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All right, now for two more averaging functions. These are Despeckle and Dust & Scratches, and I have applied the Median filter with a Radius of 16 pixels to the 3 BL layer right there. I have now selected the 4 BR layer, which is ready to be edited. Here's how it works. I am going to go to the Filter menu, choose Noise. Despeckle and Dust & Scratches in many ways are kind of opposites of each other. Despeckle is going in and averaging the non-edges and keeping the edges intact, whereas Dust & Scratches one that gives you control. Notice it's got the dot dot dot.
Despeckle doesn't. Dust & Scratches is allowing you to average the edges inside of an image and preserve the non- edges. So we'll see how that works. Let's start with Despeckle. Now Despeckle is a pretty subtle filter and you typically apply it multiple times in a row if you are going to use it at all. It's really looking for single pixel anomalies essentially inside of an image or small patches of differently colored pixels, so it's looking for that noise and trying to eliminate that noise while keeping the good edges inside the image.
The thing is it doesn't work quite that well. It does get rid of good edges too as you go through the image, but if you apply it two or three times in a row you can sometimes get good effects in a noisy image. So I'll go ahead and choose Despeckle, and notice that the amount of noise in the background that sort of bump pattern that we have back there in the background went away ever so slightly. Now of course, the first command in the Filter menu is Despeckle. So I'll go ahead and apply that first command, and so I can reapply, and from this point on of course, I can press Ctrl+F or Command+F on the Mac to reapply this Filter multiple times in a row.
So that's several applications, I can't tell you exactly how many. Let's look at the History palette and see. One, two, three, four, five, six, seven applications of Despeckle right there. And as a result we have done a fine job of softening these bumps in the background. We have definitely softened his face and it looks more like a Blur effect than it does in Averaging effect. And then right around the outskirts of this rectangle notice that we still have a variety of differently colored pixels so we still have that noise pattern intact right there at that big edge. All right, so that's Despeckle.
So again, if you have noise in an image and you just want to downplay the noise, the old-fashioned way without going to the Reduce Noise command, which is much more powerful frankly, then you can try out Despeckle. I'm going to go ahead and restore the Median version of this image right there so that we can re-approach the 4 BR layer using the Dust & Scratches command. Now I like to joke about the Dust & Scratches command. Not because I don't like the filter, I actually think it's a really great filter. The problem with it is it's horribly named. It does not get rid of either dust or scratches. In fact, if anything it does a wonderful job of preserving dust and scratches as we'll see. So I'm going to go ahead and choose the command.
Now it is ultimately the progeny of the Median filter, as I'll show you. Go ahead and choose Dust & Scratches, sort of center this dude right there inside of the In dialog box preview, and I'm going to go ahead and take that Radius up from the keyboard by pressing the Up Arrow key and you can see we are getting that same sort of effect where the lines between the teeth are going away fairly rapidly right there at the beginning and then they sort of come back with some of the higher values. If I take this value up to 16, just the Radius value. Leave the Threshold value set to 0. We are getting a nearly identical effect here from Dust & Scratches vis-?-vis what we got from the Median Filter. So the interior of the layer is exactly the same. It's the exact same effect. The difference is this command does not get applied to the transparency map. So notice that we still have sharp corners around the outskirts of the layer. But otherwise we have the exact same effect on right as we do on left.
In walks the Threshold function. And I was telling you. So Dust & Scratches is designed to average the edges inside of an image and leave behind the non-edges. So you are really trying to average everything but the dust inside the image. Everything but the noise and the particles and all that jazz. That's the kind of stuff you are trying to keep, and that way you can do a little averaging in one section of a noisy photograph and preserve the noise throughout. So it's not obvious you've been there, which is great and we'll see creative examples of this command in upcoming exercises.
What you do is you basically raise this Threshold value and it works just like the Threshold value inside the Unsharp Mask dialog box. So at 10 levels we are saying that in less two pixels are 10 luminance levels different from each other, do not average them. So instead of not sharpening them, now we are not averaging them. So anywhere where we have low level noise, see those little low level bumps right there? They are being preserved because they are not 10 luminance levels different from each other. Everything that is 10 levels or more different is being average. So again, just the opposite of what we were seeing with Despeckle.
I am going to take this guy up to 30, and you can see here that preserves sections of the face which I think is kind of nice, and if I were to take this value down the face starts leaving the territory there, and then when I increase the Threshold value, one again the face starts coming back and it comes back incrementally as you can see here so that we have a little bit of choppiness around the edges which I think looks just dandy. All right, so that's Dust & Scratches. Does not get rid of Dust & Scratches, in fact, if anything preserves dust and scratches inside of an image, do not use it to get rid of dust and scratches. We'll not work for that purpose. We'll work for other wonderful purpose, as we'll see.
All right, so I'll OK. In order to accept that modification just so that you can see the difference between averaging which we are seeing right now at the bottom of this image and blurring -- this is blurring up top if I press the Home key, because I have gone ahead and calibrated this Window so that we can switch back and forth between the top and bottom images. These are the blurry images. Gaussian Blur on left and Box Blur on right, and these if I press the N key are the averaged images Median over here on left, and Dust & Scratches over here on right all using a Radius of 16 pixels.
In the next exercise, I'll show you some more Blur filters starting with Surface Blur.
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