Re: Chris Murphy vs Bruce Fraser
Re: Chris Murphy vs Bruce Fraser
- Subject: Re: Chris Murphy vs Bruce Fraser
- From: Chris Murphy <email@hidden>
- Date: Tue, 18 Jul 2006 08:42:57 -0600
On Jul 18, 2006, at 1:28 AM, Graeme Gill wrote:
Chris Murphy wrote:
You're making it sound like there is no difference between RelCol
and AbsCol in both an ICC v4 soft proofing context, as well as a
Photoshop context.
As I said, I can't speak for Photoshop, but in ICC V4, there is no
difference between RelCol and AbsCol for display profiles,
Oh really? So why do I see a difference if there is no difference?
SWOP v2 -> display profile v4 with intent=RelCol
and
SWOP v2 -> display profile v4 with intent=AbsCol
yield two different results. So what in the world do you mean when
you say "there is no difference between RelCol and AbsCol for display
profiles" ? It makes no sense. I see the difference!
because ICC V4 mandates that a display profile have a media
white point tag the same as the PCS, and it's the difference
between the PCS white point and the white point tag that
makes a difference between RelCol and AbsCol.
It's the difference between SOURCE white and DESTINATION white. You
somehow seem to be assuming that if PCS white and destination white
are the same there will be no white simulation at all. False. The
source white being paper in a soft proofing context means it's
usually not going to have XYZ values of D50, so you still will get
white simulation. RelCol, in the above described conversion, mandates
paper white and display white are the same. AbsCol in an ICC v4
context merely says display white is the same as the PCS illuminant
because the assumption is that the end user has adapted to display
white, hence the only thing that matters is the difference between
paper white and D50, if any. It doesn't say that it's the same as
source white and thus a simulation doesn't occur.
When I use AppleScript using the Apple CMM, I do see a difference.
When I use Photoshop using ACE, I do see a difference.
Just exactly under what circumstance do you *see* no difference
between RelCol and AbsCol?
There is white simulation.
I'm sorry, what's that ? There is no "white simulation" intent
or function in the ICC standard. There are just the usual 4
intents.
paper white simulation, or Simulate Paper White, as an option
> It's just predicated on the end
user being adapted to display white, and that happens to work
whereas when it's predicated on the end user not being adapted to
display white it doesn't work.
I'm not following what you're saying I'm afraid.
Well that explains the problem. I'd try again but I'm in the middle
of selling a house. So if someone else would like to volunteer giving
it another stab, I'd really appreciate it.
Actually it didn't provide it because there was no specificity as
to the level of adaptation of the end user.
It doesn't need to have such a thing. The intents provide a certain
mechanism. The mechanisms may serve certain functions depending on
the adaptive state of the users. Reducing the mechanism for
display profiles from 4 to 3 doesn't make a shred of sense to me,
since it reduces the scope of potential functionality.
Well I would expect it wouldn't make any sense if you really are
experiencing identical results between RelCol and AbsCol. I'm not
having that experience.
Perceptual
is often well suited to a situation where the viewer is assumed
to be fully adapted to the white point. Absolute is well
suited to the situation where the user was not assumed to
be fully adapted to any one white point, hence it's
broad use in hard proofing. Nothings is fundamentally
different about displays in that regard though.
WRONG. There are *two* white points in question. The source white and
destination white. Perceptual, RelCol, Saturation all assume source
and destination white are the same. Thus no adaptation is required on
the part of the CMS. AbsCol in ICC v4 says the end use is adapted to
display white, but not necessarily to the source media white,
therefore some adaptation may still be needed. And that's what's
happening. In a v2 context where the end user was NOT assumed to be
fully chromatically adapted to display white, the CMS overcompensated.
Nevertheless there is still a difference between RelCol and AbsCol in
a v4 context. They aren't the same thing and you don't get the same
results. If you are, I'm not sure what apps you're using but it's
either a software bug or an end user bug.
> No matter what, something had
to be assumed because it wasn't specified.
It doesn't have to be assumed by the ICC standard. It's up
to the application and the user to make choices from the
available mechanisms in order to serve a particular purpose.
Something had to be assumed as a default because there are two
extreme choices, neither of which is none. Yes, clearly an assumption
about the end user's level of adaptation to display white is
necessary. Do you think the ICC made this clarification in v4 just to
confuse you Graeme? Have you read the ICC's white paper on this subject?
And yes ideally we would have a UI to inform the CMM of the level of
adaptation of the user because it isn't always the case that the end
user is fully chromatically adapted to the display. Actually they're
probably more often partially adapted, but it's a lot more true that
the end user is fully adapted than not at all adapted which was the
previous paradigm that got us dingy yellow soft proofs.
Absolute Colorimetric rendering does NOT prescribe the assumption
that the end user is NOT chromatically adapted to the display. It
never meant that and in v4 it explicitly doesn't mean that.
> And what most
implementations did was assume the end user was not fully adapted
to display white, and those implementations yielded inferior
results.
So you say, and I don't agree with you.
Yes but you're the one who's apparently seeing the same results
between RelCol and AbsCol with v4 display profiles. I'm not. You're
the one who has such an ancient version of Photoshop as to not have a
common frame of reference for us to really be having the same
conversation either. So it's fine that you don't agree with me, but
that isn't going to get us anywhere.
Irrespective of whether this
is the case though, I can't fathom the logic of folding what was a
distinct and potentially useful intent (Absolute) into being identical
to Relative for display profiles.
Maybe because it isn't identical!?
When you check "Simulate Paper White" it is using Absolute
Colorimetric rendering to the display. The on-screen result is
the same for a v2 display profile, or a v4 display profile. And
if you do the conversion using an ICC v4 display profile, and
AbsCol using the Apple CMM with an AppleScript you get the same
result as well.
But is this the same, or different to using a v2 display profile
and the
Apple CMM and AbsCol ?
It is different. The Apple CMM + AbsCol assumes the end user is not
fully chromatically adapted to the display if the display white point
is not D50. In that case, the CMM overcompensates with too much
yellow to simulate the effect of paper white (source space media white).
ACE assumes the end is fully chromatically adapted to the display
even if the display white point is not D50. Thus compared to the
Apple CMM instance, there is less yellow and a soft proof that
actually works.
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
---------------------------------------------------------
Co-author "Real World Color Management, 2nd Ed"
Published by PeachPit Press (ISBN 0-321-26722-2)
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Colorsync-users mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden