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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 gang, we have created, we have successfully created an edge mask inside of Photoshop. Here is what's left. In this exercise, we are going to sharpen the image using a better sharpening technique. We are going to use the High Pass filter combined with a couple of adjustment layers as you will see. Then in the next exercise we will bring the Edge Mask into play so that we sharpen just the good edges inside of the image, and then in the third exercise in this little group of three here also happens to be the final exercise of this chapter, we will see just how flexible this combination of edge masking and high pass filtering is, how we can go ahead and modify that sharpening to our heart's content, way after the fact, really good stuff coming at you.
Whether or not you have been working with me really doesn't matter. In fact, I am going to go ahead and be so cavalier as to just go ahead and throw away this edge mask that I created for you in the previous exercise because I have gone ahead and saved it off as a separate image. We will all be able to get access to it regardless of -- as I said, whether you have been working with me or not. Go ahead and open this image, it's called Plains dwellers.psd and make sure inside the Layers palette that the background layer is selected and active, and then it's the only visible layer in the stack here; the other two layers are turned off as you can see.
Let's set about sharpening this image the good way not using Unsharp Mask but rather using the High Pass filter instead which is -- as I say, going to be a more flexible solution and the High Pass filtering technique I mentioned this a few exercises ago, doesn't really lend itself to smart filtering inside of Photoshop, so what we are going to do is we are going to press Ctrl+Alt+J or Command+Option+J on the Mac in order to jump that background layer to a new layer. And I am going to go ahead and call this layer High Pass because that's what it's going to be after all, and I will click OK in order to generate that new layer.
Now I am going to go up to the Filter menu and I am going to choose Other, and I am going to choose the High Pass command or if we loaded Deke Keys, you could go ahead and press Shift+F10 in order to bring up this dialog box. And I am going to apply a Radius of 3 pixels because that's the Radius value that we have been using consistently here. You may recall that both of my bad unsharp mask examples employed radius values of 3 pixels and that does happened to be a good radius value where this image is concerned. So enter 3 for the Radius and click OK.
Obviously, it's not going to look very good at all, so we are going to go ahead and blend it in with the original image by changing the blend mode from Normal to Overlay here inside the Layers palette. And now things of course look a heck of lot better as is or once when we were working with a High Pass layer inside of Photoshop. I am going to go ahead and press the Escape key in order to deactivate the Overlay blend mode under Windows and I am going to go ahead and zoom in actually on a portion of the image, this area right here. And we will see that we are not really actually bringing out too much in the way of the pockmarks inside of the image, this is without that High Pass layer and this is with the High Pass layer.
So not a heck of a lot of difference where all of this art effecting is concerned, but that's because it's a very subtle effect so far, is it not? I mean, when you apply High Pass and Overlay together, you really don't get that much sharpening. It's not until you heap on the Levels command that the sharpening really starts to occur. Now I could go ahead and apply the Levels command directly to the High Pass layer, but what I want to do instead is I want to apply Levels as an adjustment layer so that I could go back and modify my Levels settings later if I want to.
And so here's what I am going to do. I am going to press-and-hold the Alt key or the Option key on the Mac then go down to this black/white icon, I want you to do this as well if you are working along with me, and choose Levels from the adjustment layer list here because you have the Alt or Option key down which you can now release by the way, you get the new layer dialog box, I want you to just go ahead and rename this layer amount because it's going to serve as our amount value, you may recall that applying Levels to the High Pass layer is just like increasing the amount value inside one of the sharpening dialog boxes.
This is very important, go ahead and turn on the Use Previous Layer to Create Clipping Mask check box, very important, you do that so that we are affecting just the High Pass layer independently of the other layers. Now click OK, and let's go ahead and take the first Input Levels value, the black point value up to 100 and then let's go ahead and subtract 100 from the white point value. So we will take that one down to 155. I am making symmetrical adjustment so that we don't overly-darken the image or overly-lighten the image, this way by making symmetrical adjustments we keep the brightness value, the overall brightness value uniform, and then I will go ahead and click OK in order to apply the change.
Now notice that we went ahead and modified the High Pass layer on its own. If we hadn't grouped the layers together, if we hadn't clipped this adjustment layer inside of High Pass so if I go ahead and Option or Alt+Click on this line right there, you can see, this is the effect we would have gotten if I hadn't selected that check box. All right, I will go ahead and undo that modification because indeed we do want to clip Amount inside of High Pass. It's looking very good at this point I think, may be we are doing a little bit of over-sharpening, but you can't see the difference, this is with Amount off, this is with Amount on. So we are increasing the amount of sharpness inside of the image, but we are also -- I am going to go ahead and zoom in here, we are also bringing out some color art effecting, are we not? If you look closely at my uncle's cheek, I am zoomed in on my youngest uncle actually; he is no longer with us, but this was my youngest uncle here. You can see that we have got some pink going on this region and then with some greenish details going on over here and so on and that's because we are exaggerating the color discrepancies that were there in the first place. But if we want to get rid of those color discrepancies, then we need to get rid of any weird colors that are going on inside the High Pass layer.
To do that, I want you to go to the High Pass layer, go ahead and click on it, press Ctrl+D or Command+D on the Mac to make sure nothing is selected, in my case, I was making selections to show you what's going on. So click on that layer to make it active, then I want you to Alt or Option+Click on this black/white icon and choose the Hue/ Saturation command. That will bring up the new layer dialog box, I am going to go ahead and change the name of this layer to desat because we are going to desaturate the layer in just a moment. Notice Use Previous Layer to Create Clipping Mask is turned on by default and that's because this new layer is going to be sandwiched between High Pass and the clipped amount layer right there. So Photoshop assumes you want to go ahead and clip this one as well, which of course we do. So go ahead and click OK, so leave that check box on in another words, then take the Saturation value down to -100%, leave Hue and Lightness alone, just take Saturation down to -100 here inside the Hue/Saturation dialog box, and notice that we get rid of all that pink and green detail that we were seeing before. So we wipe out any weird color artifact that we were introducing via the High Pass layer there.
Now at this point, go ahead and click OK in order to accept that modification. All right, let's go ahead and zoom out a little bit here folks in order to see the sharpened version of the image. So this is without the layer, this is the original version of the background layer, if I turn off the High Pass layer, and this is the sharpened version. Thanks to High Pass Sharpening, thanks to the effect of the High Pass layer combined with of course in Overlay blend mode and a desat and Amount adjustment layers. In the next exercise, we do have a problem here and that we are sharpening all the bad edges along with the good edges, so in the next exercise, we will introduce our Edge Mask into the image.
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