XAVC compression artifacts

Is there some special way to grade Slog3 recorded to XAVC? As soon as I expand contrast on some shots I see banding and compression artifacts. Happens with or without a LUT.

The more underexposed the image is, the worse the compression artifacts will be.

I've had good luck with HEVC from the Sony F7 and F55, but haven't had a lot of HAVC. It's possible some NR early in the chain might help reduce or eliminate the problem. But if it's way, way underexposed, it's gonna be tough to avoid these problems in any software, since it's a photographic/data problem.

I’m seeing that from certain FS7 footage even though it’s XAVC intra 422/10 class 100. (9.22 Mb/s) 1080/23.976

I see banding in the sky, in open prairie shots (slog3gammut3cine) which is well exposed and macro blocking/artifacts in mildly under exposed reds. I was expecting it to be a lower sampling rate but it’s not. I think it’s just sensor limits. (Spoiled by seeing to much Arri footage lately). If I zoom in I can see it in the original footage. (Reds) The sky, it’s visible full frame. Banding is not consistent in all sky shots. Qualifying shows the artifacts/poor sampling, quickly across all shots.

I’m using an ACES workflow with the correct IDT. First node is the ACES LMT Academy.fix.highlights then nodes w/grades followed by some DeNoise in the offending areas further down the node tree. (Happens w/o the LMT as well.)

If anyone else is experiencing this it’s good to know. Chime in.



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My footage isn’t well exposed, but it’s not underexposed. Thanks I was wondering if ACES would help. Guess Marc is right. Just inherent.

I’ll try Resolve’s deband filter.

Should I have them bake in Rec709 in camera so that contrast is expanded on capture? Or is it the same if I expand contrast later?

It’s worse with 8 bit recordings (like the Alpha series) but can happen even with 10 if there is massive compression like XAVC, since Slog-3 is such a flat curve that many scenes don’t really need it.
Instead of using Rec709, try one of the “Cine” profiles, they are a better choice. I like Cine 4 most of the time.