamut, and wherein correlating said device independent and said device dependent color input values includes: dividing said input gamut into a plurality of sub­spaces; and separately defining a relationship between said device independent and said device dependent color input values for each of said subspaces; said interpolating of said other device independent color input values being performed separately for each of said subspaces using said relationships.

Claim 9

The method as defined in claim 6, comprising the further step of smoothing said device independent color input values over said subspaces.

Claim 10

The method as defined in claim 7, wherein said smoothing is performed by interpolating at least some of said device independent color input values using a weighted average of values interpolated using the one of said relationships for said subspace in which said color input value is located and another of said relationships from at least one of said subspaces adjacent thereto.

Claim 11

The method as defined in claim 5, comprising the further step of smoothing said device independent color input values over said intermediate color space.

Claim 12

The method as defined in claim 9, wherein said smoothing is performed by, following said interpolating, averaging each of said device independent color input values with a predetermined number of closest color input values thereto.

Claim 13

The method as defined in claim 3, wherein calibrating said second calibration comprises the steps of: printing with said output device a plurality of color patches in accordance with a set of device dependent color output values; measuring colorimetrically said patches to obtain a set of device independent color output values corresponding to said patches; correlating said device independent and said device dependent color output values for said patches; interpolating other device independent color output values from said set to correspond to output not represented by said patches; and creating from said device independent and said device dependent color output values an output lookup table mapping said intermediate color space data to said output CMY color data.

Claim 14

The method as defined in claim 11, wherein said intermediate color space defines an output gamut, and wherein correlating said device independent and said device dependent color output values includes: dividing said output gamut into a plurality of sub­spaces; and separately defining a relationship between said device independent and said device dependent color output values for each of said subspaces; said interpolating of said other device independent color output values being performed separately for each of said subspaces using said relationships.

Claim 15

The method as defined in claim 12, comprising the further step of smoothing said device independent color output values over said subspaces.

Claim 16

The method as defined in claim 13, wherein said smoothing is performed by interpolating at least some of said device independent color output values using a weighted average of values interpolated using the one of said relationships for said subspace in which said color output value is located and another of said relationships from at least one of said sub­spaces adjacent thereto.

Claim 17

The method as defined in claim 11, comprising the further step of smoothing said device independent color output values over said intermediate color space.

Claim 18

The method as defined in claim 15, wherein said smoothing is performed by, following said interpolating, averaging each of said device independent color output values with a predetermined number of closest color output values thereto.

Claim 19

The method as defined in claim 3, wherein said converting of said intermediate color space data to said output CMY color data includes processing said intermediate color space data for matching an input gamut to an output gamut for said output device.

Claim 20

The method as defined in claim 17, wherein said intermediate color space is a uniform color space.

Claim 21

The method as defined in claim 18, wherein said input gamut comprises the full gamut of said input device.

Claim 22

The method as defined in claim 18, wherein said input gamut comprises the full gamut of an input image.

Claim 23

The method as defined in claim 18, wherein said processing includes identifying at least one unprintable device independent color output value which, when converted to a device dependent color output value, cannot be represented by said output device, and determining an adjusted device dependent color value for representing said independent color output value which is within said output gamut.

Claim 24

The method as defined in claim 21, wherein said adjusted device dependent color value is determined within said intermediate color space.

Claim 25

The method as defined in claim 22, wherein said adjusted device dependent color value is determined as the shortest vector distance within said intermediate color space between said unprintable color output value and a color output value which is printable by said output device.

Claim 26

The method as defined in claim 23, wherein said shortest vector value distance is determined while maintaining one coordinate within said intermediate color space as constant.

Claim 27

The method as defined in claim 24, wherein said intermediate color space is defined by the coordinates lightness, chroma and hue.

Claim 28

The method as defined in claim 25, wherein said one coordinate maintained as constant is lightness.

Claim 29

The method as defined in claim 26, wherein said coordinate hue is also maintained as constant.

Claim 30

The method as defined in claim 22, wherein said adjusted device dependent color value is determined by maintaining at least one coordinate within said intermediate color space as constant, and compressing all color input values along at least a second coordinate between zero and said unprintable coordinate value until said unprintable value is within said output color gamut.

Claim 31

The method as defined in claim 28, wherein said intermediate color space is defined by the coordinates lightness, chroma and hue.

Claim 32

The method as defined in claim 29, wherein said second coordinate is chroma.

Claim 33

The method as defined in claim 22, wherein said adjusted device dependent color value is determined by maintaining at least one coordinate within said intermediate color space as constant, and clipping all color input values along at least a second coordinate between the outer edge of said output color gamut and said unprintable coordinate value such that said unprintable value is at said outer edge of said output color gamut.

Claim 34

The method as defined in claim 31, wherein said intermediate color space is defined by the coordinates lightness, chroma and hue.

Claim 35

The method as defined in claim 32, wherein said second coordinate is chroma.