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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, the final exercise of this chapter, we are going to fix this fringing around the edges of these rocks here inside of the Stonehenge composition. I am working inside of a version of the image called Knockout gradient.psd found inside the 11 Layer masks folder and I am zoomed pretty far in here so that we can see a detail up close and personal, so you can see this little bit of light edge, and its even more prominent down here on the interior of the rock surfaces.
Now its a kind of thing that might drop out in print if we printed this at a sufficiently high resolution but if we were to view a detail inside of a web image or something along those lines, it's going to show up. So might as well take care of the problem is what it comes down to. Now by virtue of the fact that we have an independent knockout layer that's filled with a gradient that's taking care of the problems that we had at the tree lines down here, we can now modify the contents of the Layer mask independently without harming that gradient, and that's what we are going to do here. So we are going to choke the edges of the Layer mask inward and we are going to do it at this time using a combination of Gaussian Blur and the Levels command. This is an old school technique here, an oldie but a real goodie as you'll see.
So go ahead and make sure that the Layer mask is active. The Layer mask for the sky layer that is to say. And then I am going to move this over so that I can see a couple of bits of this fringing problem that we have here. I am going to -- because Gaussian Blur was the last filter we applied, we can go ahead and reapply it by pressing Ctrl+Alt+F or Command+Option+F on the Mac and I am going to apply a single pixel of softening, just by setting the Radius value to 1. It's going to work out very well for us.
It appears at first to kind of exaggerate the problem, but you'll see we are going to take care of that. What it's really doing for us, is it's blurring the edge so that we can move the edge around. So now we can make it sharper again using the Levels command and move it as we do so. So click OK in order to accept that modification. Now I want you to press Ctrl+L or Command+L on the Mac to bring up the Levels dialog box. And if we wanted to spread the edge, we would drag the Black slider and notice that's going to move the edge outward, as we are seeing happening on screen right now.
So that would expand the masked image. But I want to do exactly the opposite; I want to choke these rocks right here. So I am going to change the Black point back to zero and I am going to move the White point radically over to the left here, until I get to about 45, actually works out pretty nicely. Now we have some sharp edges going on. So we pretty much defeated the Gaussian Blur but we use those softened edges to move them into a different location and we move them inwards by moving this White point value.
Now I click OK after you have set that White point value to 45 go ahead and click OK in order to accept your modification and we are basically done. You could take care of the little corner problems that you have here and there but they are pretty slight and I am not too terribly worried about them frankly. So this is the final version of the Stonehenge combination. I am going to tab away my palettes and press the F key a couple of times and you can see just how great this dramatic sky looks. It's a combination of a lot of things working together. We've converted the sky to a smart object, we up sampled it, we applied a Smart Filter in the form of Gaussian Blur. We masked the sky, we created an independent Knockout layer in order to lift the sky away from a tree line and finally we edited the layer mask independently using Gaussian Blur and finally we choked the Layer mask independently of the Knockout layer using a combination of Gaussian Blur and the Levels command here inside Photoshop CS3.
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