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Re: [Openexr-devel] Embedding ICC profiles in OpenEXR
From: |
Geraldine Joffre |
Subject: |
Re: [Openexr-devel] Embedding ICC profiles in OpenEXR |
Date: |
Tue, 22 Nov 2005 02:35:58 -0500 |
On Mon, 21 Nov 2005 20:21:13 +0100 (CET), Kai-Uwe Behrmann wrote
> Geraldine,
>
> a profile can be created on the fly out of the exr primaries and
> back written from the same on the fly created ICC profile into the
> OpenEXR header.
Yes, I know that. My point is that it requires additional code that would not
be needed with
embedded profiles.
> CinePaint obtained such a small layer recently based
> on lcms.
Yes, it is a very small layer and we have implemented it in our Photomatix
software as well. But why
impose it to all applications on the workflow that will process the OpenEXR
file? With the
mechanism of embedded profile, color specification would just need to be done
once at file
creation time. All subsequent color managed applications processing the file
would not have to
change the way they work to handle OpenEXR files.
> The same is possible with TIFF and I think as well with PNG.
Yes but both offer the option of embedding an ICC profile as well. I'm not
asking for removing the
current chormaticities attribute but for adding the ability to embed ICC
profiles as well. This way,
the OpenEXR format can be handled similarly as other image formats that color
managed
applications are supporting.
> Only it seems not an good solution to me to open an second path for
> describing colour characteristics in parallel if not realy needed.
It may not be needed for CG work but for a photography workflow it is needed.
> Of course if OpenEXR could hold an API to convert from exr primaries
> to ICC and accepting an ICC profile to convert to its native header
> format, that would be great.
But it will not change the fact that ICC profiles can not be embedded in
OpenEXR files. I believe the
OpenEXR format won't gain wide acceptance among the photographer's community
until it can
support embedded profiles.
> Saving of device characteristics for HDR devices is not covered by
> the ICC standard.
Why is it so? As far as I know, ICC specifications do not fordib a TRC with a
gamma of 1? I don't see
any reason why the colorimetric behaviour of an HDR camera or display could not
be described by
an ICC compliant matrix-shaper profile.
> Where there practical suggestions to hear at
> Scottsdale regarding ICC and HDR device characterisation?
>
> regards
> Kai-Uwe Behrmann
> + development for color management
> + imaging / panoramas
> + email: address@hidden
> + http://www.behrmann.name
>
> Am 21.11.05, 07:44 -0500 schrieb Geraldine Joffre:
>
> > I've been to a conference on HDR-Photography and 3D-Visualisation in
> > Hamburg last week.
The
> > audience was mainly professional photographers, so when Spheron talked
> > about their HDR
> > camera, they were asked about how the HDR files are color managed and
> > whether they have
> > ICC profiles (color management is very important for quality photography).
> >
> > The answer was that the SheroCam HDR camera had been characterized but that
> > no ICC profile
> > is available for the HDR files produced. The only way to get an ICC profile
> > is to shoot an LDR
> > image so that the profile gets embedded in a 16-bit TIFF file. So, I
> > intervened to explain that a
> > newer version of the OpenEXR format makes it possible to define the
> > chromaticities of the RGB
> > primaries and white point, which means the camera just needs to populate
> > the chromaticities
> > attribute when writing the HDR file in order to get a 'color managed' HDRI.
> >
> > However, from the discussions I had afterwards, I realized it might be more
> > convenient for a
> > photography workflow to have the chromaticities values available in the
> > form of an ICC profile
> > embedded in the OpenEXR file. The responsibility for creating and embedding
> > the profile
would
> > be left to the application that produced the OpenEXR file -- the HDR camera
> > or the software
that
> > created it from multiple exposures. The advantage is that the CMM of color
> > managed software
> > could directly handle OpenEXR files that have an embedded ICC profile.
> > Otherwise, additional
> > coding is necessary to extract and convert the chromaticities attribute for
> > correct handling by
> > the CMM.
> >
> > I think it could be a good idea to add the ability to embed ICC profiles in
> > a future version of
> > OpenEXR, the same way it can currently be done with the TIFF and JPEG
> > formats.
> >
> > Thanks.
> >
> > Geraldine Joffre
> >
> > --
> > HDR Imaging for Photography
> > http://www.hdrsoft.com