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7.1. Tips for Using SelectionsOf course, a big part of targeting specific areas of the image for adjustment is knowing how to most effectively and credibly isolate that portion of the image. It's important that the isolated portion blend smoothly with the rest of the image so that your adjustments look natural in all respects. It's also important to make sure that the adjustment is accomplished in a nondestructive way. NOTE
I assume you have some knowledge of Photoshop and the basic selection tools such as the Marquee, Magic Wand, and Lasso tools. 7.1.1. Checking Alpha ChannelsAny time you spend more than 10 minutes making a selection, it's a good idea to save that selection so that you can recall it if you decide to make more changes to that same image (choose SelectSave Selection). The saved selection takes the form of an alpha (transparency) channel, which will be bundled with the file only if the Alpha Channels checkbox in the Save As dialog is checked. The downside of saving each selection is that it increases the file size by approximately one-third from the original RGB file. So you dont want to save alpha channels if you won't be using them again for a final version of a file or for a file that has to be optimized for the Web. So it's a good idea if, before you save the final version of a file, you open the Channels palette and take a look at the alpha channels. If you won't need them in the future, drag them out of the palette and into the trash at the bottom of the palette. 7.1.2. Making Accurate Selections Easier with Brightness/ContrastYou can use the ImageAdjustmentsBrightness/Contrast... control to make your selections easier. Duplicate the layer you're selecting, boost the contrast so that the Magnetic Lasso can see the edge clearly, and make the selection. Then you can save the selection as a mask (alpha channel) and throw away the duplicate "contrasty" layer. Sometimes you'll have to select an object whose edges are a lot less contrasty along different segments of the profile you want to trace. In that case:
NOTE
To easily duplicate a layer, select the layer you want to duplicate in the layers palette, press Cmd/Ctrl-A to select the whole layer, and then press Cmd/Ctrl-J to lift it to a new layer. 7.1.3. Making a Mask from the ImageThere will be times when you want to use the image itself as a mask, especially if its edges are really complex. There are a couple of ways you can do this:
7.1.3.1. Making a selection from a black-and-white imageIf you're going to make a mask from a photo, you will want to photograph the subject against a background that contrasts with it as much as possible. This is one of the best techniques for flying hair or skylines full of trees and trellises. The image in Figure 7-3 is a pretty good example. Figure 7-3. The selection as it looks after tracing one adjusted layer and then selecting another. Once you've made a mask from a black and white image using the Threshold adjustment, you might want to use it to darken or equalize the sky. You could also use it for isolating a color effect or for compositing in a sky from another day or location. You could also use the same technique for a fashion shot or head shot that is crying for a new or inaccessible background. (For those specific techniques, see Chapter 9.) What we're going to do here is nondestructively create a mask from the photo, then add interest to the sky using an adjustment layer made from that mask. Here's the procedure for making a mask from a black and white image using the Threshold adjustment to pick a hairline or a skyline.
You can now do anything you like to the sky without affecting the rest of the image at all. One of the most useful things you can do with the mask (if you're going to use it for a targeted adjustment layer) is to load the selection (you may want to name its channel something like Skyline Mask), then choose the adjustment you want to make from the Adjustment Layers menu in the layers palette. I chose the Hue/Saturation adjustment layer. I used the sliders to darken the sky, increase saturation, and change the Hue of the sky. The result is shown in Figure 7-6. Figure 7-6. The result of using the Hue/Saturation adjustment layer on the masked sky. Another useful trick in a situation like this is to simply darken the sky. You can raise the selected sky to a new layer and then put the new layer in Multiply Blend Mode. You can keep darkening the sky by duplicating the Multiply layer multiple times. 7.1.3.2. Making a selection from a knockoutIn a sense, a knockout (something extracted from the rest of the image) is a selection. That is because knockouts always rest on their own layers and everything else on that layer is transparent. So anything you do to the knockout will be separate and distinct from the rest of the image. Still, there are reasons you may want to knock out a portion of the image just to use it as a selection:
It's pretty easy to make a mask from a knockout. The trick is to make the best possible knockout (see the "Homemade Backgrounds" section in Chapter 10). The only difference here is our purpose in making the knockout. Once it's been made, you have an objectoften with very complex edgesfloating on a transparent layer. Figure 7-7 shows a knockout of a thistle on the lefthand side. The right of the same figure shows a mask made from that knockout. Figure 7-7. A knockout (left) and the mask made from it (right). To make the mask from the knockout:
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