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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."
In this exercise, I'm going to show you a technique that I picked up from the highly esteemed, Scott Kelby, who wrote this really awesome book called "The Photoshop Channels Book" from Peachpit; definitely check it out, if you get a chance. It's a fast read, you can pick up a lot of techniques very quickly. This is one of them and basically what I'm going to show you is Scott's method for using the green channel of an image in order to boost the overall contrast of the image. I'm actually going to show you two flavors of this technique, one is Scott's way of approaching this process, and then I'm going to show you my spin on the technique. I like to think that I've improved upon it. I think that I could improve upon a Scott Kelby technique, its blasphemy, but in fact, my approach is better, as you'll see, for a variety of reasons.
They're both great techniques. So if you walk away with either one of them, you're going to walk away a smarter, more powerful Photoshop user. Here I am looking at this image that's called MICMC.jpg, that's found inside of the 13_channel_mix folder. MICMC, of course, stands for My Irises Contain Many Colors. If you zoom in on this image and check out her irises, they're like little marbles, they're both blue, and brown, and green, and all the colors that eyes can be. Isn't that amazing? Hence, the name of the file.
Now this image comes to us from photographer, Lise Gagne, one of my favorites over iStockPhoto.com, one of everybody's favorites I think, actually. She has purposely shot an image that's a little bit washed out, a little bit of a high key image but let's say, that's not what I want, even though it's actually a beautiful composition. Let's say that I want to increase the contrast, bolster some of the darker colors inside of the image, some of the quarter tones, and so on. I can do that as follows. Here is the way Scott spells things out, all right? So we're starting with a flat image, then you go Ctrl+Alt+J or Command+Option+J in order to create a new layer, to copy the image to a new layer, and we'll just call this Green, and press Enter; and because it's going to be the green channel in just a moment--- Now we're going to convert it to the green channel by going over here to the Image menu and we're going to choose this command right there, Apply Image. Now I don't use this command all that often, it's something of a dinosaur inside of Photoshop. It used to be, back in the old days, that Apply Image and Calculations were your only way to merge images and channels together.
Nowadays, we have layers, of course, which limits their utility but still every once in while, they prove to be helpful in calculations for masking, as we'll see in a future chapter, can be widely helpful at times. Anyway, I'm going to go to the Apply Image command and it's basically set up to go ahead and replace the contents of the current layer with a different channel; or you can merge a channel with a composite image, if you want to, using a blend mode and so on. I'm just going to go ahead and change Channel to Green, so that we're lifting the green channel, and I'm going to change the Mode to Normal. So that's all we have, right? It is the green channel and nothing else now inside of this layer. Then I'll click OK.
Next, I'm going to go ahead and change the blend mode, assigned to this layer here, to Luminosity. We're not doing like multiply or something along those lines, we're just doing straight luminosity, this time. You can see what a difference it makes. Here's without that layer and here's the image with that layer. That's the effect of turning that Green layer off and then back on. So you can see that it does bolster the contrast inside of the image, just a little bit. So if you just need that extra little bit of contrast, that's a way to go.
Now you might wonder, how in the world would I improve on that? I mean, that was a really simple technique. I mean, what comes to mind is maybe being a better approach is a straight copy-paste, so that you don't have to fool around with Apply Image, which is, kind of, a bizarre command. Well, let me just very quickly show you why copy paste doesn't work. I'm going to go ahead and turn off the Green channel for a moment. Let's go back to the Background image, let's go over to the Channels palette, we'll switch to the Green channel, as that's the channel we want, right? Ctrl+A or Command+A on the Mac in order to select the whole thing, Ctrl+C or Command+C on the Mac in order to copy it. Let's go back to the RBG image, I'm going to de-select the image by pressing Ctrl+D or Command+D on the Mac. Let's go to the Layers palette and press Ctrl+V or Command+V on the Mac in order to paste the image into place.
Once again, it's the Green channel, right? Actually, we'll call it Green paste just so that we know that it's a little different there. I'll go ahead and change it to Luminosity and there it is, right? But doesn't look the same, does it? Let me turn that off for a moment and then turn it back on. It actually robbed the image of contrast. It made it even more of a high key image whereas that Green channel, that we created with the Apply Image command is darker. Now why in the world is that? They're both the Green channel, they're both versions of the Green channel. Well, the thing is, when you grab the Green channel using the Apply Image command, you are getting a color managed version of that channel. So Photoshop is putting it through the color management process, which is the proper thing to do.
When you just paste it, it's not managed. So it ends up being lighter in our case. All right, so obviously Scott's technique is much better than a straight copy and paste. You don't want to do a copy and paste, I'm going to go ahead and throw that guy away. So what in the world do I think could be better than this? I mean, so straightforward, so easy, so effective. Well, my technique is better, you're going to see and I would like to show you in the next exercise.
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