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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, I am going to show you one of the simplest but most gratifying applications of layer masks and that is the unidirectional Motion Blur. Basically if you're familiar with the Motion Blur filter inside of Photoshop, which is what we'll be using eventually here, you probably know that it's a bidirectional effect, meaning that it blurs the image in two opposing directions. But what we want is we want basically a jet of blur coming off of this jet right here. So we want a unidirectional effect and we're going to create that unidirectional effect using a layer mask. As I say, a very simple layer mask of that.
So I would like you to open this image here. It's called Jet on blue sky.jpg, it's found inside of the 11 layer masks folder. It comes to us from photographer Christoph Ermel, and this plane is obviously at an angle. Now one of the things that I suggest you do is to go ahead and rotate the plane so that it's upright, because it's just easier to gauge if your Motion Blur is on the right axis or not, if you're working with an upright image in the first place. Then we'll rotate it back in place later.
So first things first, let's go ahead and convert this plane to an independent layer by double-clicking on it, double-clicking on the background layer that is inside of the Layers palette, and let's call this new layer plane, then we'll click OK, and the deed is done. Now we have an independent layer, an independent floating layer that has the plane on it. Next, we're going to go ahead and rotate it so that it's completely altogether upright and we're going to do that using the Ruler tool. Go ahead and grab the Ruler tool from the Eyedropper tool fly-out menu, and I am going to drag from the nose of the plane right there all the way down to this part of the tail, don't drag to here, drag to here instead, this corner right there. That will give you the exact axis of the jet.
Notice it's telling us that the axis is 48.2 degrees or rather -48.2 degrees, we don't really care. I am going to go up to the Image menu, choose the Rotate Canvas command and then choose Arbitrary or you can press that keyboard shortcut that I've given you, which is Ctrl+Shift+Alt+R for Rotate or Cmd+Shift+R on the Mac, and Photoshop will go ahead and automatically load that value, that angle value right there. Even though it's not the same value, this is the value that needs to be used as we'll see. Go ahead and click OK to accept its wisdom here, to accept its default setting. That's going to go ahead and rotate the plane so that it's going straight up in the air. We want it to be horizontal, so the next step is to go to the Image menu. Choose Rotate Canvas and then choose Rotate 900 CCW, which is Counter Clock Wise or you can press once again my keyboard shortcut that I included along with my Deke keys, if you loaded those back in the Preface, which is Ctrl+Shift+Alt +[ or Cmd+Shift+Alt+[ on the Mac.
Anyway, choose the command and there it is. It's all rotated nice and horizontally there. If you want to confirm, you could bring up your rulers by pressing Ctrl+R or Command+R on a Mac and then drag out a guideline, just to make sure that your jet is exactly horizontal, which in my case it is. So I am going to undo that guideline, I don't really want that in my image. Press Command or Ctrl+R once again to get rid of the rulers. We want to create the Motion Blur and we're going to do that by using a jumped version of the image. So let's go ahead and zoom out a little here. I am going to suggest just to give ourselves a little wiggled room that we add to the canvas. So let's add a little room over here on the left side of the canvas by going up to the Image menu and choosing the Canvas Size command. I am going to go ahead and add, I've got, notice my relative checkbox is turned on, I am going to go ahead and add about 300 pixels over on the left-hand side, so I'll click on this right-hand chiclet in order to make sure that we're expanding to the left. Then I'll click OK in order to accept that modification.
The next step is to jump the image, so let's press Ctrl+Alt+J or Command+Option+J on the Mac and we'll call this new layer blur and then click OK in order to create it. Now the thing with Motion Blur is because it's a bidirectional effect, it blurs not only outward but also inward, which means it has the effect of making, if we were to just apply it to the plane right now. It would have the effect of making the plane look smaller. We want to enlarge the plane; we want to stretch it before we apply Motion Blur to it.
So let's go ahead and do the stretch by going up to the Edit menu and choosing the Free Transform command or that would be Ctrl+T, if you're on the PC you are Command+T on the Mac. Now I am going to go ahead and Alt+Drag this side handle here, that would be an Option+Drag on the Mac in order to stretch it in both directions. And you know what I really need to see what I am doing here. So I am going to change the Opacity of my layer, I need to be able to compare the stretch version of the plane to the original version, so I am going to change the Opacity of the this blur layer to 50%. Now you can't do it by just pressing the 5 key when you are in the Free Transform mode, instead you actually have to go over here to the Opacity value and change it to 50%. So that's what I am going to do. And now I can see both, in fact it's half-transparent, half-opaque.
Notice now that I've stretched the plane a little bit actually, and by the way, I also need a little bit more room to the sides to work here. So I am going to go ahead and switch to the Full Screen mode. Again, you've got to choose that manually from this little icon down here at the bottom of the toolbox, you can't just press the F key. So I am going to switch this Full Screen mode with menu bar, that guy right there, that gives me more room to work. I am going to Alt+Drag the plane further in order to stretch it in both directions away from that center point actually. Now let's go ahead and drag the plane over. Now you can see that it's kind of at the wrong angle, now I am stretching the wings at a different angle than they were before. So we've got to fix that. And here's how I suggest we fix it. First, make sure that you get one of these corners of the wing in exactly the right place. So I am suggesting this guy gets locked in the position right there.
Then, go ahead and grab that center point of your transformation, we're still working inside the Free Transform mode and move it over to there, so that becomes the anchor point for the skew that we're about to apply. Now I am going to zoom out actually quite a bit and I am going to scroll down, hopefully we'll avoid an auto-scroll here, because they're pretty pesky at times. I am going to press the Ctrl and Alt keys or the Command and Option keys on the Mac and drag that top point right there, and actually I'll press the Shift key as well so that I am performing a just strictly horizontal skew.
So again, the keys that I have down are basically all of them. I have Ctrl+Shift+Alt+Down or Cmd+Shift+ Option+Down on the Mac as I drag this top point and that way we're skewing because the Ctrl key is down, we're skewing exclusively horizontally because the Shift key is down, and we're skewing with respect to this anchor point right here, this transformation origin point as it's called, because we have the Alt or Option key down. That's what's going on. All right. Well, that looks pretty good to me. We could still stretch it further if we wanted to, depending on how much tail you want to have flying off the back of the jet there, you could continue to stretch that a little bit if you want to. So you can be as radical as you want. Just every time you stretch you're going to have to go back there and skew again as well. So I'll do a little more skewing in order to make sure those wings are aligned.
And that's good! I like what I see; I am going to go ahead and press the Enter key or the Return key on the Mac in order to accept that transformation. Now I am going to restore the Opacity of my plane to 100% here. We are now ready to apply the Motion Blur filter and eventually, apply the layer mask as well and we will do both of those things in the very next exercise.
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