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Tuesday, March 21, 2006

TAGA Day 3 Session 5: Color 2

How Big Is Color?

John Seymour, QuadTech, Sussex, Wisconsin, U.S.A.

Notes:

  • Human visual system is subjective.

  • Can a computer system be designed to objectively measure sets of printed sheets (Standard vs. Reference)?

  • 3 obstacles:

  • 1. What type of input device should such a system use? Can scanners provide true colormetric data? They can be built, but would be costly.

  • 2. No color science to compare the color of two images. Only two colors can be compared when surrounds are neutral.

  • 3. Halftone images are being measured, but the software system would be using pixels. Misregistration of the sheet when scanning would create a misreading in color values.

  • Sigg published a TAGA paper in 1983 that looked at measuring errors due to poor densitometer positioning.

  • Sigg's work is excellent theoretical work, but no experimental validation.

  • Sigg's predictions were slightly off.

  • Positioning error described by Sigg is essentially a problem of moire.

  • How can digital image filtering be used to reduce sheet positioning errors.

  • Images are downsampled.

  • The software simulation eliminated almost all positioning errors.

Compensation by Black (CB) - A New Separation?

Emmi Enoksson, University of Dalarna, Borlänge, Sweden, and Anders Bjurstedt Royal Institute of Technology (KTH), Stockholm, Sweden

Notes:

  • :UCR and GCR were tested in Adobe Photoshop, GMB PofileMaker, and Heidelberg's PrintOpen.

  • In practice UCR is a light version of GCR.

  • Authors proposed a need to Discard the term UCR and use only GCR or discard both terms and use a new term CB - Compensation by Black.

The Effect Of Colorants In Proofing Systems In Comparison To Standard Four Colour Process Inks

Martin Habekost, Ryerson University, Toronto, Ontario, Canada

Notes:

  • How big are the differences between process color inks and randomly selected proofing system inks.

  • CMC Delta E tolerances used.

  • Gamut size evaluated for each system.

  • Look at inkjet and toner-based proofing systems.

  • Results: Cyan inks showed the smallest color difference and magenta showed the largest. The smallest metameric index was with cyan and the largest was with yellow.

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