How do I remove this weird ghost outline? (C4DTOA)

[Frankiealeeks]

I've added some plants into my scene from Megascans that include all the layers I need and have been correctly set-up for use but whenever I render out a frame using the GPU renderer (CPU doesn't include this issue) the plants have a weird plastic wrap outline around them but only when an object with a metal material is behind it.

I've tried increasing the transparency amount, adding in some transmission and just increasing the samples in the render settings but nothing seems to work. And yes I do have an Arnold tag added so that the opacity works.

[lee_griggs]

GPU only? What happens if you put the plant in front of a metal plane? Do the leaves have opacity maps? Can you upload a simplified scene somewhere?

[Frankiealeeks]

Here's a simple scene setup showing the issue I'm having. Just a simple HDRI sky and a plane with a metallic material. As you can see, there's still weird outline on all of the plant but on in the GPU render. Also yep, the leaves have an opacity map.

[adrien.herubel · Accepted solution]

I can easily repro the problem with a basic alpha cutout. The cutout needs to have specular, and the background as well. The bug disappears if you lower the value of the Indirect Specular Blur option, which is not recommended as it will increase the noise. It looks like on GPU there is a bug when combining specular bounces and transparency.

I will log a bug to investigate the issue internally, thank you for reporting the issue.

[douglas.addy]

what if you put the alpha in geometry/opacity?

,

what happens if you put the alpha mask in geometry/opacity?

[Frankiealeeks]

Hey Adrien,

Thank you for finding a solution. It's unfortunate that it's not a great fix but if it's the best I can do for now it's very much appreciated.