I'm intrested in this as well. Not to highjack this thread, but how would one recreate a logC2lin conversion using the log2lin node?
2011/9/27 Dan Walker <[email protected]> > Has anyone answered Andreas's questions below in this thread or offline? > > > > > > On Sat, Sep 17, 2011 at 12:06 PM, egoman < > [email protected]> wrote: > >> ** >> Great to have someone from Arri here! Unfortunately that post left me more >> confused than I was before [image: Smile] >> >> To start with, when I said "Arri's own Log C LUT (as well as the original >> Cineon LUT), are really designed for video output", I wasn't referring to >> the LogC to REC 709 LUTs. I meant that the concept of a black point is >> related more to output-referred rather than scene-referred image states. >> When using the LogC or Cineon formulas, anything below 95/1023 will be >> mapped to negative values. No scene-referred encoding of a physical scene >> should ever contain negative values. No matter how much one increases the >> exposure of such an image, the negative data can never be regained. >> >> I'm not saying that the LogC Log to Lin is wrong in any way, I'm just >> saying it's more geared towards making a pretty picture (when viewed through >> the appropriate monitor LUT) than it is to giving color values suitable for >> VFX work. I therefore expressed an interest in using the Josh Pines math for >> reading these images instead. The question was what parameter values would >> best decode the LogC data. As is stated in that pdf you referred to, 18% >> gray is mapped to 400/1023. The other things that one needs to know is the >> negative gamma and negative density per log code value. These are of course >> film properties (as the formula is designed for cineon film scans), but >> unlike pseudo-log formats (such as FilmStream, ARRI Log F, Panalog, S-Log) >> Log C should have corresponding values. Assuming a density of 0.02, some >> empirical testing gives a negative gamma of 0.45 to match the look of an >> image converted by the ARRI equation. This is what we are using on our >> current production. >> >> We can leave that question for now though, as reading the documents you >> recommended has left me with new questions [image: Smile] >> >> You say that the math in the ALEXA Log C Curve pdf is correct, and the >> one used in Nuke. You also say that the math in the Alexa Color Pipeline >> for Nuke pdf is not up to date, and should not be used. But as far as I >> can tell, it's this latter formula that is actually used in Nuke (6.3v2)! >> >> Another interesting discrepancy is the ALEXA Wide Gamut RGB primaries. >> When using the Nuke Colorspace node to convert from the Alexa primaries to >> CIE (or anything else), one gets a somewhat different matrix than is given >> in the ALEXA Log C Curve pdf. If The Foundry has gotten this wrong, >> perhaps someone should inform them? >> >> Andreas Bravin Karlsson >> Compositing Supervisor >> >> _______________________________________________ >> Nuke-users mailing list >> [email protected], http://forums.thefoundry.co.uk/ >> http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users >> > > > _______________________________________________ > Nuke-users mailing list > [email protected], http://forums.thefoundry.co.uk/ > http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users > -- -------------------------------- Stiller Studios Lidingö/Sweden Simon Björk Stiller Studios +46 (0)8 555 23 560 Ekholmsnäsvägen 40, S-181 41 Lidingö [email protected] www.stillerstudios.se find us: http://www.eniro.se/query?search_word=stiller+studios&geo_area=liding%F6&what=all
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