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Arri Log-C workflow

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Jon Mitchell
Arri Log-C workflow
on Aug 15, 2017 at 3:34:58 pm

Hello,

I am working w/ some Arri LOG-C footage. I normally work on it after color, but not this time around. I was wondering what the best workflow is. I've tried a few things but can't seem to get what i'm looking for.

I've read/watched this https://www.provideocoalition.com/after-effects-and-alexa-part-1
But it seems a bit outdated? No? Since it seems we have the color spaces/LUTs in AE now.

What I want to do is: Import the assets, pull a Key, export the plate and subject w/ Alpha in LOG-C for color. (All while working in REC 709, so i'm not looking at the flat image)

Asset Info:
Shot in Log-C Arri Mini
Rec. 709 LUT
2x Anamorphic

What i've done thus far is.
Set up project as: 32 bit
Working space: HDTV (REC. 709)
Interpret footage
Now, how how do I export them in LOC-C w/ an alpha channel?
If I change the "Interpret footage" back, all my key's are off.

Or am I just not able to work in a LUT? Or do i need to apply the LUT as an effect then turn it off before i render?


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Steve Bentley
Re: Arri Log-C workflow
on Aug 16, 2017 at 3:11:34 am

Normally the LUT is just so a 32 bit file can be seen on an 8bit monitor. So if you work in 32bit and render back to the same format in 32bit, nothing should change. Check your color managment in AE to make sure you aren't altering the colorspace.

But if you have to convert the format you were given to a format you can work with and that's what your LUT is for, you will need the reverse LUT to get it back to the original format, or perhaps the post house can take your export format and they can do the coversion - this is usually the best because the reverse LUTs are never perfect and often they don't need it to be perfect since they are going grade it anyway. So better to do as little processing on it as possible so that the Post CC doesn't magnify any changes and so the grader has the headroom he/she needs to get the looks they are after.



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Chris Wright
Re: Arri Log-C workflow
on Aug 16, 2017 at 8:56:55 pm

steve is spot on. in a big budget environment, you wouldn't even burn in a lut as color management changes and lut burns slightly reduce quality. the changes are made to normalize into a log to linear monitor, then rendered as half float EXR with the lut first turned off again. you now have a rendered half float alpha channel with no color transform. that's done in the grading stage later on so vfx easily match shots.

occasionally, the lut needs to be burned in(or as hollywood likes to call it, baked), for final tonal mapping as prores 444 in some lower budget films. in this case, the technical lut is then passed around from the vfx supervisor (so there's only one version of the log-to-linear and linear-to-log luts floating around the building) then its back to digital or older film/dpx workflow (now outdated thanks to the native linear EXR format developed by ILM.)

nowadays, technical luts burn straight from log-to-linear right into P3 or XYZ mapping for DCP for digital theatre projection all lut conversion gives 1% digital loss so its always done last step from a float or half float master.

OCIO is compatible with the Academy Color Encoding Specification (ACES)
http://opencolorio.org/


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