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Another way to make a selection is to use information that's already in the image in the form of a color channel. When you are working with an image like this, that has fine detail in the foliage or hair you can sometimes get a good selection using the Refine Edge or Refine Mask dialog boxes, as I have shown how to do in other movies. But even with those improvements to the selection and masking technology in Photoshop CS5, the channel technique that I am going to show you here can sometimes get you the best, and fastest selection.
Here, for example, I'd like to select the sky from in between all of the detail of the foliage, so that I can replace that area with a less bland sky that I have on the layer below. To do that, I am going to go to the Channels panel, and I am going to click on each one of the Red, Green, and Blue channels, one at a time, to view it here in the document window. Notice that each of these is a grayscale channel, and as I go through these, I am looking for the channel that has the most contrast.
In this case, it's the Blue channel. So I am going to make a copy of the Blue channel by dragging it down to the Add new channel button at the bottom of the Channels panel. With the Blue copy layer selected, I am going to try to increase the contrast between the foliage and the sky even further by adding a direct adjustment from the Image > Adjustments > Levels menu. In the Levels dialog box, I am going to pull the white Input slider over to the left, and as I do, notice that I am pushing the highlights to white, but I don't want to go too far, or I will lose all this detail in here.
So I will back off, and then I will work with the Black slider. I will pull that to the right, and as I do that, I am making the darker parts of the photo even darker. I can also work with the Gray slider, trying to drag that one to the left, and then maybe the White slider a bit more, but I don't want to go too far there, and then I will click OK. Now what I am trying to do is to make the sky white and the foliage black. To make the foliage black, I will use the Lasso tool, and I will come in, and I will make a selection just around the edge of the foliage here to include all of this area, and I am just going to fill that selection with black on the Blue copy channel.
I'll go to the Edit menu, I'll choose Fill, and I will use Black, and click OK. Then I will deselect by pressing Command+D on the Mac or Ctrl+D on the PC. I can select the Brush tool, and with my foreground color set to black, I can come in and paint over any little white dots that may be left here. But I want to be careful not to go over the edge. The next thing I am going to do, in order to protect the edges as I paint, I am going to go up to the Mode menu and set the blend mode for the Brush tool to Overlay.
When I paint at the edges with the tool set to Overlay, it won't replace either pure black or pure white. I see that there are still some areas here that are gray. To try to force those to white, I am going to get the Lasso tool and make a rough selection just around that area. And in that area, I am going to run the levels adjustment again on the Blue copy layer. Going to the Image menu, choosing Adjustments and Levels and try dragging the White slider over to the left, and I am able to push that area to the White without affecting the detail in the other areas of the photo.
I'll try dragging the Black slider to the right, increasing the contrast there. Then I will click OK, and I will deselect. Now I am going to load this high-contrast channel as a selection. To do that, I'll hold the Command key on the Mac or the Ctrl key on the PC and click on the thumbnail on the Blue copy channel. Now I'll go back to the Layers panel, and I will use that selection to add a layer mask to the aspens layer. With the aspens layer selected, I will go down to the bottom of the Layers panel and click the Add layer mask icon here.
I will invert that layer mask by making sure it's selected and then pressing Command+I on the Mac or Ctrl+I on the PC. I am going to make the sky layer temporarily invisible by clicking its Eye icon so that you can see the results of making that selection based on the highest contrast channel, and then converting that selection into a layer mask to hide the sky on the aspen layer. And I think that's done a pretty good job. I will make the underlying sky layer visible again.
So, often, you don't have to look any further than the color channels in the image to find the basis for a selection.
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