Re: Grayscale profile for offset printing
Re: Grayscale profile for offset printing
- Subject: Re: Grayscale profile for offset printing
- From: Klaus Karcher <email@hidden>
- Date: Fri, 17 Aug 2007 08:47:05 +0200
Steve Kale advised me of QTR Create ICC (<http://www.quadtonerip.com>)
in a personal mail.
I gave it a trial and created a newspaper profile with data from
<http://color.org/IFRA26.xalter> and consulted ISOnewspaper26v4.icc as
reference.
Here are the results:
- Congratulations to Roy V Harrington: he made the first grayscale
profile I know of with A2B0 and B2A0-Tags :-)
- Sadly they are not allowed in v2.1 profiles (but would be in a v4 profile)
- kTRC is missing (it is required in monochrome v2 and v4 profiles, also
Apples ColorSync Utility complains that it is missing)
- Best grayscale profile for proofing purposes I've ever seen:
device to PCS abs. col. max DE only 0.04
- Ugly roundtrip results: 100%K becomes 63%K (Delta E = 12) in
PCS-to-device-direction abs. col.
- Device to PCS abs+rel (with and without BPC) seems to work
as expected (even though the A2B1 tag is missing)
- PCS to device abs+rel (with or without BPC) leads
to strange results (dark areas are partially much too light)
- PCS to device perc is o.k.
- Device to PCS perc. does not expand the Gamut. It maps 100%K (Lab
36.76/1.48/4,46) to Lab 44/1/2. Therefore there is a huge difference
between perceptual with and without BPC. Perc with BPC maps 100%K to Lab
0/9/15 (!).
Conclusion: QTR Create ICC's grayscale profiles might be useful for
(soft-)proofing purposes (device to PCS abs. col.) and perceptual
conversions (PCS to device), but the profiles are not conforming to the
ICC v2.1 Spec and therefore should be taken with a pinch of salt IMHO.
Regards,
Klaus Karcher
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