Re: BCP or no BCP to epson without rip
Re: BCP or no BCP to epson without rip
- Subject: Re: BCP or no BCP to epson without rip
- From: Graeme Gill <email@hidden>
- Date: Fri, 12 Jun 2009 00:21:08 +1000
Gerhard Fuernkranz wrote:
IMO the basic ICC philosophy is indeed that the A2B0 tables of the
source profile should map the source device gamut to the PRMG, and the
B2A0 tables of the destination profile should do an inverse gamut
mapping, from the PRMG back to the destination device gamut, in order
that source and destination profiles do not need to know anything about
each other.
Right, but I'd be really interested to know how many profiles are
actually labelled as using the PRMG as an intermediate perceptual
gamut are in use. [An interesting tangent to this that has a bearing on the
ICC V2 vs. V4 question is that there's nothing to stop you using
the PRMG when creating V2 profiles.]
But this was clearly an unsolvable problem in former days, due to the
lack of a standardized reference medium and PRMG. So any V2 profile
unfortunately has to make proprietary assumptions regarding the PCS
gamut and PCS black point. And somehow we still have to cope with old
profiles already existing in the field...
Right, which is where Perceptual intent and BPC or some other form of
dynamic linking come in.
I also think there are no doubts that this "universal" approach (going
through a common PRMG) may not be optimal, and that a direct gamut
mapping from source device gamut to destination device gamut will likely
give superior results in many cases. But that's not topic of this
discussion.
Using the PRMG has three disadvantages as far as I can see: one
is that the gamut gets transformed twice, implying that that it
will introduce more inaccuracies due to the finite precision of
such mappings; two that there may be additional inaccuracies due to the
two gamut mappings not being complementary (ie. even if the source and
destination was exactly the same gamut, there is no guarantee that
colors within that gamut will map to themselves) and three, it is
only possible to do (what I would call) a saturation intent, where
the source gamut is both expanded and compressed to fit the destination
gamut.
cheers,
Graeme Gill.
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