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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."
Now that you have a sense of how add and subtract work and albeit, it might be a vague sense at this point. Actually it should be a fairly specific sense. But your understanding of it may be vague. You may be the kind of person that when faced with a mathematical equation goes, hmm, that's interesting! But when faced with a practical application goes eureka! So this the eureka moment or at least these next few exercises will be your eureka moment. I have opened an image from photographer Chris Schmidt from the U.K., and it's called Superhero hair.psd, and I have named the file -- by the way it's found inside the 14 Calculations folder. I have named the files for his bluish hair.
And if you have ever read sort of old style color comic books with superheroes in them, the superheroes as often as not, not Aquaman but the other guys. Not Thor either, but the other guys have such dark hair that just this jet-black hair that absorbs every single light spectrum, except for blue. Just reflects back blue and occasionally white as well. I am not sure what that's about. I think their hair is so shiny, so very greased or what have you, that it reflects back the sky colors even at night.
Anyway, that's what this guy has going here. Now we want to mask him, and he has just got this brilliant hair, and he has got it hyper-greased and he is reflecting back just sky colors. Actually, it's a treated photo. But, the great thing about it is the hairs are not treated and we have got all kinds of different levels of focus associated with these hairs, and that's going to be a challenge for us to select the hair and select the hair at its proper degree of focus. And we are not going to be faking this. We're not going to be going in there and selecting some hairs and applying Gaussian Blur and that kind of thing, we are going to create a mask that's going to do the selection, the right way in the first place.
And if you take a look over here at the Channels palette, you will see that I have got a couple of Alpha channels for you. Just to take a look at here. One is called Mixer and that's the mixed version of the Alpha Channel. Thanks to the Calculations command, a little bit of additional work as well. And then we have the Masker, is what I am calling and basically the Masker is just the same thing. It's really just the same channel, with all the stuff inside of the face deleted. So you can compare those two. And what we are going to do with though is we are going to zoom in on the hair so that you can see what a very decent job, I think, we are going to be doing of selecting this hair, of masking this hair, and you can see that we are in the process of observing the original focus, the original focus that's inherent inside the image. We are also picking up a lot of digital noise which is part-and-parcel of the digital photography process, just as film grain is part-and-parcel of the film photography process.
One day we may have such sophisticated technology that digital noise is a thing of the past, and that will be great. Cameras will pick up the world the way we see it. But right now, we do get digital noise. And we see more noise in the lower focused portions of the image, and you can see that that's what I am doing. I am just using that noise in order to simulate the original degree of focus, which is a good thing. That way you get an organic mask, and we are even getting the noise down to this very low level of focus on this hair right here, which looks pretty ratty, but the fact of the matter is, it's accurate. And that's what we want, we want an accurate mask obviously. And we are going to generate this accurate mask using the Calculations command.
Now, before we go to Calculations as we will do in the next exercise, I want to show you what we have to look out for. Notice here, in the RGB composite image that we have got a bunch of blue hair against the blue background. And so then it's a little bit of a challenge because we've got blue on blue. But generally speaking, we have a high degree of contrast because the hairs are dark and the background is light. We also have some decent contrast along the chin because the chin is more or less flesh colored, sort of orangish-reddish, and the background is bluish. And then we have got some low focus darkness over here in the shoulder, but it's lighter once again than the background.
Where we are going to have the most problem is up here where we really don't much detail to work with. I will go ahead and zoom in. You can see that at the top of the image, we have black on black. So we are going to have to do a little manufacturing up there. We are going to have to invent the edge, and here we've just got blue on blue, I mean just full bore, medium, high saturation blue going in the foreground, in the hair and in the background, which is going to make for some blue on blue heartache of course, excellent! So we've got some challenges ahead of us. Make sure that you are scrolled down so that you can see the worst of the image, that is to say the worst of the image where masking is concerned so you can keep an eye on it. Because if you have the image scrolled up like this, you are going to think the entire thing is going to be a breeze or least, a moderately challenging experience. Well, really, it's hideously challenging.
In the next exercise we are going to use the Calculations command and the Add mode in order to generate a mask, and in the exercise after that, we are going to use Calculations combined with Subtract to generate an Alpha channel, and we will end up seeing which one we like better.
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