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In this exercise, I am going to show you how to use the Unsharp Mask function, an oldie but a goody sharpening filter inside of Photoshop. Notice that I am working inside the Happy family.jpeg image found inside the O3 Sharpen Filters Folder. It comes to us from Justin Horrocks of iStockphoto.com. We are going to sharpen the image by going to the Filter menu, choosing Sharpen and choosing Unsharp Mask. Two things to note: I have gone ahead and given this filter a keyboard shortcut of Shift+F5. You can do the same using the Keyboard Shortcuts command under the Edit menu.
It is a pivotal filter, that's why I have given it a keyboard shortcut, a very useful filter inside the program. But what's with the name? If it sharpens, which it does, why is it called Unsharp, which is the opposite of what it does and whats with the mask? Well, it's basically masking an unsharpening effect. It's masking actually Gaussian Blur in order to create the effect of sharpening and if you don't believe me- well, you will. Just check out the next exercise. It's amazing; it's just utterly amazing, that's what is going on under the hood. It's that Photoshop is actually blurring the image in order to create the effect of sharpening.
But that's what it is doing. So I am going to go ahead and choose the command. Here is the dialog box. We have three sliders in all, we have already talked about how Amount and Radius work in Chapter 1, but we are going to see these functions at work inside of this image and I will explain how the Threshold function works right there. Instead of focusing on the baby's face this time, lets check out this gentlemen right here. In fact, I want to take a look at his ear. I am going to go ahead and zoom in on his ear a little bit here, so that we can take in a little bit of the razor stubble and he has got this piercing hole right there that I want to focus in on.
And of course if we raise the Amount value, we are going to get a heightened perception of sharpening. So I am going to go ahead and crank this value all the way up to its maximum, which is 500%. I actually wish we could go higher with value, I wish that Adobe would change this filter. Since the beginning of time, we have been able to go as high as 500% for the Amount value, but these days I wish we could go even higher than that. And of course the Radius value is going to control the thickness of those edges, so of course the filter is exaggerating the degree of difference around the existing edges inside the image, around the previous original edges inside the image.
It's drawing light halos on one side and dark halos on the other side and the width of those halos is defined roughly by the Radius value. Again, this is a Gaussian distribution, so its distributed across a larger area than 3.2 pixels. Then finally we have got this Threshold value. Now notice right now that I am exaggerating the contrast of everything. Of his pores, of his razor stubble, just a little bit of it going on. He is clean shaven. Just all this granularity that's associated with the skin and with the digital photography process and that's because I am currently saying, with the Threshold of zero, I am saying that any two neighboring pixels, you want to go ahead and sharpen them, Unsharp Mask, as long as they're at least zero luminous levels different from each other.
Well of course any two pair, any pair of pixels, is going to be at least zero different from each other. It can't be less than zero different from each other. So everything is getting sharpened. But if I raise this value, then I am going to sharpen fewer and fewer details. So if I take this value up to lets say 40 luminance levels, then I am saying any two neighboring pixels have to be at least 40 luminance level different from each other in order to be sharpened and that's not much. So you can see that this entire range right here of skin tones and this area appears- well, its not getting sharpened. So if I click and hold, that's the original- this is the sharpened version, so this area is getting ignored, the piercing hole that's getting sharpened and some of the highlights and the shadows are getting sharpened as well and some of the razor stubble, just little bits and pieces of the razor stubble. I will go ahead and zoom in here, that's getting sharpened as well.
So we are getting this kind of pockmarked effect. I don't like it. Actually, I am not really fond of the Threshold value because it is an on or off proposition. Either the neighboring pixels don't get sharpened at all or they do get sharpened according to the values I have specified for Amount and Radius, but there is no gradual drop off between the two, which means that you either want to leave the Threshold value set to zero or you just want to take it up a little bit. If you are trying to avoid noise inside of an image, random pixel variations that are associated with digital photographs for example, then you want to take this value up to two or three or even four, maybe even five pixels, but not higher than that.
What you don't want to do is try to account for things like razor Stubble and pores and little tiny variations and get rid of them using Threshold because if you do that, you will end up with that pockmark effect that I have showed you before. So that's whats going on with Unsharp Mask. I just want to introduce you to the filter. In the next exercise, I am going to show you why this command is called Unsharp Mask and we will see how we can mimic the effects of the command using Gaussian Blur and nothing more.
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