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Photoshop Top 40
Illustration by John Hersey

15. Alpha Channels


From:

Photoshop Top 40

with Deke McClelland

Video: 15. Alpha Channels

(Music playing) Deke's Photoshop? Deke's Photoshop? Top 40! In Photoshop masking is a black art, or white art depending on your perspective. See where a mask is concerned is black conceals and white reveals, or put differently everything that is black is protected, everything that is white is selected. The melting pot, the place where black, white, and all the shades of gray come together, is the alpha channel. The alpha channel is where masking begins.

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Photoshop Top 40
7h 13m Intermediate Dec 21, 2009

Viewers: in countries Watching now:

There's nothing people love more than lists, and Photoshop Top 40 offers a great one, highlighting the best features in Photoshop. Deke McClelland counts down to #1 with a new video each week, detailing one great feature after another in this popular digital imaging application. The videos cover tools, commands, and concepts, emphasizing what's really important in Photoshop.

This is an ongoing course that will be updated monthly.

For the newest updates please go to our blog entry for Deke's Photoshop Top 40.

Topics include:
  • Assembling multiple pieces of artwork with layer comps
  • Creating a black-and-white image from a color photograph
  • Merging multiple channels to create an alpha channel with calculations
  • Selecting images with the Pen tool
  • Masking images using the Brush tool
Subjects:
Design Photography
Software:
Photoshop
Author:
Deke McClelland

15. Alpha Channels

(Music playing) Deke's Photoshop? Deke's Photoshop? Top 40! In Photoshop masking is a black art, or white art depending on your perspective. See where a mask is concerned is black conceals and white reveals, or put differently everything that is black is protected, everything that is white is selected. The melting pot, the place where black, white, and all the shades of gray come together, is the alpha channel. The alpha channel is where masking begins.

Feature #15 is alpha channels, and an alpha channel is a means of saving a selection outline for later use. You can also develop a full-blown mask that you can use to create a highly articulated selection outline. By extension we are going to a look at layer masks, which are nothing more than alpha channels that are associated with independent layers inside Photoshop. Now it's a brand-new year, so I thought it was only fitting to serve up a model that we've already seen so far, back in feature #18 Smart Objects. You may recall she comes to us from Valua Fotolia.

And I have set her against this otherworldly, futuristic 2010 background here, from Men in Black, also of image vendor Fotolia. So now how did I go ahead and create this effect? I am going to show you inside of this video how to generate a highly articulated mask that will serve as a layer mask you see before you right now. So notice what's going on here. I've got one layer that set to Multiply. You may recall this back from feature #18. That allows us to burn in this dark hair into the background.

So we'll firm up the edge details. Then in front of that I've got this layer that set to the Normal blend mode as you can see in the top left corner the Layers palette, and it has a layer mask assigned to it. So what I'm going to do as I am just going to get rid of this layer mask by right-clicking on it, and choosing Delete Layer Mask like so. Then the layer mask goes away. She was originally set against the white background, as you can see right here. Now just to make things a little bit easier to work with. Notice that we don't have much white background down here in the lower right corner of the image.

So we are running out of room. And just to give myself a little more room to work I added a layer of white. Because when you're working inside the Channels palette, you are always seeing the composite version of this image. Now here is a cool technique I came up with. And you're either going to think this is the best thing you've ever seen in your life or you are going to go huh! But here's the idea you may recall again from the Smart Objects video that both of these images are Smart Objects that are linked to a single Camera Raw original. So if I were to double-click on either of them, I open up the Camera Raw window like so.

Now eventually I want as much contrast between the model and her white background. So I am going to cancel out for a second, and I am going to show you what the contrast looks like right now. I'll switchover to the Channels palette. Here is what the image looks like in the Red channel. So we have a little bit of contrast going on, a lot where the hair is concern. The hair shows up very well against the background, but the skin tones don't show up so well. So we are looking for differences in luminance levels. That is we want her to be either very dark, against a very bright background or very bright against very dark background.

So a lots of contrast. So Red isn't so good, Green is getting better, and then Blue is best. But we can increase that contrast if we want to before we embark on the mask from Camera Raw. Let me show you what I mean. I'll switchback to RGB, switch to the Layers palette, double-click on this thumbnail to bring up the Camera Raw dialog box and I am going to do something ridiculous. I am going to go ahead and send this slider triangle all the way to the right, here for the Temperature value. So I am raising that Temperature value to +100 in this case, because I am making relative modifications.

But what really counts here is that I am maxing out that Temperature value, and now I am going to max out the Tint value. So in other words I've made her as warm as possible, I'm subtracting as much blue from this model as I can. And we'll see why that's useful in the second. I'll go ahead and click OK, bear in mind these are temporary modifications. We can always come back and change your minds later as we will. I will go ahead and click OK. And now having made that ridiculous adjustment I'll switch back to the Channels palette. Now check out the Red channel. Totally blown out. It's not going do us any good whatsoever.

Here is the Green channel. Better obviously. Here's Blue. Oh, my gosh! Look how much contrast we have now. We just did a ton of our masking work inside of Camera Raw. This is a heck of a trick. All right, now I am going to go ahead and grab that Blue channel and I am going to make a copy of it, by dragging it onto this little page icon, dropping it, and now we have this channel called Blue copy. But what it really is, it's an alpha channel. I'll go ahead and rename it alpha , because it is independent of the color bearing channels.

So these channels right here Red, Green, and Blue are necessary to make up the RGB composite. Alpha is extra, and we can do whatever we want with it. We can build our own mask. Now as I was saying at the very outset white represent selected areas inside the image, and black represents deselected areas. That is to say white reveals, black conceals. We want her to be totally white so that were revealing her and we want her background be totally black. So we are concealing that. So in other words what we need to do is go the Image > Adjustments > Invert, or of course the easier thing is just to press Ctrl+I, Command+I on the Mac in order to invert this channel.

And notice we are not harming the image at all. So it's a totally independent color channel that we are working with. Next, I am going to go up to the Image menu, I am going to choose Adjustments, and I am going to choose Levels, because we need to increase the contrast of our mask, and Levels is the easiest way to do it in my opinion. So I'll go ahead and choose the Levels command, and I'm going to increase this black point value to 10. So I am saying that anything that has luminance level of 10 or darker will become black. So just a slight modification there. Then I am going to drag this white point value until that third numerical value that you're seeing changing right there reduces to 120.

So in other words anything with a luminance level 120 or brighter bearing in mind that 255 is white is going to change to white so that's about half of the luminance levels inside of this image. Actually, a little more than half. And we get this effect right here. So we are not going for photorealism, we're trying to create a mask. We want as much contrast as possible. Now click OK in order to except that modification. The next thing to do, and we saw this way back when I demonstrated feature #31 the Brush tool. I showed you how to do overlay painting, and that's what we are going to do here. I am going to grab my Brush tool, I'm going to switch my brush so it has a Hardness value 0% like so.

Then I am going to switch the mode from Normal to Overlay, and what that allows me to do is protect the highlights and shadows. So as long as I'm painting with white, I am going to affect just the Highlights and Midtones, as long as I'm painting with black, I'm going to affect just the Shadows and Midtones. You know what, I'm going to start with black. I am going to press the X key so then my foreground color is black like so. Then I'm going to increase the size my brush by pressing the bracket key a few times. I'm going to paint into this hair detail, because I really want to scale back the hair as much as possible, because we already had that wonderful Multiply layer to fall back on.

Then I will paint away the hair a little bit, and now scroll down to the bottom portion of the image. In the case of this area, the flesh tones here, we need to brighten the image so that she appears totally white. So I am going to press the X key to once again switch the foreground color, this time to white. Then I am going to paint inside of her. Notice that I'm only affecting the Highlights and Midtones. I'm not affecting the Shadows that is to say the black background, because I've set my blend mode to Overlay. Now I am going to go ahead and change my blend mode from Overlay to Normal like so, because I want to paint away the stuff that's inside the model.

We don't need Overlay anymore. It's not our friend now. I'm going to click the down pointing arrowhead right next to the brush preview, and I am going to change the Hardness value to 100%. Now I'll just paint inside these regions like so in order to paint them away. I'll paint up here in the hair just little bit as well just to make sure that I am getting rid of these little snivels here and there. All right, this looks pretty good to me. Let's now convert this alpha channel into a layer mask, which as I'd say it's just an alpha channel that's assigned to an independent layer. I switch back to my Rectangular Marquee tool just because I get a cross-cursor.

It's a little less intrusive. I'll switch back to the RGB composite image, to load an alpha channel as a selection outline. You press-and-hold the Ctrl key. This is the simplest way to work. Or the Command key on the Mac, and you click on that channel. So it's just Ctrl+Click or Command+ Click any place on that channel in order to convert that alpha channel to a selection outline. The deed is now done. Switch back to the Layers palette, and because I want to go ahead and apply this mask to the top layer, I'll click on the top layer. I'll turn off the white layers so we can see what we're doing, and then I'll drop-down to this Add a layer mask icon, and click on it.

And we have now created a layer mask that quickly. We did so much work inside of Camera Raw by virtue of the fact that we warmed up the images much as we could buy maxing those Temperature and Tint values, we got rid of the blue information, and we've created the highest degree of contrast possible. Now we just need to finesse the mask at this point. What I wanted to do as I want to do as I want to reveal some of that background image right there, the Multiply image that is to say. That way we won't have some of these slight edge artifacts that we've going on.

Sometimes it just doesn't look realistic , right in this area for example the way the hair is kind is chipped away. It's not what we want. So what we are going to do is we are going to choke the mask ever so slightly. And I am going to do that by making sure the layer mask is selected, and then I'll go up to the Select menu and I'll choose Refine Edge. You've got a keyboard shortcut right there Ctrl+Alt+R, Command+Option+R in the Mac. In order to see what I'm doing I want to switch to this very first previewing option, Standard. So I'll click on it. Now if you see marching ants, like we do right here, that's getting in our way.

We can't see what we were doing with those marching ants there. So just press Ctrl+H or Command+H on the Mac for Hide, to hide those ants. And then we're ready to work. Now we saw Refine Edge back in feature #35. So I've already explained how these options work. What I am going to do in this case when I'm choking a mask, the way you want to work is you want to go ahead and reduce the Radius value to 0, and you want to take the Smooth value down to 0 as well. So Radius and Smooth should both be 0. You can fool around with Contrast value if you want to, but for this image I am going to leave it set to 0.

I'm going to take the Feather value up to 2, which gives us a little softness to work with. Then what you want to do is you want to contract into that softness. So I am going to Contract value down to -75 actually it works out pretty darn good for this image. You can see that we are contracting the mask. We are introducing some darkish edges around the hair detail and around the face detail as well. Click OK in order to accept that modification and we get this result here. Now you're going to have hand- finesse the mask at this point, because we actually have made a change to the contents of this layer mask right there.

I'll go ahead and grab my Brush tool once again. A few changes that I am going to make. I make sure in my case that the foreground color is set to white. And notice that there is a little bit of blue in her forehead. I'll click in order to get rid of it. And what I'm doing in this case is I am reestablishing the detail that's inside this layer, and covering up the detail that's found inside the Multiply layer. We were seeing through her forehead to the blue forehead in the background. I might also paint inside of the hair up here, this sculpted hair. And I'll paint pretty small, I am just doing individual clicks every once while here.

Then finally what I wanted to do a couple of finallys. Actually one is I want to paint into her chin a little bit so she doesn't look like she has this quite this weird blue, so I am cutting into her chin. I want things to look little more organic to our background. Then finally, and this I am just going to have to do by hand. Finally, notice that I've got this bad back detail going on here. Many of you may have bad backs and here is how you solve it. I am going to go ahead and bring up my Brushes palette like so. And then I am going to click on Brush Tip Shape and I'm going to decrease my Spacing value so that I have a very smooth brush.

I will take it down to about 10% let's say for now. I will reduce the Size of my brush by pressing left bracket key a few times and then I am going to click right here, and then I am going to Shift+Click right there. When you click and Shift+Click with the brush, as I just did, you connect the click and Shift+Click points with a straight line of brushes, and the reason that I had to decrease the Spacing value was so that we didn't have a real lumpy brush. Notice if it was too big, we'd have a bunch of lumps going on. Even at 25% you have too many lumps. You notice those little lumps right there, and the back would not have been smooth.

That's why I took that value down. Anyway, the deed is done now, so I don't care about the Spacing value. Now the final step is to reestablish her original appearance. I am going to do that inside of Camera Raw. But I actually want to go little bit farther than I did before. So for starters I am going to double- click on either one of these thumbnails to bring up the Camera Raw interface and I will establish those same values that we had at the outset of this lesson, 20 for Temperature and in 0 for Tint and I'll click OK. Even though she looks much better, in my opinion she doesn't quite match her environment.

If she was really in his ultra cool environment , then her skin tones would be cooler as well. Because we're all informed by our environment, don't you know? So I am going to double-click on the Multiply thumbnail again, either thumbnail will do actually and I'm going to lower the Temperature value to -40. And then I am going to take the Tint value down to -20 in order to remove some of that pink and add a little bit of green. Then finally I am going to take that Vibrance value down to 0, and I'll click OK.

This is the final version of the composition folks. Thanks to the power of alpha channels combined along with Camera Raw and the common everyday average layer mask here inside Photoshop.

Find answers to the most frequently asked questions about Photoshop Top 40.


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Q: Is there a way to batch convert an entire folder of photos from the RBG color mode to the CMYK color mode without having to open and convert each individual image?
A: In the Actions panel in Photoshop, create an action that converts an image from RGB to CMYK. Then link to that action from File > Automate > Batch inside Photoshop.
Next, in the Bridge, select a folder of images. Choose Tools > Photoshop > Batch. Select the action inside the ensuing dialog box.
Or, in Photoshop, select File > Automate > Batch, and select the action and the folder inside the dialog box.
See also: Photoshop CS2 Actions & Automation, Chapter 2 “Action Essentials.”
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