Alpha Channel Support

[Zack Black]

Jumping in here in 2023 with Affinity Photo 2.1.0. Still seems like AF doesn't have proper alpha channel support. I can paint with white/black on the RGB channels, but only with white on the Alpha. I can make a selection and invert it on the RGB channels, but not on the Alpha. Developers... please, PLEASE fix this!!

[NotMyFault]

To paint on alpha channel, you can adjust the opacity of the color (not the color channels), or use the erase brush.

Affinity does treat the alpha channel different from color channels for technical reasons to provide alpha blending etc for regular image editing.

It would probably require a major re-design of UI and rendering engine to allow editing alpha channel.

Never the less, with some minimal extra effort you can separate the alpha channel as mask layer, or additional pixel layer, which gives you the wanted freedom to edit that channel with all regular brush tools.

The extra effort is required only when opening a file, or before exporting the file, to ensure channel separation and/or channel packing to avoid erasing color channel data where alpha is 0.

This topic has been discussed extensively before. 
i support your feature request, my workaround tips are only for those who want to use Affinity even in the current state.