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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."
So far all the Displacement Maps that we've seen have been single channel files. For example, this guy right here this Wave GBlur.psd file that I saved out in the previous exercise, if we take a look at the Channels palette you can see that it's a single channel files so it's a Grayscale image that's it. And when you are working with a single channel Displacement Map you are using that displacement map to distort the image both horizontally and vertically according to your Scale values inside of the Displace dialog box. But what if you want to distort the image differently, horizontally and vertically. You want one displacement map to affect the horizontal axis of the image and another to affect the vertical axis of the image. Why then you need a two channel file. For example, let's take a look at this three channel file right here, it's called Wave RGB.psd.
Once again it's included inside the Dmaps sub-folder which is inside the 18_Displace_Maps Folder. And what we've got is this I suppose kind of a fairly pretty colorful red to green sort of rainbow effect here. I am not really terribly concerned about what this image looks like, it's an RGB image. I am more concerned about the individual channels. Notice we have a Red channel which is filled with a gray to white to gray to black to gray vertical gradient. And then we've got the Green channel which is filled with a gray to black to gray to white to gray, horizontal gradient. And then we've got this Blue channel which is filled with black.
And here is what's going on. If we were to apply this RGB image as a Displacement Map, then the Red channel would affect the horizontal distortion, and the Green channel would affect the vertical distortion, and the Blue channel would be ignored. So it's always the first channels is horizontal; the second channel is vertical. So in another words the Red channel is going to distort the image back and forth, and the Green channel is going to distort the image up and down. So now, we don't need that Blue channel. I can go ahead save this out. We can apply an RGB image as a Displace Map if you want to. And anything after the second channel even if there is some more Alpha Channels here, doesn't matter, those will be ignored. Or you could just go ahead and save out a multi channel image. You can grab this Blue channel and throw it in the Trash for example.
And then you just be left with two channels, and of course since this is a multi channel image by default Photoshop thinks that the first channel as being Cyan and the second channels as being Magenta we saw that way back when. But I will just go and rename these, just so I know what's going on. This doesn't affect Photoshop's behavior. But I'll just say this is the H dmap, and this guy right here is the V dmap, and then I could go ahead and save out this file. I would go up to the File menu and choose the Save As command. And then I might just go ahead and call this something like Wave 2-chan or something along those lines.psd and click on the Save button, and that's all I need to do.
Now, I'll go back to the American flag image this guy right here, and it's all distorted and might as well go ahead and revert the file to its original appearance. So I'll press the F12 key here. Now let's go up to the Filter menu, I believe the last command I applied was Displace, sure enough. So I'll just go ahead and press Ctrl+Alt+F or Command+Option+F on the Mac. Same settings 50-50 Stretch To Fit, Wrap Around, that's fine go ahead and click OK. And this time we'll go ahead and grab ourselves one of two images. You can either - you can just grab that Wave RGB.psd file that's inside the Dmap sub-folder there, or if you were working along with me, you can grab Wave 2-chan.psd; either ones is going to work. I'll go ahead and work with the 2-channel image and I'll click Open.
Photoshop goes ahead and applies the first channel horizontally so it uses that first channel to bend the top half of the image over to the left, and the bottom half of the image over to the right. And then it uses the second channel to bend the left half of the image down and the right half of the image up. Now, again we have something of a zigzag effect going, so we've got some hash corners going down here and up here and over to the left here, and over to the right this way as well. It's harder to see the right zigzag, you can see it actually over this location pretty well. So again if we wanted a Gaussian distribution, we would go back to that same file once again, this guy right here. And I'll go ahead and bring back the Channels palette so that we can see, there is the H dmap, there is the V dmap. And we would go ahead and select both the channels by clicking on one and Shift+Clicking of the other, so that both channels are active.
Then we would go up to the Filter menu; choose Blur and choose Gaussian Blur. And I would apply a big huge Radius. Let's go even higher this time. Let's go with the 200 pixels Radius, and then I will press the Enter key or the Return key on the Mac, and you can see it doesn't really appear to make that much of a difference. This is before, and this is after. So the after effect is a little less colorful, but other than that it doesn't look terrifically different. Let's go ahead and save that out. I would press Ctrl+Shift+S or Command+Shift+S on the Mac to invoke the Save As command, and we'll call this one Wave 2-chan GBlur.psd this time around, actually I guess I should give it a capital B as well to be consistent. And then I'll click on the Save button in order to save out that file.
And now let's go back to the Flag image, I will Shift+Tab away my palette. I'll go and revert to the original version of the flag. Go up to the Filter menu, because Gaussian Blur was my last applied command so I have to choose the command manually once again. Choose Distort, choose Displace, and 50-50 Stretch To Fit, Wrap Around is fine, go ahead and click OK. Let's find that newest file I just created, Wave 2-chan GBlur.psd right there. Click Open, and we have a nice rounded wave pattern in both directions. Both vertically and of course horizontally here.
Now, then, and when I say horizontally it may look like I am tracing a vertical line, because I am but I am saying that the distortion goes back and forth. So it's a horizontally distortion this way, it's a vertical distortion this way. It can be a little confusing at times. Now the thing that I just don't like that's just purely -- completely unacceptable about this effect is that we are wrapping the edges around. So I've got this blue wrapping around to the other side, and I've got this red wrapping up and it just ruins the whole flag effect in my opinion. And it's not any better if were to repeat the edge pixels. So what in the world is the solution? I will show you in the next exercise.
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