Challenge 2: Where "Unsharp Mask" Actually Comes From — Solution Walkthrough

The explanation:

Per this chapter's own material, "Unsharp Mask" is a counterintuitive
name historically borrowed from a darkroom photography technique. The
tool increases apparent sharpness by boosting contrast specifically at
edges — and it detects where those edges are by comparing the image
against a deliberately blurred, "unsharp," version of itself, used as
a reference mask. The name describes the reference mask used inside
the process (an intentionally unsharp/blurred copy), not the final
sharpening result the tool produces.

Why the name feels backwards at first:

It's natural to assume a tool named "Unsharp" would blur an image,
since "unsharp" sounds like the opposite of sharp. The name actually
refers to an internal step in the sharpening process — creating a
blurred reference copy specifically to identify edges — not to what
the tool does to the final image overall.

Why this is worth knowing, not just trivia:

Understanding that the "unsharp" part refers to an internal reference
mask, not the output, helps make sense of why the tool's own settings
(radius, amount, threshold) work the way they do — the radius setting,
for instance, controls how blurred that internal reference mask is,
which directly determines how wide an edge the sharpening affects.

WHY THIS WORKS AS AN ANSWER
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This exercise checks that the historical/mechanical reason behind
Unsharp Mask's own confusing name is genuinely understood, not just
memorized as an arbitrary fact.