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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 next pair of exercises, we are going to merge our two Levels iterations that we just got through creating, and if you are not sure what I am talking about, I have this catchup document opened. It's called Levels iterations.tif. It's found inside of the 16 Tough Stuff folder. You can see that there is a trio of Alpha channels right here. We have the base alpha channel that we've created using the Calculations command and then we have two different Levels adjustments. This first Levels adjustment works for all of the edges; it counts for all of the edges outside of this marquee that I drew at the end of the previous exercise.
Then, the other adjustment works for the area inside the marquee. So basically what we need to do is we need to draw a selection outline that indicates the boundary between the good areas outside the selection and inside the selection between the two iterations. Then, in the next exercise, we will combine them together using the Mask check-box inside of the Calculations dialog box. So our job in this exercise is to just draw an accurate selection in the first place, an accurate boundary selection.
So let's go to this first Levels iteration, the one that's called 20/0.6/235. I am going to press Ctrl+D or Command +D on the Mac to deselect the image. I am going to zoom in on the image as well,= and I am going to grab my Lasso tool. We are just going to vaguely lasso the area that looks bad inside of this channel. So we know these edges look pretty darn good, they need some work, but they are in good shape. These edges down here from the finger on down, and including the shoulder, they look good as well.
But this region looks very bad and this happens to be the region that is better accommodated by the 160/1.3/235 Alpha channel. So here is what we are going to do. Just go ahead and draw a lasso around the area that seems to be the problem area like so. A big blobby sort of lasso selection, doesn't have to look like anything pretty. It just needs to enclose this region right there. Now, let's go back to the 160/1.3/235 Alpha channel and make sure that the area inside of the selection is in good shape, and we might say, well, you know, the flame, maybe let's cut down the flame a little bit.
So I am Alt+Dragging or Option+ Dragging around this area to take it away from the selection outline. Then notice this knuckle. It's in very bad shape indeed. It's much better accommodated by this Levels iteration, the first Levels iteration. So let's go ahead and deselect it, and I will do that by Alt+dragging like so, and I will drag up like this in order to get it out of there. That would be an Option+Drag on the Mac, and this is our selection outline. Not a great one, but as I say it's just supposed to represent the boundary between the good area of one Levels iteration and the good area of the other Levels iteration.
Now, let's create a soft edge to this boundary by going up to the Select menu and choosing Modify, and then choosing Feather. We will just choose the dumb Feather command, the one that doesn't provide a preview as opposed to Refine Edge of course, the better command. Because we just need to apply a quick feather radius of 6 pixels, and that's it. Then click OK in order to blur that selection outline. It will appear to round off a little bit as well. Now at this point, I could just perform a quick and dirty solution which is to copy the area from this channel and then paste it into the other channel.
I will show you what I mean. I will go ahead and back out a little bit here. I am going to the final channel right there, the 160/1.3/235. Let's go up to the menu and choose the Copy command in order to copy the information inside the selection outline, and then I will go back to 20/0.6/235, and I will go up to the Edit menu, and I will choose the Paste command. That goes ahead and paste the image right there inside the selection. So it is registered in place. That's a good thing because the selection outline survives even though we are switching channels here.
I will go ahead and press Ctrl+H or Command+H on the Mac. So this is before, and this is after. So we have the best of one Levels iteration married with the best of the other Levels iteration. That's great, but the problem is, the reason I say this is the quick and dirty solution is because we just modified this alpha channel, we just modified the 20/0.6/235 alpha channel. That may not be the way you want to go. You may want to leave this alpha channel nice and pristine, and if you do, there is a better way to work, and more careful way to work anyway, that involves the Calculations command along with that Mask check-box.
So let's go ahead and press Ctrl+Z, Command+Z on a Mac to undo that modification. I will also press Ctrl+H or Command+H on the Mac in order to bring back my selection outline and then I will impress you to join me in the next exercise.
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