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Color conversions for texts and graphics to eliminate mis-registration

IP.com Disclosure Number: IPCOM000013286D
Original Publication Date: 2002-Jan-10
Included in the Prior Art Database: 2003-Jun-18
Document File: 1 page(s) / 41K

Publishing Venue

IBM

Abstract

Disclosed are methods of color conversions for text and graphics in several different color spaces.The mis-registration of cyan, magenta, yellow, and black toners/inks is a common problem in color printing. It severely effects print quality, especially for print jobs containing black text, or graphics with sharp edges. For example, there are cyan, magenta, or yellow dots around the edges of black text when registration is not properly adjusted, thus the edges of the text look fuzzy. In production printing, operators have to adjust registration from time to time to keep up print quality. It is very inconvenient and impractical. As such, care needs to be used in the design and implementation of color lookup tables in CIELAB, RGB, and CMYK( printer to printer, swop, and Euroscale conversions) color spaces. Additional lookup tables are generated for text and graphics based on existing tables which serve general purposes of color conversions, including CIELab-->CMYK, RGB-->CMYK, and CMYK-->CMYK. Methods are described below: 1. Lab-->CMYK conversion for text and graphics: (1)Analyze the black halftone screen of the printer, and measure CIELab values with percentage of black toner/ink. (2) Compare lightness of the input values (L, 0, 0) or the most neutral entries in the lookup table with L* values of black wedges.

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Color conversions for texts and graphics to eliminate mis-registration

Disclosed are methods of color conversions for text and graphics in several different color spaces.The mis-registration of cyan, magenta, yellow, and black toners/inks is a common problem in color printing. It severely effects print quality, especially for print jobs containing black text, or graphics with sharp edges. For example, there are cyan, magenta, or yellow dots around the edges of black text when registration is not properly adjusted, thus the edges of the text look fuzzy. In production printing, operators have to adjust registration from time to time to keep up print quality. It is very inconvenient and impractical. As such, care needs to be used in the design and implementation of color lookup tables in CIELAB, RGB, and CMYK( printer to printer, swop, and Euroscale conversions) color spaces. Additional lookup tables are generated for text and graphics based on existing tables which serve general purposes of color conversions, including CIELab-->CMYK, RGB-->CMYK, and CMYK-->CMYK. Methods are described below:

1. Lab-->CMYK conversion for text and graphics:
(1)Analyze the black halftone screen of the printer, and measure CIELab values with percentage of black toner/ink.
(2) Compare lightness of the input values (L, 0, 0) or the most neutral entries in the lookup table with L* values of black wedges.
(3) Convert CMYK values for input points(L,0,0) to the wedge k values with linear/nonlin...