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In this exercise I am going to introduce you to the basic selection calculations that are available to you inside Photoshop. Now I don't want to scare you with the term calculations, there is no math involved here. These are merely ways to add to existing selection outlines, subtract from them and so forth. And they are ultimately ways of combining selections so that you can create more complex ones. Now notice up here in the options bar we have four icons right at the outset when you're using any one of the selection tools that we've seen so far. The first icon is the one that's selected by default, it says New selection.
So any time you drag or click with a tool you're going to create a new Selection Outline. Next we've got one that allows you to add to an existing selection, or you can subtract from that existing selection and finally you can find the intersection of two selections and I'll show you what that looks like in just a moment. But in the meantime, let me tell you that you're much better off learning a few keyboard shortcuts, so that you don't have to go up to the options bar over and over again, and let me show you what those are. I'll go up to the Window menu and choose the layer Comps command and that brings up the layer Comps panel.
Notice that I've created a few layer comps in advance. I am going to go ahead and click this Right Pointing Arrowhead at the bottom of the panel to switch to the PC keys, so I've separated the PC and Mac shortcuts from each other. Assuming that you have a base selection outline going, then if you press the Shift key while using any of the selection tools you'll add to that outline. If you press the Alt key while using a tool you'll subtract and if you press Shift and Alt together you'll find the intersection. On the Mac the only difference is you substitute the Option key for the Alt key. So you press Shift to add, you press the Option key to subtract and you press both Shift and Option at the same time to find that intersection.
All right, I am going to go ahead and switch back to my base image comp and close the Comps panel. The best way to get a sense of how these calculations work is to use the Elliptical Marquee tool. So I'll go ahead and switch to it here in the toolbox, and then I'm going to create a base selection like so around the iris here and I'm just trying to generally select the iris, I am not terribly interested in getting it exactly right, this looks pretty good. Now notice that my cursor appears as a little cross. If I go ahead and drag outside the selected area then I'll create a new Selection Outline, like so.
That's not what I want, so I'll go ahead and press Ctrl+Z or Command+Z on the Mac to undo that modification. Now if I press and hold the Shift key, notice that I get a little plus sign next to my cursor, and also notice that Photoshop goes ahead and automatically selects the second icon up here in the options bar. Now I'll drag with the Shift key down and you can see that I end up adding to the Selection Outline. So I have this kind of double-blob outline. We'll go ahead and press Ctrl+Z or Command+Z on the Mac to undo that. Let's say what I want instead is a kind of crescent shape.
Then I'd press the Alt key or the Option key on the Mac, I get a little minus sign next to my cursor and you can see that the third icon becomes selected. Once again automatically up here in the options bar, now if I drag. And I can press the spacebar at the same time, by the way, so I have both the Alt key and the spacebar down. That would be Option and spacebar in the Mac and then after I release I go ahead and subtract the new selection from the old one. All right, once again I am going to press Ctrl+Z, Command+Z on the Mac. Let me show you now how intersecting works.
Let's say I want to keep just that portion of the iris that appears inside of the eye. So I want to get rid of that little bit of eyelid at top. Then I'll press both the Shift and Alt keys, these would be the Shift and Option keys on the Mac. I see a little X next to my cursor and Photoshop goes ahead and automatically selects that fourth icon. Now I'll draw a big selection like so, so I still have those keys down, I am adding the spacebar in order to drag. So I've got three fingers down at the same time here. Now I'll go ahead and release the spacebar and resize that Marquee a little bit.
Notice I've got a big Marquee around the smaller one. As soon as I release I keep just that portion of the iris Marquee that occurred inside the larger eye Marquee and as a result I go ahead and clip-away that eyelid. So those are your basic three selection calculations. They become even more powerful when you start combining selections created by different tools and I'll show you how that works in the next exercise.
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