On Nov 28, 2006, at 5:07 AM, Phil Cruse wrote: Terry, but what happens in the real world where many of us are using "generic" Source Profiles to (we hope!) ISO, SWOP, etc. standards, specifications originally made by FOGRA, etc. from IT8 or ECI characterization data sets measured with who knows what UV filtration?
As far as I know, most "generic" data sets as you call them are measured with no filtration so you're liable to get less than optimum results if you're measuring with a UV-cut instrument. You're best option is to have a spectro that has switchable filtration (Spectrolino, X-Rite DTP70, GMB SpectroEye) or simply get two inexpensive spectros, like Eye-One or Pulse, each with a different filter.
Here's a line right from the header of the latest GRACoL2006 data which was derived from FOGRA39 data:
MEASUREMENT_GEOMETRY "0/45 Spectrophotometry, No Filter, White Backing"
Can we assume that the source ISO standard 1 or 2 paper should have little or no OBs? As should "good" proofing paper?
But lets talk "real world" for a moment. At least in MY real world of measuring actual press stocks, most printer's "house gloss coated" sheet can have OBs (b* -3 to -5) and an uncoated offset stock can have a significant amount of OBs (b* -5 to -8). Even in those cases, I generally get a better visual match if I measure using no filtration (DTP70). My only guess why this is so is that, if the paper OBs have an effect on how we percieve the press sheet or press-to-proof match, then it would be a mistake to EXCLUDE the effect of these OBs when taking measurements. Bottom line for me is that anytime I measure a set of press sheets with both UV-cut and no filtration, no filtration always wins in terms of the better visual match.
In order of priority, I would want to know the following about a source profile that was provided to me: 1) What filtration was used? 2) What spectrophotometer was used? 3) What backing was used during the measurements?
In my experience, #1 is of prime importance, the rest not so important but still good to know.
Regards, Terry Wyse
_____________________________ WyseConsul Color Management Consulting G7 Certified Expert 704.843.0858
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