2009/3/11 Florian Kainz <[email protected]> > Bo Schwarzstein wrote: > > Hello folks, > > > > Would you like to explain how the OpenEXR format should be used in > > color management pipeline ? > > > > OpenEXR files usually store "scene-referred" RGB data, that is, > linear real-world light values. "Chromaticities" and "white luminance" > attributes in the file header define the relationship between RGB data > in the file and CIE XYZ tristimulus values. > > Color rendering, or converting RGB values in OpenEXR and other HDR files > into colors on a display, has not been standardized. A working group at > the Academy of Motion Picture Arts and Sciences is progressing towards > a digital color management standard for the movie industry. > > The exrdisplay and playexr OpenEXR viewers include a mechanism for > describing the mapping between in-file and on-screen RGB values in a > portable way. For more information, please see the OpenExrViewers.pdf > and UsingOpenEXRandCTL.pdf documents on the OpenEXR web site. > > > In my opinion, the EXR support FP16/32 format, we can record linear > > light in real world with nearly unlimited dynamic range, take an > > example, in Paul Debevec's HDRI tutorial, the sun is brighter than the > > perfect diffuser nearly 46000 times, so if we record the reference > > white with CIE XYZ, the part about the sun on image should be 46000 > > greater than the white part, a ( thick white paper or silk ) ? We can > > apply this image (also maybe RGBE format) to HDR illumination in > > generating CG content (gather in RSL?). > > That sounds about right. > > > > > But because even the high-end digital camera such as Panavision > > Genesis can't record scene in 46000:1 such a huge dynamics range, we > > still work with the limited dynamics range in CG production. > > The dynamic range of a real scene that includes the sun is > significantly greater than 46000:1 if the scene includes > objects that are darker than a white diffuser illuminated > directly by the sun. > > You are right, there is no motion picture camera that can record > the full dynamic range of an outdoor scene that includes the sun. > However, the sun is rarely depicted directly in movies. > > HDR environment maps (also known as light probes) for image-based > illumination are captured separately, typically with a digital SLR > camera (using exposure bracketing) or with a special HDR panoramic > camera. The dynamic range of captured environment map images can > exceed one million to one.
OpenEXR files usually store "scene-referred" RGB data, that is, > linear real-world light values. "Chromaticities" and "white luminance" > attributes in the file header define the relationship between RGB data > in the file and CIE XYZ tristimulus values. > > Color rendering, or converting RGB values in OpenEXR and other HDR files > into colors on a display, has not been standardized. A working group at > the Academy of Motion Picture Arts and Sciences is progressing towards > a digital color management standard for the movie industry. > > The exrdisplay and playexr OpenEXR viewers include a mechanism for > describing the mapping between in-file and on-screen RGB values in a > portable way. For more information, please see the OpenExrViewers.pdf > and UsingOpenEXRandCTL.pdf documents on the OpenEXR web site. If we show the complete workflow, I think it should be like this : convert the device caputred RGB (or XYZ) into a middle color space, I know the ICC PCS2 color space could be considered as a one, then convert the pixels in PCS2 to sRGB(preview on common monitor) or Rec.709( preview on HDTV ) or the others device-dependent format. During the whole progress, all the numbers are all represented by FP16/32. Hope the standard would be okay ASAP. Thanks very much for your reply.
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