Luca Leocádio Soares

ACES and Rec.709 LUTs

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Hi guys, I would really appreciate to know your thoughts on using a Rec709 print emulation LUT on an ACES project.

I've been grading the HDR version of a TV show which was graded and delivered first in SDR. The colorist who did it used the Resolve's native Rec709 Kodak 2383 LUT on many clips, I imagine this it's not ideal for HDR or any future deliverable, since it's a 709 LUT, however I can't see any real issue during the HDR grade.
Please let me know what you guys think.

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no really really sure what you are asking, but using a lut in aces is not a straight forward thing to do and generally not a good idea.

you can try to make it work using lightspace but still it's a workaround that introduce many unpredictable factor and can give you nasty artefacts.

Most of all if you want to go from an sdr odt to an hdr

The lut will clip at 100 nits anyway so it's not going to work

To go from an sdr to hdr there are not workaround (not like a trim dolby vision trim that take you from hdr to sdr)

The only safe way is to grade it for hdr starting from what you already have, after the lut.

in that way you can extend the contrast letting only the very highlight to go above 100nits and keeping most of the signal at a 100 nits where already belong. Also you will have more room to give shadow details, which is really nice.





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Thanks for taking the time to answer Orash!

I'm not sure what I'm asking either, but thing is, on Resolve, if the color science of the project is set to ACEScct, using a LUT on the node tree won't clip the highlights at 100 nits when you change the ODT for HDR, in my case, Rec.2020 ST2084(1000 nits, P3D65 Limited). 

I also agree it's not a good idea, but I've done 17 episodes that way and could't see any issue on the image, also all the HDR masters passed the QC of the TV channel without any problems.

I'm trying to find any other issue that I'm no taking into consideration right now or if there is anyone doing the same thing out there.


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