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Sharpening is an important last step in a digital workflow. You have to sharpen, because the very process of capturing an image digitally, either from a camera or a scanner, softens the image. And then at the other end of the workflow, when you go to print, you soften it further. Some people sharpen more than once. At first when they capture an image, during the editing process, and then they also sharpen for final output. I concentrate primarily on the final output sharpening when I sharpen. Before I show you how to sharpen an image, I would like to explain what sharpening does.
To do that, I have this plain image of light gray next to dark gray. I am going to go to the Filter menu at the top of the screen, and I am going to choose Sharpen and Unsharp Mask, which is the filter I most often use to sharpen. I am going to zoom way in, in the preview here, so that you can see what's happening in the Unsharp Mask dialog box. This filter has found the edge between the light gray and the dark gray. And to make that edge look sharper, it makes the light side of the edge lighter and the dark side of the edge darker.
That's what those bands are right here. And that's really all sharpening is, increasing the contrast in an edge to give the illusion of sharpness. So what do these three sliders do in the Unsharp Mask dialog box? The Amount slider affects the strength of sharpening, and the way it does that is to change the brightness or the darkness of this edge. So, for example, if I drag that slider to the left, you can see the edge becomes less bright and less dark and so sharpening doesn't look as intense. Let me put that back for a moment to show you what the Radius slider does.
The Radius determines the range of pixels at an edge that will be sharpened. So if I drag that to the right, you can see that there are now more pixels at this edge that are getting this lightning and darkening treatment, and finally there is Threshold. What Threshold does is protect those pixels that aren't really an edge from being sharpened. If Threshold is at 0, there are more lines here. More pixels are getting sharpened around the edge. But if I increase Threshold, some of this disappears, because I am setting a Threshold beneath which there won't be sharpening.
Let's cancel out of here and get a real image to sharpen. I am going to click in the second tab to see slipper.psd, and again, I am going to go the Filter menu, but before I choose Unsharp Mask, I am going to choose Convert for Smart Filters and say OK. In the Layers panel, you can see that what that has done is to convert the slipper layer into a smart object. And because this is a smart object, I can apply my Unsharp Mask filter in a way that will make it re-editable in the future.
So I am going to go to the Filter menu again and go down to Sharpen and choose Unsharp Mask. By the way, of the choices here, the only ones I recommend are Unsharp Mask and Smart Sharpen, which is similar to Unsharp Mask but has some additional features. So I will choose Unsharp Mask and I want to make sure that at least one of these previews is at 100%. In fact both of them are, as I see here and here, because 100% view is necessary in order for you to really judge the sharpening.
So when I use this dialog, I usually do set Amount really high and then I vary the Radius, because with Amount high I can see the effects of changing the Radius. Now I never go larger than about 2, and you can see that does not work in this image. Your choices for the Amount slider and the Radius slider will vary depending upon the size of the image, so I strongly recommend that you resize your images before sharpening. I usually have a master copy of a layered file, and then I make separate copies from there, resize the copies for whatever my output is, and then sharpen the copies.
So I have got my Amount, I have got my Radius. I might increase my Threshold here, because I see that some items are getting sharpening up here that aren't really edges, these little white spots. So as I increase Threshold, those will go away and it won't be sharpened. I will click OK, and that completes the sharpening. Now because I converted the slipper layer into a smart filter, I can always come back in and re-edit my sharpening settings. So if I change my mind and I think that this slipper looks a little too crispy, I can double-click Unsharp Mask and I will just turn the Amount down a bit and that looks better. I will click OK.
So that's how sharpening works. Be sure to resize your images before sharpening, and here's a tip if you are sharpening for print. You are going to want to sharpen to an extent that looks like a little bit too much on your computer screen, and that will give you a print that's just the right amount of sharp.
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