Some Thoughts on Selecting and Feathering in Photoshop
There are generally several different ways to do common function in Photoshop. And just because you learn one way to do something doesn't necessarily mean it's the best way in every situation either. With this in mind, I'd like to take some time to discuss the pros and cons of the main ways to make and feather selections in Photoshop.
We obviously have to start this discussion with how to select an area in an image to want to work on. After all, if nothing is selected or if your entire image is, there's nothing to feather, and nothing to talk about this week. Generally speaking selection techniques fall into two main categories: regular selections, and masks. The Lasso and Magic Wand are examples of regular selection tools. When you trace around an object with the Lasso or click on it with the Magic Wand, you select it. If your hand isn't entirely steady or the contrast between subject and background is low, your selection may not be as accurate as you wish it were, but you can see what you end up with because the selection boundary will be indicated by a line of "marching ants" dots overlaying your image.
The basic way to feather a selection made with the Lasso or other regular selection tool is found on the Select menu. Going to Select >> Modify >> Feather opens a dialog box asking you for the "Feather Radius." This is quick and easy, but softens all edges by the same amount. It's also rather difficult to tell just what your modified selection now actually looks like. All you see is the line of "marching ants" encompassing the area containing pixels at least fifty percent selected. If you then apply a filter or make an adjustment using the resulting selection, you may be in for a rude surprise when areas you expected to change don't fully while areas you assumed were outside the selection and thus safe end up getting modified.
Masks haven't always been in Photoshop, although they have been there for quite a few releases now. Their introduction heralded a revolution in the art of making selections. Users could now visually tell just how selected or not any given point in their image was. A mask really is just a different way of representing a selection. It lives in your document just like any other layer, except that rather than being full RGB color it's just shades of black and white: one channel rather than three. Any point in a mask layer that is completely white is completely selected. Any point that is pure black isn't selected at all. Shades of gray between those two extremes are selected correspondingly. Thus, an area that is fifty percent gray is fifty percent selected and so on.
Every new adjustment layer automatically gets its own layer mask. If you make a selection with the Lasso or other regular selection tool and create your new adjustment layer with the selection active, Photoshop will automatically turn that selection into the corresponding layer mask. You can also add them to image layers themselves by clicking on the small white circle (new layer mask) icon at the bottom of the layers panel with the target layer already selected. Layer groups can also have masks added in a similar fashion. Regardless of how you create your layer mask, you can modify it by painting on it with black, white or shades of gray. Make sure the mask itself is selected before you paint though or else you may end up painting directly on your image. If you do mess up your image by accident, just use the History panel to undo it. So long as you are actually painting on the mask, your changes aren't directly altering your image pixels, so you can tweak your mask endlessly with no loss until you get it right. And all the while the effect your mask has can be seen in the main image window. As I say, this was truly a revolution in making selections.
Masks also represent a revolution in how selections get feathered. I've already mentioned that you can freely paint on the mask layer to control the degree to which any point is selected or not based on how close to white or black it. But you can also use many other tools to affect the mask as well. The most obvious way to feather a mask is use one of the blur tools. But you don't have to blur the entire mask equally. Since a mask is just another kind of layer, you can use the trusty Lasso or any other regular selection tool on your mask itself to limit the area affected, just as you would an image layer. No, you can't make a mask on top of a mask, but you can use regular selection tools and masks together freely.
Back in Photoshop CS4 the revolution in feathering took a second big step forward with the introduction of the Masks Panel. In the past, even though masks allowed you to change the appearance of your image without altering actual image pixels, changes to masks were not themselves non-destructive. That is, changes to feather a mask (for example) actually changed pixels in the mask layer. Sure, you could paint over the mask to effectively undo any change you didn't like, but not all changes were easy to undo. If you paint on a mask with white, you can switch colors and paint back over that area with black, but if you apply a Gaussian blur to a mask, it really isn't possible to re-sharpen it later. You would have to drastically paint over your existing mask, or even delete that mask and create a new one. As of CS4, the Masks Panel lets you apply a blur to a mask that is non-destructive. Slide the Feather slider one way and the mask appears blurred. Slide it back the other way and its back to being sharp again. Now how cool is that?
So, should you always create a mask and feather everything with the slider in the Masks Panel. Well, probably not. Some changes you will never want to undo making them (in some cases) safe to do with regular selection tools. Selections you do make with masks sometimes lend themselves more to freehand painting with low-opacity brush so you can progressively paint in just the right amount of masking in each area. Even of these though it can be helpful to apply a bit of Masks Panel feathering to when you are done to avoid any brush stokes causing visible edges in the final image. I guess my point is that there are a range of both selection and feathering techniques available. Too often I see Photoshop users develop the habit of doing particular things the same way each time, without stopping to consider whether that way is the best for a given situation.
As I said at the outset, Photoshop has many ways to do most things. Just because you know one way doesn't mean you have no need to learn new ways when Adobe introduces them. Nor does it mean that when a new way of doing something comes along you should immediately abandon all old ways of doing that as being obsolete or necessarily inferior. If a quick selection is all you need, go for it. But if you really need more control take advantage of everything Adobe has put in the product. That's what it's there for.