Struggling to get multiple masks to work on Affinity Photo on iPad

[EssentialParadox]

I’ve read numerous forum posts and watched several tutorial videos on this subject and I’m not sure what I’m missing…

If I add an empty mask layer to an image and paint on the mask in white, it masks ‘in’ the image correctly, great!

But then I am trying to add a second empty mask layer of a different shape that will combine with the first mask and here’s the issue: because both masks have a black background, the blacks are adding together, whereas I need the whites to add together. So I need to blend them.

BUT, I assumed I would just need to change the top layer blending mode to screen or lighten to remove all the black, but this doesn’t work. In fact none of the blending modes do anything.

What am I missing here?

 

[EmT]

Hi @EssentialParadox

Do you mean you are trying to add an inverted Mask layer? Or are you trying to stack Mask layers? 

If you could advise what is the final effect you are trying to achieve, it may help with pointing you in the right direction. 

[NotMyFault]

My 2 cents:

• currently, if you add multiple mask layers (or vector layers as mask) they work by multiplying, giving a subtractive effect (pixels need to be opaque in both masks to be visible)
• what many users including myself want: an option to use multiple masks in additive way.
  There are many tries to get this by workarounds, unfortunately this does not work well, and long time unfixed bugs (handling alpha for nested layers) render most workarounds unusable. 

i will try to find the older bug reports and edit this post accordingly later.

My question about blend modes for masks (no reply).

Somewhere else it was stated that they simply don't work at all.

 

[EssentialParadox]

@NotMyFault Thank you for the details. That’s sad that it seems to be confirmed as a long-standing bug then 🙁

Is there any sort of workaround I can do?

I’m trying to create a mask from several brushes to get a specific and delicate shape.

@EmT I think NotMyFault has identified it as a bug. I’m trying to additively add masks together. If you could suggest anything I’d be grateful.

[NotMyFault]

2 hours ago, EssentialParadox said:

Is there any sort of workaround I can do?

Just try to follow the tutorial (first link), it should work in principle for mask layers.

The bug (2nd link) is affecting vector layers used as mask, or combinations.

[EssentialParadox]

Ah, thank you @NotMyFault, that is a MASSIVE workaround but DOES work!

Just for anyone in future who wants a quick shorthand of how to do it:

1. Go to Adjustments -> Channel Mixer
2. Select Alpha channel and change Alpha to -100% and Offset to 100% — save this as a new preset called “Additive Mask”
3. Add a copy of this adjustment layer to each mask you want to use, BUT ALSO one extra copy of the adjustment layer to sit just above all the masks in the group.