"What is it in an image that really needs sharpening? Answer: the edges. What if you could use 'Find Edges' to somehow only apply Unsharp Mask to the edges of an image—the parts that actually NEED sharpening—and leave the rest alone? It turns out this is not only possible, but it's relatively straightforward, and it works beautifully. And that's what I mean by 'smart' sharpening, since we are now only sharpening the parts of the image that actually need it."
|That's how John Brownlow began his 'Smart-Sharpening' tutorial for Photoshop users in 2001 and laid out the process that became part of the Smart Sharpen filter in CS2 four years later. PSP has Sharpen, Sharpen More, High Pass Sharpen, and Unsharp Mask for sharpening, but so far (Feb 08) no equivalent of Photoshop's Smart Sharpen. Like most other Photoshop features that PSP lacks, Smart Sharpen can be emulated successfully by recent PSP versions. This tutorial tells you how to sharpen your high-resolution photographs the smart way.|
|The screenshots are cropped from a photo that could become an 11-by-14-inch print; if your monitor is set at 1024 x 768, you're seeing the seagull as the same size as it would appear printed, though the print wouldn't be limited by the monitor's 72- or 96 ppi display. The image needs to be sharpened because the process of digital capture inevitably softened it. Camera movement, subject movement, focus, aperture, and shutter speed are less inevitable softeners, but one or more usually contribute as well. Sharpen, Sharpen More, and the controllable sharpeners Unsharp Mask and High-Pass Sharpen all affect the entire image instead of just the parts that need sharpening and almost always leave sharpening artifacts. Want to see some?
Scroll this page so that the three pictures are roughly centered in your screen and get out your screen magnifier (find the one that comes with Windows by using the Start Menu » Programs » Accessories » Accessibility; 2X or 3X is enough magnification). Look at the seagull's beak; it's okay in the original (though a little soft), but both Unsharp Mask and High-Pass Sharpen have added a white halo above and below the dark band. Look at the top of the seagull's head; again, the original's okay, but Unsharp mask has blown out (over-whitened) the top line of pixels and over-darkened the adjoining pixels in the sky. High-Pass Sharpen did a better job in this area, but it's just as bad as usm elsewhere. Around the eye and toward the beak and on the front of the throat, both create more blown-out pixels; while some lightening is essential to create the contrast that creates the sharpening, both usm and hps overdo it. (And hps did not, in this picture, make any dark haloes as it frequently does.) They can't help it; they're too stupid to know which pixels don't need lightening, why more contrast isn't better, and when to stop short of L = 255.
Before you turn off the magnifier, scroll down to the bottom of this page and look at the final result of a sharpening process that is "smart." Want to try it on your own image(s)? Here follow the steps that give PSP a 'Smart-Sharpen' capability. Use them on a number of photographs, think about what you're accomplishing as you repeat the various actions, and you'll be rewarded not just by a few sharper images but also by discovering ways that 'Smart Sharpen' can be educated to make it even smarter.
| Review: the black areas represent parts of the image to sharpen, and white areas are the parts to leave alone. Now, to make a mask that turns this map into a selection of the original image in which the black parts are selected (to be sharpened) and the white parts aren't…
7. Make another duplicate of the layer you want to sharpen, so the
Layers palette contains (from top to bottom) the black-and-white
"map," the new duplicate of the main image layer, and the main
This sharpening technique emulates the effect of Photoshop's (and The Gimp's) Smart Sharpen—I use "emulate" precisely here, for this technique improves on the Smart Sharpens. Because it works on a mask, it is totally non-destructive and more adjustable than they are. That you may have to make it harsher (if one of the other blend modes does a better job than Normal does) is a bonus: most other ways to sharpen have to be adjusted in the other direction lest they ruin your images. Its only shortcoming is that it sometimes produces a (fairly mild) halo effect along high-contrast edges. If the halo is present and unacceptable, you can edit it out of the edges map after step 4 above, or use the "Gentle Edge Mask."
"Translated" into PSP from Smart Sharpen Tutorial by John Brownlow (September 2001).
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