: What does layer mask mean in Photoshop, and what does it do ?
In: Technology
I thought of a second way to think about it, that might be slightly easier to grasp.
Let’s say you want to paint a pattern on your wall in your house. Well you’re going to use masking tape to mark the edges of your design so that you can paint over the tape and still get a clean line in the paint.
A masking layer does the same thing. Think of it like your digital masking tape.
So Gimp is my editor of choice, but layer masking does the same thing.
What a layer mask does is it selectively plays with the transparency by using a second image that tells the program how and where to do what to the image layer it’s attached to. It handles the levels of opacity on a monochrome scale, so fully white areas on the mask result in fully opaque parts of the base image layer, and black areas on the mask are transparent. Shades of gray are appropriately partially see-through.
That might not be the easiest to understand though… so let’s get an example. I personally find layer masks the most useful when I want an effect to stop at the edge of something and not bleed over into the surrounding area, so that’s what our theoretical example will do.
Imagine a photo of a cat sleeping in a large planter. It’s a cute image, but you want to make the obvious joke of how the cat plant is growing nicely, and for emphasis you want to have the cat green around the edges. But you don’t want the green to bleed out around to the dirt and planter.
So you open a new layer, trace around the edges of the cat with a greed brush, gaus blur the whole thing and do a multiply effect. Cat looks good, but that green isn’t just on the cat. Now you COULD just go in and carefully erase the edges. But what if you want to change the blur later? Then you’d have to erase all around the cat again.
The easy way to handle this is to make a mask layer. Depending on contrast sometimes this goes fast, and sometimes you have to manually trace around an object. But instead of erasing around the cat, you instead trace on the masking layer. Trace the cat, flood fill the interior of your line in white, the outside in black, and now the edges are crisp without you having to erase. You can play with that effect to your heart’s content, and it’ll always end at the edge of the cat without having to erase around every time.
Fill that cat with a starburst? Ends at the cat’s edge. Gradient fill? Ends at the cat’s edge.
Because the masking layer is telling photoshop to stop.
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