ADVANCED COMPOSITING & RETOUCHING - Chapter 8, Exercise 2
Removing the Middle Filter From a Stack: Photoshop vs. GIMP
====================================================================================

QUESTION:
Explain what happens in Photoshop if a multi-filter stack was applied inside
the Filter Gallery to a Smart Object, and the retoucher later needs to remove
just the middle filter from that stack. Then explain how the same change
would need to be handled in GIMP.

SOLUTION / EXPLANATION:

IN PHOTOSHOP:
Because the stack was built inside the Filter Gallery and applied to a
Smart Object, the entire stack exists as one single, reopenable Smart
Filter entry in the Layers panel (as this chapter describes, extending
Chapter 4's Smart Filter concept to a multi-filter stack). Double-clicking
that Smart Filter entry reopens the full Filter Gallery exactly as it was
left, with every filter in the stack still present, in its original order,
with its original settings. The retoucher can simply select the middle
filter within that reopened Gallery and delete or disable it, then confirm
- the remaining filters stay exactly as they were, in their original order,
with no need to redo any of the surrounding work. This is possible
specifically because nothing in the stack was ever permanently applied to
the actual pixels - the whole stack remained live, editable data the entire
time.

IN GIMP:
Because GIMP applied each filter as a separate, sequential, largely
destructive operation (per this chapter's own point that GIMP has no
equivalent combined multi-filter workspace), there's no single reopenable
entry representing "the whole stack" to edit after the fact. If the edits
are still within GIMP's linear undo history, the retoucher could undo back
past the point where the middle filter was applied, remove or skip that one
step, and then redo the filters that came after it - but this only works if
no other edits have been made since, and undo history in most workflows
doesn't survive across a save/reopen. If the file has since been saved and
reopened, or if other work has happened since, there's no reliable way to
surgically remove just the middle filter without starting the affected
portion of the stack over from before that filter was first applied - a
direct, larger-scale consequence of the same narrower non-destructive scope
already named for GIMP in Chapter 4.

--------------------------------------------------------------------------
WHY THIS WORKS AS AN ANSWER:
It explains specifically why Photoshop's Smart Filter stack allows surgical
editing of just one filter within it (the whole stack stays live and
reopenable), and contrasts this with GIMP's reliance on undo history, which
only works within the same session and breaks down entirely once the file
has been saved/reopened or edited further - a concrete, practical
consequence of the gap named earlier in the course.