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In this exercise, we're going to take that ideal base channel, which we've decided is Blue, and we're going to transform it into a highly accurate mask. I'm still working inside that file Glancing model.jpg, found inside the 08_everyday folder. As you may recall, when you're masking an image, the portion that you want to select needs to be white, and the area that you don't want to select needs to be black, which is exactly the opposite of what we have going here. So I've gone ahead and selected the Blue channel inside the Channels panel. I'll reverse the luminance by going up to the Image menu, choosing Adjustments, and then choosing the Invert command, or pressing Control+I, or Command+I on the Mac, which gets us pretty close to the mask we're looking for.
Here is the problem though: I just applied that change to a color bearing channel, so if I switch back to the RGB image, you can see that I've pretty well ruined it. And so the moral of the story is, leave your color bearing channels alone. If you want to convert one of them to a mask, then you need to duplicate it first. So I'm going to press Control+Z, Command+ Z on the Mac, to undo that change. Then I'll grab the Blue channel, and then drag it down to the bottom of the panel, and drop it onto that little Page icon, and that creates a new channel called Blue copy.
Then I'll go up to the Image menu, choose Adjustments, and choose Invert. And notice that we now have a white on black mask, or something very nearly approximating that, and yet the RGB image itself remains entirely intact. I'm going to switch back to Blue copy here, and a little tip from me to you: what I end up doing is I'll go ahead and rename these channels for the steps that I used to create them. So, for example, in this case I copied the Blue channel, so we'll call it B space invert, and that will tell me later on that I took the Blue channel, and inverted it.
And I cannot tell you how helpful this is. When you're looking through a layered composition, you have all the opportunity in the world to investigate the opacity values, the blend modes, the advanced blending settings, the layer masks; all kinds of stuff that's going on. However, when you're working with alpha channels, you have no idea, just by looking at them, how you achieved these results. So if you go ahead and keep notes as you're working along, that will help you like you would not believe in the future. Alright, now ultimately we want the entire interior of this model to be white, and the area behind her to be black, and then we need some gray pixels around the edges to maintain the soft, organic transitions.
So we need to enhance the contrast, and we're going to do that by going up to the Image menu, choosing Adjustments, and then choosing the Levels command, or you can press Control+L, or Command+L on the Mac. Now I'm going to go ahead and zoom in on a detail here. Notice that fine hair -- I don't know if you can see it inside the video, but it's a straight hair that I'm tracing with my cursor. And because it's a single hair by itself, it's showing up as very dim. Now watch what happens if I take this White slider triangle precariously over to the left.
I'm trying to find out at what point it disappears; that we lose that white hair. So now you can it pretty well, but it goes away once I cross 10. So a luminance level of 10 is pretty much the threshold for keeping that hair. In other words, I'll go ahead and put this guy back; let's go ahead and move it to say, about 100, so that we're retaining some pretty bright details, and we can see that hair show up nicely. What that means is, if I take that black slider triangle up too high, beyond 10 specifically, then I end up losing that hair almost entirely.
And If I go up even farther to about 12, it's totally gone. And so what that tells me is if I want to retain those fine individual hairs, I need to take it easy on this black point value. Alright, I'm going to go ahead and zoom back out here by pressing Control+0, Command+0 on a Mac. And then I'm going to back off of that black point value by taking it down to 5. Now, I realize that leaves us with a fair amount of goop here in the background. You can still see some gray values showing up. In other words, the background isn't solid black.
However, we do maintain that hair, which is very important. I want you to see something else where the background is concerned. I'm going to go ahead and take that black point value back down to 0, and I'm going to increase the white point value. What I'm trying to do is show you that this background was by no means completely white in the first place. This is a stock photo, and every once in a while you'll come across stock photos that were shot against a white background, and the backgrounds are perfectly white. However, it actually tends to be a bad thing. It usually means that the photographer went in and whited out the background somehow, which means that they could have cranked up the levels, in which case you're going to have more brittle edge transitions, or even worse, it may mean that they painted into the background.
They painted white with a big, old, soft brush, and as a result you have these weird little halos around the edges of the foreground, and you most certainly don't want that. So in other words, this is the best kind of white background photo you could hope for. The photographer did not apply any digital tricks to that background, and as a result, we have these occasional snivels, you know, these little artifacts back here: dust, scratches, and so forth. That's great; that's exactly what we want. That gives us a lot more freedom when we're masking the image. So I just want you to notice that not a uniform white background; that will become important to us during the compositing phase.
For now, though, I'm going to take that white point value back to 100, and I'm going to increase the black point value to 5. And those are the values I came up with where increasing the contrast of this image are concerned. So we are doing a heck of a number on the bright details inside the image, and we're taking it easy on the darkest details. All right, so I'm going to go ahead and click OK in order to accept that modification, and I'll go ahead and rename this channel as well. So we'll call it B invert Colon, and then 5/1/100. And any time I see three numbers separated by slashes like this, I know those are levels numbers, and that tells me 5 for the black point, 1 for the gamma value, because we didn't change that, and then 100 for the white point, and that way I can replay these settings anytime I like.
Now, you may look at this and say well, we've still got some problems. We have these details inside the face that we need to get rid of, our background is too bright; what in the world are we going to do about that? Well, we're going to adjust those luminance levels selectively using a special application of the Brush tool, as I'll show you in the next exercise.
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