If AV1 noise synthesis "removes" banding, that banding was never part of the video in the first place, but your video player system created it during bit depth reduction, since you're viewing on an 8-bit display. This can be prevented with dithering, which AV1 noise synthesis can substitute for.
Yes, that's obvious.
The dithering pattern is random in each frame, so distinguishing between dithered gradients and noise/film grain baked into the Blu-Ray source is hardly possible.
For the encoder, randomly dithered gradients and film grain are just noise. Both AomEnc and SVT-AV1 can remove this noise (thus causing banding) for better compression, but also record information about the noise to allow for statistically identical noise to be composited back on top of each frame during playback, hiding the bands again.
My issue here is simply that there is no reference for what noise that requires --denoise-noise-level=1
looks like, or how I should recognize noise that requires --denoise-noise-level=6
and so on. If my anime screenshot is level 6 already, then is "Alien (1978)", level 12? level 18? Higher even?
AV1
Community for AV1 video codec