04/02/20 Updated here: https://blog.main.wattsdigital.com/?p=2283
One of the beauties of Photoshop is the ability to make changes locally, not just globally. There are two main techniques to “localize” your changes – one is to make a “selection” using tools such as the Magic Wand or Lasso tools, then creating an adjustment layer to make your changes to that selection. The other technique, and one that can be far quicker, is by using Layer Masks.
The purpose of of a Layer Mask is to hide or reveal portions of a layer. It can be used instead of or in addition to a selection. It is more analogous to painting than to drawing, such as the Lasso Tool, and can save you lots of time.
Let’s use the images above as an example. In Image “A”, I have a nice image, but the sky is washed out. In Image “B” , I am making a levels adjustment for contrast to punch up the sky, but obviously the foreground is too dark. If I had used a selection tool such as the magic wand on the sky, it would probably take awhile to make that selection. Instead, in Image “C”, I mask out, with a few quick strokes of the brush tool, the areas that I don’t want affected by the Levels layer. These changes show up as black in the Layer Mask thumbnail.
So how did I do that? I chose the Layer Mask Thumbnail (the box on the right) by clicking on it once in the adjustment layer. Then, with the Brush Tool active, I “painted” in the image using “Black” as my foreground color to hide the areas I don’t want affected by the layer – – Where I “paint” shows up in the Layer Mask Thumbnail as black. The areas that are white in the thumbnail reveal the layer.
Just keep remembering:
Black “Hides”, White “Reveals”
So that this post is not abnormally long, I’ll post a “Part II”, coming in a few days, and we’ll go over step-by-step how this is done, as well as some other nifty pointers – stay tuned! And if you have a specific question about Layer Masks, leave it as a post and I’ll cover it in Part II.