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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."
The thing I want you to groove on here is that this is an incredibly flexible versatile sharpening solution. We can change the degree of sharpening now that we've applied it our heart's content after the fact, totally amazing. So if you're just joining me, and I know it's incredibly popular that suddenly join me in the final exercise of the chapter, but if by some stroke of chance you are just joining me right now, you can catch right up with the rest of us who have been around for a while, by opening this image called Sharp as tacks.psd, found inside the 12 Specialty folder.
It features our High pass layer right there set to the Overlay mode. It's got an edge mask applied as a layer mask, and then we've got a couple of sandwiched adjustment layers, a Levels adjustment layer that defines the amount of sharpening. Then we've got a Hue/Saturation layer that robs the High pass layer of saturation so that we're not introducing any aberrant colors. All right, now let's imagine that I want to change exactly which details are getting sharpened and which aren't. So I want to air on the side of less sharpening. So then I'm ignoring more edges inside of the image, or I want to air on the side of more sharpening, so that I'm sharpening more edges inside of the image.
Well, I could change the degree of contrast assigned to that edge mask. So go ahead and click on the layer mask thumbnail that's associated with a High pass layer right there. Go ahead and click on it to make it active. I'm going to now Shift+Tab those palettes away, so that I have a little more room on screen. I'm going to go ahead and zoom in on my uncle's face here, because he is the bellwether face where this image is concerned. Now I'm going to press Ctrl+L, or Command+L on the Mac to bring up the Levels dialog box. Now if I want to rule out more edges inside of the image, then I would bring up the black point. Notice as I do, I'm changing the edge mask, remember that, so I'm not actually changing the amount of brightness associated with the pixels inside of the image, rather I'm changing the darkness of the edge mask.
By darkening up the edge mask, which is what I'm doing, I'm ruling out more and more sharpened edges. So the higher I go, the fewer edges are getting sharpened inside of the photograph. This is of course a radical example right here. I'll go ahead and take this value down to something like let's say I decide to take it to 70, and then if I want to bolster more edges inside of the photograph, then I would make the edge mask lighter. In this case, notice that I'm adding more and more edges to the image as I do this. I'll go ahead and take this value down to something like let's say, 190 in this case. So we're adding a few more edges into the picture, and then I'll click OK, and just to give you a sense of what kind of difference it's made, let's go and zoom in my uncle's face littler farther there. This is before that modification and this is after.
So it's a subtle modification, because we did adjust both of the black and white points, but we have magnified the degree of sharpening to a slight extent. Now then, let's say we want to back off the sharpening effect overall. So we're not trying to rule out more of the non edges or add in more non edges. We're trying to just like say, temper the sharpening effect a little bit. Then we would bring back up the Layers dialog box, and I would change the opacity value. So in my case, I'm going to press the 7 key to reduce the opacity value down to 70%, for example. You can see how the sharpening dropped down ever so slightly right there. Just to give you a sense of how far we've come here, I'm going to go ahead and tab away my palettes, and switch to the overall Full Screen mode, maybe zoom out a click, so that we can see a couple of faces here.
This is the original unsharpened version of the archival photograph that we opened several exercises ago now, and this is the sharpened version of the photograph in which we sharpened just the good edges using a combination of a High pass layer, a few sandwiched adjustment layers, and an edge mask, here inside of Photoshop.
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