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The “unsharp” that drives both Unsharp Mask and its suc-
cessor, Smart Sharpen, is a function of the softly tapering
halo that the Radius value applies. Once you understand
this concept, you can master the art of focus in Photoshop.
Consider the line art in the figure below. The top-left image
features dark lines against a light background. The other three
are sharpened with increasingly higher Radius values. Through-
out, the Amount value is 200 percent and the Reduce pop-up
menu is set to Gaussian Blur. In each case, the sharpening
filter traces the dark areas inside the lines (the brown areas)
with a blurry dark halo and the light areas outside the lines
(the green areas) with a blurry light halo. Regardless of the
Reduce setting—Gaussian Blur, Lens Blur, or Motion Blur—
the thickness of these halos conforms to the Radius value.
Given that the Radius value is all about blurring, it’s no sur-
prise that this option also appears in the Gaussian Blur dialog
box, where it once again generates halos around edges. In fact,
if we were to trace the lineage of these filters, Gaussian Blur
is Unsharp Mask’s grandparent, which in turn witnessed the
birth of Smart Sharpen. It’s downright biblical, I tell you. The
missing family member in between is an obscure command
called High Pass.
Why should you care? Because Unsharp Mask’s parent, High
Pass, is in some ways a more flexible sharpening agent than
its first- or second-generation progeny.using Blur to Sharpen
Original line artRadius: 12 pixelsRadius: 50 pixelsRadius: 25 pixels224 Lesson 7: Sharpening and Smart Objects