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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 we are ready to go ahead and reestablish some of the hair details at the top of this image. I am working inside of a document called Enhanced contrast.tif found inside the 14 Calculations folder and I am going to press Ctrl+9 or Cmd+9 on the Mac to switch to my ninth channel, which is called Curves modification and this time around we don't really need to duplicate the Channel because the modifications that we are making are not all that significant, they are not going to really harm anything we have going, they are going to add to it.
All right, so what I want to do is, I want to use the Apply Image command; I am going to zoom in up here to this absence of information. I want to use the Apply Image command to bring information from other channels into this channel. Now it's telling you, calculation allows you to take two channels, merge them together in order to create a new alpha channel. So merge two channels to create a third channel. Whereas the Apply Image command also here under the Image menu, right there, allows you to merge a channel into another channel. So you are not making a new channel, you are taking some channel and putting it into another channel subject to a blend mode.
Now I am a fan and not a fan of the Apply Image command. Basically we are merging full color images as concerned, I think it borders unused list. Because there are a lot of different ways to bring images together using layers which are much more flexible. But if you are trying to bring information from one channel into another channel, it can be quite useful sometimes under very specific circumstances, and this is one of them. All right, so here's what we are going to do. We are going to check out our original information, because we can see there is nothing left up here inside the masking progress. So I am going to go to the Red Channel, also bereft of information up here. Now let's check out the Green Channel, better, we're starting to get some information down in this area and hint of information up here, and then we've got the Blue Channel which is kind of a train rack up here actually, but it does have some variation, it does have some stuff that at least might give us some hints as to what's going on.
So basically we are going to gather information from both the Green and Blue channels and bring it into the mask. So let's go to the Green Channel for starters just so that we can get a sense of how to define the area that we want to modify. Apply Image will go ahead and put the results into a selected region. So I am going to grab my Lasso tool right here, and I am going to make sure Anti-alias is turned off. So turn that check box off so that we don't get any weird edges around our selection outline so that we have a jagged selection outline which is, of course, ironically is going to give us smoother, more accurate results per our discussion long, long ago inside of our previous chapter when we were discussing everyday channel masking.
All right, and I am going to go ahead and switch to the Full Screen mode so that I can move my image down a little bit, and I am going to Alt+Click around this region right here. This would be Option+Clicking around this region on the Mac, and I am going to come down all the way down across this hair right there, that bellwether hair I was telling you about. Actually, I think I want things to be a little thicker, like so. Let's see if this works, that worked pretty nicely. All right, so something like this is a selection outline, I might even widen it a little more, like so, just to make sure that I have selected more than I reasonably need of this area.
Then I am going to go down here to the Curves modification channel, and so whenever you are using Apply Image you want to be working on the channel that you want to change, which is a rocket science. I mean, that's the way we work normally if you of course select the channel that you want to modify, and we've got a selection going. Then go up to the Image menu and choose the Apply Image command. And it's going to suggest that we go ahead and by default merge the Curves modification channel, that is, the channel itself with itself using the Multiply blend mode. Which isn't going to get us anywhere. It increases the contrast kind of in this area where we already had contrast, we don't need that. What we need is the new information. So we will change the Channel to Green. This is our Source channel by the way, hence the word Source up here. So in other words this is the channel that we are drawing information from.
Our destination channel is already determined. It is the selected channel down here. So I went ahead and selected the Green Channel, and this time I am going to change the Blend mode to Subtract, and Photoshop goes ahead and gives me the last subtract values applied, which happened to be a Scale value of 1.4 and then Offset value of 90. Let's go ahead and take the Offset value down a couple of clicks by pressing Shift+Down Arrow twice in a row, because I want to darken up the image a little bit. It's gotten over-highlighted by the Offset value, by that high Offset value. So we really want about Scale 1.4, Offset 70. You can experiment with those values of course, but if you want to get the same results I am getting, these are your guys right here.
All right, that's good, click OK in order to accept that modification. Now press Ctrl+D or Command+D on the Mac to de-select the image. Now we do have some nice sharp transitions around the edges that's just fine, but I would like to have a soft transition in this area, where we had good hairs. And so I am going to use the History Brush to brush that stuff back. So go ahead and grab the History Brush from the toolbox, it's one under the Stamp tool, above the Eraser tool. And then let's go over to the History palette and I want you to select -- as a source, I want you to select this state before you start lassoing, before you Lasso states. So in my case that's open, because I opened this document. For you it might be, if you have been along with me, you might have lots and lots of steps going inside the History palette. So go ahead and click in front of the state that occurs before the Lasso states.
Now I am going to hide my History palette and I am ready to brush, going to increase the size of my cursor a little bit and do one of these here, like so, and then I am going to press the 5 key to reduce my Opacity value to 50%, and I am going to paint in this area as well to further soften the transitions there. All right, so this looks pretty good. Now we are only getting a hint of hair up here. I am not painting by the way, I am just gesturing. We are only getting a hint of the hair that we need to use. So we need to bring in some more stuff from the Blue Channel, so I am going to go ahead and grab my Lasso tool again and I am going to Alt+Click around this region, like so in order to grab some information from Blue. And then let's go up to Image menu and choose Apply Image once again.
Now this time we are not going to get fancy, we are just going to say, we want to bring an information from the Blue Channel and by golly we just want it to be set to Normal. And the reason I am doing Normal is because this is the area that we are trying to bring information from, and there is really nothing to blend with. We are not doing ourselves any good by establishing some fancy blend formula. So Normal is good enough for our purposes. Now we don't want to really take it to slow but we'll History Brush this stuff away. We do want to bring in some of this garbage right here, and actually you know, I don't really think I selected enough. But that's okay, I will go ahead and click OK in order to accept this modification. So Blue, Normal, 100%, click Okay. I am going to go ahead and drag around this area with the Lasso tool as well because this is little fragile hair that's right there, that I want to bring back. And I will go up to the Image menu, and you know what actually, let's go ahead and do that too. Let's go ahead and back-step until I had this selection and I will add to this selection, like so. This is a better way to work because we are going to need this selection outline in just a second. So I have selected this entire area.
Now go up to the Image menu and I will choose Apply Image. I will go ahead and leave the Overlay mode set as is. So Channel should be Blue, blend mode should be Normal, Opacity 100%. So this is all grayed and you can see that I went ahead and extended the thing. And the reason I wanted to extend this area is because it's got this little hair, see that right there. That's kind of like the only good detail, we are really gathering here is this little hair, and then we can see that there are some other hairs right there that we'll have to follow, then click Okay. And then I am going to press Ctrl+L or Command+L on the Mac in order to bring up the Levels dialog box, and I am going to bring this white point over like so, so that we can see the hair better, and then I will click OK.
Now I am going to press Ctrl+D or Command+D on the Mac to de-select that region. I am going to go ahead and select my History Brush again, and if I start painting, I am going to paint away everything I did before, and actually just hit the 50% Opacity mode anyway. So I will go ahead and Undo that. Let's switch over to the History palette again and I want you to click on the History Brush state, click in front of the History Brush state before your first Lasso. If you went ahead and lassoed multiple areas like me, so right there because that was the last good state we had. And then go ahead and make that History Brush palette go away again.
Press the 0 key for 100% Opacity. I am going to reduce the size of my brush and I am going to paint like this folks, in order to paint all this stuff down here away, but I am going to leave that hair intact. And I am not painting again, I am just gesturing that hair is going to remain intact like so. Now it looks terrible, right. This doesn't look like anything we want. But it really is, is it some guidelines. It shows me where the hairs ought to be. Even though I really can't make them reappear the way. I want them to reappear. I am going to have to do some fudging. So I am going to have to paint some details in, and this just gives me basically sort of a little bit of a coloring book.
So I know where I need to paint the hairs later. All right, so that's good, so far so good believe it or not. In the next exercise, I am going to show you how to basically increase the contrast of these hairs of our good hair detail running down the side of his head here, and we are going to do that using the Dodge and Burn tools.
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