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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 my friends, it has come time to selectively improve the contrast of the individual details of those fine hairs inside of our mask. We are going to be doing this, rather than using the Brush tool set to the overlay mode, we need more control, so we are going to use tools that provide us with more control, namely the Dodge and Burn tools, which permit us to enhance contrast, while at the same time, preserving the natural focus transitions; which we have done such a glorious job of maintaining, so far.
I am working inside of an image that's called Images applied.tif. So called because we use the Apply Image function to bring in some strange details, actually, but they are going to help us from the Blue and Green channels of the document. This image is, of course, found inside the 14_Calculations folder. Now I am going to go ahead and zoom in on this image. By the way, I am working on the ninth channel, the one that's called Curves modification. Let's go ahead and duplicate it. Why don't we? We will call this one Dodge and burn because that's what it's going to be, baby. The Dodge and Burn tools are these guys right here, in case you are not familiar with them. They go by the general name, toning tools, which is why they have a keyboard shortcut of O.
However, if you have loaded my Deke keys way back in the preface, then you have got specialized keyboard shortcuts. You have got O, that allows you to switch back and forth between the Dodge and Burn tool, and then you got N assigned to the Sponge tool, which is very useful where masking is concerned. You are not going to need the Sponge tool for masking because that either adds or deplete saturation in a full color image, but you are going to need to swap back and forth between the Dodge and Burn tools, when you are performing the technique I am about to share with you. So you are going to want to remember that you can switch between them just by pressing the O key.
So just in the same way that you can paint in highlights and shadows using the Brush tool set to the overlay mode, by switching back and forth between white and black by pressing the X key; you are going to be able to do the same thing now with these tools by pressing the O key, as you will see; just, as I say, with more control and here is how that works. Go ahead and grab the Dodge tool and it probably won't be that big, originally, but we do want a fairly large soft brush. By default, notice that it's Range is set to Midtones, which is great, if you are working inside of a full color continuous tone image and you just want to brighten some of the details; and you want to, typically, brighten the mid-tones; but when you are masking, when you are doing what we are about do here, you want to affect just the highlights, you just want to brighten the lightest details inside of the image.
So go ahead and choose Highlights and wouldn't you know, there is a keyboard shortcut for all of these Range options right here. That Shift+Alt+H for Highlights, Shift+Alt+M for Midtones, and Shift+Alt+S for Shadows; that would be Shift+Option+H, and Shift+Option+M, and Shift+Option+S on the Macintosh side of things. All right, so we want Shift+Alt+H or Shift+Option+H for Highlights and then notice that I can go ahead and paint inside of the highlights in order to raise those highlights, in order to elevate them; but before I do that, I probably want to paint back in the shadows first.
So let's go ahead and undo that modification. Let's press the O key to switch over to the Burn tool right here, which allows us to darken details. I am going to change its Range, for some reason it's set to Highlights; by default, it should be set to Midtones, but we are going to switch it to Shadows by pressing Shift+Alt+S or Shift+Option+S on the Mac. I want you to see the difference here. I am going to actually switch over to the Brush tool for a moment. Let's go to the Brush tool, change its mode to Overlay by pressing Shift+Alt+O or Shift+Option+O. Notice if I start painting-oops, I am painting with white, let's go ahead and press the X key, so I am painting with black. If I paint in black, notice that I am getting rid of those shadows very nicely but if I paint over the hair, I am just decimating that hair, right? Okay, so let's undo that modification. What you would probably do in that case is you would take the Opacity down by pressing the 5 key and then you would paint. Notice that we are still darkening the highlights quite a bit. Even though we are darkening the shadows to a lesser extent, I am still painting away that hair, which is something I don't want to do. That's why we are switching over to the Dodge and Burn tools because they are more subtle tools.
Now you frequently will hear folks say that Dodge behaves a lot like using the Brush tool set to overlay and white; that's the foreground color. Whereas, Burn behaves like the Brush tool set to overlay and black. That's kind of true, meaning it's not really true. It verges on being true but the Dodge and Burn tools are more sophisticated than all that. So let's go ahead and switch to the Burn tool and let me show you what I mean. Now paint and notice that I am doing a stronger job of painting in the shadows and I am doing less of a job of painting away that hair. Even if I scrub back and forth over it, it's still there; it's still there to a larger extent than it was a moment ago, when we were using the Brush tool. All right, so I am going to undo that because I really need to paint even more subtly than that.
So I am going to press the 3 key to take my Exposure down to 30%, as we can see there, and then I am just going to paint on one side of the hair. I am going to reduce the size of my brush and paint on the other side of the hair. Then come back over here as well and you can see that we are able to preserve that hair much better than we were---- much more reliably than we were with the Brush tool set to the overlay mode. So again, if you want to up your game, this is the way to go. Now I am going to press the O key to switch back to the Dodge tool here and its Range is set to Highlights, that's good. I am going to reduce the size of my brush and then I will paint down the hair. Notice that I am brightening the hair, isn't that nice? All right, so you now have a sense of how you use the Dodge and Burn tools to enhance, selectively enhance the contrast of the mask. Dodge set to Highlights; Burn set to Shadows and, of course, modify the Exposure value to your heart's content. In the next exercise, we are actually going to do the deed. We are going to use the Dodge and Burn tools to fix the hairs inside of this channel.
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