Alpha channel missing from png render

[gabeciav11]

I noticed that if I use mtoa.cmds.arnoldRender to render a png, there is no alpha channel. However, if I use the Arnold RenderView and manually save a png, the alpha channel comes through fine (and is viewable in the render preview). Is there a flag or setting that I could use to force the alpha channel to render?

I did see this old post which @Stephen Blair replied to https://forums.autodesk.com/t5/maya-shading-lighting-and/arnold-batch-render-with-alpha-channel/td-p... but wasn't sure if using tifs is still the only workaround. Any insight here would be appreciated.

[Stephen.Blair]

You have to use a different file format if you want an alpha channel.

Arnold does not render an alpha channel for PNG, because the PNG standard does not use premultiplied alpha, which is what most users would expect.

[amcclureXCM4W]

So, what file format do you recommend? Mine need to be imbedded in an InDesign document.

[Anonymous]

this is a MISTERY, a STATE secret to Autodesk...