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description: "After Effects Compositing & Effects — With motion and easing in place, this module covers compositing — how multiple layers combine into one convincing…"---

03 · After Effects Compositing & Effects

With motion and easing in place, this module covers compositing — how multiple layers combine into one convincing image — and the Effects pipeline that adds looks, corrections, and generated visuals on top. This is After Effects' equivalent of Photoshop's blend modes and layer masks, extended across time.

1. Blend modes and track mattes

  1. Reveal the Modes column in the Timeline (panel menu > Columns > Modes, or press F4 to toggle between the Switches and Modes columns) and choose a blend mode from a layer's dropdown — Screen, Multiply, Add, and Overlay behave the same as their Photoshop counterparts.
  2. For a track matte, place the matte shape/text layer directly above the layer it should mask, then on the layer below it, use the Track Matte dropdown (also in the Modes columns area) and choose Alpha Matte "[layer above]" (mask by the matte layer's alpha/transparency) or Luma Matte "[layer above]" (mask by its brightness).
  3. The matte layer's own visibility eye can be turned off once it's set as a track matte source in most workflows, but leave it on while setting up so you can see what you're aligning.

2. Masks

  1. With a layer selected, draw directly on it in the Composition panel using the Pen tool, or select the layer and draw a shape with the Rectangle/Ellipse tool while the layer (not a new shape layer) is selected — this creates a Mask on that layer instead of a new shape.
  2. Twirl open the layer's Masks property group to adjust Mask Path (animatable, for a moving matte), Mask Feather (soft edge), Mask Opacity, and Mask Expansion.
  3. Set Mask Mode (Add, Subtract, Intersect, etc., in the Timeline's Modes area for that mask) to combine multiple masks on one layer, the same logic as Photoshop's mask calculations.

3. The Effects & Presets panel

  1. Window > Effects & Presets opens the searchable effects browser. Drag any effect directly onto a layer in the Timeline or Composition panel to apply it.
  2. Applied effects appear in the Effect Controls panel (Window > Effect Controls, or double-click the layer) with their own parameters — every parameter here can be keyframed exactly like a Transform property.
  3. Common corrective/stylistic effects to know: Lumetri Color (the same color grading engine as Premiere, usable here for consistency across a pipeline), Gaussian Blur, Curves, Hue/Saturation, and CC Light Sweep or Glow for stylized motion graphics accents.
  4. Reorder effects by dragging them in the Effect Controls panel — like layers, effects apply top-to-bottom, so a Blur above a Curves effect produces a different result than the reverse order.

4. Adjustment layers and precomps

  1. Layer > New > Adjustment Layer creates a layer whose effects apply to every visible layer beneath it in the stack, without altering any individual layer directly — the AE equivalent of a Photoshop adjustment layer, but effects-based rather than tonal-adjustment-only.
  2. To treat a group of layers as a single unit (for a shared effect, blend mode, or to declutter the Timeline), select them, right-click > Pre- compose..., choose Move all attributes into the new composition, and name it — this nests them into a new composition that appears as one layer in the parent.
  3. Precomping is the AE equivalent of grouping in Illustrator/Photoshop: it isolates a set of layers so effects, blend modes, and masks applied at the precomp level affect the group as a whole.

5. Rendering with alpha for compositing elsewhere

  1. Composition > Add to Render Queue, then in the Output Module settings choose a format that supports transparency (e.g. QuickTime with the Apple ProRes 4444 codec, or a PNG sequence) and set Channels: RGB + Alpha so the rendered element carries its transparency into Premiere or another app.
  2. This is essential for motion graphics elements (lower thirds, animated logos) meant to sit over live footage in a later edit rather than stand alone.

Worked example: compositing the title card over footage

  1. Import a short background video clip into the Title_Card project and add it to the Timeline below the text+logo group.
  2. Add an Adjustment Layer above the background footage only (below the text group) with Lumetri Color applied to grade the footage to match the brand palette.
  3. Give the background footage a soft vignette using Curves or a feathered mask darkening its edges, so the title reads clearly against it.
  4. Render the text+logo group alone (precomposed) as a ProRes 4444 file with alpha, confirming it composites correctly over a different background when reopened.

Cheat sheet — compositing & effects

Task Where
Show blend mode / track matte columns F4, or panel menu > Columns > Modes
Apply a track matte Track Matte dropdown on the layer below the matte
Draw a mask on a layer Pen/shape tool with the layer (not new layer) selected
Browse/apply effects Window > Effects & Presets, drag onto layer
Adjust applied effect parameters Window > Effect Controls
Adjustment layer Layer > New > Adjustment Layer
Group layers into one unit Right-click > Pre-compose...
Render with transparency Output Module > Format/Codec supporting alpha, Channels: RGB + Alpha

How It Actually Works

  • Alpha is a fourth numeric channel per pixel, stored and carried through the pipeline exactly like R, G, and B. Every rendered frame in After Effects is RGBA internally: red, green, blue, plus a 0-1 (or 0-255) transparency value per pixel. A layer with no alpha information (a flattened JPEG, say) is simply treated as fully opaque everywhere; compositing two layers means, at every pixel, blending their RGB using the top layer's alpha as the mix weight. This is the entire mechanism behind "rendering with alpha" mattering — a codec/container that discards the alpha channel (most standard H.264 MP4 exports) throws away exactly that fourth number, leaving no transparency data for a later app to composite against.
  • A Luma Matte reads the matte layer's brightness values as a per-pixel alpha, while an Alpha Matte reads its actual alpha channel directly — two different source channels feeding the identical masking math. A white area of a Luma Matte source (max brightness) produces full opacity in the masked layer, black produces full transparency, and any gray value produces partial opacity — the identical grayscale-as-opacity-multiplier logic from Photoshop's layer masks, just computed from luminance instead of a dedicated mask channel when using Luma Matte.
  • A Mask Path is Bézier path data — the same anchor-point-and-handle representation from every other path in this course — stored as an animatable property on the layer, which is exactly why it can be keyframed: each keyframe stores a full path shape at that time, and After Effects interpolates the path's point positions between keyframes the same way it interpolates any other spatial property, producing a smoothly morphing mask shape rather than a static cutout.
  • Effect order matters because each effect in the Effect Controls stack operates on the pixel buffer the previous effect already produced, not on the original source simultaneously. A Gaussian Blur applied before a Curves adjustment blurs the raw footage, then Curves remaps the already-blurred pixel values; reversed, Curves remaps the sharp original first, and Blur then softens the already-graded result — different pixel math at each stage produces genuinely different final values, not just a reordering of visually similar operations.
  • Precomposing moves the selected layers' actual data into a new composition and replaces them, in the parent, with a single layer that references that new comp — mechanically identical to nesting a composition as covered in Module 1's After Effects lesson. Any effect, blend mode, or mask applied at the parent level to that one layer is evaluated after the entire precomp has already been fully rendered and flattened into one frame, which is the structural reason it can treat an arbitrarily complex group of layers as a single compositing unit: by the time the parent-level operation runs, there's only one flattened image left to operate on.

Exercise

Composite the title card over the background footage: grade the footage with an adjustment layer, mask its edges for a vignette, and confirm the text+logo group reads clearly on top. Render the text+logo group alone as a ProRes 4444 (or PNG sequence) file with alpha and verify it drops cleanly over a different clip when reopened, confirming the alpha channel survived the render.