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Stable Gray Line Under Color Removal/Gray Color Removal (UCR/GCR) For Unstable Printers

IP.com Disclosure Number: IPCOM000019563D
Publication Date: 2003-Sep-18
Document File: 4 page(s) / 70K

Publishing Venue

The IP.com Prior Art Database

Abstract

Rich composite blacks provide a wonderfully large color gamut. However rich composite blacks need to be very finely tuned near the gray line otherwise the gray line will not appear to be gray (a neutral color). For this reason it is difficult to keep the gray line perceptually gray on an unstable printer. Process black is very hue stable. Using heavy concentrations of process black along the gray line improves color stability. By creating a UCR/GCR scheme that uses rich composite blacks near the gamut surfaces, and heavy concentrations of process black near the gray line it is possible to reap the benefits of both worlds.

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Stable Gray Line Under Color Removal/Gray Color Removal (UCR/GCR) For Unstable Printers

Rich composite blacks provide a wonderfully large color gamut. However rich composite blacks need to be very finely tuned near the gray line otherwise the gray line will not appear to be gray (a neutral color). For this reason it is difficult to keep the gray line perceptually gray on an unstable printer. Process black is very hue stable. Using heavy concentrations of process black along the gray line improves color stability. By creating a UCR/GCR scheme that uses rich composite blacks near the gamut surfaces, and heavy concentrations of process black near the gray line it is possible to reap the benefits of both worlds.

Given the input color c (cyan), m (magenta), y (yellow) with values between 0 and 1 inclusively:

let where c, m, and y are the input values to the algorithm.

The next few equations are used to calculate the weighting scalar s. If the input color is on the gray line, s is equal to zero. If the input color is on the gamut surface, the s is equal to one.

let where g is gray component of the input color value.

let where is chromatic component of the input color value.

let

let

The next step is to calculate the CMYK (Cyan, Yellow, Magenta, Black) vector using the gamut surface UCR/GCR algorithm.

let

let where Mc(a) is the surface under color removal function

for cyan, Mm(a) is the surface under color removal function for magenta, where My(a) is the surface under color removal function for yellow, and Mk(a) is the surface black generation function.

let where Nc(a) is the gray line under color removal function for

cyan, Nm(a) is the gray line under color removal function for magenta, Ny(a) is the gray line under color removal function for y...