I am working on a project at the moment that fills 75% of the screen with a blue metal pipe. When rendering to the internal render window this pipe looks very neat and clean but when the denoiser pass happens it adds gradient banding to tiles as it processes them.
The screenshot shows the area zoomed in, the red box has been denoised and hopefully you can see what I am talking about.
Rendering to EXR half floats
Denoiser with default settings
Clamp Direct 10 and Indirect 15 (scene also has many metal objects around it and these high clamp values remove render artifacts like black pixel crawl) Scene is several million polys.
Blue pipe uses Principled BRDF shader with metallic at 1.0, Specular 0.5 (it makes a difference to reflections) and roughness at 0.385 to blur the reflections.
Scene uses two point lights with a 3.0 and a 5.0 scale, an 8k HDR for reflections and a Light Path node for a background solid. No AO. sRGB. Gamma at default 1.0. GPU (GTX 1080 Ti) + Cycles.
When rendering the view looks spot on, just how the client wants it but when the denoiser applies to tiles it causes a gradient band to appear all over the blue pipe. Other areas which also use similar Principled BRDF look fine though.
So, any ideas what is wrong? I have tried tweaking all settings from extreme low to extreme high and the denoiser simply adds the banding no matter what I change to other settings.
I will try and upload a screenshot with and without denoiser to show how it looks but it’s churning away on another comp for the next 10 hours.
Without the Denoiser I have to up the samples to around 1000 per frame which kills render time so would prefer to avoid that. It is a 34 hour render as it is.
Blender 2.79 (5bd8ac9)