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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."
Our final method for selecting a complex foreground image set against a busy background is to take multiple stabs at the image, poor image using the Calculations command. So for example, we might first try to select the green regions inside of the macaw here using one calculation and then we will select the red area this red tuft using another calculation, and then we will merge those two calculations using a third calculation, and then we will approach the beak using a fourth calculation and then we will try to merge that with the other two using a fifth calculation and so on and so on.
So basically you might end up applying a dozen calculations to a single image in order to select it. Now it does take a some more reasoning skills. You have to gain some comfort with the Calculations command, but as you will see it is the most automated approach, and it also tends to deliver better results than High Pass, because you are asking Photoshop to do the work for you instead of making the decision on your own. So instead of going brain dead like with and High Pass and laborious like with High Pass you are going intelligent using Calculations and you are saving yourself some time and effort and maybe making a better mask as a result. But you've got to be able to reason your way through it. Now it's not rocket science. And I am just going to ask you to use three different blend modes here over the course of next couple of exercises.
So here I am, I am working inside of Military macaw.jpg. It's found inside of the 16 Tough Stuff folder. We are back to the original military macaw. It doesn't alpha channels or any paths. And the reason is that we are going to be filling this image up with new channels. As I said, let's start with the green, that's the best place to start because he has got so much green. After all he or she I don't really know the gender of this animal. So let's check out the channels, control one red, fine. It's kind of the blend channel, although it's bright where the tuft is concerned and obviously it's bright where the white area is concerned, but not a lot of contrast elsewhere.
And here is green, lots of contrast between the green of the animal and the background and lots of contrast overall. Then of course blue which is very dark inside of the beast, and I am not sure if you can call a bird a beast. But still, never call him a fish, that's where I draw the line. Now I think we have got the most contrast between green and blue. So the most difference between those channels where the green portion of the animal is concerned so that should make you think difference mask, right? Because the difference mask is going to find the areas of greatest difference.
So let's take advantage of that. I will go ahead and press Ctrl+~ or Command+~ in order to return to the RGB composite image. Let's go up to the Image menu, choose the Calculations command. And I am going to go ahead and change the first channel to green. Your image should of course be Military macaw in both, Source 1 or Source 2 layers background, because that's all we get to work here. Channel one should be green, channel two should be blue and Blend mode should be difference way down here, La Difference. We will get this effect right here which looks great. It's the green of the bird against the black background. We have turned the green of the bird white and everything else, everything that's not green is basically turned black on this, which is awesome. So go ahead and click OK in order to accept that new alpha channel and you can confirm that you have got a new alpha channel by going down here to the bottom Channels palette.
Let's call this green stuff or something along those lines, because it's the green stuff in the bird. Let's press Ctrl+L for the Levels command, Command+L on the Mac because after all we need to increase the contrast and I am going to make the black point something 20, it looks pretty good and let's make the white point something like 90 actually. Let's take it down pretty light. I think this looks very nice. And we've made the area inside the green portion of the bird very bright indeed. We have really highlighted it. It was very easy to select using Calculations. Let's click OK.
Next door to the green portion of the bird is the red tuft right there. So moving counter-clockwise around the bird once again. There is the red tuft. Let's go ahead and try to select it. We are still going to stick with a difference mask I think, because in a Red channel we have got a light tuft and in both the Green channel and the Blue channel, we have a dark tuft. So we should be able to use Red along with either Green or Blue in order to get a nice difference mask, in order to isolate that redness. So let's go back to the RGB image, go up to the Image menu, choose Calculations, it probably will go ahead and show you your last applied settings. Go ahead and change the Source 1 channel to Red and then we've got the Source 2 channel set to Blue. Let's try just for the heck of it. Let's try Green and see how, that looks that's nice.
We only have the tuft selected this time. That's great. Blending should be difference of course. Opacity 100%. All the check boxes are off except Preview. Go ahead and click OK in order to accept that new channel. Let's go ahead and name it red stuff of course and let's go ahead and increase the levels as well by pressing Ctrl+L for the Levels command. That's Command+L on a Mac. I might as well try 90 again. Let's see how that works. That works pretty darn good. We've got a very bright tuft. And I am going to take the black up to like 25 this time around. The exact values aren't all that important and I would just say mess around with until you get a very bright tuft like this. But if you want to follow along with me, this is what I have done 25 and 90.
Click OK and now we need to combine green stuff with red stuff in order to select as much of the bird as possible. So I am going to select Green Stuff alpha channel there. I am going to go up to the Image menu. I am going to choose Calculations yet again, and this time when we are combing two masks we each other, you know the mode. First of all we want to set one channel to Green Stuff, the other channel to Red Stuff. The mode we want to apply ain't Difference, although it doesn't half bad, but what we really want is green. Green is the mask combiner, and look what we get.
Nice, nice bird. Click OK in order to accept that. Grab your Dodge tool friends, make sure that Range is set to Highlights and let's merge these two guys together. So, the seam that is being created here, we want to get rid of the seam. I might as well just go ahead and use Lasso tool. Let's check here. What is this? Is this in or out of the tuft? Let's press Ctrl+~, Command+~ on the Mac. That's inside the bird. All right, let's go back. I think we are working on the sixth channel now. So Ctrl+6 or Command+6 on a Mac and I am going to Alt click round this region to select it. I just want to make sure that we are doing a good job here.
And grab all this garbage. And this area too, go ahead and select this and it's I and stuff like that and fill that with white by pressing Alt+Backspace or Option+Delete. Now we are doing pretty good. We have some massive horrible posterization down here that we can deal with later. We have got a very nicely selected head region. I am going to add to that selection a little bit and press Alt+Backspace again. But the bill, what do we do about the bill? I mean check it out. Here is Red channel, here is the Green channel, here is the Blue channel. It could be the exact same bill, it's just getting darker and darker, but certainly we don't have difference to work with. We can't say wow! We've got light bill in one channel and a dark bill on the other channel. So we are going to have to work with a different calculation this time. I will show you that calculation in the next exercise.
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