Method and a device for determining multi-ink color separations

• US 20030002061A1
• Filed: 05/09/2002
• Published: 01/02/2003
• Est. Priority Date: 05/10/2001
• Status: Active Grant

• Current Assignee: Agfa Graphics Nv (Agfa-Gevaert N.V.)
• Original Assignee: Agfa Graphics Nv (Agfa-Gevaert N.V.)
• Inventors: Van de Capelle, Jean-Pierre
• Granted Patent: US 7,123,380 B2
• Time in Patent Office: Days
• US Class Current: 358/1.9
• CPC Class Codes: B41J 1/00 Typewriters or selective printing mechanisms characterised by the mounting, arrangement or disposition of the types or dies
• CPC Class Codes: H04N 1/54 Conversion of colour picture signals to a plurality of signals some of which represent particular mixed colours, e.g. for textile printing

Abstract

A method to convert a color provided in a first color space into a color in a second color space defined by more than four colorants and a reproduction process. The method includes converting the color into a third color space, determining which of a set of gamut volumes defined in the third color space is appropriate for the color, with each point in the gamut volume achievable by an area coverage greater than zero and less than 100% of two of the colorants and an area coverage greater than zero and less than 100% of one or more darkening colorants with the remaining colorants either absent or at 100%. The method further includes carrying out any gamut mapping on the converted color so that the converted color is in the appropriate gamut volume and converting the gamut mapped color from the third color space into a set of the colorants of the second color space, such that the surface of any gamut volume with no darkening colorant is part of an umbrella surface for the N inks.

Claims

1. A method to convert a color provided in a first color space into a color in a second color space defined by more than four colorants and a reproduction process, the method comprising:

converting the color into a third color space;

determining which of a set of gamut volumes defined in the third color space is appropriate for the color, each point in the gamut volume achievable by an area coverage greater than zero and less than 100% of two of the N colorants and an area coverage greater than zero and less than 100% of one or more darkening colorants with the remaining colorants either absent or at 100%;

carrying out any gamut mapping on the converted color so that the converted color is in the appropriate gamut volume; and

converting the gamut mapped color from the third color space into a set of the colorants of the second color space,

such that the surface of any gamut volume with no darkening colorant is part of an umbrella surface for the N inks.

2. A method of determining a set of gamut volumes defined in a device independent color space, each point in a gamut volume achievable by an area coverage greater than zero and less than 100% of two of a set of more than four colorants using a color reproduction process and an area coverage greater than zero and less than 100% of one or more darkening colorants with the remaining colorants either absent or at 100%, such that the surface of any gamut volume with no darkening ink is part of an umbrella surface for the set of colorants, the method comprising:

determining an umbrella surface in the device independent color space having a set of umbrella parts, each umbrella part being a surface on the gamut of the printing process on the high lightness side with two of the set of colorants varying while the remaining colorants are either absent or at 100%; and

for each umbrella part,

determining one or more darkening colorants from the set of colorants; and

determining one of the gamut volumes vu varying the amounts of the darkening colorants and of the two varying colorants of the part.