Re: Proofing Pantone
Re: Proofing Pantone
- Subject: Re: Proofing Pantone
- From: Chris Murphy <email@hidden>
- Date: Sun, 9 Feb 2003 01:14:44 -0700
On Saturday, February 8, 2003, at 11:00 PM, Matthew Kelly
<email@hidden> writes:
We are a commercial printer currently using AGFA's Sherpa 43 as our
large format proofer, and have been getting fairly good results, with
the profiles we have made, matching our presses. Using that proofer
for Pantone simulation has caused problems with customers'
expectations, even though we mark the proofs as being a process
simulation of the Pantone color.
Using Pantone's CMYK equivalents will almost certainly result in
disappointment unless your press behavior is exactly like theirs was
when printing the guides. What AGFA should allow are two options
depending on whether the file specs Pantone to be printed composite
CMYK or as spot:
1. If as spot - uses a table to convert the Pantone color directly to
ideal CMYK values for the Sherpa 42.
2. If as process - uses the press's Pantone to CMYK table to convert
the Pantone color, then simulates those CMYK values on the Sherpa 43.
I'm not sure if AGFA has this option, but they really should or Pantone
matching isn't going to be effective without 3rd party software. I
suspect they, like other vendors, can do at least the first part of #2
which is allow you to build a custom table that will automatically
parse and replace application specified CMYK builds in PostScript/PDF
files.
What we would like to do is present
the customer with some definitive information as to what are the
limitations of a CMYK proofer.
If I may get some information on the following:
1) What percentage of Pantone colors fall within the average CMYK
color gamut that are within a Delta 2? (It is my understanding that
the human eye cannot perceive any color difference in colors that have
less than a Delta 2 variance.)
For a press with the behavior of U.S. Sheetfed Coated v2, looks like
about 430 of the roughly 1018 Pantone Coated colors. That's using
regular delta E 76. If you use delta E cmc then 534. Delta E 2 is
probably unreasonable though considering that value isn't going to be
held throughout a press run. I'd let it be more open than that, like
around delta E 6. Also, it depends on the color you're talking about.
Delta E 6 isn't much of a problem with yellow. With blue it's more
noticable.
2) I am aware that Pantone colors vary in dot gain on the press. What
curve is applied in Photoshop to each channel of the duotone to render
gain, and what curve is then applied at the RIP for the proofer? Does
the RIP of a CMYK proofer convert the Pantone color in the duotone to
CMYK and print according to the profile information?
You can almost forget about proofing screened Pantone colors unless
equipment is specifically designed for it. A few proofing systems do
this. Getting good CMYK equivalents to proof spot colors is hard enough
as it is, let alone computing them for screened spot colors that will
interact with each other.
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
---------------------------------------------------------
Co-author "Real World Color Management"
Published by PeachPit Press (ISBN 0201773406)
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