How to Use the Roto Brush in After Effects

A workflow taught by Adobe Certified Instructors at Adobe Video World.

The Roto Brush is After Effects’ AI-assisted tool for cutting a moving subject out of its background without a green screen. Instead of tracing every frame by hand, you paint a rough selection and the tool propagates it across the clip. This guide covers painting a selection, refining the edges, and getting clean cutouts from real footage.

What the Roto Brush Does

The Roto Brush automatically separates a foreground subject from its background, frame by frame, based on a selection you paint. It’s essentially intelligent rotoscoping, doing in minutes what manual masking would take hours to achieve.

This lets you isolate a person or object from ordinary footage — no green screen required — so you can place them on a new background, grade them separately, or build a composite. It’s one of the biggest time-savers in After Effects compositing.

Roto Brush vs. Manual Rotoscoping

Traditional rotoscoping means drawing and animating masks around a subject by hand across every frame — precise but extremely slow. The Roto Brush automates most of that work, propagating your selection through the clip intelligently.

For many shots the Roto Brush gets you most of the way in a fraction of the time. You still refine its results, but starting from an automated selection rather than a blank frame is what makes it so much faster than pure manual roto.

Paint Your Initial Selection

To begin, double-click the layer to open it in the Layer panel, select the Roto Brush tool, and paint a stroke down the middle of your subject. After Effects analyzes the stroke and draws a selection boundary around the foreground.

You don’t trace the edges — you paint through the subject’s interior, and the tool finds the edges for you. Add more strokes to include missed areas, and hold Alt to subtract background that got included.

Propagate Across Frames

Once your first frame looks good, move forward and After Effects automatically extends the selection to following frames. The tool tracks the subject’s movement, adjusting the boundary frame by frame as you advance through the clip.

This propagation is the Roto Brush’s core power, carrying your selection through the footage. Work forward a span at a time, checking the result, since the tool builds its understanding as it goes and benefits from you guiding it along.

Correct the Selection as You Go

Propagation isn’t flawless, especially with fast motion, fine detail, or similar foreground and background colors. As you advance, fix any frames where the selection slips by adding or subtracting brush strokes to correct the boundary.

A little correction at the right frames keeps the whole sequence clean, since each fix improves the propagation ahead. Patience here, checking and nudging the selection across the clip, is what separates a usable cutout from a messy one.

Refine the Edges

After the selection is set, use Refine Edge to handle tricky boundaries like hair and motion blur. The Refine Edge tool captures soft, wispy detail that a hard selection misses, blending the cutout’s edges naturally.

This step is what makes a Roto Brush cutout look professional rather than cut-out-with-scissors. Spending time on edge refinement, particularly around hair and fast-moving limbs, dramatically improves how believably your subject sits on a new background.

Freeze and Render the Matte

When you’re happy, Freeze the Roto Brush to lock the calculation, which prevents After Effects from recomputing the selection and speeds up your project. The frozen matte holds your cutout in place.

From there, the isolated subject behaves like any layer — you can place a new background beneath it, grade it independently, or add effects. The Roto Brush has effectively given you a green-screen-style key from footage that never had a green screen.

Know When to Use It

The Roto Brush shines on clips where shooting a green screen wasn’t possible but you still need to isolate a subject. It works best when the subject is reasonably distinct from the background and the motion isn’t extreme.

For very complex shots, manual roto or a real green screen key may still be better. Knowing when the Roto Brush is the right tool — and when another approach wins — keeps your compositing efficient.

Roto Brush Best Practices

• Paint through the subject’s interior, not along its edges.
• Propagate a span at a time, checking the result as you go.
• Correct slipped frames with added or subtracted strokes.
• Use Refine Edge for hair and motion blur, then Freeze.

Common Roto Brush Mistakes

• Tracing edges instead of painting through the subject.
• Propagating the whole clip without checking frames.
• Skipping Refine Edge, leaving hard, fake-looking edges.
• Using it on shots too complex, where manual roto wins.

A Real Roto Brush Cutout Example

Imagine a clip of a presenter filmed against a plain office wall that you need to drop onto a branded background. You open the layer, paint a Roto Brush stroke down their body, and After Effects wraps a selection around them. Moving forward a second at a time, you nudge the selection where it slips off a moving hand, then run Refine Edge over the hair.

After freezing the matte, the presenter sits cleanly on the new background as if they’d been shot on green screen. A shot that would have been impossible to use is rescued in a fraction of the time manual rotoscoping would take — the everyday value of the Roto Brush in real compositing work.

Combine the Roto Brush with Effects

Once a subject is isolated, the Roto Brush opens up creative grading and effects. You can grade the cut-out subject separately from the background, add a glow or a shadow to seat them in the new scene, or apply a stylized look to only the person while the background stays untouched.

This separation is the gateway to convincing composites, where foreground and background are treated independently so they truly belong together. Pairing the Roto Brush cutout with the blending modes and grading tools you’d use on any layer is what turns a clean cutout into a finished, believable shot.

Key Takeaways

• The Roto Brush cuts out a moving subject without a green screen.
• Paint through the subject and let the tool find the edges.
• Propagate across frames, correcting where the selection slips.
• Refine the edges and freeze the matte for a clean cutout.

Frequently Asked Questions

How do I use the Roto Brush in After Effects?

Double-click the layer to open the Layer panel, select the Roto Brush tool, and paint a stroke through the middle of your subject. After Effects finds the edges, and you propagate the selection across frames, correcting as needed.

What’s the difference between the Roto Brush and rotoscoping?

Manual rotoscoping means drawing masks by hand on every frame. The Roto Brush automates most of that, painting a selection that propagates across the clip, so it’s far faster while still needing some refinement.

How do I get clean edges with the Roto Brush?

Use the Refine Edge tool to capture soft detail like hair and motion blur, which a hard selection misses. This blends the cutout’s edges naturally, then Freeze the Roto Brush to lock the result.

Sources: Adobe’s guide to the Roto Brush and Refine Edge.