ADVANCED COMPOSITING & RETOUCHING - Chapter 3, Exercise 1
Clone Stamp/Healing vs. Compositing: Same Goal, Different Scale
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QUESTION:
Explain how the Clone Stamp/Healing skill from Raster Editing Fundamentals
Chapter 7 and the compositing skill in this chapter share the same underlying
goal, and what specifically changes between the two.

SOLUTION / EXPLANATION:

The shared underlying goal is: make a seam between two pieces of pixel data
invisible, so a viewer can't tell where one ends and the other begins.

The Clone Stamp and Healing tools do this within a single photograph. You
sample pixels from one area (say, a clean patch of sky) and paint them over
another area (say, a blemish or a distracting object), and the healing
algorithm (or your own careful sampling with the Clone Stamp) blends tone and
texture at the boundary so the patched area matches its immediate
surroundings seamlessly. The two areas being blended already share the same
lighting, color grade, camera, and shooting conditions, because they came
from the exact same photograph - the only real challenge is matching the
immediate local texture and tone at the small boundary being patched.

Compositing keeps the identical goal - an invisible seam - but scales it up
to two (or more) completely separate photographs, each with its own
lighting setup, color cast, camera angle, and shooting conditions. This is
what specifically changes:

  - Instead of matching a small local patch to its immediate surroundings,
    you're matching an entire subject's overall color and tone to an entire
    different scene's color and tone (this chapter's "Matching Color and
    Tone Across Sources" section).
  - Instead of assuming lighting direction is already consistent (guaranteed
    within one photo), you have to actively check and correct for
    potentially conflicting light sources between two separate photos
    ("Matching Lighting Direction and Perspective").
  - Instead of a small, local blend radius, you're managing a large-scale
    boundary - the entire outline of a subject - which is why the precise
    masking work from Chapter 2 has to happen first, with feathering applied
    to that boundary the same way healing blends a small patch's edge.

So the tools and scale differ, but the test for success is identical in both
cases: can anyone tell where the seam is?

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WHY THIS WORKS AS AN ANSWER:
It names the shared goal explicitly (an invisible seam) rather than treating
the two techniques as unrelated, and then walks through what specifically
scales up between them (local texture matching vs. whole-scene color/lighting
matching, small blend radius vs. a full masked subject boundary) rather than
just asserting they're similar without detail.