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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, it is time for the second project in this chapter. This time around we are going to mask the woman you see before you on screen. This image is called Woman with flame.jpg. It is found inside of the 16 Tough Stuff folder and it comes to us from Photographer, Andre Barack (ph) of iStockPhoto. And this image presents us with three challenges, count them, three here. And the first challenge is that we have a warm subject against the warm background and we have a very warm subject indeed. Though she has actually sort of pink skin tones with these reddish shadows, some red eye make up on, she has got red straps on her shoulders, she has got pink lips, she has got, kind of, this yellowish platinum hair and the only part of her that is the least bit cool is her irises but that is not going to help us out in this case, because she is set against this screaming red background. So we don't have the complementary colors to work with that we have in the case of examples from previous chapters. So that is challenge number one.
Challenge number two is that she has blonde hair, and as I mentioned she is, kind of, a platinum blonde and we saw in previous examples how when you are working with dark haired people especially if their hair is very dark. You can multiply their hair into a new background. So your might expect with a light-haired person you could go ahead and screen the hair but that does not work because it gives you something of a glowing effect. It is very unnatural. It is kind of a fiery effect. And speaking of fire you may have noticed this flame right here, and that is challenge number three and we are going to mask that flame and posited it against a different background and it's going to look absolutely amazing. I guarantee it.
So those are our three challenges that lie in wait for us. I should say just by a way of little FYI here. That I feature this exact same image inside of a masking example in my book Photoshop CS3 One on One and for those of you who have seen that example and even worked through it. I want you to know that we are not going to be doing exactly the same thing. We are going to be compositing this Woman against a different background for a one thing. Also in a book, I do some of the steps for you so I have some stuff prepared for you in advance. In this example, I have nothing prepared for you in advance. So are going to do all the work yourself and then finally we are going to take advantage of the few different techniques as we move through this image; so familiar image, different stuff in lying in wait for you.
All right, so let's start things of by creating the base alpha channel, shall we. And, of course, in order to do that we need to take a look at the channels that we already have inside of this image. So Ctrl+1 for red; a very, very bright channel here, that's Command+1 on the Mac. Ctrl+2 or Command+2 for the Green channel; Lots of contrast going on, very nice channel. And Ctrl+3 or Command+3 for the Blue channel less contrast than the Green channel and if you take a look here. We have some very good shoulder detail inside of this channel but we are loosing some of the hair; some of the finer threads of hair have gone away inside of this channel. And the flame is extremely weak.
Let's go back to the Red channel for a moment. Here you can see the flame is very, very strong inside of this channel and we have these tiny little hairs all over the place inside this channel, very nice. Also good shoulder detail, a lot of banding in the background that's a bad thing and, of course, a very bright background especially in this region on the left side of the head that's going to be difficult to mask, all right. Let's go to the Green channel for a moment. It is really good. I mean we have some nice little hair is going on, not quite as much as in the red channel. The flame is a little weaker but it is still very evident. Nice shoulder detail, you'll have some problems with the dress dropping off there. So we are going to have to work on that and we also have a low level of contrast going on, on the left side of the head. So, again, it's going to take some work to get this area right.
All right, so here is what we are going to do. We are going to establish a base alpha channel by blending the Red and Green channels together with the Calculations command. In fact we are going to add them together as you will see. So I am going to click off the selection to deselect it. Let's just go ahead and reinstate the RGB composite image by pressing Ctrl+~ or Command+~ on the Mac. And I am going to press the F key to enter the full-screen mode so that I can move over a little so I have room for the Calculations dialog box. Now let's go to the Image menu and choose the Calculations command. And I will go ahead and move the dialog box down a little bit. Source one and Source two should both be set to Woman with flame.jpg. Layers, both of the layer options should be set to background. The first channel should be set to Red, the second channel should be set to Green. Both of the Invert check boxes are turned off, my friends; and let's go ahead and change the blend mode from screen which is pretty good actually to add, which will work better for our purposes.
And then that is too hot, as you can see the highlights are way too hot, we need to darken up the image a little by taking the offset value down to -70. Now if I felt like the shoulders were too harsh, the transitions and the shoulders were too harsh then I could go ahead and increase the scale value in order to soften that information but I actually like this quite a bit. And I think this is going to work out very nicely for us. So, let's go ahead and click OK in order to create the new alpha channel and let's move the image over here so that we can bring back the palettes. I am going to switch over to the Channels palette.
Let's rename that new alpha channel. R+G and we will also say -70 right there and that will tell us that we have- 70 offset value. I should enter the Add mode as well. So we have R+B, add -70. And, of course, the only thing that can be -70 is the offset values. So that is a great name; it will remind me of exactly how I got this channel in the first place. That is our base alpha channel. We are going to modify it to make it work better. We are going to create two iterations of this channel using the Levels Command starting in the next exercise.
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