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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."
In this exercise we are going to use a displacement map. We are going to actually prepare a displacement map and employ it as well to wrap the stone along the contours of this guy's flesh. Now I am working inside of an image, if you are just joining me, I am working inside of an image called, Your mother was right.psd found inside of the 18_Displace Maps folder because his mother was right. His face is gradually turning to stone. The only problem is it's not wrapping around his face properly, so let's make a displacement map.
Now I can't just load him as the displacement map, we went through that whole sad affair with the moon image and we saw how the red and the green channels are not necessarily going to reconcile properly in order to do the right amount of wrapping. So we need to prepare our own customed displacement map and we are going to do that in this exercise and we are going to try it out and see how well it works. All right so go to the Background layer, turn off the Stone layer for now and let's check out the channels. Let's see what we have to work with, Ctrl+1 or Command+1 for the Red Channel, overly bright in my opinion, fairly alarming as well. Bear in mind, if we have a very, very bright displacement map, we are going to be moving pixels up into the right and we don't necessarily want to do that. We want to wrap them all over the place; we want an even distribution of luminance levels inside of the channel.
Ctrl or Command+2 for the Green Channel, looks pretty good actually. This might work out. And then Ctrl or Command+3 for the Blue Channel, this is my favorite of the channels. It has the most contrast going on; inside of it we have some nice light regions in the face. We have some nice shadow regions as well. I am just telling you this now to implant this in your head, I am going to want to eventually to wrap the stone down into the shadows and up into the highlights, which is typical behavior for a displacement map. But I am also going to want the highlights to move the stone pixels to the right, and the shadows to move to the left. And so we are going to have to reverse the default behavior where the horizontal axis is concerned. So I am just telling you that now, we will see it happen in just a few moments.
So this is the good channel, let's go over to the Channels palette and I want you to drag that Blue Channel onto that little page icon but before you release your mouse button, I want you to press and hold the Alt key on the PC or the Option key on the Mac. So drag down there, press and hold Alt or Option and release and you will display the Duplicate Channel dialog box which allows us to put the channel into a separate image. So I am going to go ahead and choose from document, I am going to choose New. Then we will go ahead and call this new document, JCE Blue. And click OK in order to display a new image window here on screen. And notice I will go ahead and zoom in a little so that we can see it up close and personal because he is such a beautiful guy.
Notice here in the Channels palette that we have a new channel called Alpha 1; in other words, it's a multi channel image that contains a single alpha channel. It's a little more versatile the image will be more versatile if we go ahead and convert it to Gray Scale. So let's go up to the Image menu, choose Mode and choose Gray Scale. Gray scale images are more widely compatible, it's not going to affect the behavior of the Displace filter but it might affect other things we do with the image in the future. So just a good idea, and it doesn't change the image at all so go ahead and choose gray scale. We now have a Gray Channel; this is an official gray scale image.
Go to the File menu, choose the Save As command and we will want to save this image into the 18_Displace Maps folder JCE Blue.psd. Make sure that you are saving the format as the native Photoshop format. Click Save and we are done. All right, now leave the image up on screen because we are going to come back to it in the next exercise but for now we are going to leave it. I am going to go back to this image right here, Your mother was right.psd, and lets return to the RGB composite image, lets go the Layers palette here. Turn on the Stone layer and click on it to make it active and now let's try applying that displacement map that we just created.
I want you to go up to the Filter menu, choose Distort and choose Displace. And we are going to go with the Horizontal and Vertical Scale value of 12. So 12 for both of those values there, the only difference is because I want white to go to the right and black to go to the left where the horizontal axis is concerned I have to reverse the horizontal scale behavior. So I am going to change that value to -12, so Horizontal Scale -12, Vertical Scale 12. Stretch to fit and repeat edge pixels, we do not care about. Go ahead and click OK and we will now have to locate that JCE Blue.psd file that you created, I didn't create it for you, you created it and then click Open in order to apply that distortion.
Now lets go ahead and zoom in, and you can see it's done a heck of a job of distorting the stone. This is before and this is after, a couple of problems however, one problem is let's zoom in closer on the eye, you can see that we distorted some stuff into his eye, we got some stone in his eye. That must be awfully scratchy, and well he definitely deserves that. I don't want that to occur. What's happening here, lets go over to the Layer mask by Alt+Clicking on it or Option+Clicking on it on the Mac and you can see that we have managed to distort the Layer mask. This is before, this is after. So a heck of a distortion applied to the layer mask, we don't want that. So we will take care of that in a moment, I will just go ahead and undo that modification.
I will go ahead and click on that Stone Layer thumbnail in order to make the RGB image active once again. All right, so this is the other thing that's wrong, I will Redo by pressing Ctrl+Z, I will redo the displacement. You can see how we have an awful lot of those ripped pixels going on; that we saw with the moon reflection and you can see them here in front of the nose wrapped around the nostril right there. You can see a bunch of pixels bring ripped along his lip, that's very obvious there, a few other areas where it's happening as well. But generally, check it out, this is before and this is after, it is doing a good job of wrapping the stone around the flesh. We just need to take care of a few of these issues. So one of the issues, is very easy to take care of. I will go ahead and undo that modification; you turn off the link between the stone and the layer mask. If you turn that link off then a layer mask will no longer be affected by the filter and this is true for just about all filters by the way. If you have the link turned on, you are going to filter both the layer and its layer mask together. If you turn the link off, you are going to filter just whichever item is selected, either layer mask or layer contents.
Now in our case of course we want to change the layer contents, so let's try it out again. Go ahead and click on the stone thumbnail and press Ctrl+F, Command+F on the Mac and you can see at least we haven't got a bunch of junk in his eye. And if I was to Alt+click or Option+click on the layer mask thumbnail here so that we can see the layer mask by itself. This is before; this is after, no difference whatsoever. I will click on this Stone thumbnail once again to return to the RGB composite image. This is better of course than it was when we were getting stone in the guys eyes but its not acceptable, its not as good as it could be so go ahead and press Ctrl+Z or Command+Z on the Mac to restore the non-distorted, the un-distorted, if you will, stone. We are going to perform some modifications that will keep that ripping from occurring in the very next exercise.
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