Great Big Bite

2) Beta 1.9 on macOS already allows us to apply filters to Masks in the same way as it allows applying filters to Spare Channels. If you want to see the Mask in greyscale, opt/alt+click its thumbnail in Layers panel.

First off -Thanks for the ability to edit spare channels in the new Beta 1.90
I have two feature requests:
1)I request that we have the ability to rename spare channels while creating macros. Some macros can be quite complex requiring the use of multiple spare channels and it would not be possible to create them if all spare channels have the same name!
2)In the new Beta 1.90 we can now apply filters to the spare channel , similarly I request that we have the same ability to apply filters to the Mask Alpha to allow us to edit/modify already existing masks with filters.
Best regards,
Robin

I'm here to give similar feedback. As a Photoshop power-user, I would use channels religiously. Copying and pasting channels into Alpha/Mask, and directly manipulating channels to create complex masks quickly.
Would love to be able to make levels adjustments to mask and alpha channels after cutting and pasting from an RGB channel. Have found a work around, but it's not quick or intuitive.

This was requested and talked about before, but here goes again.
Spare Channels don't behave as simple additional alpha channels.
When I create a new Spare Channel, specially if it is created out of a color channel, I expect it to behave just like a color channel, except that it describes "luminosity" or "opacity/transparency" information.
But I assume I could still use all painting/editing tools on it. Stuff like brush, dodge, burn, smear, blur, etc. Also, Levels, Curves, Brightness/Contrast, or any filter.
In effect, a Spare Channel should be treated as an additional greyscale image, and I should be able to deal with it exactly like it was a simple greyscale image.
I could, after editing it (again, like a regular greyscale image), decide if I want to use the luminosity information as a mask or simply load it as a selection or whatever.
BUT, PLEASE, make spare channels work like regular greyscale images inside the document, and not like a "special transparency information type of thing".
Professional editors need to be able to create complex masks and we need to be able to use all the available tools to do so.

Also please let us create a selection by cmd/ctrl clicking a channel.
Right clicking a channel to create a selection is awkward.

Honestly, I have been trying to give Affinity Photo a chance, dealing with channels and trying to do in Affinity Photo whatever I do in Photoshop, with the composite channels and with additional alpha channels.
And, either it is very cumbersome and not very intuitive, or I can’t do it at all.
This is really forcing me to avaluate the type of work I need to do, to decide if I should use Photoshop of Affinity Photo.
I really hope the way channels operate, and the amount of stuff we can do with them, improves in the future. Hopefully, in a nearby future.

You could either
- (if the precise K values matter for some reason) use the channels panel to create a mask, the result will most likely be rather bright but you can work around this by duplicating
... or apply a gradient mask from 0/0/0/100 to 0/0/0/0 without additional stops
 
 

2020-11-02_13-22-29.mp4

Working on this, on/off over the past three months or so. There's a bit more detail alongside a somewhat 'accrued' competency sorting through managing layers since the previous illustration and still a ways to go (re-work/editing). My finalised goal is an under cover carpark environment with reflective effects also the 'asphalt' like texture is procedural, generated from scratch in gimp.

Finally calling this done. Certainly put more that a few hours into it but nonetheless overall, pretty happy with the end result alongside learning a heck of alot as well. Anyways I'm going to further explore this particular illustrative method as too whether other subject matter I've in mind can also be rendered realistically. 
Cheers.

 

Hi @Great Big Bite,
Welcome to Affinity Forums
Thanks for reporting this. It affects all apps where a modifier is used in conjunction with Backspace for a shortcut. Issue logged to be looked at.