How to create vignette without color banding?

"So in After Effects (this also works very well in Premiere) to add noise simply head to: Effects > Noise & Grain > Noise, and set your ‘Amount of Noise’ value somewhere between 0.5% and 0.8%. By doing this when you render out your clips, you should see those nice smooth gradients, and by setting your noise level low enough you are not harming the quality of the image. Here’s that process in image form." See full solution here.