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The elusive alpha channel remains one of the most misunderstood yet powerful tools in Photoshop. Alpha channels are collections of luminance data that control the transparency of an image, and they inform just about every aspect of Photoshop. As he builds transitional blended layers, fashions a depth map, makes edge adjustments, and takes on extreme channel mixing, Omni Award-winning expert Deke McClelland teaches Photoshop users that where there's a will, there's a way. Photoshop CS3 Channels and Masks: Advanced Techniques covers mapping texture on an image, turning flesh into stone, using vector masks, working with all different channels, creating a rustic edge effect, and much more. Exercise files accompany the tutorials.
Download Deke's customized keyboard layouts for Channels and Masks from the Exercise Files tab."
If you have been working along with me, you may recall this image. This is the image that we used to explore the world of everyday channel masking a few chapters back. And it features this model captured by photographer Lise Gagne set against a couple of images from another photographer who goes by the handle Kataev, at iStockphoto.com, and it's this background that I want to explore in this exercise. I am going to go ahead and switch images here. This is the image that I want you to open. It's called Grass & sky.psd, and it's found inside the 11_Layer_Masks folder. I am going to bring up the Layers palette, and you can see that it's actually a combination of two layers working together. Both of these images do come to us from the same artist, from Kataev.
I am going to go ahead and turn off the sky layer here, so that we can see the background layer by itself, and you can see that it features this beautiful synthetic grass set against the fairly plain gradient blue background. I wanted to jazz things up by adding some clouds, so I did so, and these are the clouds, of course, masked by a layer mask to avoid overlapping the grass. Now we are going to build that layer mask inside of this very exercise, and we are going to base the layer mask off of the existing channels inside of the background image. So go ahead and turn off all of these layers.
Actually for now you can go ahead and throw away the sky layer if you want to, because we are going to be rebuilding it. So you should just have background and clouds, with the clouds turned off. Go ahead and make sure the background layer is active. Then go to the channels palette, and we will check out the composition of each of these three channels. Here is the Red channel. So pretty low contrast. Here is the Green channel, better, and here is the Blue channel, best of all, very obviously the highest contrast channel. All right, so let's just go ahead and load that channel as a selection outline. As oppose to building an independent alpha channel, let's do all of our work inside of a layer mask, which is just as acceptable by the way.
So go ahead and Ctrl+Click or Command+ Click on that Blue channel here, in order to load it as a selection outline. Then go back to the RGB image. We will switch over to the Layers palette, click on the clouds layer to make it active, and then turn it on. And you can see that the clouds largely overlaps the grass down here, and it overlaps the grass all the way across the image, so that we have plenty of room to work. Now I am going to go ahead and apply that channel information, this selection here as a layer mask. So just go ahead and click on the layer mask icon down here at the bottom of the layers palette, and just like that you've applied the Blue channel as a layer mask to this clouds image.
Now I want you to Alt+Click on that layer mask, because it's not dark enough. It doesn't have enough contrast. Notice if we go back to the sky image, you can see a bunch of sky overlapping the grass still. Even though we can't see the grass now showing through the sky, we've got kind of a combination of grass and sky going on that doesn't look at all acceptable, I would say. So once again, Alt+Click or Option+ Click on that layer mask to make it active there inside of the clouds layer, and let's increase the contrast by pressing Ctrl+L, or Command+L on the Mac, which brings up the Levels dialog box, and I am going to take the black point over to the right, fairly significantly up to about 90, let's say.
Then I am going to take the white point down to the left to about there, to about 150. That provides us with a high degree of contrast, but still leaves a little bit of softness along these edges. Now there are some clean up work we are going to have to do down here. But generally speaking we've done just about everything actually at this point. Go ahead and click OK after you have 90 for the black point, 150 for the white point. We are not concerned about the gamma. Click OK. And now at this point we need to do a little clean up work. I suggest the easiest way to do that. I am going to tab away my palettes. The easiest way to do this cleanup work, is to just Alt+Click with the Lasso tool here. You could also try overlay painting with the Brush tool if you wanted to, but then we are going to end up darkening up these edges.
And the edges, the way they exit right now, the grass edges that is to say are great, actually. Let's auto scroll over a little bit, grab these things, and notice I am going up and down pretty often here. I just want to make sure that we get anything that might be part of the foreground grass, and there's a lot of highlights going on inside this grass. So we need to get pretty close to the blades up at the top of the image. Now I auto scroll back over. Notice that I am moving my mouse across the far bottom of the image across the scrollbar down here. And I am even like Alt+Clicking inside this percentage value right there. That's perfectly acceptable, just make sure you drag finally around the side of the image to get the whole thing, and then release Alt or Option in order to select that entire area. Black is my background color, so I can just press the Backspace key, or the Delete key on the Mac in order to fill that selection with black. It's really all that is to it.
Now let's bring back the palettes, and I am going to Alt+Click on the layer mask in order to show the clouds layer again. You can see that it blends just amazingly well with the grass. We have a little bit of edge stuff going on, but you know what? I don't actually want to work with the sky set to the normal mode. I want to try applying one of the contrast modes instead. So I am going to click on the sky thumbnail to make it active there, and then I am going to try out my keyboard shortcuts. I am going to press Shift+Alt+O for the Overlay mode. That looks pretty good.
Then I am going to press Shift++ that would Shift+Option+O on the Mac of course. Then I am going to press Shift ++ to advance the Soft Light, that's all right. Shift++ again for Hard Light. That's my guy right there, looks perfect in my opinion. So I am going to tab away my palettes so that we can take in the entire image, fill the screen, and I am going to go ahead and scroll it down a little as well. That's the final version of that background composition. Thanks to a very quick and easy application of layer masking inside Photoshop.
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