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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."
If you were with me in the previous exercise, you may recall that we created a kind of high pass sandwich in order to sharpen the details inside of this archival photograph, so called, because we have a High pass layer right there with two adjustment layers more or less sandwiched inside of it, and these adjustment layers ensure that we have a high amount of sharpening going on, and then we've got this desat layer right there that ensures, that we're not introducing any aberrant color art effecting. If you weren't with me in the previous exercise, I don't know why in the world you would choose to join me now, but just in case, then you can catch right up by opening this image called High Pass sandwich.psd, that's found inside the 12 Specialty folder.
Now I want you to go ahead and click on the High pass layer here inside of the Layers palette. The idea is, now we need to go ahead and mask the effects of the High pass layer using our Edge Mask that we created a couple of exercises ago. Now you may or may not have created that edge mask for yourself, even if you didn't, I have got it ready for you. Here it is, in fact, right here. It's this image, it's called Edge mask. tif and it's a grayscale image that you can go ahead and open on up, or you can work from your own edge mask if you prefer. But it's identical, it's exactly the same edge mask that we created a couple of exercises ago. You can see all of its oowie goowie goodness here, all these sort of ghostly figures that are haunting us in a good way, of course.
So now let's switch back to High pass sandwich, we've gone ahead and scrolled to a different portion of the image, but that's all right, actually, might as well look at these people, just for the sake of variety here. So as I say, make sure that the High pass layer is selected inside of the Layers palette, you want these bottom four layers to be turned on, the top two layers should be turned off. I want you to go up to the Select menu and choose Load Selection, you may recall from several chapters ago now that you can load a selection, you can load an alpha channel, from a different open image as long as the two images are exactly the same size, the same number of pixels wide, the same number of pixels tall as is the case with these two images, of course. So go ahead and choose Load Selection.
You will see the Load Selection dialog box, and I want you to change the document from High pass sandwich to Edge mask.tif, assuming of course that the Edge mask.tif image is open for you. Then we will be loading from the channel called gray, because that's out only channel, we don't have any alpha channels going on. We'll just go ahead and load the selection from that gray channel, Invert should be turned off, New Selection should be turned on, click OK, and we've gone ahead and loaded that edge mask as a selection. Now if you've been working along with me, and you're going, well, I don't want to work from that particular mask, I want to work from my own, then go the Channels palette, you should see your edge mask alpha sitting right there, go ahead and Ctrl+Click on its thumbnail or Command+Click on its thumbnail on the Mac in order to load the selection outline, same def, you get exactly the same effect.
All right, now let's go back to the Layers palette, again, make sure that the High pass layer is active. Then go down to the Add a layer mask icon, and click on it, that little circle on the rectangle icon, and that will convert the selection to a layer mask, as we're seeing right there. We are now sharpening exclusively the edges inside of the image. This is the difference. I'll go ahead and Shift+Click, let's go ahead and zoom in actually on a detail inside this image. I'm going to go ahead and zoom in on my uncle's face once again, because these are good bellwether face inside of this image. I'll go ahead and Shift+Click on the mask, so this is before and this is after.
So you can see how we are now sharpening fewer bad edges inside of the image. So exclusively concentrating on the good edges, the good detail inside of this archival photograph, and just to give you a sense of how much better it looks, than anything else we can create inside of Photoshop. Let's go ahead and compare it to these USM layers right up there. So this is the good sharpened edge mask, sharpened version of the image. Let's compare it by turning on USM 200/ 3/0. This is the standard Unsharp Mask Application, so I just went in and applied Unsharp Mask using an amount of 200%, a radius value of 3, and a threshold of 0, you may recall this from a few exercises ago. It looks okay, in terms of its overall color distribution, but we've got a lot of color wandering as you can see going on here. We have sharpened a lot of bad edges inside of the photograph.
So this is the Unsharp Mask version of the image, this is our version of the image, which is actually much sharper, much heavier edges going on, except that we are eliminating the bad edges. Now we do have a few bad edges. There is this little sort of pockmark inside of my uncle's nose, some weird details down here on the right side of his mouth. That would be the left side of his mouth, if you were still with us, which of course he isn't. But by and large, we've avoided those bad edges inside of the photograph. Let's also compare this by the way to the USM 350/3/25, so that is an amount value of 350%, which is more in keeping with what we have right here, a radius value of 3, of course, we've got a radius value of 3 throughout, all of these examples, and a threshold value of 25, meaning that we're sharpening fewer edges. This is what we got with the Unsharp Mask filter. Now you can see really truly how hideous that solution is.
I've got to be honest with you now, I just hate that threshold function inside the Unsharp Mask dialog box. I think it just delivers absolute an utter garbage as you can see right here, just terrible, terrible stuff, compared with the results of our lovely, wonderful Edge Mask. So Edge Mask, of course, the solution of champions here inside of Photoshop. In the next and final exercise of this chapter, we will see just how amazingly flexible the solution that we've created is.
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