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In Photoshop CS5: Selections in Depth, author Jan Kabili offers a comprehensive tour of Photoshop CS5's selection features. Selection options are the key to performing creative imaging tasks, such as isolating photo adjustments and making image composites. This course covers selection basics as well as the nuances of selections, including selecting hair, refining masks, saving and recalling selections, working in Quick Mask mode, and creating selections based on image properties, such as luminosity and color channels. Exercise files are included with the course.
When you're making a selection to use in a composite with other images, or to place against another background, you're going to want to be sure that the selection edge blends well with the other images. There are a couple of ways to accomplish that. One is to use anti-aliasing, an option that's enabled by default in Photoshop's selection tools and Methods. Another way to blend the edge of a selection with other images or backgrounds is called feathering. Anti-aliasing and feathering are very different features and give you different effects.
In this movie, I'm going to compare a feathered edge to an anti-aliased edge and to an edge that has neither, an aliased edge, so that you can see the difference and make better informed choices about which features to apply to your own selection edges. I'm going to use the Magnetic Lasso tool to make selections in this movie, but keep in mind that what I'm going to show you here isn't special for the Magnetic Lasso tool; it applies to all the selection methods. By the way, if you're following along with the exercise file for this movie, and you don't feel like making selections along with me, you can take a shortcut and load all of the selections I'm about to make by going to the Select menu, going down to Load Selection and choosing from the Channel menu, saved and clicking OK.
I'm going to cancel out of here, so that I can make the selections as you watch me. The first selection I'm going to make is an anti-aliased selection. Anti-aliasing is a method for partially selecting pixels along the edge of a selection border, and this makes a curved selection edge looks smooth and helps to blend the edge in with other images. With the Magnetic Lasso selected in the toolbox, I'll go up to the Options bar for this tool. Notice that, by default, Anti-alias is checked here, and I'm going to leave that checked.
And then I'm going to come into the image, and I'm going to make a selection around this pinto fur hat by clicking at one corner and then releasing my finger from the mouse, and just floating the mouse along the edge, allowing the Magnetic Lasso tool to lay down anchor points and lines in between those points. When I get back to the beginning, I'll click on the first anchor point to close the selection. By the way, if you want to know more about using the Magnetic Lasso tool, there is an entire movie devoted to this tool in the chapter on Drawing Selection Tools.
Now, notice that you can't tell from the marching ants whether this is an anti-alias selection or not. If you hang on just a minute, I'll show you how you can see the anti-aliasing at the edge of this selection. But before I show you that, for point of comparison, I want to make a selection without anti-aliasing, around this hat in the middle. So I'll go up to the Options bar, I'll uncheck Anti-alias - and this is important - I want to go over to the left side of the Options bar and click the Add to selection icon.
Then I'll move into the image, I'll click at a corner point on the black hat in the middle, and I'll release my finger from the mouse as I float around the edge of this black hat. And when I get back to the beginning anchor point, I'll click to close this selection. And you can't tell whether this selection is anti-aliased or not either. Now I'll make one more selection. I'll make a feathered selection around the white hat. There are several ways to feather a selection.
I think the best way is to first make a selection and then to open the Refine Edge dialog box and use the Feather slider there to feather a selection you've already made. So, for example, if I wanted to see how these two selections would look when feathered, I can just drag the Feather slider to the right. However, because I'm creating three different kinds of selections in this example, I can't use the Feather slider. This slider would apply the feather to all of the selections in this image. So, I'm going to cancel out the Refine Edge dialog box, and instead, I'm going to go up to the Feather option in the Options bar for the Magnetic Lasso tool.
And here, I'll just type in some number of pixels by which to feather this edge. The problem with doing it this way is it's just a blind guess, but I'm going to take a guess, and I'll type in 10 pixels. I'm also going to leave Anti-alias unchecked, although I could feather an aliased edge or an anti-aliased edge; it doesn't really matter. Now I'll move into to the image, and with the Magnetic Lasso, I'll click to add one anchor point, I will remove my finger from the mouse, and I float around the edge of the white hat. I'll click at this edge, and then I'll click at the first anchor point to close the selection.
Now that I have these three selection borders, I'm going to expand them a little bit, so that later you'll be able to get a really clear view of each border. To expand a selection border, I can go up to the Select menu, down to Modify and choose Expand. It's really a guess as to how much to expand the selection borders. I'm going to expand them by 5 pixels and click OK. Now it's finally time to view the difference between the three borders: the feathered border around the white hat, the aliased border around the black hat, and the anti-aliased border around the pinto fur hat.
You may remember that I told you in other movies in this course that another way to view a marching ant selection is as a mask in an alpha channel, and that's where we need to go in order to see the difference between these three borders. So I'm going to go to the Channels panel, I'll move to this icon at the bottom of the Channels panel, and I'll click there to save this selection as an alpha channel. And then I'm going to deselect by pressing Command+D on the Mac or Ctrl+D on the PC. And to view my selection as a grayscale mask in this alpha channel, I'll click on the blank area of the alpha channel.
Here, at 100% view, you can see that the anti-aliased edge looks smooth, even where the edge is curved. The aliased edge looks stair-stepped or jagged, and the feathered edge also looks smooth, but it looks different than the anti-aliased edge. Let's zoom in to see more closely what's happening here. The aliased selection border is following the square edges of the pixels in the image. On either side of the border, there are either completely selected pixels or completely non-selected pixels, and so the edge of this selection looks jagged.
There are very few times when you're going to want to use a jagged edge like this. One example might be, if you were creating a very small icon for a web site. But in most cases, you want your selection borders to be smooth. As I explained earlier in this movie, one way to do that is to use anti-aliasing, as I've done over here on the border that I made around the hat on the right. I'm going to zoom in even closer, so you can see that this anti-aliased edge is made up of pixels of varying shades of gray.
And this anti-aliasing is also useful for blending this edge in with other images on layers behind. Now I'll move over to show you the feathered edge in this close-up view. And as you can see, it looks very different than the anti-aliased or aliased edges. Here, there are gray pixels along the edge, but these are created with a different method: by blurring the selection on either side of the selection border. I'll go back to 100% view by double-clicking the Zoom tool.
Now, let's see how these different selection edges look when put to use. I'll bring back my marching ant selection by holding the Command key on the Mac or the Ctrl key on the PC as I click right on the thumbnail on the Alpha 1 Channel. And then I'll go back to the regular image view by going up to the RGB channel in the Channels panel and clicking on a blank area of the RGB channel. I'll move back to the Layers panel by clicking the Layers tab. Here, I could use my selection edges for any purpose for which I'd normally use a selection.
I could fill the selections with color, stroke them, delete them, copy them, and so on. I'm going to use the selection borders to delete some of the content of the hats layer, so that we can see down through to the purple background below. With the hats layer selected, I'm going to press the Delete key on a Mac, or the Backspace key on a PC, and then I'll deselect. Notice that I now have a smooth edge where I deleted using the anti-aliased selection border, I have a jagged edge along the area that I deleted using the aliased selection border, and I have a very soft edge where I had feathered my selection border.
So as you can see, both feathering and anti-aliasing can be really useful when you're preparing a selection to combine with another background or with other images. Now that you know how these features compare, you can make more informed choices about how to use them in your own selections.
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