Method and a device for determining multi-ink color separations
View Patent ↗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.
1. A method for determining a set of M color gamut parts of a color reproduction process that uses N inks (N>3), M and N being integers, said color reproduction process having a device independent color space having a first, a second and a third dimension corresponding with first, second and third magnitudes respectively, the method comprising the steps of:
determining a set of M umbrella surface parts in said device independent color space, each surface part obtained by the following steps:
defining a domain corresponding to a range of a first ink in combination with a range of a second ink;
identifying a point belonging to said domain having a first amount for said first ink and a second amount for said second ink;
setting a third ink to a predetermined minimum amount and determining a first magnitude corresponding to said first dimension of a color of said first amount of said first ink in combination with said second amount of said second ink in combination with said minimum amount of said third ink;
setting said third ink to a predetermined maximum amount and determining a second magnitude corresponding to said first dimension of the color of said first amount of said first ink in combination with said second amount of said second ink in combination with said maximum amount of said third ink;
defining an umbrella surface part as a locus of colors in said device independence color space corresponding to said domain in combination with said third ink that yields a highest of said first and said second magnitudes corresponding to said first dimension of said device independent color space;
identifying for each of said set surface parts at least one darkening ink that is different from said first, second and third inks; and
developing each one of a set of M umbrella surface parts into a color gamut volume part by varying said at least one darkening ink in combination with varying said amount of said first ink and varying said amount of said second ink over said domain.
2. The method of claim 1 , wherein the method is applied to a data processing system.
3. A computer readable medium comprising computer program code adapted to perform the steps of the method of claim 1 , when said program is executed on a computer.
4. A method for transforming an image represented in a first color space into an image represented in a second color space, said second color space representing amounts of ink of a color reproduction process that uses N inks (N is an integer greater than 3), the method comprising the steps of:
receiving image data represented in the first color space;
determining a set of M color gamut parts by the following steps:
defining a domain corresponding to a range of a first ink in combination with a range of a second ink;
identifying a point belonging to said domain having a first amount for said first ink and a second amount for said second ink;
setting a third ink to a predetermined minimum amount and determining a first magnitude corresponding to said first dimension of a color of said first amount of said first ink in combination with said second amount of said second ink in combination with said minimum amount of said third ink;
setting said at least one third ink to a predetermined maximum amount and determining a second magnitude corresponding to said first dimension of the color of said first amount of said first ink in combination with said second amount of said second ink in combination with said maximum amount of said third ink;
defining an umbrella surface part as a locus of colors in said device independence color space corresponding to said domain in combination with said third ink that yields a highest of said first and said second magnitudes corresponding to said first dimension of said device independent color space;
identifying for each of said set surface parts at least one darkening ink that is different from said first, second and third inks;
transforming said image data into image data represented in said device independent color space;
using a set of M (M is an integer) color gamut volume parts for applying a gamut mapping step in said device independent color space; and
transforming said gamut mapped image data into said second color space.
5. A computer readable medium comprising computer program code adapted to perform the steps of the method of claim 4 , when said program is executed on a computer.
6. The method of claim 4 , wherein the method is applied to a data processing system.