System to improve printer gamut

• US 5,710,824 A
• Filed: 03/13/1996
• Issued: 01/20/1998
• Est. Priority Date: 03/13/1996
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Mongeon, Michael C.
• Primary Examiner(s): Coles, Sr., Edward L.
• Assistant Examiner(s): Williams, Kimberly A.
• Application Number:
  US08/614,599
• Time in Patent Office: 678 Days
• Field of Search: 358/461, 358/501, 358/520, 358/518, 358/298, 358/525, 358/529, 358/406, 358/504, 358/519, 358/222, 395/106, 395/109, 382/162, 382/167
• US Class Current: 382/162
• CPC Class Codes: H04N 1/6022 Generating a fourth subtractive colour signal, e.g. under colour removal, black masking
• CPC Class Codes: H04N 1/6058 Reduction of colour to a range of reproducible colours, e.g. to ink- reproducible colour gamut

Abstract

In a printer which produces images as a function of the combination of cyan (C), magenta (M), yellow (Y) and black (K) colorants on an output color print, responsive to device independent colorimetric description of an image, there is provided a method of printing in a color printer so that scanned color images defined in terms of colorimetric color signals may be printed on a color printer responsive to printer colorant signals to render a color print with a set of three primary colorants and black on a substrate, the printing method comprising the ordered steps of scanning an image to derive a set of device independent colorimetric color signals, converting said colorimetric color signals into device dependent primary colorant signals, each primary colorant signal defining a density of colorant to be used in rendering a color print, said conversion accounting for a subsequent black colorant addition, determining, for minimum and maximum values of the combination of primary colorant signals a black colorant signal, to add black colorant as a nonlinear function of the primary colorant signals so as to expand the printable color gamut, to the color print, gray balancing the primary colorant signals and linearizing black to generate a set of corresponding printer colorant signals to control the printer and using said printer colorant signals to control the printer to produce an image colorimetrically matching the scanned image.

Claims

1. A method of expanding the color gamut of a color printer so that color images defined in terms of colorimetric color signals may be printed on a color printer responsive to printer colorant signals to render color prints with a set of three primary colorants and black on a substrate, the method comprising the ordered steps of:

a) linearizing the printer response by;

i) producing a set of printer colorant signals to print a corresponding set of varying density samples of each of the three primary colorants and black on a substrate,

ii) determining Δ

E_p between the printer colorant signals and the substrate; and

iii) generating a printer linearization table for each of the three primary colorants and black whereby a linear increase in a colorant signal produces a linear increase in a printer colorant signal;

b) determining, for a given density characteristic of a combination of primary colorant signals to generate a color on the substrate, a black colorant signal, to add black to a color print as a nonlinear function of the primary colorant signals so as to expand the printable color gamut;

c) producing a color transform and correction table by;

i) producing a second set of printer colorant signals of colors from combinations of the three primary colorants, with black colorant signals added in accordance with the determined density characteristic of the combination of primary colorant signals, to print a corresponding set of color samples from combination of the three primary colorants and black on a substrate,

ii) measuring the color of each printed color sample in terms of colorimetric color signals, and

iii) generating a color transformation table mapping measured colors in terms of the three primary colorants used to generate the color samples to colorimetric color signals;

d) storing an addressable mapping of colorimetric color signals to colorant signals in a printer memory.

2. A method of printing in a color printer so that scanned color images defined in terms of colorimetric color signals may be printed on a color printer responsive to printer colorant signals to render a color print with a set of three primary colorants and black on a substrate, the printing method comprising the ordered steps of:

scanning an image to derive a set of device independent colorimetric color signals;

converting said colorimetric color signals into device dependent primary colorant signals, each primary colorant signal defining a density of colorant to be used in rendering a color print, said conversion accounting for a subsequent black colorant addition;

determining, as a function of minimum and maximum values of the combination of primary colorant signals a black colorant signal, to add black colorant so as to expand the printable color gamut to the color print as a nonlinear function of the primary color signals;

linearizing each primary colorant signal and black with respect to Δ

E_p to generate a set of corresponding printer colorant signals to control the printer; and

using said printer colorant signals to control the printer to produce an image colorimetrically matching the scanned image.

3. A method of printing in a color printer so that scanned color images defined in terms of colorimetric color signals may be printed on a color printer responsive to printer colorant signals to render a color print with a set of three primary colorants and black on a substrate, the printing method comprising the ordered steps of:

scanning an image to derive a set of device independent colorimetric color signals;

converting said colorimetric color signals into device dependent primary colorant signals, each primary colorant signal defining a density of colorant to be used in rendering a color print, said conversion accounting for a subsequent black colorant addition;

determining, as a function of minimum and maximum values of the combination of primary colorant signals a black colorant signal, to add black colorant as a nonlinear function of the primary colorant signals so as to expand the printable color gamut, to the color point, wherein the black colorant is added as a parabolic function of the primary colorants;

gray balancing the primary colorant signals and linearizing black to generate a set of corresponding printer colorant signals to control the printer; and

using said printer colorant signals to control the printer to produce an image colorimetrically matching the scanned image.