Question [URP] - Using Albedo Alpha for smoothness

We're trying to reduce the number of textures in the project by using the Albedo Alpha to get the smoothness on some of our props. (For the time being, we've been exporting 2 separate textures - the Base Map and a Smoothness Map).

The questions are:

1. Is this the right definition of what Albedo Alpha means?
2. And how do you go from having 2 separate textures to just 1 to make use of Albedo Alpha in a tool like Photoshop?

​

Any pointers are appreciated.
Cheers.

 

For anyone seeing this, what we discovered so far is that PNGs have a funky way of saving the alpha channel so it's much easier to use TGA for use cases like this. (Note: Its still doable in PNGs by creating a mask layer but its a little bit more hairy)

More info here: adobe photoshop - Handle a transparent layer in Targa file - Graphic Design Stack Exchange

 

photoshop does not have native functional RGBA read/write support

https://www.fnordware.com/superpng/
This plugin for it allows you to chose to encode an Alpha based on
1) Transparency
2) A selected Alpha channel

to re-open the PNG with an alpha channel you also will need this plugin