I’ve looked at the info at Using Texture Masks | Unreal Engine Documentation
But does not explain how to create the black and white image per mask per channel?
I use photoshop when I select say “blue channel” some parts of my UV image disappears too making it hard to create masks for each channel. I’m guessing im doing it wrong and would appreciate a step by step on how to do this?
Thanks
It’s best to create the masks in another image/psd and then copy + paste in place in a new document, in the respective channel (red, green, blue). Make sure the new document has a black background and that the mask you are copying from the original is filled with white. You can then use each channel as an individual mask in the material editor.
Ok thanks SE_JonF 
Hi, SE_JonF
I find that when i copy the white (masked) part into a channel of a new image it puts it in the middle of the new image rather then were it should be as in the previous image it was taken from. The only way to stop this was to fill the the rest of the image with the black 1st then copy it. I dont see the need for making sure there is a black background in the new imge 1st, I’m i doing it wrong?
Basically, you want to create the selection (using the selection tools) when you have all channels (RGB) visible and the layers panel active, then switch to the channels panel to modify the individual channel.
https://youtube.com/watch?v=ImF_du32ZU8
You might need to increase the resolution on the above video to 1080P to see it clearly.
I got it doing it that way from not using and UV overlay. If i have created the mask channels from another image which were created using complex shape of my UV image and copy them red,green,blue to the new image thats where my problem lies.
Thanks for the video though Ben85
Expresso Exporter for Photoshop CC can export to specified channels by unlocking the output.
it makes for a really nice easiliy readable psd.
Cheers dude, might give it a go