I am baking out diffuse maps for use in low-res billboard textures (lowest LOD).

Currently I export to .png. It includes RGB channels and can also export a separate Opacity map.

However Unity URP does transparency based off the alpha channel.

So for each texture being exported, I need to bring it into Gimp and run "Alpha From Color".

It's certainly not a backbreaking amount of work, but I'm curious if there's a way to do this from inside Houdini.

Certainly I could call some external program using a Unixnode, but this sort of sparks a more broad question - is it possible in Houdini to loop through the per-pixel attributes of an image and change them? Or does this need to be done in a separate program?

Ok so this took me a couple days to work out, but I wanted to leave my solution here since it seems to be where google took me.

In 'Maps Baker' there is 'cops_baking'. Inside that is 'rop_Diffuse'
In the 'Metadata' tab, find: 'PNG/TGA Premultiplication'. Set to 'Unpremultiplied'

Obviously you'll want the Alpha attribute included in the composite tab.