Can I use the luminance (brightness) of one layer as a mask for another layer?

[Scott Smyth]

Basically exactly how layer masks behave, except I would like to be able to have full non-destructive editing control over the masking layer (eg have it as a smart object). The problem with layer masks is that (afaik) only destructive editing is possible.

If it means anything to anyone here, what I'm after is effectively the same as what a 'luma matte' does in After Effects.

Is this at all possible in PS? Or is there another way to achieve what I'm after?

Thanks.

 

[Hoogle]

There is a luminosity blending mode you can set a layer to but without seeing your picture and a brief explanation of what you want to achieve then it is hard to advise the best route for you.

 

[Scott Smyth]

I'm not sure that's what I want. As I understand it that applies the luminosity of one layer to another. What I want to do is use the luminosity of one layer as the alpha of another (ie use the luminance to mask, as you can do in AE with luma mattes). Sorry if that wasn't clear.

Imagine I have a black and white image layer (A). I want to use A to mask another layer (B) such that where A is black, B is visible and where A is white, B is transparent (or vice versa).

I know I can effectively do this with layer masks / alpha channels. However, my workflow for this job (a digital illustration) would benefit if I could keep the masking layer (A) as an actual layer which I could edit non-destructively, similar to a clipping mask, and not relegate it to a channel.

Does that make sense?

 

[Scott Smyth]

I figured something out using the 'blending options' box, not quite what I was describing but it suits my needs. I'll edit it in here later for anyone else who's interested later on but I'm off to play with it now.

 

[ibclare]

I can't help you with your answer; hoogle is definitely your AE/PS guy, but what do you mean by editing layer masks is destructive? The whole idea, well at least one important purpose, is that layer masks are not destructive. I must be missing something . . .

 

[Hoogle]

I sort of get where you are coming from you basically want an easy mask based on alpha channel. Now I am sure there are many ways to achieve this but will it always work for every image I have no idea.

make a duplicate of your image layer and play with different black and white options maybe try image adjustment thresholds and tweak that so you have just a pure black and white image. Alternatively you can go to image >adjustment> levels. Once you have what could look like a mask if you were to use a normal mask select that whole layer edit > copy and then paste it onto a layer mask.

That will essentially give you a pure alpha mat mask.

Alternatively you can actually use after effects masks on images just load the image or psd into after effects and copy the mask into ps.

 

[Scott Smyth]

What I mean is the editing of the layer mask itself can only be done destructively (afaik, do tell me if I'm wrong). For example, you cant use a smart object as a layer mask, nor apply adjustment layers to them.

I needed to use an actual layer (a smart object) as a mask based on its luminance (the same as a layer mask) so that certain elements of the mask could be edited easily and non destructively without having to go back and forth copying/pasting things into layer masks from other layers which I'd need to keep showing and hiding.

In the end I worked out how to use 'blend if' in 'blending options' to effectively create transparency from luminance in a layer, so that I could then just use it as a regular clipping mask.