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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 of mine. We got a moon, we got some water, we got the moon reflecting in the water in a highly unnatural way. So we are all set to go. We are going to ripplize that moon in the water so that it actually exactly matches the contours of the water. This is a very cool thing. I am working in this document called Moon & water.psd. If you want to join me the water is fine. And you also want to make sure that you have opened this image. But you don't really have to have it opened actually; I need to have it open, so I can show you something.
We are going to use this Fake Water. psd image and both of these images are found inside the 18_displace_maps folder and the thing I need to show you about this image, it's obviously an RGB image, which means that if we were to apply it as it is as the Displacement Map, then Photoshop would go ahead and interpret the Red Channel as the Horizontal Displacement and the Green Channel as the Vertical Displacement and the Blue channel as nothing. Blue Channel will be ignored. Now that's a little dangerous, check it out because the Red Channel is very, very dark. So it would sit there and move the pixels, it would move the moon down into the right. And the Blue channel if we were to use it somehow is very, very light. So it would move the moon up into the left and meanwhile the Green Channel is actually fairly balanced in terms of its luminance levels, so hopefully it wouldn't move the moon around all that much. So I just want you to see that.
Let's go back to the Moon and Water image right here. And we want the reflection layer to be active, and I would like you to go up to the Filter menu, choose Distort and choose Displace once again. And let's go ahead and change the Horizontal and Vertical Scale values to a 100 a piece. Stretch To Fit is fine. We don't care about the Edge Pixels so don't worry about those. The Edge Pixels are black is the reason. Then go ahead and click OK. Then I would like you to go to the 18_ displace_maps folder, and find the Fake Water.psd image and click Open in order to apply it to the moon, and you will get a complete total mess. What gives, I mean we have got this blob of a moon, that's shoved over to the right, and also its edges don't match the water in the least. Well the reason that it shoved over to the right of course is because we have that dark Red channel.
The reason that it doesn't match the water at all is because the Displacement Map has been stretched to include this entire image. So it's been stretched to the top of the image. And as a result we no longer have alignment between this water layer and the fake water displacement map. All right, so that's a bad thing. Go ahead and press Ctrl+Z or Command+ Z on the Mac to undo that modification there. Let's zoom in once again, and what I am going to have you do in order to constrain the behavior of the Displacement Map, I want you to Ctrl+Click or Command+Click on the Reflection layer thumbnail and that will go ahead and select that layer and a selection outline is a great way to limit the behavior of any of the Distortion filters inside Photoshop, works beautifully.
All right, now let's go up the Filter menu and we will just choose Displace again, or you could just press Ctrl+F, Command+F on the Mac, and this time we get a properly scaled Displacement Map, it's only affecting the reflection and nothing else. So there is a one to one relationship between the pixels inside of this Reflection layer and the pixels inside the Fake Water image that we are using as the Displacement Map right here. You can see that the moon is indeed following the contours of the waves. Isn't that amazing? But here is the problem. This is before, this is after. So it's going to the right, shifting over to the right which means that it's out of alignment with the moon. Notice this moon is up here, and its reflection is kind of over here and that's a bad thing. It's completely a function of that dark Red Channel being employed as a Horizontal Distortion.
So what do we do? Well, we are going to have to go with a different channel. We could go ahead and try to move that moon over, like so to the left in order to put it directly under the moon, but then it wouldn't exactly match the contours of the water anymore, and even if you forgive that, I will go ahead and press Ctrl+H or Command+H on the Mac, we have got kind of a noticeable edge here, thanks to the effects of the Soft Light Blend mode. So that's not the solution. So let's go ahead and Undo that modification. Let's go ahead and press Ctrl+Alt+Z a couple of times in my case. That would be Command+Option+Z on the Mac. The layer is still selected, I will press Ctrl+H so we can see that selection outline. Now I will make it go away. We just want to make sure that the layer isn't deselected, and now I am going to press Ctrl+Alt+F or Command+Option+F on the Mac in order to bring back up the Displace dialogue box. These values are fine for now.
Click OK and instead of working with the Fake Water.psd file, I am going to enter this sub-folder right here called Water Maps and notice that I have got ahead and broken out Fake Water B, G, and R, and those are the individual channels. That's the Red Channel right there, that's a Green Channel and that's a Blue Channel. If I were to select the Red Channel and apply it, then I would shift the moon down into the right dramatically as you can see. So I will undo that modification. Go ahead and press Ctrl+Alt+F, click OK. Let's try the Blue channel so you can see how because it's so light it shoves the moon up into the left, so that's a problem, right? Let's go ahead and undo that modification and then let's try out the channel that's just right. Click OK which of course is the G Channel, the Green Channel, and click Open.
Now notice that it goes both directions, up-down, left-right, all over the place. That does apply a huge distortion, but you can see how it exactly matches the contours of the rippling water. It's so great that you can use an image as its own displacement map. So sometimes you don't have to do a lot of work, you just take this piece of artwork and use it to map the moon on top of itself. It's a glorious thing. As long as you have a lot of variety in terms of the luminance levels inside of the image, and that they are balanced as they are in the case of the Green Channel.
All right, let's go ahead and undo that, because I want to apply different scale values. I am going to go ahead and press Ctrl+Alt+F or Command+Option+F and I am going to change that Horizontal Scale value to 50% and I am going to leave Vertical Scale at a 100%. I will click OK, go with Fake Water G, click Open and we get that effect right there, which I think is very becoming I have to say. Let's go ahead and tab away the palettes, and fill the screen with the image against the black background here. Then I will go ahead and zoom out so that we can take the moon and its reflection in all at once. This is the final effect. Thanks to our ability obviously to Blend the moon so it looks like a reflection but also use the water pattern, that fake water pattern as its own Displacement Map in order to displace the reflection into its new home.
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