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All right, now you have a sense of how these three options work. Amount determines the amount of sharpening, Radius determines the thickness of the edges, and Threshold determines who's in edge and who is not in edge. Who gets sharpened, and who gets ruled out. Now, Amount is ultimately a personal decision on your part, and it's pretty easy to understand how the feature works. I'll be providing you with a little bit of guidance in the next exercise. Threshold is a little harder to understand, but it doesn't work all that well. I don't like the way it's put together, because it has no fuzziness built into it. It's just an on off proposition, and therefore it doesn't work as well. So could, if you are going to use it at all, then use it very sparingly, just a few levels.
And then finally we have the Radius value, which is the hardest one to understand. The most mysterious of the bunch and the most important to the Unsharp Mask process, because it defines the size of the halos and those halos are what generate the sharpening effect, or what our eyes read as sharpness. I really want you to have a very keen sense of what the Radius value does. Let's go ahead and cancel out the Unsharp Mask dialog box. I'm still working inside Orange on blue.jpg, found inside of the 14_ sharpen folder. I am switching over to the Channels palette, already did it in fact, and I could get to that palette of course by going to the Window menu and choosing the Channels command, were I of a mind to, or just clicking on that Channels tab right there. Notice this is an RGB image made up of a Red, and a Green and a Blue channel. The reason I'm showing you this is because Unsharp Mask like all the filters in Photoshop, and just about all commands in general inside Photoshop, when you apply a filter to the RGB image, you are actually applying to the Red, Green and Blue channels independently.
So every one of the channels get sharpened to the same degree, and that can create some artifacts and weird problems as we will see in the future exercise. But for now, I'm just going to go ahead and switch over to the Red channel, because it's the one that has the highest degree of contrast between the very bright snake in the foreground, and the dark background here, and that kind of contrast is going to help us understand what's going on with the Radius value. Radius is a concept that makes most sense in gray scale, as you will see. There's something about gray scale that just makes the most sense when you are trying to learn it. So I'm going to go on to the Filter menu, choose Sharpen, choose Unsharp Mask once again, and this time we are only affecting the Red Channel, because Green and Blue are not selected. And you will never do this. I mean, you don't just go around, "hey, I think I'll sharpen the Red Channel, leave the other two alone." That's not a recommended practice.
We are just trying to learn how the function works. I'm going to take the Amount value up to something like, let's say 350%, something arbitrarily high there, and then I'll scoot down to the Radius value by pressing the Tab key. Notice my guys are a little off-kilter here; I could of course drag him around, or check this out. You move your cursor outside of the dialog box; this is true of all of the best filters ones that preview the effect in the dialog box and outside the dialog box. You can just click outside the dialog box in order to extensively center that location inside of this square region, and I guess this is the center point. I guess if I wanted, and be scooted it over to the right a little bit, I would click more like here or something, and that looks pretty good, or I could just drag in inside. Just want you to know that that's an option also, by the way, when you are trying to get a sense of how the effect works, what it looked like before? Do a little bit of a before after preview.
You can turn off the Preview check box to see the before view of the image in the background. Turn it back on, to reinstate that preview. If you want to see a before and after inside the dialog box and you click and hold on that preview like so, that's your before view, then release for the after view. Just stuff to keep in mind. All right, the Radius value. I'm going to take it down to something pretty low. Now notice, if I press the Down arrow key, I'm reducing the value in increments of 0.1 pixel. So you do have pixel fractions to choose from here. And that's because it is a soft radius effect. All right, I'm going to go ahead and take it down to 1 pixel to start with, so that we can see we've got a very thin amount of blackness above the snake's snout, and a very thin edge of whiteness below the snout or inside the snout I should say.
Now I want you to keep your eyes on that snout, and now I'm going to press Shift+Up Arrow, in order to raise that Radius value in whole pixel increments, and notice how the edge is getting thicker right there, and I'm going to keep pressing Shift+Up Arrow, and watch that edge grow. See that big thick goopy edge that I'm tracing around that snake now here at a radius of -- I'm going up to 12 pixels. So we have 12 pixels of dark edge up the top and 12 pixels approximately, not exactly, approximately of light pixels down below, and notice it is a soft effect, so it's sort of blurring away. It's a nice soft halo that's getting drawn around the snake. Now why is it only getting drawn around the snake? How it is that Unsharp Mask is smart enough to trace this big thick gooey outline here, just around the snake? Well, as I was telling you a few exercises back, Unsharp Mask is looking for areas of rapid contrast in increasing the contrast at those points. It's all in proportion to the original contrast inside the image where it finds low level edges. It applies a low level effect. It just slightly increases the contrast. Where it finds big edges, it thoroughly increases the effect.
So that's why we are seeing the big thick edge drawn around the area of most obvious contrast here, but it's happening all over the image. So remember that the Radius value is all about the thickness of that edge, and that thick edge is what translates in our eyes and our minds as sharpness inside the image. So notice, if I break it down to a radius of just 1 pixel, that actually resembles real sharpness on screen, instead of just big thick gooey edges. So this would be before, and this would be after, and reason that this works for us is that our eyes are looking for edges when we are trying to discern focus inside of an image. So anything that has a lot of rapid contrast, lot of rapid transition from light to dark, that's in the area that we read as being a nice crisp edge, a tactile edge, inside of that image. All right, I'm going to cancel out yet again, because we really want to apply this effect to the entire RGB image.
The question you might have at this point is how do I actually sharpen an actual image? And I'm going to show you that in the next actual exercise. Please actually stick with me.
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