Challenge 2: 50% Opacity vs. a Half-Transparent Mask — Solution Walkthrough

50% opacity:

Per this chapter's own material, opacity affects the entire layer
uniformly — every single pixel on that layer becomes equally
semi-transparent, blending evenly with whatever is beneath it across
the whole layer. There's no part of the layer that stays fully opaque
and no part that becomes fully transparent; the effect is applied
identically everywhere.

A mask making exactly half the layer transparent, half fully visible:

This produces a genuinely different visual result — one half of the
layer remains completely visible (0% effective transparency there),
and the other half is completely hidden (fully transparent there),
with a hard or soft edge between the two depending on how the mask
itself was created. The layer's own opacity setting itself would
remain at 100% throughout; the mask is doing the work of varying
visibility by area instead.

Why these produce visibly different results even though both
"average out" to some sense of half-visible:

50% opacity shows a faint, blended version of the ENTIRE layer's
content everywhere at once. The half-transparent mask instead shows
one complete half of the layer at full strength and hides the other
half completely — a spatial split rather than a uniform blend. These
are visually and practically very different outcomes, even though a
casual description of both might loosely say "half visible."

WHY THIS WORKS AS AN ANSWER
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This exercise directly applies this chapter's own opacity-vs-mask
distinction to a concrete comparison, correctly explaining why uniform
blending and area-based visibility produce genuinely different visual
results despite sounding similar in casual description.