Re: Color Management with EXR
Bo Schwarzstein <[email protected]> Wed, 11 Mar 2009 16:19:18 +0800
| Newsgroups | gmane.comp.video.openexr.user |
|---|---|
| Message-ID | <[email protected]> |
--===============1686679194== Content-Type: multipart/alternative; boundary=00221532c5b423bdfd0464d386c4 --00221532c5b423bdfd0464d386c4 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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. --00221532c5b423bdfd0464d386c4 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable <div class=3D"gmail_quote">2009/3/11 Florian Kainz <span dir=3D"ltr"><<a= href=3D"mailto:[email protected]" target=3D"_blank">[email protected]</a>></spa= n><br><blockquote class=3D"gmail_quote" style=3D"border-left: 1px solid rgb= (204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> <div>Bo Schwarzstein wrote:<br> > Hello folks,<br> ><br> > Would you like to explain how the OpenEXR format should be used in<br> > color management pipeline ?<br> ><br> <br></div> OpenEXR files usually store "scene-referred" RGB data, that is,<b= r> linear real-world light values. =C2=A0"Chromaticities" and "= white luminance"<br> attributes in the file header define the relationship between RGB data<br> in the file and CIE XYZ tristimulus values.<br> <br> Color rendering, or converting RGB values in OpenEXR and other HDR files<br= > into colors on a display, has not been standardized. =C2=A0A working group = at<br> the Academy of Motion Picture Arts and Sciences is progressing towards<br> a digital color management standard for the movie industry.<br> <br> The exrdisplay and playexr OpenEXR viewers include a mechanism for<br> describing the mapping between in-file and on-screen RGB values in a<br> portable way. =C2=A0For more information, please see the OpenExrViewers.pdf= <br> and UsingOpenEXRandCTL.pdf documents on the OpenEXR web site.<div><br> <br> > In my opinion, the EXR support FP16/32 format, we can record linear<br= > > light in real world with nearly unlimited dynamic range, take an<br> > example, in Paul Debevec's HDRI tutorial, the sun is brighter than= the<br> > perfect diffuser nearly 46000 times, so if we record the reference<br> > white with CIE XYZ, the part about the sun on image should be 46000<br= > > greater than the white part, a ( thick white paper or silk ) ? We can<= br> > apply this image (also maybe RGBE format) to HDR illumination in<br> > generating CG content (gather in RSL?).<br> <br></div> That sounds about right.<div><br> <br> ><br> > But because even the high-end digital camera such as Panavision<br> > Genesis can't record scene in 46000:1 such a huge dynamics range, = we<br> > still work with the limited dynamics range in CG production.<br> <br></div> The dynamic range of a real scene that includes the sun is<br> significantly greater than 46000:1 if the scene includes<br> objects that are darker than a white diffuser illuminated<br> directly by the sun.<br> <br> You are right, there is no motion picture camera that can record<br> the full dynamic range of an outdoor scene that includes the sun.<br> However, the sun is rarely depicted directly in movies.<br> <br> HDR environment maps (also known as light probes) for image-based<br> illumination are captured separately, typically with a digital SLR<br> camera (using exposure bracketing) or with a special HDR panoramic<br> camera. =C2=A0The dynamic range of captured environment map images can<br> exceed one million to one.=C2=A0</blockquote><div><br><br></div></div><br><= blockquote style=3D"border-left: 1px solid rgb(204, 204, 204); margin: 0pt = 0pt 0pt 0.8ex; padding-left: 1ex;" class=3D"gmail_quote">OpenEXR files usua= lly store "scene-referred" RGB data, that is,<br> linear real-world light values. =C2=A0"Chromaticities" and "= white luminance"<br> attributes in the file header define the relationship between RGB data<br> in the file and CIE XYZ tristimulus values.<br><br> Color rendering, or converting RGB values in OpenEXR and other HDR files<br= > into colors on a display, has not been standardized. =C2=A0A working group = at<br> the Academy of Motion Picture Arts and Sciences is progressing towards<br> a digital color management standard for the movie industry.<br><br> The exrdisplay and playexr OpenEXR viewers include a mechanism for<br> describing the mapping between in-file and on-screen RGB values in a<br> portable way. =C2=A0For more information, please see the OpenExrViewers.pdf= <br> and UsingOpenEXRandCTL.pdf documents on the OpenEXR web site.</blockquote><= div><br>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 pix= els 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.<br> <br>Hope the standard would be okay ASAP.<br><br>Thanks very much for your = reply.<br></div> --00221532c5b423bdfd0464d386c4-- --===============1686679194== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ Openexr-user mailing list [email protected] http://lists.nongnu.org/mailman/listinfo/openexr-user --===============1686679194==--