Re: MS Color Control Applet
Re: MS Color Control Applet
- Subject: Re: MS Color Control Applet
- From: Chris Murphy <email@hidden>
- Date: Tue, 11 Jul 2006 09:54:30 -0600
On Jul 10, 2006, at 7:52 PM, Graeme Gill wrote:
You can't really make a "blended perceptual/relcol" using
matrix/shaper, it is simply colorimetric.
Of course you can. You can do anything you want to do with the
perceptual intent because it isn't defined at all in v2. Nothing in
the spec or the guts of the profile prevents a vendor from populating
a matrix profile with fudged values.
What combination
of display characteristic, white point setting and
matrix/LUT setup lead to the problem you say justified
the radical change in V4 display profiles ?
Any time the display white point is not D50, and the profile claims
the media white point is also not D50, and the rendering intent to
the display profile is AbsCol, and any time a CMM then decides to
compensate for a non-D50 display *and also* assumes the end user is
not fully adapted to a non-D50 display white, you then get
*excessively* yellow soft proofs.
Hence why Adobe started ignoring the media white point tag in display
profiles.
I still haven't seen a case that problem 2 exists.
I have two profiles for an identically calibrated display. One is v2,
one is v4. The wtpt tag for the v2 profile uses XYZ values for the
actual white point, which is not D50. The wtpt tag for the v4 profile
uses XYZ values for D50.
I take a CMYK TIFF filled with white space. I take a modified "Match
to chosen profiles" AppleScript, modified to use AbsCol rendering.
The source profile is set to SWOP v2, the destination profile is set
to the ICC v2 profile and the image is converted. I do it again with
a separate copy of the image using ICC v4 profile as the destination.
So I now have two RGB TIFF images. One the result of ICC v2 profile
as destination, and the other the result of the ICC v4 profile as
destination. The RGB values of the v2 profile are 255, 255, 216. The
RGB values of the v2 profile are 219, 219, 212. These are
*completely* different colors. One is decidedly very yellow as well
as bright and the other is more gray than it is yellow. And that is
the visual experience that best simulates a true publication grade
stock on a display. The yellow simulation is simply wrong. It looks
obviously wrong.
Now if I perform this experiment in Photoshop of any version I have
easily available to me, Photoshop 7 and higher, there is no
difference between the two profiles. I get a paper white simulation
that is more gray than yellow, as it should be.
There is a continuum from no adaptation to full adaptation for
the end user. This is not defined in v2, so vendors make an
assumption for less than full adaptation, and then they bake in
compensation for the remaining non-adaptation into the resulting
profile. It's hardwired at that point *and* it isn't reversible.
This simply isn't true.
This conversation is simply a waste of time if you're not going to
qualify your statements. I have several bits of information in there
and your suggesting none of it is true. You think there is only full
and zero adaptation? Or that the level of adaptation is defined in
the v2 spec? Or you're denying that some vendors bake varying levels
of assumed adaptation into their profiles?
, and the ICC V4 display changes do exactly that,
they break absolute colorimetric for display profiles,
so that you can't (using the ICC Absolute Colorimetric
machinery) recover the display absolute response.
Then why is it Adobe has been disregarding wtpt tags for almost a
decade? You're proposing that Adobe has broken absolute colorimetric
for display profiles in all of their applications this whole time
that people have been effectively doing soft proofing, including with
displays that do not have D50 white points.
I haven't seen this with the (rather old) version of Photoshop I have
access to. The behaviour has been reasonable, and consistent with
other CMMs with all the display profiles I've stumbled across.
Absolute and Relative do the things you would expect, just like
printer profiles.
Have you got an example of a V2 Display profile that
has this "double chromatic adaptation" problem you describe ?
Can you send it to me ?
The problem is with the CMS honoring the wtpt tag in an absolute
colorimetric conversion in a manner inconsistent with the state of
adaptation of the end user, in effect over compensating for a non-D50
white point. This is why I get different results with the same
display profile depending on whether I use an Adobe application and
its CMS, versus some other CMS like the Apple CMM + an AppleScript.
That you see consistency between other CMMs and your version of
Photoshop (which is what version exactly?) indicates you indeed have
an old version and you're completely unaware of today's state of
technology.
Now ideally we'd be able to choose the level of adaptation of the end
user, so that we could better compensate for partial end-user
adaptation which we currently cannot in existing UI.
I simply can't agree. It is quite possible to deal with partial
adaptation in V2, as long as absolute colorimetric can be
recovered. Doing this in V4 is actually harder, because it's
been made harder in V4 to recover absolute colorimetric for
displays.
The data in the profile is reversible to AbsCol. That was not a
guarantee in v2 profiles because the data was munged for reasons
previously described. Just because you have a wtpt tag doesn't mean
you can simple adapt and get back measurement data. The data was
altered in ways that aren't described in the profile.
It really isn't soft proofing if you're looking at a screen and
you're looking at a hard proof in a viewing box, is it?
Um, yes it is. Customers were keen about doing this.
It's a fantasy at this point. If you have two different light
sources, the human visual system cannot simultaneously adapt to both
of them. And a viewing booth is a completely different light source
than a display even if the white points match. There's more to this
than just white point matching.
Soft proofing by definition does not involve a hard proof.
Hard proofing by definition does not involve a soft proof.
When you combine both of these events together, best practices, for a
number of years now, has dictated that you don't view one in the
field of view of the other.
They're really mutually exclusive events.
Not at all. Difficult under many circumstances, but quite
a common request. The Color Management machinery
certainly shouldn't stand in the way of attempting such matches.
Yes and peace on earth is a common request too, Graeme, and see where
that's gotten us? Desire is not an indicator of success.
There are two completely different light sources being viewed at
the same time, and the level of partial adaptation between those
two light sources isn't something the CMS can know.
Yes it can, and the whole point is to make it so that the
user doesn't have to be partially adapted, but can be fully
adapted to the one white point, because the aim is to
make the white points of the two media (print and display)
match in an absolute sense, if they are displaying the
same proof.
!
Yes the CMS can know the level of partial adaptation? How? What UI
element does this? What CMM supports it?
If you have two completely different light sources in field of view,
a human is not fully adapted to either one of them!
gmb ProfileMaker 5.05b, produced a v2 and v4 profile from the
same measurement data. I get the same apparent white simulation
using either profile in PSCS2. So I'm not sure what you're seeing
different between them, especially since the wtpt tag has been
ignored for a while now in v2 display profiles by Adobe
applications.
Sorry, I don't have ProfileMaker 5.05b, nor examples of it's V2 and V4
profiles to examine. It would be interesting to do so.
They behave the same in Adobe applications. They behave differently
in other applications.
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