Understanding selection outlines - Photoshop Tutorial

- At a very basic level the selection outline is pretty simple to understand. It draws a line around the area that's selected, then everything outside of that shape is not selected. But, things are not always as simple as they seem when it comes to selections. So, lets take a look at what that selection outline is actual telling us. If we start with the very basic selection here. I'll just make an elliptical selection just over here on this side of the image. You can see that we have that animated line indicating the area of the image that is selected verses the area outside of that ellipse, that is not selected. It's very simple, the selection outline is the boundary that defines selected verses not selected. But, the selection outline doesn't always give us the most clear picture of our selection. Let's take a look at an example of that. I'll de-select that elliptical selection. And I'm just going to make a selection based on a color range within the photo. So that I can create a selection of those clouds. For example, I'll go ahead and create the selection and it looks like I have a perfect selection of just the clouds and nothing more. Well, let's take a closer look. I'll apply a curves adjustment. For example, and I'm just going to apply an exaggerated darkening to the clouds. And in fact if I take those clouds nearly to black, you might start to notice that my selection wasn't as clean a selection as I thought it actually was. In fact, because I've used that selection as the basis of a targeted adjustment, I now have a layer mask. I can reveal that layer mask and start to get a better sense of what the selection actually looked like. And so, within the clouds here, for example, you'll see various shades of gray. So, if we think about our selection as a stencil, white areas are going to be effected by whatever adjustment we apply. Black areas will not be effected. And so we think of a selection as being black and white. But, in many cases, that selection can have shades of gray as well. Areas that are partially selected and therefore that will be partially effected by our adjustment. Well, let's get back to that selection outline. It actually defines areas that are at least 50% selected. So, in the context of a black and white stencil, remember there can be shades of gray there. So, it is showing us areas that are brighter than 50% grey, than middle grey. If I load a selection based on the mask that we are looking at right now, you'll see, that once again, that selection edge follows the edge of the clouds. Let's zoom in, in fact, so we can get a better sense of what that selection edge is actually showing us. And first of all, you'll see that the selection is not shown up here where we transition all the way to black. But rather, it is showing me where we reach the point that those pixels are brighter that 50% gray on the white side of things here, and where the pixels are darker than 50% gray. So the selected area, in terms of that selection outline, is based on brighter than 50% gray is selected and darker than 50% gray is not selected. But, in reality when we have these shades of gray in between that selection edge, certainly looks like a clean precise line, but it's not always an accurate view of what our selection really looks like. Keep in mind that, that edge is just showing us that transition between greater than versus less than 50% selected. There are of course other ways that we can evaluate that selection. So, for example, if we use the selection as the basis of a layer mask, we can look at that layer mask, we could use quick mask mode to view the actual selection shape. There are a variety of ways that we can deal with that. But, the key is to keep in mind that the selection outline, it looks very precise, but its really showing us, essentially, what would equate to a black and white selection or stencil. When in fact, there are shades of gray involved there. So, remember that what looks like a very clean line, is not always a selection with a very clean edge.