Joel Chan

Abstract

ICC color management system (CMS) has become a major tool for color image rendering and color matching in the printing and publishing industry. It attempts to automate color management functions, e.g., from scan to print, and from press sheet to proof, with the use of device profiles, a CMM, and an application programming interface. Earlier studies, conducted at RIT, showed that ICC-based digital proofing did not perform better than a well calibrated film-based proofing system. Specifically, the average AE between ICC color managed proofs and a reference press sheet was found to be 6-9 while the average AE between a film based proof and its correspondence press sheet was 5. Realizing that sources of AE errors exist in many places, e.g., printing consistency, proofer's color gamut, proofing consistency, measurement conditions, this paper discussed an improved methodology for testing the performance of color matching in a digital proofing workflow. The source profile was a SWOP press profile, supplied by Kodak, which characterizes the ANSI CGATS TR 001-1995 - Type 1 Printing condition. The destination profile was built from an Epson SC3000 ink jet printer using the Kodak Colorflow ProfileEditor at the printer's default color gamut. The IT8.7/3 basic (CMYK) target was transformed with the use of the Mac OS, ColorSync 2.5, Kodak CMM, and Adobe Photoshop 5.0.2, and output to the Epson SC3000 ink jet printer. The IT8.7/3 basic target, containing 182 patches, was measured colorimetrically (D50, 2) and compared to ANSI CGATS TR 001-1995 -Type 1 Printing (SWOP) data. The average AE between an ICC color managed Epson proof and the CGATS TR 00 1 data set was 3.7 AE. This represents a significant improvement over previous research findings. The improved color matching performance was due to the following: (1) an accurate press profile, (2) no printing inconsistency in the experiment since no press run was conducted, (3) EPSON SC3000 being a very stable device after the first two hours of the print out, and (4) improved profiling software. Like most color proofing systems, the Epson SC3000 proofer has a larger color gamut than that of SWOP. This researcher was curious if the color matching can be improved if the Epson profile was built under the condition where its color gamut is only slightly larger than SWOP as indicated by solid ink densities. Reducing color gamut of the Epson printer was implemented by means of transfer curves in software. The results showed that there is no improvement whatsoever in color matching. Two reasons shed light on the subject: (1) only hardware adjustments can change the behavior of the proofer; software adjustments only clip its color gamut, and the overall color gamut of the proofer stays unchanged; (2) While solid ink density of the adjusted CMY showed larger a*b*plot in the proofer, it does not assure that the C* of these inks remains to be larger as L* decreases. In other words, a proofer with a wider a*b*plot than a printer does not necessarily have a larger gamut slice in the L*C* dimension. These are the reasons why reducing color gamut as a part of the proofer calibration did not improve its color matching performance.

Library of Congress Subject Headings

Color printing--Digital techniques; Electronics in color printing; Color printing--Quality control--Research

Publication Date

5-1-1999

Document Type

Thesis

Department, Program, or Center

School of Media Sciences (CIAS)

Advisor

Chung, Robert

Comments

Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works. Physical copy available through RIT's The Wallace Library at: Z258

Campus

RIT – Main Campus

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