How to Use Layer Masks in Photoshop
courtesy of Digital Tutors
Using Layer Masks in Photoshop are a great way to work non-destructively to hide any visual elements you want without creating any permanent edits to the image you’re working with.
For example, let’s say you have an image of a sculpture that you want to isolate from a background that contains several trees and bushes. You could use the Eraser Tool to carefully remove the background while trying not to erase any portion of the sculpture. However, once you have saved and closed the document, that edit will become permanent. By using a Layer Mask you can achieve the same result in a more controlled fashion with the option to reveal any portion of the background later on if you need to.
Think of a Layer Mask as a veil that you spread over any part of an image by means of painting it in with the Brush Tool or defining where it’ll cover by creating a selection using the Marquee or Lasso Tools for example.
There are a couple of easy ways you can apply a Layer Mask to a layer you’re working on. One way is to navigate to the Menu Bar at the top of the Photoshop interface and choose Layer Mask on the drop down menu. Another way is to click on a button at the bottom of the Layers Panel that looks like rectangle with a circle in the middle of it.
Using our sculpture example again we can discuss applying a Layer Mask from the Menu Bar. Let’s assume you’ve already defined a selection around the statue and your goal is to hide the foliage covered background behind it. With the layer selected, simply navigate to the menu bar and click on Layer then Layer Mask. You’ll now see the options Reveal All, Hide All, Reveal Selection, Hide Selection. These options will determine how the mask is applied to the layer.
If you choose Reveal All you will see a white thumbnail appear to the right of the layer thumbnail. This is the Layer Mask. Since it’s completely white this means that everything on the image is completely visible. Anything in black would be completely invisible or masked out. This option also disregards the selection you currently have in place and simply applies the mask to the entire image. Alternatively, if you had chose Hide All the mask would be a completely black thumbnail causing the entire image to be hidden and revealing any visible layers underneath.
Again assuming that you already have a selection defined around this sculpture you could choose another option in this fly-out menu called Reveal Selection which would apply a Layer Mask to the layer but only mask out the information not contained within the selection. The result would be the sculpture isolated by itself while everything around it would appear completely transparent. The reverse affect of this would be a result of choosing the option Hide Selection instead where the sculpture is masked out the environment around it only remains visible.
Once you’ve tested these options, you may prefer a quick method of clicking on the Layer Mask button in the Layers Panel to apply a mask. So with your selection still defined around the statue you can click on this button and the result will be the same as if you had chosen Reveal Selection from the Menu Bar where the background bushes and trees are no longer visible. If you want to see the reverse affect of this simply hold down ALT on your keyboard when clicking on the Layer Mask button. Everything within the selection will become masked out revealing any visual information on layers below.
As mentioned earlier, you can define the appearance of a mask by painting with the Brush Tool. This time with no selection at all and the sculpture layer selected, click on the Layer Mask button at the bottom of the Layers Panel. Again you will see the Layer Mask thumbnail. By default it will be completely white in appearance meaning nothing is currently masked out. Now grab your Brush Tool and use the color black to paint where the mask will cover. If you accidentally paint your mask over an area that you didn’t intend to simply choose white as your foreground color to paint away the masking effect.
Using black and white will allow you to define the mask as completely opaque or completely transparent. Any values of gray between the two will provide you varying degrees of transparency with the mask.
If you have never used Layer Masks before, you’ll find that they not only provide more control, but also spare a lot of heartache when it comes to making edits.