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I've been noticing several instances where specific materials are rendering with an incomplete alpha channel, where it should be completely white. The CPU render on the same material/scene renders fine. As a consequence, in some cases half of my render area is rendered semi-transparent! I have been rendering to SL12.

I seem to have narrowed this down to Bump/Normal maps. When disabled the alpha renders as expected. Enabled, the bump/normal map appears in the alpha channel (as varying shades of grey).

This occurs both with a v4 mxm, as well as a v5 mxm created from scratch.

When using a material with a very fine normal texture, the alpha renders seemingly how it should, but does not clear until at least SL11/12. Other textures I have tested are not clearing even at SL16.

Has anyone else experienced this?

Thank you for your test. We have a known issue about some render channels showing artifacts on GPU. Those artifacts are like black borders on some objects. Your issue is similar, just the border, or the whole object?

It is the whole object and it follows the bump/normal map. Removing this gets a clean alpha.

I tested a simple base material, just a single bsdf and rendered just with ref0, roughness and normal individually. Only the normal map affects the alpha.

As I mentioned, smaller less pronounced normals/bump maps seem to be resolved when rendering to higher SLs.


This alpha is just a plane without any subdivision.


This alpha was a more complex scene using a number of existing materials. As you can see there are various transparencies across the image, depending on the material. I can repair this somewhat by placing a 50% grey layer under the render in photoshop to replace the transparent areas. This is fine for draft images, but not good for when I come to do a final render.

Yes, this is a different issue. We will check all channels on gpu, and maybe adding one or two of the not supported ones. Thank you for your images.