[argyllcms] Re: ICC files and OSX ; Missing target gamma in icc issue?

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Wed, 07 May 2008 01:03:46 +1000

Christopher E. Brown wrote:
I started by picking up beta8, and decided to do the all in one pass via dispcal.

There are a few issues with the profiles from dispcal, as they aren't
terribly accurate in Beta 8. The next release should fix this.
The targen/dispread/profile workflow should work though.

Everything looked good, until I fired up Aperture, colors just off, severe blowout in the highlights, etc...

Went back to the multi stage method, tried removing the cdm target, etc.

No luck.

Make sure that the universal access controls haven't been set accidentally
(it's quite easy to do this with certain key presses). Having
"Enhance contrast" set will stuff up calibration and profiling.

I understand that some of the very recent Mac's also have an adaptive
brightness mode. This will also mess up calibration and profiling.

All of the other profiles have a "Curve: Curve is gamma of <value>" in each of the R G B tags.

The output of argyll does not.

It would seem to me that the color managed apps are assuming a default display gamma around 1.8, and pre-adjusting for the source material (sRGB). So I end up with photos being pumped to display as 2.2 on a 1.8 display when the display is already 2.2

Well, no. Color managed applications don't assume anything about
the displays gamma, they have the profile to tell them exactly
how it behaves. Apple doesn't believe in sRGB being the default
for un-tagged source material though, and tends to use a different
profile for such source material. This can lead to odd results
if you are actually dealing with material encoded for sRGB.

The Mac convention is to have a display gamma of 1.8, and the
non-color managed applications are the ones that will be affected
by this. This is why dispcal defaults to a gamma of 1.8 on
a Mac.

I had assumed that I should calib for 2.2, so that even apps without color management ability would display material the same as all of my other systems (everything else I work with is 2.2).

If that's the case, then yes. But typically things like the windows
decorations are not color manages, so they won't look that good.
Non-Apple applications are often not color managed either (ie.
3rd party web browsers).

Re-running everything with -g 1.8 produces profiles that closely match expected.

Should I just stick with 1.8 and accept that non-managed apps will look off with sRGB material?

If the sRGB material is correctly tagged, and displayed using a
color managed application, it all should be fine.

Is there an option to profile or dispcal I am missing?

It's more likely to be in your system setup. There was some
discussion on the ColorSync list recently on how to deal with the
gamma 2.2 vs gamma 1.8 setup, but I don't recall the details.

See <http://lists.apple.com/archives/colorsync-users/2005/Sep/msg00268.html>
for some posts that may be pertinent.

Is there some reason that the gamma target is not being included in the icc profile tags? I was very confused for some time, but I cannot find anything in the mailing list or google, or any suggestive command line options beyond -g.

The profiles contain per device curves as part of the shaper/matrix style
display profiles. There are two tag types the curves, one being
a single gamma number, and the other being a detailed shape curve define
by a table. The simpler profiles use a number. Because Argyll generates
more detailed profiles than this, it uses shaper curves, hence the lack
of gamma tags. It's unlikely this has anything to do with your issues.

Graeme Gill.

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