Re: scanning in RGB vs. CMYK: a major issue here!

Andrew Rodney <andrew@...>

on 3/28/01 6:54 AM, Dan Margulis at 76270.1033@... wrote:

Putting a profile in your RGB file does not solve the problem of how to get
the file into CMYK.

It helps in we need a description of the RGB to get to CMYK. That was true before ICC profiles (using a monitor preference in versions previous to Photoshop 5) and it’s true today. It’s of no use of she is going to do the conversions (the user will know the recipe of RGB to get to CMYK. Still embedding the profile in the original RGB file does no harm and actually does some good should a conversion need to be made in the future).

If the RGB file is given to another person, having a profile is quite useful. Without it, what assumption should be made about the recipe of RGB for the CMYK conversion? The fact that a good number of printers will get hostile seeing an embedded profile or not know what to do with a file with an embedded profile doesn’t change the facts that a description of RGB is always required to get to CMYK.

It must be understood that different printers will get different results
from the same CMYK file.

That’s an understatement! Yesterday I was showing a student just how varied a certain manufacturer of contract proofs could be from shop to shop. Since I have made dozens of profiles from the same proofing system (but at different printers all over the country), I can use ProfileMaker Pro’s measure tool to look at all 600 spectral readings from patches used to build the profiles and get some very useful stats. In best case, two completely different shops running the same proofing system (Matchprint) were showing an average deltaE of 4 which is quite good. But more often than not, the average deltaE was well over 10 and in some cases double that. Now consider sending the same CMYK file to shops using vastly different proofing systems and the numbers go sky high. A deltaE variance of 6 or less is said to be “acceptable” matching for most clients. Some would reject that much difference in colors. But a deltaE of over 10 means big surprise when that proof does come back!

Andrew Rodney

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