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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, welcome to the final project inside of this chapter. This time around we are going to take this image that I shot of Stonehenge last time I was in England, and we are going to add a more dramatic sky, which is like something we have done several times now adding a dramatic sky to a dramatic shot, so that the entire image conveys a high a degree of drama, for the druids after all. But we are going to do it in a different way, so that we learn a few new techniques. In this exercise we are going to go ahead and up sample the sky, so that it matches the size of Stonehenge, the size of its host image, and we are also going to mask the sky, so that it fits into the background. Then in the next exercise I am going to introduce you to a little thing called knockout masking, which is a really phenomenal technique inside of Photoshop, very flexible, you have to really see it to appreciate it. So stay tuned for that.
So here I am working inside of an image called Ancient doorway.psd found inside the 11 layer mask folder, and as I say, I shot the background image, but the sky comes to us from that artist who goes by the name Kataev, at iStockphoto.com we have already seen this sky a couple of times including inside of this chapter. Now I am going to increase its size, now normally I don't suggest you enlarge images inside of Photoshop. Like if I was just taking a flat image, and I wanted to print it, very, very large, I would just print it very, very large. Even if it had a low resolution, that's better than enlarging the image. So it has a high, but meaningless resolution.
However, in this case when you are trying to match one image to another, it's completely acceptable to up sample, especially given the fact that I will go ahead and turn off the sky layer for a moment. You can see that the trees in the background here are well out of focus; that means that the sky needs to be blurry too, and when you increase the size of something inside of Photoshop, you naturally blur it, that just happens, you introduce anti-aliasing. So that's actually going to work to our advantage this time around, because we want some blurriness. All right, so go ahead and click on the sky layer, turn it on, so it's active and visible. Then I want you to scale it by pressing Ctrl+T or Command+T on the Mac to enter the Free Transform mode, but first before you transform, first thing I want you to do, is convert the layer top a smart object. So click on Layers palette menu icon right there, and then choose Convert to Smart Object, or if you loaded my D key shortcut, you can press Ctrl+, or Command+, on the Mac and now you have got a smart object, that's all that takes.
Now let's go ahead and transform it, and because it's a smart object, we can transform multiple times non- destructively. So press Ctrl+T or Command+T on the Mac, and then I am going to Shift+Alt+Drag this lower corner handle right there, that would be Shift+Option+Drag on the Mac, because the Shift key is down, I am constraining the proportions, and because the Alt or Option key is down, I am scaling out from the center of the sky image, and that's good. Now I am going to go ahead and release, and I appear to have scaled my image to a little bit more than 150%, both wide and tall.
So you want to scale it outside into the pasteboard region as you are seeing here, then press the Enter key or the Return key on the Mac in order to accept the new size of the sky. Next I want to go ahead and mask the sky, so turn this guy later off for a moment, go to the background layer. Let's go over to the Channels palette, and notice that I have already created the sky mask for you in advance. Now if you are wondering how I did that, I could have approached in one or two ways, I could have either gone to the various channels here, inspected the channels that I have to work with, the Red channel, the Green channel, and the Blue channel because all of them have a high degree of contrast between the stones and the sky in the background.
The problem with the Blue channel which on face value seems to have the most contrast, is that it lacks contrast right there. So the stone and the sky are very similar colors, we would have a hard time creating a mask out of that transition. Whereas the Green channel and the Red channel have a lot more contrast in that area, especially the red channel. The problem is with these two channels that sometimes the rocks are darker than the sky, and another times the rocks are lighter than the sky. So how would we increase the contrast properly so that the rocks are uniformly darker than the sky in the mask for example? Well, we could take advantage of something called arbitrary map, which is something that you can apply form the Curves command, and we will take a look at arbitrary maps toward the end of this series. But for now there is an easier way to work where this image is concerned. I am going to go ahead and click on the RGB composite image, and I am going to go up to the Select menu, and choose the color range command.
And if I am painting this picture that the color range command comes to your rescue a lot when you are masking inside of Photoshop, then I am painting an accurate picture. I am very, very fond of this command, it's very useful, especially for selecting images that have smooth transitions, it's when you are selecting filigree details like hair and feathers and so on that it starts to break down. So go ahead and choose the color range command, brings up the color range dialog box of course, let's go ahead and switch the selection preview to none, so we can see the full color composite in the background. I am going to click in the sky in order to select it, and I am going to Shift+Drag around the sky,and Shift+Drag inside of the archery as well, and notice that the sky is turning black for me, that's because I still have my Invert check box, because the last thing I selected was that glass image, a few exercises ago. So I am going to go ahead and turn off Invert, so that we are selecting the sky, and not deselecting it, and I am going to reduce the Fuzziness value to something along the lines of this right there, 65 is actually going to work out pretty well.
Now I click OK,in order to accept this new selection. Let's go ahead and finish off the selection outline inside of a layer mask. So let's go to the sky layer, click on it to make it active, turn it on, so it's visible, and then I want you to click on the layer mask icon in order to add the layer mask to the sky layer. Now let's Alt+Click or Option+Click on that layer mask thumbnail in order to see the Layer mask inside of the image window, and I am just going to paint away all this garbage that's around the edges here using the Brush tool set to the Overlay Mode.
So I am going to go ahead and press Shift+Alt+O or Shift+Option +O after selecting the Brush tool. Make sure that your foreground color is set to black, as it is for me, then increase the size of your brush, and paint away, just paint to get rid of all of that garbage that is inside the black area of the image that ought to be black actually. And I am going to be pretty aggressive about painting these details away. Now if you get too aggressive, if you do this number where you start painting in some grays in the sky, then you need to switch back to white. So I'll press the X key to switch to white and paint that area away, and I might just paint a little white here and there inside of the sky just to make sure that it's nice and light, and then I have got this little detail right there, I am going to get rid of it just by selecting it with the Lasso tool, and black is now my background color, so I will just press the Backspace key or the Delete key to fill with black.
Now let's zoom out, I have got all this stuff going on towards the bottom of the image, it's well away from the sky region though, so I can just select this area using the Rectangular Marquee tool like so, and then press Backspace or Delete to get rid of it. And that's the Layer mask, that's all it takes, very easy to pull off. Alt+Click or Option+Click on that layer mask thumbnail once again to return to the RGB view. And I want the sky to be out of focus just as the trees are, because it doesn't make any sense that the trees would be out of focus, and then farther away still the sky is suddenly in focus.
So I am going to click on the Smart Object thumbnail right there, and I am going to go over to the Filter menu, I am going to choose Blur, and Gaussian Blur, and notice that Lens Blur is not available to us, so we are going to have to go with the Gaussian Blur. You can press Shift+F7 if you have loaded my D Key shortcuts, and I am going to change the Blur value to something along the lines of 6, and then press Tab and see how that looks, and I think that looks actually pretty darn good. So now I will click OK in order to accept the result, and that gets applied, because we are working with the Smart Object. Gaussian Blur is applied automatically as a Smart Filter, meaning that we can edit it, where you can double-click on the word Gaussian Blur there, and enter a different blur value if you think you went too far, for example.
So I will go ahead and take it down to 4. What the heck, this does actually look better. So now I will click OK in order to accept that modification. So that's step number one. We have got the sky now in the background, the problem is we have some bad edges if you were to zoom in on the sky, you would see that the trees have an unnaturally sharp sort of edge associated with them, and we are going to take care of that problem using as I say, a Knockout Mask in the next exercise.
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