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  • LOG colour workflow

     Seb Harder updated 1 month ago 5 Members · 8 Posts
  • Seb Harder

    March 2, 2021 at 11:21 pm

    Hi! Doing VFX for a Canadian TV show. Shot on Arri, delivered to me in LOG colour space. My workflow has always been to set the Working Space to “HDTV (Rec. 709), interpret the footage to “Universal Camera Film Printing Density”, composite and then when I export under the “Color Management” tab. Select “Universal Camera Film Printing Density” from the Output Profile. This mostly works OK but I’m finding that the whites in the video are tending to clip. I was provided with a LUT that looks much better but can’t think of an efficient way to use it on all the video.

    I tried–> interpret the footage to ARRI Rec 709 Preview and then exporting in that colour profile which looks better and much more like the LUT but causes an odd glitchy effect wherever the whites clip. Not a big deal but it can be annoying to always keep the whites from clipping (explosions, lasers etc).

    NOTE ** “talk to your colorist” is not the advice I need here.

    Thanks!

  • Seb Harder

    March 3, 2021 at 12:37 am

    After some digging I think my issue may have been related to using 16 bit instead of 32 bit.

  • Walter Soyka

    March 3, 2021 at 10:29 am

    Yes, I think you’ll need to comp at 32bpc — not just for the extra precision, but also for the ability to express and retain overbright color values across color conversions from larger color spaces to smaller ones.

    I’m not sure what LUT you were given, but After Effects does ship with a number of ARRI LogC3 wide gamut ICC profiles now; maybe that’s more appropriate to what your production is shooting than Universal Camera Film Printing Density?

  • Chris Wright

    March 5, 2021 at 11:42 pm

    Log c and cineon use different gamma curves so I always try to avoid mixing and matching gamma curves due to posterization errors. I’d stay…

    Log c and cineon use different gamma curves so I always try to avoid mixing and matching gamma curves due to posterization errors.

    I’d stay away from rec 709 working space if indeed, the logc also is encoded in arri wide gamut which is much larger and rec. 709 could cause gamut clipping of colors.

    If you are encoding in an ACES environment, you can use the opencolorIO plugin which they use to encode EXR files which supports color display mapping, but if you want to use luts manually, you can get all sorts of luts generated on the arri site, refined right down to the iso they were recorded at as there is always a shift in the gamma curve.(this is probably why it was clipping)

  • Douglas Bowker

    March 10, 2021 at 1:54 pm

    I am far from a color expert but I do use After Effects extensively and have dealt with a lot of situations re:different color spaces. Here are a few principles to keep in mind.

    As another already said, 32 bit is going to be your starting point if you know transforms are going to be needed.

    Interpret Footage: This is especially important. This is like the lens or filter even by which everything that comes after with be dictated by. If used incorrectly it’s like straining your sauce before you add it to a meal! Luckily, “Interpret Footage” is not a destructive process of course, but my point is that if you reduce the color space in this step (which is what you’re doing by going from Log to rec709) then you can get that range back until you reinterpret said footage, right? So always start “wide” apply whatever LUT is appropriate afterwards within your layers or Composition.

    Output: This may or may not involve a final transform, depending on the customer. I would think for a Canadian broadcaster they’d provide you with whatever that final spec. should be, but in any case I usually Pre-compose my entire final Comp and add an Output Transform to match whatever is appropriate. That might as simple as going to sRGB for compression for web or MP4 compression, rec709 for most broadcast and some film. Or nothing at all because whomever is getting your file will do it themselves.

    When in doubt, with mixed Footage or from sources I’m not sure about, I just set the project up with Adobe RGB color space as it plays nice with 32 bit and is reliable for keeping things artifact free. Hope some of that helps!

  • Paul Carlin

    March 10, 2021 at 3:13 pm

    A suggestion would be to not try to convert the Log footage to anything. Log in, Log workspace, Log out. Use the “View > Use Display Color Management” to view the workspace on your computer display. This way you SEE what it looks like without having to go through any color space conversions.

  • Walter Soyka

    March 10, 2021 at 9:19 pm

    Working in log the whole way through will certainly avoid the color transforms, but please note that using all the tools and blend modes will feel very different.

  • Seb Harder

    March 19, 2021 at 5:35 pm

    Thanks all for the replies!

    <b style=”font-family: inherit; font-size: inherit;”>Chris Wright: If you are encoding in an ACES environment, you can use the opencolorIO plugin which they use to encode EXR files which supports color display mapping.

    …I’m using After Effects and c4d mostly and am not familiar with ACES. I’ll look into it.

    Douglas Bowker with mixed Footage I just set the project up with Adobe RGB color space as it plays nice with 32 bit and is reliable for keeping things artifact free.

    …This doesn’t look right. Footage still looks flat.

    Paul Carlin not try to convert the Log footage to anything

    …working in the flat LOG colour space doesn’t seem like a good option for me. Keying won’t work well, blend modes etc.


    Here’s my typical workflow and resulting issues below (images)


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