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Now strange is that may sound, any discussion of focus altering filters inside a Photoshop has to begin with Gaussian Blur. And if you know anything about Photoshop and youve spent six seconds using Gaussian Blur, you maybe thinking, "Give me a break, Deke!" Not only do you not need to show me Gaussian Blur, you don't need to show my grandmother Gaussian Blur, it is that easy to use. It just has a Radius value, you raise the Radius value, you get more blur, you lower the Radius value, you get less blur, that's all there is to it. But heres the deal, it's responsible for the way Unsharp Mask works.
In fact, its so responsible for Unsharp Mask, I can actually duplicate the effects of Unsharp Mask, down to the last pixel, using Gaussian Blur by itself and no other filter. Out standing is that sounds, that incredibly boastful statement, I will bear out in an upcoming exercise, I'll show you what I mean by that, because it really is helpful to understand that sharpening is really blurring, that they are one and the same. But first, lets understand whats going on with sharpening and I also want to show you whats meant by the term Gaussian. We'll start off with this image called Happy family.jpg that's found inside the 03_sharpen_filters folder.
And it comes to us from photographer Justin Horrocks of iStockphoto.com, and I am going to go up to the Filter menu, I am going to choose Blur and I am going to choose Gaussian Blur, the most essential of these many blurring functions. Notice that I decide to keep our shortcut to it of Shift+F7 for my own purposes. You can likewise assign a keyboard shortcut to this filter using the Keyboard Shortcuts command under the Edit menu. Alright, I am going to go ahead and choose the command, brings up the Gaussian Blur dialog box. Lets go ahead and center the zoom on this baby's face here and I am going to click on the plus (+) sign to zoom-in and increment here to 200% and if I click and hold, you can see that this is the original baby face, and when I release- if you look closely, you can see the effects of this default Radius value of one pixel.
The idea is that Photoshop is applying this series of scrubbing bubbles to the image and each bubble is emanating from a single pixel at a time. So at any given nanosecond, Photoshop is applying a bubble to one of the pixels inside the image and the bubble currently has a Radius of one pixel, that is to say, a diameter of two pixels. But as well see in the next exercise, that Radius actually gets distributed, so that's larger than whatever the Radius value we entered here. But when it comes to just blurring the image, all you really care about is if you raise the value you're going to get more blur.
For example at Radius value of 12 pixels, we're pretty much obliterating the focus of this image and we can much farther with it. If you take the value down, I'll go ahead and click on that Radius value again and lower it to, lets say 0.6 pixel, then you're going to reduce the amount of blur you apply to the image, but you can still see the effects. If you closely, I am going to zoom-in on the baby's face even more, click and hold, this is the original baby eye, and release, this is the blurred baby eye. So it's just a slight amount of blurring. Now the minimum value that will produce any effect whatsoever inside this dialog box, and inside Unsharp Mask as well by the way, is a Radius of 0.3 pixel.
If you go below that, I'll press the down arrow key to go down to 0.2 pixel and I'll click and hold, this is before, I'll release, this is after. No difference. It's just a function of the way the math is calculated inside a Photoshop, that you have to have a Radius value of at least 0.3 pixel or higher to get any effect whatsoever. So if you ever just want to assign just a tiny little bit of sharpening to an image, something that verges on anti-aliasing, it's so subtle then a 0.3 Radius is the smallest you can apply.
Just bear that in mind, of course you can raise the value by pressing the Up arrow key, that will raise it in increments of 0.1. You can lower it in increments of 0.1 by pressing the Down arrow key, for whole number increment you press Shift+Up arrow or Shift+Down arrow. It's just standard filtering stuff. Many filters actually don't subscribe to that role. The bad ones will ignore you when you press the arrow keys, but the good ones will pay attention. So anyway, I don't really feel like blurring these good people. They might as well remain nice and sharp, we'll come back to them actually when its time to sharpen the image.
The image that I really want to blur here is this guy. It's a demonstration image, in fact its called Gaussian demo.PSD and its going to allow us to see the difference between a Gaussian luminance distribution and a Linear luminance distribution in the next exercise.
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