Compositing
How layers combine, once each one has been drawn.
Blend modes
All 38 of After Effects’ blend modes, Dissolve and Dancing Dissolve included, set per layer in Properties ▸ Blending and switches. They decide how a layer combines with what is already beneath it in the stack.
| Family | Modes |
|---|---|
| Normal | Normal, Dissolve, Dancing Dissolve |
| Subtractive | Darken, Multiply, Colour Burn, Classic Colour Burn, Linear Burn, Darker Colour |
| Additive | Add, Lighten, Screen, Colour Dodge, Classic Colour Dodge, Linear Dodge, Lighter Colour |
| Complex | Overlay, Soft Light, Hard Light, Linear Light, Vivid Light, Pin Light, Hard Mix |
| Difference | Difference, Classic Difference, Exclusion, Subtract, Divide |
| HSL | Hue, Saturation, Colour, Luminosity |
| Matte | Alpha Add, Luminescent Premultiply |
| Utility | Stencil Alpha, Stencil Luma, Silhouette Alpha, Silhouette Luma |
Dissolve and Dancing Dissolve are the two that need per-pixel randomness rather than a per-pixel function of the two colours. They are seeded, not random per render, so a frame dissolves the same way every time it is drawn.
Stencil, Silhouette and Preserve Underlying Transparency
The four stencil and silhouette modes act on everything beneath the layer in its composition, not just on the layer below: a stencil keeps what is inside the layer’s alpha or luma, a silhouette punches it out. That is what makes them the tool for cutting a whole stack at once rather than pairing mattes layer by layer.
Preserve Underlying Transparency is the switch beside them: with it on, a layer draws only where the composite beneath it is already opaque.
Track and alpha mattes
A layer chosen as another layer’s matte 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
Applied per layer without going through the effect stack: Drop Shadow, Outer Glow, Inner Shadow, Inner Glow, Satin, Bevel, Colour Overlay, Gradient Overlay, Stroke and Glass.
They compile into structured effects the renderer draws directly, emitted in
Photoshop’s stacking order and appended after the layer’s own effect stack —
matching After Effects, where layer styles evaluate after effects. For finer
control, such as several shadows at once, use the drop-shadow and glow
effects instead.
Layer styles work on 3D and extruded layers, not only on flat ones. Since 0.9 they are drawn on the GPU — an Inner Shadow on a 1080p layer went from about a second per frame to 3 ms. Set them in the Layer styles section of the Properties panel.
The two outward styles — Drop Shadow and Outer Glow — used to render in the layer’s colour rather than their own, because the style colour was passed as a tint and a tint multiplies. Only a black shadow was ever right, and only by accident: black is the absorbing element of a multiply. They now take RGB from the colour and alpha from the silhouette. A white glow cannot test this — white is the identity of a multiply, so the broken and fixed paths agree exactly. The inward styles were never affected.
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.
The blur is sized from how far a layer’s silhouette travels, so spins, scale pops and card flips blur rather than strobe. Shutter angle, shutter phase and the sample count are per layer, in Properties ▸ Blending and switches.
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 per layer — Best, Draft or Wireframe — trading fidelity for speed while you work. Wireframe is a viewport view; the layer exports as Best.
- Colour LUTs and colour matrices for grading pipelines.