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In this exercise I'm going to show you how to limit your sharpening to just the luminance information inside of an image and why you'd want to do that. As it so turns out, you almost always want to do that. It's just that you'll notice the problem for some images much more than others. For example, this image right here, we're really going to know there is a problem. It's called The dragon.jpg. This is a Komodo dragon. This Komodo dragon, he is so pimply and there is so much rippling information, detail, wonderful stuff going on inside of this animal's flesh, that I really want to bring it out that much more. I really want to call attention to it with the Unsharp Mask filter.
So if I go to the Filter menu, you will notice that the last filter I applied is Unsharp Mask, and its right up there at the top of the menu along with the keyboard shortcut, Ctrl+F, Command+F on a Mac. If you choose that command or press that keyboard shortcut, you will reapply the last settings. So you won't get a dialog box at all. Watch, I'll just go ahead and do it. You'll just sharpen the image the same way you sharpened it last time. All right. That's not what I want, so I'll press Ctrl+Z, Command+Z on the Mac to Undo. Instead, I want to bring the dialog box back up on screen. So I press and hold the Alt key or the Option key on the Mac. Go to the Filter menu and choose Unsharp Mask, or you can press Ctrl+ Alt+F, Command+Option+F on the Mac, and that will bring up the Unsharp Mask dialog box, complete with the last settings.
Now, I really want to exaggerate the effect that we're going to get here. So I'm going to keep my In dialog box preview at 100%, and my Out dialog box preview here is at the 50% Zoom level, for what that's worth. I'm going to increase my Amount value to 500% and I'm going to take my Radius up to 4 pixels. Now, this is totally over sharpening this guy, but I'm trying to demonstrate to you this problem that we're going to see here. I want to exaggerate the problem for your viewing pleasure. Then I'm going to reduce the Threshold value to 0.
All right. So the problem is we've got these weird color artifacts. Can you see them? There's all these little weird blue spots that are showing up, and elsewhere inside of this eye in particular, we're seeing a bunch of yellow spots that are showing up as well. We've got some sort of aberrant magenta and green and orange tones going on. I mean, this guy is really very close to monochromatic and all of a sudden he has developed colors all over the place. Now, if I click-and-hold on this eye, you'll see that those colors I guess are there, those aberrant colors are there to some extent, but they weren't this bad until we decided to sharpen the image.
All right. So why in the world is this happening? I'm going to go ahead and click on the OK button to accept that modification, and I'm going to Shift+Tab my palettes back on screen. Let's go ahead and move this guy over so that we can see all of what's out there. The problem comes because we're sharpening an RGB image and we're sharpening all of the channels at once, and each channel is getting sharpened independently, but to the same extent. So we've got a sharpened version of the Red Channel and a sharpened version of the Green Channel and a sharpened version of the Blue Channel. Now, if any of these channels contains a lot of noise, and the Blue Channel does; you can see that its a total mess, and it contains disproportionate amounts of noise compared with the other two channels, which is what we're getting right here, the Blue Channel is much more noisy than either Green or Red is, then we're going to start seeing colors pop -up out of nowhere essentially.
This all makes sense. We're getting blue and yellow spots, and the blue spots are caused by light noise inside the Blue Channel, and then the yellow spots are caused by black noise inside the Channel, which is leaving Red and Green, which makes the form yellow. However it happens, it's just a big huge problem, and what we need to do is we need to sharpen that Luminance information only and leave the Color information alone. So how do we do that? Well, let's go back to the RGB image, two ways that we can approach this. Of course, we undo this command right there and I'll go ahead and do that. One is to convert the RGB image, before you sharpen it, to the Lab mode. We saw a little bit of Lab back in the previous chapter. We're going to see a little bit of Lab again by going up to the Image menu, choose mode, and choose Lab Color right there, and that will convert this image to a Lightness, a, and b image right there.
I should say that you'll hear people sometimes call the Lab mode, L-A-B, but a and b don't stand for anything, so this isn't technically like, RGB, that stands for Red, Green, Blue. Now JPEG stands for Joint Photographer Expert Group or something along those lines. It stood for something as well, but people pronounce it JPEG, people go ahead and pronounce it the way it's spelled essentially. So sometimes you do letters, sometimes you don't. But in the case of Lab, a and b just don't stand for anything. They're just random letters that have been assigned to the Tint and Temperature information right here. L stands for lightness or luminosity if you prefer.
All right. So what you do at this point is don't have all the channels selected, because if you have all the channels selected and you go ahead and apply Unsharp Mask again, same settings as before, you are going to bring out that bad color information once again. So Lab by itself doesn't solve the problem. Go ahead and press Ctrl+Z, Command+Z on the Mac. What solves the problem is clicking on the Lightness Channel to make it active, here inside the Channels palette, and then click in front in order to turn on its eyeball so that you're seeing the composite color image. But only the Lightness Channel is active. Now, go up to the Filter menu, choose that first command, and notice that, even though I've sharpened the holy heck out of this image, its way too sharpened, it's over sharpened at this point. But even so, we do not have any problems whatsoever associated with those colors, they are not coming out like they were before. We don't have colored dots all over the place. So that's one way.
I would recommend this way strictly if you are already working inside Lab. If you've already decided to visit the Lab mode in order to tweak some colors and do some of the stuff I was telling you is possible back in the previous chapter, well then, might as well sharpen inside the Lab mode as well. But you don't have to go to Lab just for the sake of sharpening. So I'm just going to go ahead and press the F12 key in order to revert the image. You can also choose the Revert command from the File menu. All right. Here inside the RGB mode, we can still accomplish our goal. By going up to the Filter menu, choosing Unsharp Mask, Ctrl +F, Command+F on the Mac, that's going to make the image look awful, of course, as we saw before. Let's go ahead and zoom in so we can see it in all of its beautiful awfulness.
Now, you will immediately follow Unsharp Mask with the Fade command. Go to the Edit menu and choose Fade. So you need to choose this before you perform any other operation, because Fade can only operate on the last pixel modification that you just applied, and if you do anything else; like you select a region or something like that, the command dims on you, and then you're going to have to back step and reapply and so on. So anyway Fade, Ctrl+Shift+F, Command+ Shift+F on the Mac, so it even has a keyboard shortcut that resembles the Filter shortcut we just saw a moment ago. All right. So I'll choose that command. You don't need to change the Opacity value, although we will because we need to back off this effect, it's over the top. But what you really need to do is change the mode and we're going to change it to Luminosity. That way we're only affecting the Luminosity and we're not affecting the color. And we'll learn more about blend modes later, but Luminosity is the way to go.
Now notice that those color problems went away just like that. It looks much, much better now. It's not an identical effect. You're not going to get exactly the same thing out of sharpening just Lightness and Lab and sharpening in RGB and then fading it just in Luminosity mode. They are two distinct operations, but while you could compare them and figure out exactly what the differences are, they aren't qualitative differences. In other words, one isn't necessarily better than the other. They're just different ways to work. All right. So I change mode to Luminosity. Now, just in the name of coming up with a better setting here, I'm going to back off my Opacity value here to 65%.
So essentially what we're doing is we're treating this filtered version of the image as a temporary layer and then we're fading it to 65% and applying the Luminosity blend modes to merge the before and after versions of the filtered effect. Click OK, and we get this much better luminance only sharpening effect. Now, as I say, this is the kind of thing that you're going to notice on some images but it's happening to some degree or other on all images. So if you want to be very careful in your imaging life here, after you apply Unsharp Mask or one of the other sharpening filters, you will always fade it to the Luminosity mode, as I've done here.
All right. In the next exercise we are going to transition from Unsharp Mask to Smart Sharpen. Stay tuned.
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