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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 there is one more adjustment I want to make to this composition before we hang it up and move on to the next project. If you are just joining us you can catch up with me by opening this image called Density mask.psd. It's found inside the 12_specialty folder. Notice that in addition to sharpening the really great stuff inside this image, such as the eyes and the eyebrows and the nose and the mouth and the hair and so forth. We also have sharpened the effects of the color modification that we made to this image. So you can see this edge next to her hair, for example, at least inside my composition it's really coming out nicely. I will go ahead and zoom in there a little more so that we can see that edge up close and personal. So you can see that there is almost a razor sharp edge along this hair.
Then it's something of a function of this horrible edge that I left behind inside of the layer mask. It's associated with the yellow layer and you can see that I did leave a bad edge there and sort of bad in this region as well. This is that jagged edge that was a leftover from having worked with the Lasso tool with the Anti-alias checkbox turned off, which was a good thing to do at that time, but it has left its mark here inside of the layer mask. Now that's not something I noticed before I applied this sharpen layer. So I am going to go ahead and Alt+Click on the layer mask thumbnail in order to revisit the RGB Composite view. Now you might say, well if that turns out to be a problem and notice we are sharpening the edges down here along the blouse and over here on this side, we have got a wicked sharp edge going there as well.
You might say, well if that's a problem, why don't you just go ahead and move the sharpen layer below yellow? Well, that doesn't really take care of the issue. If I do that, I will go ahead and move sharpen below yellow. You can still see that we have some sharpened edges going on and you will see those elsewhere inside the image, including these sharpen sort of noise details inside of her skin. So the better thing to do is to go ahead and knock out those areas of the sharpen layer that are causing its problems using a knockout layer, and I am going show you a new thing about the knockout layer that you can take advantage of. The difference between shallow and depth will become clear in just a moment.
So let's go ahead and pop that layer back to where it used to be. Put the sharpen layer back on top, which I did by pressing Ctrl+C or Command+C on the Mac. Now I am going to zoom out from the image until I am seeing the image at the 25% zoom ratio. Incidentally the good zoom ratios in order to judge sharpness inside of Photoshop are 25%, 50% and a 100%. Then anything bigger than a 100% is fine as well, but 33% and 66.7% and anything in between, 25, 50 and a 100 is bad, because Photoshop ends up just kind of glomming pixels together and creating jagged transitions where jagged transitions don't actually exist.
All right, go ahead and click on the sharpen layer to make it active. Press Ctrl+Shift+N or Command+Shift+N on the Mac to make a new layer. Let's go ahead and call this new layer knockout, because it will be a knockout layer. Then click OK to accept that new transparent layer. Now we are going to surround her face and much away that we surrounded that glass back in the magazine cover example using a Radial Blur. So I want you to go ahead and select the Gradient tool and I want you to switch the foreground color to something aberrant, something really vivid so that we can see it very easily.
So I am going to bring up my Color palette like so, and I am going to change the Hue value to 210, which is cobalt, and I am going to raise the Saturation and Brightness values to a 100% a piece, so that we can really see this gradient. Now I will hide the Color palette once again. Make sure that the gradient goes from foreground to transparent as I have selected right there. Then you want the Radial Gradient, of course, so go ahead and click on the Radial Gradient icon there, and a Mode of Normal is just fine, leave it set to that, we want a 100% opacity. You want Reverse turned on. So we are drawing from transparent in the center to opaque on the outside. Now I want you to drag from the center of her face down like so to about here in order to create a Radial Gradient that surrounds her face, as we are seeing right there. That's great! Now we need to use the Opacity of this layer in order to knock out the layer immediately below, but no farther, which means that we need to constrain the knockout using a layer group. So here is what I want you to do. Click on knockout, Shift+Click on sharpen, so only the sharpen layer is going to be active. So these two are working together.
You go up to the Layer palette menu and you choose New Group from Layers, with those two layers selected, and we will call this a KO group, because that's the purpose it's going to serve. Then click OK in order to make that group and I am going to twirl it open so we can see its contents by clicking on the twirly triangle there. Now I am going to double-click on the knockout layer, in order to bring up the Blending Options dialog box and check this out just so that you have a sense of what's going on. I want you to change Knockout to Deep. And you may recall, changing the Knockout setting from the previous exercise, we saw that changing the Knockout settings by itself does nothing. We have to add a 0% Fill Opacity value to the mix.
But notice now, because we have Knockout set to Deep, that we are burrowing all the way down the layer stack back to the Background layer, thereby revealing her crimson blouse once again. We don't want to do that, we only want to burrow down to the bottom of the KO group here. So instead of having Knockout set to Deep, we are going to set it to Shallow and that's going to once again reveal the contents of the yellow layer. So we are just burrowing through the sharpen layer and that's it. Now I will go ahead and click OK. So once again, Knockout, Shallow, Fill Opacity 0%, click OK, and you can now see if we zoom in on the image to -- let's go ahead and zoom into the 100% zoom ratio.
You can see that we are no longer sharpening this lower region of the image. So this is what the effect looks like without that knockout layer. Let's go ahead and zoom in even farther here so that we can really take it in. I want to take in the side of this wacky hair as well. This is what things look like now with the knockout layer. So you can see that sharpened edge very clearly. This is what things look like with the knockout layer. Now we are burrowing through the sharpening effect. So we are in effect removing the sharpness from this region of the image which is a good thing, obviously. We don't want people to know that we have been here. Here is the unsharpened edge there on the left collar. This is what it looks like with the knockout layer which is good. This is what it looked like without the knockout layer, bad.
So I am going to turn the knockout layer back on. Now you might say gosh! I would like to not only sharpen her face, which we have done here, but I am going to zoom out to 25% so that we can see things accurately. But I would also like to sharpen her hand, because it's basically about the same focal distance. So it should be sharply focussed as well. It's a nice element of the photograph. It has got some rings and some other sort articulated details that might look nice if we were to sharpen it. So I am going to go ahead and erase a whole in the knockout layer in order to reveal the sharpening using the Eraser tool.
So go ahead and grab your Eraser tool from the toolbox and then I am going to go with a really big brush. So I am going to increase the size of the brush so it's bigger than the hand. Then I am going to press Shift+ [four times in a row] so that I have a soft edge brush. I am going to have to press the Right Bracket key a couple of more times, in order to make that brush bigger. Make sure that the Opacity is set to a 100%; Flow should be a 100% too. That way we are going to burrow through with a 100% erase. So we are going to completely erase this area by clicking on it.
So just click once and you will sharpen the hand, you will resharpen the hand. If you think you want to sharpen a few other details like the fingers, then reduce the size of the brush and paint over those fingers. Then finally, I am also going to paint inside of a few details of her face here. I am going to paint over her sunglasses in order to make sure those are sharpened. I am going to paint around her face just to make sure we are getting all of her face nice and sharp. Then I am going to click on that dandy line in order to sharpen it up as well. That's the final version of the image folks. You can see all the little holes I put in the knockout layer there. They are revealing, of course, the effects of the sharpen layer. I am going to tab away my palettes. I am going to fill the screen with the image and I am going to go ahead and zoom in to the 50% zoom ratio so that we can take in the sharpen version of her face and the dandy line and her hands a throughly professionally sharpened image, thanks to the power of a High Pass layer, of a Density Mask and a Knockout group here inside Photoshop.
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