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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, we are going to take that Alpha channel that we generated using the Calculations command and we are going to turn it into a proper mask. I am working inside of a catchup document, that's called Blue screen channel.tif, which is found inside of the 14_Calculations folder, and it contains that mask, that Alpha channel that we created in the previous exercise, here it is and you will find it at the bottom of the channel palette of course. Go ahead and click on it to take a look at it. And bear in mind that we haven't done anything so far, but blend a couple of channels together. So this is the result of blending the Red channel with an inverted version of the Blue channel, subject to the Color Dodge mode, and that gives us this. And as you can see it, a ton of our work is done now.
Our background is a lot lighter than we would like to be. We would like it to ultimately be black. But the foreground image is nice and white and almost all of her hair and her head and her arms and shoulders and all that jazz is already selected for us. Now, we do have some weird looking eyes left over right. You can see, if you turn on the RGB composite at the same time as you click on the eyeball, that those areas do align with the eyes. All right, so I will go ahead and turn the RGB image off again. Lets just go ahead and select those guys, and delete them by pressing the backspace key and this assumes that the Foreground color is set to black and a Background color set to white.
Incidentally, your foreground and background colors may vary of course. All right, now I am going to deselect the image and I am going to press Ctrl+L or Command+L on the Mac in order to bring up the Levels dialog box and I am going to change the black point to about 110. Now notice I could go a lot farther with this. I could take the black point all the way up to the right side of this big hump in the histogram which would send all of the dark colors to black. But I don't want to go that far because if I do, I will ruin the hair. You can see that the hair is all getting clumped together now. So that's no good. So let's go ahead and take this value to about 110 and then let's reduce the white values slightly. I will take that white point down to 235 right there.
Leave Gamma alone. Its fine as it is and click OK. And as usual, we have done most of our contrast work using the Levels dialog box. We still have some brush work to do. So I am going to Shift+Tab away my palette so I have a little more room to work. I will grab my Brush tool. This is the same old, same old stuff we have done several times now. Switch over to the Brush tool inside the tool box. I am going to change the mode to Overlay by pressing Shift+Alt+O or Shift+Option+O on the Mac, and then I am going to increase the size of my brush. Make sure that I have a nice fuzzy brush going, so the Hardness should be set to 0%.
Now I think, I would like to go ahead and reduce field Opacity to 50% when I am painting around the hair, just so that I don't lose too much hair at a time. As you can see, this area of hair wants to go away pretty quickly. So I will go ahead and click now to send it away. And if you go too far, of course, just undo. And then I am going to paint down the left side of the head, her right of course. But what really counts since it's our left, who cares what side it is for her? We can barely tell she is a human being at this point. Let's reduce the size of the brush a little to paint away that. Just sort out just a little stray pieces of hair that are all by themselves like little dust particles, and this looks pretty good.
Now, I am going to increase the size of my brush again and increase the opacity value to a 100% by pressing the zero key and I am going to paint and click along the left side of this arm over here and it may take me several drags in order to send that background to black. And then I am going to click under this arm a few times, actually it looks like four times in all, in order to send that area to black and I will click once under this arm to send it to black. I am going to press the X key so that I have white and I am going to paint some of this fabric away. Then I might need to paint a few additional times over next to the underarm area, that little gap there in order to get rid of some more. We will come back to that in a minute. Then I will press the X key so that I am back to black and I will paint away this area right there and paint up around the head and so on.
And then finally, I am going to zoom out to click here and I am going to grab my Lasso tool. And I am just going to do a very generalized Lasso and of course, I selected the Lasso tool by pressing the L key and I will select this area that's outside of her and I will fill it with black by pressing Alt+Backspace or Option+Delete because my Foreground color is black. I am moving through this fairly quickly because we have seen this about 17 times now inside this series, by which I mean, you know 3 or 4. But we are awfully familiar with this, I think. But of course, it helps to practice your skills, right? Sure, it does.
I am going to go ahead and select this region too. I am just making sure I am sort of selecting tight to that little triangle there, so I can get as much fabric as possible, and I will press the Backspace key or the Delete key to delete that area. So it sends it to white. Select this area, Backspace it as well. So I am doing a combination of Lasso work along with Brush Overlay work in order to get the blacks there blackest and whites the whitest of course, increase the contrast throughout the mask. I am switching back to the Brush tool. I am going to click right there, in order to send that corner to black and then I will click a couple of times in this underarm area in order to make that area black as well. I might click on a few more spots inside the image But I don't want to overdo it in the hair. Don't you either. We don't want to get completely rid of that hair there.
So I will go ahead and undo that modification, in my case and your mask should look something like this, essentially. With most of the hair fairly kept in place, fairly sprayed down and then a few strands of hair allowed to go loose so that we have an organic, naturalistic feel to our final composition. All right, I am going to switch back to my default Marquee tool there. I am going to Shift+Tab my palettes back up and I am going to switch back to my RGB image . We now have an image with a good mask and we are going to put that mask in play. We are actually going to move her into a different image and we are going to see how well our Blue Screening technique has worked in the very next exercise.
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