Arnold Alpha Problems!!

[Red171]

Hey guys, I know there have been a few questions regarding this - I just can't get a working solution.

Basically, any transparent object doesn't render correct alpha channels using the Arnold renderer, it's always opaque and simply reflects the environment background.

I've setup the standard surface material with transmit aovs turned on as suggested on the arnold documentation. 

I am using the OSL environment map to light the scene.

And here is how the alpha looks in Arnold, basically the bust is wearing a transparent helmet. the second shot shows how it SHOULD look when rendered out of the box with Corona Renderer. The only reason I got Corona was as I needed it for better product shots... due to this transparency issue! Otherwise I'd probs have still been using Arnold.

Any ideas guys?

Thanks.

Jonny. 

[Stephen.Blair]

You'd have to use the Arnold Skydome, because then you can control the visibility to transmission rays.

With the OSL Environment, the background is visible to transmission rays, and so you get solid white in the alpha.

[Red171]

Hi Stephen, thanks a lot for your reply.

How do I set this up properly?

- I disabled the "use map" from environment and texture dialogue box.

- Then, I created an arnold light and set it to sky dome - still got solid alphas even when just using a colour or an HDRI image texture.

Thanks again,

Jonny. 

[Stephen.Blair · Accepted solution]

With a default new scene, I set it up like this (the sphere is glass)

or

[Red171]

Hey Stephen,

You are a legend.

Simply setting the background(backplate) in the Arnold Renderer panel to none sorted it. I am still using the OSL HDRI environment map in the environment slot on the environment and effects panel as the only thing lighting the scene. Working no problem. Amazing how annoyingly simple but obscure that fix was lol. Really appreciate your time,

Thanks again.

Jonny.