Section 8 · Image Construction & Compositing

Layer Masks

Definition

A grayscale channel attached to a layer controlling which parts of it are visible — black conceals, white reveals, gray produces partial transparency — without deleting pixels.

Why it matters

Masking is non-destructive. Erasing is permanent; masking is a decision you can revisit at any point, which is exactly what iterative compositing requires.

Example

Painting black into a mask to hide a source image’s background, then painting white to bring back an edge removed too aggressively.

Note

The eraser tool is the enemy here, and it’s the instinctive reach. Try it both ways on the same image — an erased edge can’t be recovered, a masked one can — the five minutes it takes settles the argument.