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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."
Now that we have run a series of calculations on this image from Chris Schmidt and you may recall, in the previous exercises we experimented with the Add blend mode. We created an Alpha Channel with the Subtract Blend mode and then we used the Difference Blend mode to compare the two Alpha Channels to each other. We are going to work from the best of the bunch which happens to be the Subtract mode variation, now what edges out the Add mode variation by a nose. It's just slightly better, but I want you to work with this channel Subtract 90, 1.4 because I want you and I to get the same results as we work along here.
Now we are going to develop this channel into a full fledged mask by enhancing the contrast and doing the overlay painting and all that good stuff but we have got to up our game because we need more control this time around, because we are trying to match the focus of the original image. So instead of enhancing the contrast using the Levels command, we are going to use the Curves command, which gives us more control. Then we are in the exercise after this one, we are going to reestablish the details up here in the hair regions over the top of the image using the Apply image command. So we'll see a new use for that command. And then in the exercise after that I am going to show you an alternative to using the Paintbrush combined with the Overlay mode, instead we are going to use the Dodge and Burn tools which once again, give us more control.
All right, so if you are working along with me, you can open this image if you want to. It's called Vive la difference.tif. And it's found inside the 14_Calculations folder. Obviously, if you are still working along successfully inside the Super hero hair document, then stick with it. I love it when you make your own progress of course because you are learning that much more. All right, so let's grab that Subtract Channel in the Channels palette, let's make a duplicate of it. And the reason is that way we can always come back to subtract if we need to. Now we are not going to need to inside of this project, but I want you to get in the habit of making good choices. And really it is a good idea to duplicate a channel from one operation to the next and it doesn't really add that much to the file size. We went just now a moment ago before we created that new channel. The size of the file which we can see down here in the lower left corner of the image was 19.2MB after the slash so it shows us all the extra stuff inside of the image.
After we add that channel, after we duplicate it, we stepped up the size of the image to 21.7MB so that's 2.5MB bigger which is fairly small in the grand scheme of things. I mean we only added 10% to the file size which makes sense because this is our 9th channel. So we probably added a 9th of the file size again. All right, now let's go ahead and call this new channel, Curves modification or something along those lines. Then I want you to bring up the Curves command, you can do that by going up to the Image menu, choosing Adjustments and choosing Curves or you can just press Ctrl+M, Command+M on the Mac. But before I do that actually I am going to switch to the Full Screen mode so I have a little more room to work and I am going to tab away my palette, move this guy over here, so I can see him. And now press Ctrl+M or Command+M on the Mac to bring up the Curves dialog box.
Now normally you are going to be working in the Point Edit mode which means that this tool right here is selected. And what happens when you work in this mode is you can drag your sliders over like so, these sliders are new to Photoshop CS3 by the way. This command got a face lift inside of Photoshop CS3 and actually it makes a big difference in terms of how useful it is. We now have a histogram for example which is a great thing. You can drag this white slider over; you can add point and notice as you add points that Photoshop automatically determines the curvature for you. So that's one way to work. I am going to suggest with this image that we work with the Pencil tool so that we can gain a little, additional control. And when you are working with the Pencil tool, go ahead and select it here.
Notice when you are working with the Pencil tool, that you can draw any sort of curve you want to just by scribbling around inside of the dialog box. And when you do this -- by the way, you can't kind of go back and forth with erasing what you did before because it has to be continuous in a diagonal direction here. So you can do these loopty loops if you want to. Notice as you do you are saying that, you sometimes want the luminance levels to go lighter and sometimes darker, and then lighter and darker again. And if you really spike it, you are going to get some pretty trippy looking results in the preview area, notice that.
So you'll get all of these weird edges going on, almost as if you had applied the Difference Blend mode which is why these kinds of graphs are called arbitrary maps often times because you are applying arbitrary luminance modifications to your image. Now these sorts of radical arbitrary maps can sometimes be useful believe it or not when masking extremely complex images. And I am going to be showing you that in a later chapter when we take a look at masking the tough stuff, that is complex foreground images set against complex backgrounds.
But for now what I am going to have you do, let's go ahead and press the Alt key or the Option key on the Mac and click on the Reset button, in order to reinstate our straight line there. And I want you to do the following. I want you to go ahead and draw along the bottom of the graph, draw a horizontal line along the bottom of the graph and keep your Pencil down toward the bottom here, so that you don't make some little bumps like so. And I want you to drag all the way over until reading those output and input values. I want you to drag over until the output value is zero. That's just telling you that you are staying straight along the bottom of the graph, and input which you can see directly below my pencil or cursor. I can't move it down to point it out because then you wouldn't see it anymore. Input should say 30.
All right, so I want you to drag to that location. Then see it down there, see it disappears as soon as I move towards it. Then I want you to move your cursor up toward the top of the screen like so, until the output value is 255, and the input value is 100, and you can see them down in the lower left corner of the screen still. Then I want you to Shift+Click like so. And because you Shift+Click you just drew a straight line between those two click points. Now you can either drag along the top of the graph like so, or you can move your cursor all the way to the top right corner, so that output and input say 255 and you can Shift+Click again in order to create a straight line there. So you want a straight line at the bottom, all the way to an input level of 30.
Then you want to move your cursor up, so you've got output 255 and input 100. You want to Shift+Click there and then you want to move your cursor over to here, 255, 255 and Shift+Click again. And you'll get this graph that you see before you right now. Now notice, and I want to zoom in by the way. I want to zoom in on my hairs, if I press the Spacebar in order to scroll or if I press Ctrl+Spacebar, I am of course going to activate the active button here on the Window's side of thing. This isn't a problem on the Mac, I hate this feature. I think I have griped about it before. It's a real old school DOS thing. And it just fatigues me that it still exist. I wish there was some way that Adobe could overwrite it. There possible is, they just haven't done it, but anyway.
What you have to do is you have to click on something else that's not a button. For example I am going to click over here in the Presets and just establish Custom that doesn't make any change but it makes sure that Custom is active there. Now I can press the Spacebar in order to get the Hand tool. And I want you to do that, if you are working along with me, go ahead and Spacebar+Drag the image over if you want, then Ctrl+Spacebar, click a couple of times that would be a Command+Spacebar click on the Mac, in order to zoom in on these fragile little hairs right here. We want to make sure that we keep those hairs, but right now we might have something of an abrupt transition between our lightest whites here and our darkest Blacks down here. So I would like to soften these corners a little bit and you can soften your corners using this guy right here the Smooth button.
Now you can't enter a smooth value. You can't determine the degree of smoothing that you apply, instead you get a little bit of smoothing every time you click the Smooth button. So I want you to click once and you'll see that you smooth things off a little bit up here at the top and the bottom, and then click Smooth a second time in order to Smooth them a little more. Now every time you click Smooth, you create a Smoother graph, if you want to sharpen it on up again you have to redraw it. So be careful with your Smooth button clicking, just twice in this case. We're now done, we have these nice, fragile hairs still in place here and we are mimicking the natural focus variation inside of the image. So we are doing a great job, is basically what I am saying.
Now go ahead and click the OK button in order to accept that modification. Now zoom out in order to check what you have right here. This is the before version of the image, a little low contrast version. Or at least the original contrast version thanks to the Subtract mode and this is the higher contrast version thanks to the Curves command. In the next exercise we are going to reinstate these hairs that we have lost up here at the top of the image using the Apply Image command.
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