Re: Anomaly between Photoshop 7.0.1 and 6.0.1
Re: Anomaly between Photoshop 7.0.1 and 6.0.1
- Subject: Re: Anomaly between Photoshop 7.0.1 and 6.0.1
- From: email@hidden
- Date: Sun, 08 Sep 2002 21:01:23 -0700
Bruce,
Contrary to what your point suggested, my original statement was
correct, however, we were talking about two different things, so your
statement was correct too.
I see, after doing several experiments, that there was indeed a bug
(or oversight) in PS 6 which caused the user-selected rendering
intent in the Convert to Profile dialog to be ignored, when doing
conversions from a source profile (such as a Mntr type RGB space
profile with multiple rendering intents in it in the form of multiple
tables) into another RGB profile. The perceptual tag was always
called when the default intent of the source profile was perceptual,
regardless of the intent chosen by the user in the pop-up in Convert
to Profile. This is per your observation (I didn't test whether
other intents were actually possible with different default intents
in the profile, but no big).
In PS 7, the conversions (and the preview) in the Convert to Profile
dialog, now respect the user choice of intents made in the pop-up, in
this circumstance, again, per what you said. The bug is fixed,
however it would be good if the users knew which legs of the journey
involved which actual intent(s)! Now if we pick RelCol to get from a
source profile to a printer profile, we will get whichever RelCol
result is possible for the Source to Lab section, and whichever
RelCol result is possible for the Lab to Printer section. Before,
the first part would have been either Perceptual, or whatever the
default was in the source profile.
I was referring to another situation. In PS 6, the rendering intent
chosen by the ACE v.1 for source simulations (source profile to
monitor profile for screen appearance) was always Perceptual,
regardless of the default intent of the profile itself, or the intent
chosen in the Color Settings dialog.
In PS 7, with ACE v.2, this has changed, so that the intent for
source simulations is RelCol, with the ACE calling the Colorimetric
tag instead of the Perceptual tag. This change is the problem that I
wrote to Paul about. I think it may be a wise change (because RelCol
is a better default for such conversions), but one can still get
caught by it, if one's profiles don't have the character that one
wishes them to have in the Colorimetric tag, as my older chroma
variants of Ektachrome Space and Ekta Space PS 5 did not. (All fixed
now, with every RGB to Lab tag having the same edits.) Note,
however, that the Apple CMM, when chosen in PS 7, does not behave
this way, and instead still uses the Perceptual tag to perform the
source simulation in PS 7!
So, we all might want to keep this in mind--that source simulations
in PS 7 (when using the ACE) use whatever is available in the way of
a Relative Colorimetric result based on the AtoB1 (RelCol, RGB to
Lab) tag (if any) in whatever source profiles we may be using. This
will have no bearing when using a matrix type source profile (like
Adobe RGB or Ekta Space PS 5), but often will with table type
profiles containing multiple RGB to Lab tables, including some
scanner, some DCam and some RGB space profiles, albeit a fairly small
minority of each of those types.
In other words, source simulations with the ACE are now RelCol to
whatever extent the profile itself allows, whereas they were
previously Perceptual, to whatever extent the profile allowed (they
often turned out as RelCol anyway, such as when a matrix type source
profile was used, or when the table type profile only contained
tables that were designed to yield a RelCol result such as Linotype
scanner profiles).
See you tomorrow at your seminar in the City.
Joe Holmes
Date: Thu, 5 Sep 2002 11:28:28 -0700
To: email@hidden, email@hidden,
email@hidden
From: bruce fraser <email@hidden>
Subject: Re: Anomaly between Photoshop 7.0.1 and 6.0.1
>I discovered the day before yesterday that Adobe changed their CMM
>(the ACE), which they now call version 2, in Photoshop 7. The CMM
(ACE) now looks for the RelCol tag in RGB source profiles instead of
looking for the Perceptual tag, as it had previously. I remade the
profiles
and will send them to anyone who had purchased the set from me in the
past. These profiles will work in both versions of Photoshop, as well
>as
>in Live Picture and should work in all apps (from Joe Holmes)
Photoshop 7 simply lets you choose the rendering intent, which
Photoshop 6 ignored in one-way input profiles. It will look for
whatever tag you specify. Photoshop 6 always used the default tag,
which was usually labelled perceptual but was often something else.
Bruce
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