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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."
Okay, so welcome to the second exercise in the masking a woman with blond hair who happens to be holding a match that's on the fire again. It's a red background project. In this exercise we are going to take the mask, this base alpha channel that we created in the previous exercise and I am still working on that same image Woman with flame.jpg. So you will only have this alpha channel if you created it along with me. We are going take this alpha channel and we are going to make two iterations of it using the Levels command. One of the iterations will enhance the contrast for all of the edges except this area right here. This low contrast are right there and then the second iteration will take care of this region. So here how it's going to work.
I want you to go ahead and grab this alpha channel here and make a duplicate of it. And for now we will just leave its name the way it is. We will rename and after we get down and apply the modification and we are going to change this alpha channel by pressing Ctrl+L or Command+L on the Mac to bring up the Levels dialog box. And I want to increase the blacks just a little bit. I will take the black point up to 20 and then I am going to reduce the white point to 235. So I am taking it down to luminous Levels as well and then I am going to the darken the gamma significantly here by dragging it over to right until I get a gamma value of 0.60. It is one I am looking for.
So we are enhancing the contrast of the image and darkening it slightly as well, and that works very nicely for a most of the edges, as I say all of the edges except for this region right there. Go ahead and click OK and let's go ahead and name this alpha channel after the modifications we just made so would be 20/0.6/235 and I will know that a Levels adjustment, because it involves three input values right there. Next let's go ahead and create a another duplicate of that R+B, Add, -70 channel. Go ahead and drag it down on to the little new page icon here at the bottom of the Channels palette. And we are going to bring up the Levels command again by pressing Ctrl+L, Command+L on the Mac. I am going to take that white point value down to exactly the same point it was before 235, but this time we are going to make a radical modification to the black point. Let's take it up all the way to 160 here. Check that out.
We are making the shadows very, very dark indeed and then I need to brighten the hair just a little bit. So I am going to take that gamma value this time up to 1.3 and let's just go ahead and make it exactly 1.3 like so and then click OK to accept that modification. And again let's go ahead and name this new channel 160/1.3/235 with slashes in between and again we will know that it is a Levels adjustment. Now the next step that lies in way for us is to combine this area of this channel with the area outside with the remaining area of this channel right here and we are going to do that using calculations once again and we are going to take advantage of a little masking function that resides inside the calculations dialog box. Join me for that in the next exercise.
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