Just want to add some info about this issue since i'm also having color banding on image viewer. I don't think this was caused by denoise node, since i'm also having colour banding without that node.
From what i found, :
- Colour Banding occurred on every colour view transform except Raw.
- Colour Banding occurred when ImageDisplay Method are using GLSL, setting it to automatic seems choose GLSL method.
also for some reason GLSL method also slow down the image viewer (i'm getting lag when panning/zooming on image viewer),
GLSL method also reduce blender perfomance on 2D drawing method and windows compositor ie. put blender on windowed mode and try to drag blender around or any blender windows
- Workaround i can find is changing the image display method to 2DTexture
It removed the Colour Banding issue, and fix the performance issue with the image viewer and windows drawing.