So is it really Impossible to get a transparent background using GPU Rendering with Arnold?

[zedblade]

I'm at the end of my rope here and pulling out what little hair I have left. I've scoured the interwebs and everything I've found seems to imply that it's impossible to have a transparent background when using GPU rendering, which just seems too stupid to be true. Being able to render out something with the background masked out seems like a basic rendering feature.

With CPU everything works fine but it can take up to 40 minutes to render one frame and look the way I want. With GPU it gets to the same quality level in 3 minutes! However, my pipeline requires the background to be transparent. I have 1000s of frames to render. Spending the next 500 hours of my life just rendering is not an option. I'd rather just quit the project and give up. There has to be something I can do for the GPU to render with a mask? Some little trick or something I've yet to find?  Something within Maya to be exact. I'm not going to to do multiple renders in both GPU and CPU so I can composite the CPU mask into the GPU renders That would take just as long as just rendering with the CPU almost. I'm also not going to make the background a 'greenscreen' so I can color select it out because that introduces it's own ugly problems.

Thanks for any tips. I'm not really expecting anyone to have a solution, this is just my final last gasp before I give up.

[Kahylan]

Hi!

I'm not quite sure if this workflow works with the GPU render since I never used it like that, but from a quick google search it seems it does, atleast with the latest Arnold Version.

To create masks, you can create custom AOV passes in arnold on which you then just assing a flat shader, either in white if you want to use an alpha workflow or in a very specific color if you want to use a colormask workflow.

Here's a Tutorial on setting up AOV's

https://www.youtube.com/watch?v=_PN_bdNvn44

I'm not quite sure if this is what you are looking for, but I hope it helps!

[_sebastian_f]

still on maya 2020 here and probably don´t understand you correctly but rendering with arnold GPU gives me the same alpha as the CPU!

[zedblade]

hmm that's interesting. I'm using 2022.3. I'll get 2020 and see if there's any difference. Thanks for the info!

[zedblade]

Thanks for the reply! My end goal is for PNGs, and as far as I know AOV's require the format to be exr. Though maybe if AOV method works I can create an action in photoshop to convert the AOV channel into a mask? I've already been using an action to covert the CPU tif renders into a PNG. Hmm that's definitely something I haven't tried yet. Thanks for the video link, this at least gives me an option to test out. Thanks!