Yep, as Luma3d suggested you can try with 32 bit output. With color gradients like in the sky where the values shifts in really small steps for big area, this banding can be very noticeable. One way to fix it is to not use Denoiser and leave some low level of noise in the image.
Thanks for the responses guys, I’ve tried the EXR’s and have the same problem, I’m not using Denoiser so that’s ruled out. It’s a strange one and I can only put it down to the moving sun and clouds.
Banding happens when you have a low intensity gradient.
This is usually fixed by dithering the image, something the V-Ray VFB has since some time, but we don’t have it in Vantage.
I guess it should be possible to apply dithering in a post processing or image manipulation program.