What's new
Photoshop Gurus Forum

Welcome to Photoshop Gurus forum. Register a free account today to become a member! It's completely free. Once signed in, you'll enjoy an ad-free experience and be able to participate on this site by adding your own topics and posts, as well as connect with other members through your own private inbox!

Mutiple Layer Masks on Single Layer


Chava Drummond

New Member
Messages
3
Likes
0
Dear Everyone,

A student of mine asked why you would create multiple layer masks on a single layer; it's a good question, and I can't find an answer online - ideas?

Thanks!
Chava Drummond
 

ibclare

Queen Bee
Messages
11,034
Likes
4,638
The second layer mask is a vector mask, but I can't help with that much. Here is a tut from adobe that might help you. I don't really understand the difference as I use vectors (pen tool) to create a pixel layer mask. The tut shows vector shapes to demonstrate and also image cuts.

I'm sure someone will come by who can explain this to both of us. Check it out in PS; if you add a second layer mask on a layer, it will be a vector mask. Maybe just that info will help you find your answer. I'm sure your students will appreciate it. So hang in there. We have lots of members who are very familiar with the many nooks and crannies of PS, and tech-savvy as well.
 

Tom Mann

Guru
Messages
7,223
Likes
4,343
Instead of a vector mask on a pixel mask, another possibility is to use a 2nd pixel based mask.

I don't do this very often, but when I do, it's more for convenience and speed than absolute necessity. For example, suppose I have one layer mask / alpha channel that selects on the basis of luminosity and a second one that selects some area or set of areas in the image, and I want to restrict some adjustment to just the brighter pixels in those areas.

I could do this by multiplying the two alpha channels and forming a new single layer mask from the result, or I could apply the two pixel-based layer masks sequentially to the same adjustment layer.

One way to do this is shown in the attached screen shots. In this (not very artistic) example, suppose I wanted to warm up only the very brightest areas of sky. If I used just a luminosity mask, the bright wake of the boat would also be warmed up. If I used a mask that selected just the sky, it would warm up both the dark and light areas of the sky. However, by using both, I can select only the bright areas of the sky.

The attached screen grabs illustrate the technique. The file names describe each screen grab.

HTH,

Tom M
 

Attachments

  • original.jpg
    original.jpg
    113.3 KB · Views: 26
  • luminosity_mask.jpg
    luminosity_mask.jpg
    65.5 KB · Views: 25
  • mask_to_select_only_sky.jpg
    mask_to_select_only_sky.jpg
    10.4 KB · Views: 24
  • layer_stack.jpg
    layer_stack.jpg
    18.5 KB · Views: 25
  • result.jpg
    result.jpg
    118.8 KB · Views: 24

ibclare

Queen Bee
Messages
11,034
Likes
4,638
Tom, do you do this only with adjustment layers as opposed to putting two masks onto a layer with a pixel-based image? If so, why would you do this?

I can see maybe doing it by copying a layer, then merging them. (though I always group original adjustments of any kind and turn them off; I hate to not be able to go back and make changes; or make a smart obj.)

And if you should add a 2nd mask to the pixel layer, how do you do that? I always end up with a vector mask when I add an additional. Would the mask be done similarly? On a second layer above? But can you even add a mask to a blank layer. My PS know-how is a cliffhanger at this point.
 

Tom Mann

Guru
Messages
7,223
Likes
4,343
Hi Clare -

Tom, do you do this only with adjustment layers as opposed to putting two masks onto a layer with a pixel-based image? If so, why would you do this?

No, the technique I described above also works with ordinary pixel layers, not just adjustment layers.

I would use two masks on a pixel layer for exactly the same reason as one might do it on an adjustment layer, ie, you want a two step selection process where the first selection / mask is refined further by the second selection/mask.

I can see maybe doing it by copying a layer, then merging them. (though I always group original adjustments of any kind and turn them off; I hate to not be able to go back and make changes; or make a smart obj.)

I try to use adjustment layers (not pixel layers) as much as possible for a number of reasons including future editability (as you correctly suggest), and doing so reduces memory requirements.


And if you should add a 2nd mask to the pixel layer, how do you do that? I always end up with a vector mask when I add an additional. Would the mask be done similarly? On a second layer above?

As you describe, one always gets a vector mask when one tries to add a 2nd mask to a layer. That's why I do it as I described above, ie, putting the 2nd pixel-based mask on a folder that includes the layers with their own pixel-based masks.

When I'm working on a completely photographic image, I rarely end up using any pure vector selection masks or related techniques. I might start a selection with an outline made with the pen, but then I usually rasterize it so I can use techniques such as "refine edges" and similar techniques on the mask to keep a nice organic feel. In contrast, if I'm doing vector art, it's the opposite - I rarely use pixel based selections. However, if I'm doing vector art, I'm usually working in Illustrator, not Photoshop.

But can you even add a mask to a blank layer.

You can. Actually, it is a common technique is to put the needed mask on an adjustment layer (eg, levels) set to do nothing. This saves lots of memory compared to masking an intermediate pixel-based layer.

However, the technique I favor is the mask on a folder (as described in my earlier post). Even though you can get similar memory savings from both techniques, the reason I favor this over a mask on a do-nothing adjustment layer is because it saves computational steps, and hence processing time. My understanding is that all the same mathematical computations must be done (ie, with zero'ed parameters) even if an adjustment layer is set to do nothing. However there are no mathematical computations involved if a folder is placed around a single or group of layers. The folder merely tells the program how to group the operations and in what order to execute them, but doesn't introduce any extra math.

To complete the answer to your question about using a mask on a blank layer, of course you can do this, but it's usually not very useful unless it's not really a truly blank layer and/or the blend mode set to something other than "normal". An example of this might be a masked solid color layer set to "color" blend mode.

HTH,

Tom
 

Top