Re: [Openexr-devel] Embedding ICC profiles in OpenEXR

[Kai-Uwe Behrmann]

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
>