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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 this exercise we're going to try to create a mask using a single Arbitrary Map and then in the next exercise, we'll take a more realistic approach that involves several applications of Arbitrary Maps. I want to let you know, we're not necessarily going to follow every single one of these masking techniques to its ultimate conclusion because that would get a little tedious to select this bird over-and-over again. We will make Arbitrary Maps work, but the other is not necessarily so, and we're not going to be taking this bird and compositing it against a different background because we've already done that ad-nauseam by now. We're just going to be focusing on masking techniques for the rest of this chapter.
Now then, you may notice that I am working inside of an image called Military macaw.jpg, that's found inside the 16 Tough Stuff folder. And now before we go any farther, I just want to remind you of what an Arbitrary Map is. It's basically a wacky curve that you apply from the Curves dialog box. I am going to press Ctrl+M or Command+M on the Mac. For the moment I am going to go ahead and switch to the Point tool which is selected by default. And an Arbitrary Map is an arbitrary redistribution of brightness values of luminance levels inside of an image, and you can see that if you apply an Arbitrary Map like the one we have here to a full color image, you are going to get something of a psychedelic effect like we're seeing on screen right now. So it's far from a color correction. In fact I would go, so far as to say these are absolutely the incorrect colors for this macaw.
But, if we were to use this kind of arbitrary map in order to formulate a mask, then we could set the colors that appear inside of the bird to white and the colors that appear outside the bird to black thereby constructing a mask. Now you can use the Point tool for this purpose if you want to, but the better tool to use to create Arbitrary Maps is this guy right here which is the Pencil tool. So that's the tool we'll be using. Anyway, go ahead and cancel out of this dialog box for now, because we're not going to get too far trying to modify the full color image, we need to work from a single channel. So let's check out what channels we have to work with.
Here's the Red Channel, not too promising. It's okey-dokey over here on the far right-hand side. We have some clear distinctions between the feathers which are dark and the background which is light. But this area is for beings really -- that's not going to help us out too much. This area is lukewarm, this is okay, it is tuft at the front of the bird, it is red after all against just about any background it's going to show up light. The bill is in kind of rough shape, sometimes it's lighter than the background, sometimes it's darker than the background, and then this area of the bird, not too good.
All right, so let's check out the Green Channel, this is it right here, and again the back of the bird is good. It's good in all the channels actually. The top of the bird is in pretty good shape. This area right here is not quite as good as it was inside the Red Channel because now it's darker than its background and not quite as much contrast going on. The bill is in very similar shape because the bill is fairly gray actually if you take a look at the Full Color image. And then this area down here is actually handled better -- this area right there, it's handled better in the Green Channel than it is anywhere else. But, this area down here is not too good.
All right, now let's check out the Blue Channel, and of course you remember the keyboard shortcuts for these which is Ctrl+1+2+3, red, green, blue, that's Command+1+2+3 on the Mac. This area, very good contrast, the best contrast we've seen so far. This area, pretty darn good contrast we would say. This area, great contrast, dark against light. This area, same darn build we've been seeing over-and-over again. This area is muddled, look at the banding that's going on inside of there, and actually this Blue Channel is a very noisy channel in general. So you have to be aware of that.
And then this area down here is good. It's actually pretty darn good. We have a high degree of contrast. The only problem is, who is inside the bird and who is outside, there is a little bit of confusion right around this area. But overall, I have to say that the Blue Channel is probably our best channel. It's not super-great channel because it's so noisy, there is so much posterization going on, but it's as good as it get. So we're to start from a single channel, this is the one we work with. So let's start from here. Let's go ahead and grab that Blue Channel, drag it onto the little New Page icon and I am going to go ahead and name it Mask of course because that's what it is.
Now then let's try out an Arbitrary Map. I am going to go ahead and Shift+Tab away my palettes and I am going to switch to the Full Screen mode so I can move the bird over just a little bit, so I can see all of it. I am going to press Ctrl+M or Command+M on the Mac to bring up the Curves dialog box. Now, here's what you want to do. First of all, you want to switch to the Pencil tool, that's your first step. Secondly, you want to just sort of drag around and watch the bouncing ball, see the bouncing ball down there in the lower left quadrant of the Curves dialog box, and I am watching as it moves along and obviously that lower quadrant is inside bird territory. So I am going to go ahead and take that lower quadrant and I am going to set it to white, like so, because we want everything in the bird to be white.
Now, obviously I have set too much stuff to white. So I am going to drag down here. Notice this is what you do with the Pencil tool when you're creating an Arbitrary Map for the sake of masking is you drag along the top of the graph, then you drag along the bottom of the graph. No sense in doing this kind of stuff, this isn't going to do us any good to actually draw a curve. Just go ahead and drag along the top and then drag along the bottom to create some extreme, so you can figure out who is inside and who is outside. I am going to go ahead and drag along the top from 0 to about -- well, I dragged too far. I went ahead and dragged over to about let's say, what is that, that's about 70, and then I am going to start down here at about 60 actually, it works out pretty well and then I am going to drag along the bottom. And then I am going to come up here to about 82 actually, and this is just based on experiments, I have just sort of played around inside of this bird image. Actually 83 is more what I want, and I am going to drag along the top until I come to about 128.
Now, I do need to watch my graph. Okay, I went too far, that's why because I will come down here at 128. Then you need to watch this junk, see how I am not quite along the top of the curve at this point. Go ahead and take it all the way to the top. We want these extremes of course, these extreme brightness values to work with at the beginning anyway, and then I'll show you how to smooth it out. Then I am going to go ahead and drag from an input value of 129 along the bottom, like this. And you can see that, that gets us pretty far there. It's not perfect by any stretch of the imagination, but it's about as good as that we're going to get with a single application of an arbitrary map. So again, I went from 0 to about 59 and sent that to white and then I went from about 60 over to 82 to black, and then I went from about 83 over to 128 for white, and then I went from 129 all the way over to 255 for black once again.
We're taking the darkest colors in making them white and the lightest colors in making them black with some variations in between. Now, you may not figure this is exactly the settings that you want to use, in which case go your own way. Try some different settings, drag around, watch the bouncing ball, see where it is, this is obviously stuff that should be outside the bird, and I have changed it to white. But, if I go black with it, I am going to change a lot of stuff that's inside the bird to black too. You sort of have to pick and choose your battles at this point. Anyway, I am going to go back where I was. I am going to stick with the settings I come up with here, so 83 over. Then, you want to click on the Smooth button at least once in order to create smooth transitions between these extremes, and if you feel like that's not quite enough, you can click on Smooth again. But be careful, be sure you want to smooth before you click on Smooth because you can't undo this button. So once you've clicked on it, it's done and then if you want to back up, like I go, oh, darn, that was too far. Then you've got to re-draw your darn graph. You've got to go back to 59 right here and drag over to the left and then I'd have to go down to 60. You can see how this stuff gets a little involved and if not down right ponderous, it definitely takes some time to work through a successful mask on a difficult image like this one.
That's why it's so much easier to just shoot a good photo in the first place, I have to say. I mean it's almost easy enough that you go, gosh, I think I will get in the car and go find this Macaw again and shoot a picture of it that really works for me. But if not, if you don't have the option to do it, this is the way you work. Then click Smooth once this time around so that I don't over-smooth it. And you might want to go ahead and save out a preset, and you save a preset by clicking on this little button here and choosing Save Preset and then saving a preset to disk so that you can load it up later for a different curve so that you can come back to it. And all of the presets will actually appear. Once you've saved them, they'll appear in this preset pop-up menu here and I will show you that later, actually in the next exercise. But for now I will go ahead and click OK in order to accept this modification and then of course we'd go in with the Lasso tool and the Dodge tool and the Burn tool and fix this mask and make it as good as it can be.
This was a what-if scenario, what if we could pull off a mask using a single arbitrary map? I would say, actually we're not going to be able to do it for this Macaw here. So we're better off approaching the bird with multiple arbitrary maps, and that's what we're going to do in the next exercise.
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