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The all we have going here a two-parter. We've got two exercises in a row. I am just basically trying to break things up a little bit to show you whats going on under the hood with the Unsharp Mask Command, because once you understand how Unsharp Mask is put together you're going to understand a lot more about how sharpening works inside the program. In the next exercise actually, I am going to show you how to build your own Unsharp Mask using nothing more than Gaussian Blur and Apply image, but first, I want to tell you this is going to be a little bit of a talky exercise. I am not really showing you too much at this point. I want to tell you where Unsharp Mask came from just so that you know that, in case you want to know that.
You know by now that Unsharp Mark uses blurring hence the unsharp part, in order to create the effect of sharpening and it's basically masking away the edges. that's why we have the word Mask in there. But still you might think this is very tenuous. I mean what kind of engineer would come up with this crazy name? And in fact, no engineer did. Unsharp Mask is based on a traditional darkroom technique that I believe began in the 1920s, 1930s, somewhere in that range. So it's a very old technique. It's actually a fairly obscure technique. It wasnt very popular, it wasn't used very often, but the idea was, youd be working with a photo enlarger and you have a glass plate negative, just give you a sense of how old this technique is.
You duplicate the glass plate negative onto a low contrast positive, and then you would take that low contrast positive and you would put it on the other side of the glass plate on the non-emulsion side of the glass plate. So on one side of the glass plate youve got the negative, on the other side youve got this low contrast positive. They are separated by the plate. Then you would put the plate into the enlarger, you would focus the enlarger on the negative, on the emulsion side of the glass plate, and that way the positive was a little bit out of focus, so it is little bit out of the focal range and that blurring effect would cancel out the low detail information and you would end up with this higher contrast effect.
Now unless you have traditional darkroom experience and you've worked with an enlarger, I doubt that makes much sense. It's hard to wrap your mind around whats going on there. that's why I am going to show you how to do it with Gaussian Blur because actually the Unsharp Mask command that's available to us here inside Photoshop does a heck of a job of simulating the traditional darkroom technique. We can see that whole glass plate positive negative thing going on using Gaussian Blur. I am working inside of an image that's called Test shapes.PSD and its found inside of the 03 sharpen filters folder and notice that I've got this flat version of that familiar serpentine line with light dots inside of it that we saw back in Chapter 1, but I've gone ahead and flattened that image so that we have a single background layer here and then in front of that I've got this layer that's called USM which stands for Unsharp Mask 100/12/0. Those are range settings, the Amount value of a 100%, a Radius value of 12 and the Threshold of zero, and this is the effect we get right there.
We can simulate this effect down to the last pixel using Gaussian Blur and Apply Image, nothing more. I am going to go ahead and turn off that layer just so that we can confirm that these are the settings I applied. I am going to go ahead and select the Background layer. I am going up to the Filter menu. I'll choose Sharpen and I will choose Unsharp Mask, and there are my settings right there, Amount of a 100%, Radius of 12 pixels, Threshold of zero. Now we are going to set our Gaussian Blur filter to a Radius of 12 pixels in order to exactly match this effect. Its important to note, however, that we can't vary the Amount value.
We have to stick with a 100%. We cant vary this Threshold value, it has to be zero. This is the part that we can really simulate. So it has to be a 100%, it has to be a Threshold of zero, and then whatever for the Radius- we can change that. I am going to cancel out. In the next exercise I am going to show you how this is done because it's multi-step technique, this is really weird technique, but I think it's pretty interesting. It helps you understand whats going on under the hood. If you're inclined to think that its going to help you understand then please join me in the next exercise.
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