Challenge 1: Faking Shallow Depth of Field — Solution Walkthrough

The general approach:

  1. Use a selection tool from Chapter 3 (Lasso/Free Select, or Magic
     Wand/Select by Color if the subject stands out clearly enough)
     to select the subject specifically.
  2. Invert the selection (Chapter 3's own Select Inverse/Invert),
     so everything EXCEPT the subject is now selected — the
     background.
  3. With the background selected, apply Gaussian Blur from this
     chapter. Per this chapter's own core rule inherited from Chapter
     3 ("nothing happens outside an active selection"), the blur only
     affects the selected background, leaving the subject completely
     untouched and sharp.

Why this combination works:

Gaussian Blur on its own would blur the entire image uniformly, with
no awareness of "subject" versus "background" at all — it's Chapter
3's own selection-restriction rule that lets a filter be confined to
only part of the image, exactly the same principle already used for
brushes, adjustments, and now filters.

Why doing this on a duplicate layer matters too:

Per this chapter's own material, applying any filter destructively
alters pixel data — working on a duplicate layer (Chapter 7's own
habit) keeps the original sharp image safely available underneath, in
case the blur selection needs adjusting later.

WHY THIS WORKS AS AN ANSWER
------------------------------
This exercise ties together selections (Chapter 3), the duplicate-
layer safety habit (Chapter 7), and this chapter's own Gaussian Blur
into one coherent workflow, demonstrating that filters obey the exact
same selection-restriction rule established much earlier in the
course.