Rendered PNGs not creating alpha channels/transparency?

[Anonymous]

Just upgraded from Maya 2012 to 2017, and have to dive into getting a project rendered. My previous workflow was to use Mental Ray to render layers as PNG sequences then composite onto still renders in After Effects. I've setup the new file with Arnold and started the render sequence when I noticed that it wasn't rendering the Alpha channel mask. I saw something about Arnold not doing PNG alpha channels in a different thread. Is there a way to get arnold to do it, or is there a preferred format to render to instead?

[mspeer]

Hi!

2 threads that might be helpful:
https://forums.autodesk.com/t5/maya-shading-lighting-and/transparency-renders-black-in-arnold/td-p/6...
https://forums.autodesk.com/t5/maya-forum/arnold-maya-2017-transparency-with-file-texture-showing-bl...

[Anonymous]

Thanks, but I don't have any transparency within the scene. The alpha channel that I need is on the output files. Back in Maya 2012, I would render with Mental Ray to create RGB+Alpha PNGs with transparency. 

Because it was a simple render, I was able to get around it this time by duplicating the image sequence in After Effects and cranking up the levels to create a black and white silhouette of the object shape. I then used that as a Luma matte for the duplicated Image Sequence. Had the desired effect, but not the most elegant solution.

[mspeer]

Hi!

Yes, sorry, but the problem is related to the other threads as Arnold does not support Transparency as used in PNG in opposite to Alpha as used in TIFF or EXR

Choose an other format like "tif" (best as replacement for png) or "exr" or render a separate image sequence as alpha pass in PNG.

[Anonymous]

Ah, okay, I had started reading those before posting, but only understood that the renderer wouldn't properly display the material transparencies.

Thanks, will experiment with the other formats.