Hi Guys Thanks very much for the input - very interesting
The plates are 10it DPX I’m clicking RAW on the read node - so not changing any color then : 1/ changing primaries from sRGB to AlexaV3LogC - get rid of a ton of negatives ( values lower than -1) I’m taking a guess here ( shares the same primaries as rec709) white point still D65 2 / an add to eliminate the tiniest leftover negatives…. yes adding in Log space to up exposure and eradicate tiny negatives…. 3/ A final OCIO colorspace node going from ARRI V3 LogC (EI800) wide gamut - to ACEScg 4 / And then a final reverse out of everything at the end it is a bit weird i know - and i don’t know how the plate was exported - but I’m guessing that the primaries were effected or not adjusted - whereas the tone mapping is LogC…... N Neil Rögnvaldr Scholes Director | VFX Supervisor www.neilscholes.com <http://www.neilscholes.com/> +44 (0) 7977 456 197 > On 30 Oct 2016, at 23:33, Joseph Goldstone <jgoldst...@arri.com> wrote: > > Deke, thanks for getting to this first. Yes, something does seem peculiar, > doesn’t it. > > Neil, when you say RAW do you mean ARRIRAW, or do you mean ARRI LogC (e.g. in > a DPX file)? At ARRI we don’t describe the latter as ‘raw’, but some people > do. > > Where does sRGB fit into all this? Most often ARRIRAW decodes into LogC > (which is ALEXA wide-gamut primaries and a D65 white point), so your “just > changing the primaries from sRGB to AlexaV3LogC” sounds pretty odd to me. > > And Lucien mentions “the offset added in the LogC”. Perhaps this is black > mapping not to 10-bit DPX 0 but to 10-bit DPX 95? > > Regarding “the tiniest negatives”, a plate that was shot with the lens cap > firmly on will show up in ACES with an average value of 0.0, since ACES is > about relative exposure value, but there may be individual pixels that will > be below 0, since noise will cause some values to be slightly higher than > zero and some slightly lower. I’d be somewhat surprised if you saw a negative > value below -0.0038 or so. Yes, you can add a tiny offset if your pipeline > demands it, subtracting it back off at the end if you’re (e.g.) handing a > plate back to a client who would be taking it through a pipeline that > expected black to be distributed around zero. > > Best— > —joseph > >> On Oct 30, 2016, at 12:44 PM, Deke Kincaid <dekekinc...@gmail.com >> <mailto:dekekinc...@gmail.com>> wrote: >> >> What file format are the raw plates? Quicktime or Arriraw? How did you >> try to convert direct from Arri to ACEScg? IE which colorspaces did you use? >> >> On Sun, Oct 30, 2016 at 7:24 AM, Neil Scholes <n...@uvfilms.co.uk >> <mailto:n...@uvfilms.co.uk>> wrote: >> Ok - so thanks for the tips - and the solution >> >> I’ve now got RAW plates first going through a regular colorspace node - just >> changing primaries from sRGB to AlexaV3LogC >> >> Next an add to eliminate the tiniest negatives…. >> >> A final OCIO colorspace node going from ARRI V3 LogC (EI800) wide gamut - to >> ACEScg >> >> And then a final reverse out of everything at the end >> >> >> >> - And this gives me the right results - zero negatives and a good looking >> pic. >> >> This tells me that the OCIO colorspace node doesn’t change primaries when >> going from ARRI to ACES / in fact expects the right ARRI primaries - and >> that this plate has been adjusted somewhere along the way. >> >> I’m guessing which primaries with the first conversion from sRGB to ARRI >> primaries ( which eliminates 99% of the negatives) - but it works and I can >> now work in ACES. >> >> Anyway - thanks for all the pointers >> >> N >> >> >> Neil Rögnvaldr Scholes >> >> Director | VFX Supervisor >> >> www.neilscholes.com <http://www.neilscholes.com/> >> >> +44 (0) 7977 456 197 <tel:%2B44%20%280%29%207977%20456%20197> >> >> >> >> >>> On 29 Oct 2016, at 19:25, Neil Scholes <n...@uvfilms.co.uk >>> <mailto:n...@uvfilms.co.uk>> wrote: >>> >>> Thanks for that I'll check it out. That might be a solution. >>> >>> Strange though as the whole point of the IDT is to bring the footage into >>> ACES without needing to offset etc. >>> >>> Yesterday I was also made aware that the plate may have peculiar primaries >>> so I've got a few ideas now to try out >>> >>> Thanks for the help >>> >>> N >>> >>> Sent from my iPhone >>> >>>> On 29 Oct 2016, at 17:21, Lucien Fostier <lucienfost...@gmail.com >>>> <mailto:lucienfost...@gmail.com>> wrote: >>>> >>>> Hey Neil, >>>> >>>> I had a similar problem than you on a show shot in Arri wide gamut. >>>> >>>> The first thing to notice is that Arri Wide gamut have very different >>>> primaries than Aces CG. >>>> >>>> In other words, some colors in Arri Wide gamut correspond to negative >>>> chromacities in Aces CG gamut. >>>> >>>> Besides this, the offset applied in the LogC can also introduce negative >>>> values. >>>> >>>> For working with your plate converted in Aces CG, you could intoduce an >>>> offset at ingestion time that would get reverted at output time. >>>> >>>> Cheers >>>> >>>> Lucien_______________________________________________ >>>> Nuke-users mailing list >>>> Nuke-users@support.thefoundry.co.uk >>>> <mailto:Nuke-users@support.thefoundry.co.uk>, >>>> http://forums.thefoundry.co.uk/ <http://forums.thefoundry.co.uk/> >>>> http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users >>>> <http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users> >>>> >>> >>> _______________________________________________ >>> Nuke-users mailing list >>> Nuke-users@support.thefoundry.co.uk >>> <mailto:Nuke-users@support.thefoundry.co.uk>, >>> http://forums.thefoundry.co.uk/ <http://forums.thefoundry.co.uk/> >>> http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users >>> <http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users> >>> >> >> >> _______________________________________________ >> Nuke-users mailing list >> Nuke-users@support.thefoundry.co.uk >> <mailto:Nuke-users@support.thefoundry.co.uk>, >> http://forums.thefoundry.co.uk/ <http://forums.thefoundry.co.uk/> >> http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users >> <http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users> >> >> _______________________________________________ >> Nuke-users mailing list >> Nuke-users@support.thefoundry.co.uk >> <mailto:Nuke-users@support.thefoundry.co.uk>, >> https://protect-us.mimecast.com/s/bAlZBbsmv1Ghr?domain=forums.thefoundry.co.uk >> <http://forums.thefoundry.co.uk/> >> https://protect-us.mimecast.com/s/Jq6bBwUA015hG?domain=support.thefoundry.co.uk >> <http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users> > > > This email has been scanned for email related threats and delivered safely by > Mimecast. > For more information please visit http://www.mimecast.com > <http://www.mimecast.com/> > _______________________________________________ > Nuke-users mailing list > Nuke-users@support.thefoundry.co.uk, http://forums.thefoundry.co.uk/ > http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users
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