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Re: [Openexr-devel] Embedding ICC profiles in OpenEXR
From: |
Kai-Uwe Behrmann |
Subject: |
Re: [Openexr-devel] Embedding ICC profiles in OpenEXR |
Date: |
Tue, 22 Nov 2005 09:38:48 +0100 (CET) |
Am 22.11.05, 02:35 -0500 schrieb Geraldine Joffre:
> > 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.
What CMMs are known, that handle HDR content properly, including
support of:
o floating point precission,
o a value range greater than one and possibly lower than zero.
?
Without such a CMM, ICC profiles could only be used for displaying or
could easily degrade the content by integer math manipulations.
Wich CMM is used in Photomatix?
> > 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
>