Compositing
How layers combine, once each one has been drawn.
Blend modes
All 17 of After Effects’ blend modes, set per layer in Style → Compositing. They decide how a layer combines with what is already beneath it in the stack.
Track and alpha mattes
A matte layer sits above the layer it mattes and stops drawing on its own.
| Type | Uses |
|---|---|
| Alpha matte | The matte layer’s alpha channel |
| Luma matte | Its luminance — white keeps, black hides |
Either can be inverted. Full treatment: Masks & mattes.
Adjustment layers
Effects on an adjustment layer apply to everything rendered beneath it. Create one with Ctrl/⌘ + Alt + Y.
Layer styles
Two, applied per layer without going through the effect stack:
- Drop Shadow
- Outer Glow
They compile to the CSS-filter path, which makes them cheap. For finer control —
multiple shadow layers, keyframed softness — use the drop-shadow and glow
effects instead.
Motion blur
Available per layer and gated by a composition-level switch, the same two-level arrangement as AE. Turn the composition switch on, then enable it on the layers that should have it.
Motion blur costs render time, so leave it off while blocking out and turn it on before the final render.
Nested compositions composite as one unit
This is the part worth understanding.
A pre-comp’s subtree renders to its own framebuffer, then that single result is composited into the parent. The isolation is real, not simulated. So:
- Group opacity fades the group as one image, rather than fading each layer and revealing the overlaps.
- A group blend mode blends the composited group, not each member.
- An effect on the pre-comp sees the finished group.
If overlapping layers “go see-through against each other” when you fade them, you are fading them individually. Pre-compose and fade the pre-comp.
Layer quality and baking
- Quality switches per layer, trading fidelity for speed while you work.
- Effect baking for effects that do not need to be recomputed every frame.
- Colour LUTs and colour matrices for grading pipelines.