Alpha channel not correct

[ruby_vandeursen]

Hi, anyone familiar with this alpha problem? It has a Vray tag with Visible to camera, Show in reflections, Show in refractions enabled. Can't seem to get rid of the black spots. Tried to replace the material with a non 2-sided material but same result. Would be great to hear how to solve this. Thanks in advance!

[sirio76]

Hi Ruby, I saw you have posted on our discord channel too, if you can share the scene (the bare minimum to reproduce the issue) I’ll check it out

[wolfgang_himmelfarb]

Do you have 3d plants in the foreground with visibility turned off, shadows, etc turned on?

[ruby_vandeursen]

Yes Wolfgang, exactly that!

[wolfgang_himmelfarb]

Ah ok. I believe this is an unavoidable result for vray if you do your workflow and I believe will be the result in most render engines. No kidding, Im drawing from when I tried '3d trees excluded visible' maybe 10y ago and havent done it since. I would guess it has something to do with transparency depth. It could potentially be z-fighting in the mesh as well, since plants are typically procedurally generated and not modeled. That's a guess though. If it were me I would take those same plants and render parallel camera(or very long), save out alphas and use cards to cast shadow insead of the 3d. It's more efficient and you are only get the effect of the profile anyhow. All that internal geo isn't doing any work on the image. If you want them for reflection you can add the diffuse.

[ruby_vandeursen]

Hi Wolfgang. Thanks for replying, saves me a lot of trouble looking for a solution. I'll work my way around it, I think the latest version doesn't have the issue anymore.