Layers: Non-Destructive Stacking

Chapter 3 covered how to restrict where an edit applies. This chapter covers a genuinely different foundational concept — keeping different pieces of content on separate, independently editable layers, rather than merging everything into one permanent, flattened image.

The Core Idea: Layers Are Independent, Stackable Sheets

A layer works like a transparent sheet stacked on top of others — each one holds its own content, editable, movable, or deletable entirely independently, without affecting any layer above or below it. This is the direct opposite of a flattened, single-layer image, where everything has already been permanently merged into one and can no longer be separated.

Layer Order & Stacking

Layers stack top-to-bottom in a panel or dialog, and whatever is higher in that stack visually covers whatever sits below it — exactly like physical transparent sheets laid on top of each other. Reordering layers directly changes what's visible in the final image.

Opacity

A layer's own opacity setting controls how much of whatever's beneath it shows through — 100% is fully opaque, 0% is fully invisible. This is distinct from a layer mask's own selective transparency (Chapter 5): opacity affects the entire layer uniformly, while a mask can make different parts of the same layer transparent by different amounts.

Blend Modes

A layer can combine with whatever's beneath it using math well beyond simple opacity. Three of the most commonly used starting points: Multiply (darkens), Screen (lightens), and Overlay (increases contrast). This blend-mode math is genuinely identical in both Photoshop and GIMP — these are standard, well-defined compositing operations, not something proprietary to either tool.

Layer Groups/Folders

Many layers can be organized into a collapsible group — Photoshop's own Groups, GIMP's own Layer Groups — genuinely useful once a project accumulates dozens of individual layers and the panel itself starts becoming hard to navigate.

Hands-On Exercises