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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."
All right gang, in the previous exercise I showed you that splendid method for just ever so slightly boosting the contrast of an image using the Green Channel, and I created that Green Channel using the Apply Image function. The Green Channel is then set to the Luminosity blend mode, and you can see this is what the image looks like without that Green Channel boosting, without that slight boost in contrast, and this is what it looks like with that green channel. This technique comes to us from Scott Kelby of course and his awesome Photoshop Channels book, really great book. But, I have got a different spin on this technique that I think is better for several reasons as you will see. I think you are going to agree, it's better as well because it is. It is better. But, I have got to say, I wouldn't have come up with it, unless I had taken a look at Scott's technique. So there it goes, knowledge builds on knowledge my friends.
So I am working inside of an image called the Kelby goes green.psd for obvious reasons because, Scott Kelby and his green channel. Here is the better variation that I am going to show you. Let's go ahead and turn off that Green layer, the layer that's called Green. Click on the Background layer in order to select it, and then I want you to press and hold the Alt key or the Option key on the Mac, click on the Black/White icon and choose Channel Mixer, all right, Channel Mixer is the better way to go in this case. I am going to call this Green because it's going to be the green channel, and then I will click OK, and I am going to turn on Monochrome which is going to give us that default to grayscale mix that Photoshop is ever so fond of. I am going to change the Red value to 0. I am going to change the Green value to 100 and I am going to change the Blue value to 0.
So we have 100% Green Channel going on. Then, I will click OK, and then I am going to set it to Luminosity blend mode, and the effect is identical this time around. So this is what the image looked like originally, this is what it looks like boosted, bolstered here with some additional contrast, thanks to the Green Channel, versus the Green Channel right here. The Green layer that we created using the Apply Image command. So the two results are identical to each other is basically what it comes down to. All right, so why in the world is my approach better? For three different reasons, it's better. Reason number one, check out the size of the image down here in the lower-left corner of the Image Window, and you can see that it says Doc, and then it says 6.69 Mb, that's the flat version of the image. With all of its layers, it's 13.4 megabytes. The reason being it's twice as big because we have an extra layer of information in there. If we didn't have that extra layer of information in there, I will just go ahead and throw it away by Alt+Clicking or Option+Clicking on the Trash Can icon there. Notice that the size of the image drops down to 6. 69 megabytes with all layers intact.
So in other words, this adjustment layer right there as it's true for all adjustment layers inside Photoshop, doesn't really take up any room. It does take up a little bit of room; it takes up a few bytes though instead of a few megabytes. So just this tiny little bit of room, meaning that it's a more efficient image, it's not going to take up a lot of room on our hard drive, and if you do this kind of thing regularly, it's going to make a big difference in terms of Photoshop's performance, and how often you need to buy more hard drives. So that's one big massive advantage. Here is another one. I am going to go ahead and undo the deletion of that Apply Image layer right there. The thing about that is it's a static layer. We have now created a layer that's filled with green and if we wanted to fill it with some other channel for some reason, we would have to go up to the Image menu, choose Apply Image, and choose a different channel to work with.
Whereas, with the Channel Mixer adjustment layer, all I have to do is just double click on the Channel Mixer and I could say you know what, I don't want the green channel, I want the blue channel. You will get a completely different effect this time or I want some kind of on the fly merging of these two channels, and I will see what that looks like. So you can change your mind and see the results immediately, thanks to using Channel Mixer. So that's a big advantage. I am going to cancel out, because I like the green channel actually for this. Here is another completely unexpected advantage. This is advantage number three to this technique, and I would have never predicted this. I don't know why it works this way. I was just fooling around, and I happened upon it. So I have no idea of what's going on.
All right. I am going to turn off this Green Channel for a moment. I am going to turn on the Green layer the one that actually contains pixels, and notice if I jump it, so I create a duplicate of it, it doesn't make any difference, does it? It looks just the same as it did before. So we could have 15 of these piled on top of each other, and we would get exactly the same effect. We would just have a larger image as a result. Compare that, I am going to throw those away now. Compare that to what happens if we duplicate the Channel Mixer adjustment layer. If I press Ctrl+J, it actually made a difference, did you see that change? I will do it again. It made even more of a difference. So every time you pile one of these on, you get more and more and more contrast, and we are not adding to the size of the image, we are adding a few bytes as I say. So we can keep these on until we are crazy whatever. In my case of course, that wouldn't take very long.
All right. I am going to add one more layer to this because I actually like the effect I have so far except for the lips, the lips are too dark. We will come back to that in a moment. But, I do want to enhance the saturation of the colors now a little bit. So I am going to Alt or Option+Click on this Black/White icon and choose the Hue/Saturation command, and I am going to call this More sat, and then I am going to click OK. I am going to raise the Saturation value to 15. So we are just going to pop it up a little bit just because we have added so much contrast. I figure a little more color saturation would help things out as well.
Now, I will click OK. Now, at this point you might think, this image is kind of getting garish. Well, we can now pull it back a little bit by masking everything that we have got going here. So here is what I recommend you do if you are working along with me. Go ahead and select all of the adjustment layers. So click on one, Shift+Click on the other one, and let's group them together and you can make a layer group just by pressing Ctrl+G or Command+G on the Mac will group all of the selected layers. Then, let's call this Booster or something along those lines because it's a collection of layers that are boosting the contrast of the image. Now, turn it off for a moment and that's the original version of the image there.
Let's go to the Background layer, and let's switch over to the Channels palette. What I want to do is, I want to take the green channel, and I want to load it as a selection. So we are going to use the Green Channel as a Luminance mask. So go ahead and Ctrl+Click or Command+Click on that green channel to load it as a selection outline. Go back to the Layers palette, click on Booster again to turn it on. I will press Ctrl+ H or Command+H on the Mac, so we hide those selection outlines there. I have got the Booster group selected, and then I am going to go down to this layer mask icon, and I am going to click on it. Notice, you can add a layer mask to an entire group of layers if you want to and check out what happens there. It goes ahead and reins in the effect.
So this is what things look like without that group of layers. THIS is what the image looks like with that group of layers. I think that looks great. This is what the effect would like if I didn't have the layer mask. I will go ahead and turn it off for a moment. Notice that she is way too dark in the lips and some of her shadows are getting quite dark and we are getting some posterization as well. This is what it looks like with the layer mask, much better. So a ton of advantages to working this route, with the Channel Mixer adjustment layer. It's your buddy, does all kinds of things, including allowing you to boost the contrast of the image using the green channel.
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