US 5,692,071 AGranted

Color image processing method and apparatus for generating device-dependent color signals

AssigneeAGFA-Geveart

InventorRene Raymond Govaert

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Abstract

A method and apparatus for finding the stored device independent coordinate triplet (CIEL*a*b*triplet) which is closest to the device-independent target color triplet and then looking up the coordinates in device-dependent ABC space which correspond to this best fit among the color patches. A set of new points is defined in ABC space about the best fit point. The raster for the selection of these points in ABC space is independent of the stored color patch points. The magnitude of the increments away from the best fit color patch can therefore be made as small or large as desired. Using this new set of points about the best fit color match, each point of this set is converted back into CIEL*a*b* space points by interpolation and each of these points is compared with the target color in CIEL*a*b* space and the point determined with the smallest difference thereto, .DELTA.E.

Claims32

Dependent claims

Method for generating device-dependent signals representative of target colors, using a first conversion table containing device-dependent color image signal triplets of a color output device and their corresponding device-independent coordinate triplets, said method comprising:

(1) determining in said conversion table a first device-independent coordinate triplet having the smallest first color difference value .DELTA.E with respect to the device-independent coordinate triplet of a target color, and
(2) determining from said first determined device-independent coordinate triplet a device-dependent color image signal triplet which, when employed to generate a color with said output device at least approximates said target color wherein said second determining step (2) is based on a group of known preselected device-dependent color image signal triplets surrounding a given device-dependent color image signal triplet, the device-independent coordinate triplets of said preselected device-dependent color image signal triplets being either known or calculated by interpolation from device-independent coordinate triplet/device-dependent color image signal triplet sets known from said first conversion table, each one of the group of said device independent coordinate triplets of said preselected device-dependent color image signal triplets is compared with the device independent coordinate of said target color and the device-dependent color image signal triplet corresponding to the device independent coordinate triplet of said group for which a second color difference .DELTA.E with respect to the device-independent coordinate triplet of said target color is the smallest is selected as said generated device-dependent color image signal triplet.

Apparatus for generating device-dependent signals representative of target colors, comprising:

(a) first input means for receiving a device-independent coordinate triplet of a given target color;
(b) first memory means in which a conversion table is stored, said first conversion table containing device-dependent color image signal triplets of a color output device and their corresponding device-independent coordinate triplets;
(c) first data processor means for performing, on the basis of said first conversion table, a conversion of said device-independent triplet of said given target color into a generated device-dependent color image signal coordinate triplet which, when employed to generate a color with said color output device, at least approximates said target color, said first data processing means further comprising:
first determining means for determining, in said first conversion table, a first device-independent coordinate triplet having the smallest first color difference value .DELTA.E with respect to the device-independent coordinate triplet of said target color;
and,
second determining means for determining from said first device-independent coordinate triplet said generated device-dependent color image signal coordinate triplet;
wherein said second determining means bases the determination of said first device-dependent color image signal coordinate triplet on a group of known preselected device-dependent color image signal triplets surrounding a given device-dependent color image signal triplet, the device-independent coordinate triplets of said preselected device-dependent color image signal triplets being either known or calculated by interpolation from device-independent coordinate triplet/device-dependent color image signal triplet sets known from said first conversion table, each one of the group of said device independent coordinate triplets of said preselected device-dependent color image signal triplets is compared with the device independent coordinate of said target color and the device-dependent color image signal triplet corresponding to the device independent coordinate triplet of said group for which a second color difference .DELTA.E with respect to the device-independent coordinate triplet of said target color is the smallest is selected as said generated device-dependent color image signal triplet.

4 more elements

Color output device, comprising:

(a) first input means for receiving device-independent coordinate triplets of target colors;
(b) storage means for storing generated device-independent color image signal triplets output by an apparatus for generating device-dependent signals representative of target colors, respectively as input and output triplets of a first conversion table, said apparatus comprising:
(1) second input means for receiving a device-independent coordinate triplet of a given target color;
(2) first memory means in which a second conversion table is stored, said second conversion table containing device-dependent color image signal triplets of said color output device and their corresponding device-independent coordinate triplets;
(3) first data processor means for performing, on the basis of said second conversion table, a conversion of said device-independent triplet of said given target color into a generated device-dependent color image signal coordinate triplet which, when employed to generate a color with said color output device, at least approximates said target color, said first data processing means further comprising:
first determining means for determining, in said second conversion table, a first device-independent coordinate triplet having the smallest first color difference value .DELTA.E with respect to the device-independent coordinate triplet of said target color;
and
second determining means for determining from said first device-independent coordinate triplet said generated device-dependent color image signal coordinate triplet;
wherein said second determining means bases the determination of said first device-dependent color image signal coordinate triplet on a group of known preselected device-dependent color image signal triplets surrounding a given device-dependent color image signal triplet, the device-independent coordinate triplets of said preselected device-dependent color image signal triplets being either known or calculated by interpolation from device-independent coordinate triplet/device-dependent color image signal triplet sets known from said second conversion table, each one of the group of said device independent coordinate triplets of said preselected device-dependent color image signal triplets is compared with the device independent coordinate of said target color and the device-dependent color image signal triplet corresponding to the device independent coordinate triplet of said group for which a second color difference .DELTA.E with respect to the device-independent coordinate triplet of said target color is the smallest is selected as said generated device dependent color image signal triplet,
(c) second data processing means for determining for a device-independent coordinate triplet of a target color, received by said first input means, the corresponding device-dependent color image signal triplet on the basis of said first conversion table stored in said storage means;
and,
(d) output means for outputting a color represented by a device-dependent color image signal triplet determined by said second data processing means, said output color at least approximating a target color.

9 more elements

Dependencies are inferred from the claim text.