The RGB channels in PS are really handly, I don't believe Painter has them, so I needed a way to make them. So I'll share how I did it. Here is how you automate it.
Open any file.
Start recording a script.
Select a layer (make sure it's a layer and not your canvas).
Duplicate the layer.
Go to curves. Go to advanced. For Red channel, drop all blue to -100 and all green to -100, etc. (you will repeat this process for the other 2 channel scripts)
Drop saturation to 0 just to make sure.
Go to select -> Auto select, image luminance. Press ok.
Go to channels. Save the selection as a channel.
Go back to your layers, delete the layer (clean up lol).
Stop your scipt. Name it Red Blue or Green, depending on what you picked in the curves window.
Repeat this process for the other 2 channels.
This is the result, RGB channels from PS in Painter in a few seconds:
Awesome. I cant wait to try it. Thank you