Rotoscoping, keying, rotomation and matchmove all start with the same thing — a filmed plate — and all exist to help new elements sit convincingly inside it. That’s why they are often mixed up in briefs and bids. But they solve different problems and produce different outputs, and asking for the wrong one costs time. This guide explains what each technique does, how to choose between them, and how they combine on real shots.
What each technique does
Rotoscoping
Rotoscoping is drawing and animating shapes around an element, frame by frame, to create a matte that isolates it from the rest of the plate. It works on any background, which is why it is used when there is no green or blue screen.
Output: 2D mattes (alpha channels), usually one per element or layer, often with separate treatment for hair, motion blur and soft edges.
Keying
Keying extracts a matte automatically from a uniform colour — normally a green or blue screen — and then refines it. A good key preserves detail that would be slow to roto, such as fine hair and transparency, and removes the screen colour that spills onto the subject.
Output: a matte plus a despilled foreground, ready to be composited over a new background.
Matchmove
Matchmove, or camera tracking, reconstructs the movement of the real camera in 3D so that CG elements can be rendered from exactly the same viewpoint. Object tracking does the same for a moving object in the scene.
Output: a solved 3D camera (and lens distortion data), a point cloud and simple scene geometry, or tracked object transforms.
Rotomation
Rotomation is matching a 3D model or rig to an actor’s performance, frame by frame, so that CG elements — armour, prosthetics, a digital costume, a creature limb — follow the body exactly. It builds on a matchmoved camera.
Output: animated 3D geometry that matches the performer in the plate, used for rendering attached CG, shadows, reflections and interaction.
Side-by-side comparison
| Roto | Keying | Matchmove | Rotomation | |
|---|---|---|---|---|
| Purpose | Isolate an element from any background | Isolate a subject from a coloured screen | Recreate the real camera in 3D | Match 3D geometry to a performer |
| Input | Plate, plus a brief on which elements to isolate | Screen plate, ideally evenly lit | Plate, lens data, camera reports, survey | Plate, solved camera, a model or rig of the performer |
| Output | 2D mattes per element | Matte and despilled foreground | 3D camera, lens distortion, point cloud | Animated 3D geometry |
| Typical shots | Background replacement without a screen, stereo conversion, colour isolation, holdouts | Studio and virtual-set work, set extension, sky and window replacement | Any shot with CG or 3D set extension on a moving camera | CG costume, armour, prosthetics, digital doubles, body-attached effects |
| Depends on | Edge complexity, motion blur, frame count | Screen quality, lighting, spill, hair | Trackable detail, lens information, motion blur | An accurate camera solve, a good rig, a clear view of the body |
| Common pitfalls | Chattering edges, unmatched motion blur, loose fit on hair | Hard or crunchy edges, residual spill, lost fine detail | Sliding CG, wrong lens distortion, scale errors | CG drifting off the body, intersections, mismatched contact points |
Decision guide: if your shot has… use…
- A subject in front of a usable green or blue screen → keying, with roto for anything off the screen or where the key breaks.
- A subject in front of a real, detailed background → roto.
- A shot that needs depth layers for stereo conversion → roto, usually in many separate layers.
- A CG object, set extension or 3D element on a moving camera → matchmove.
- CG that must stay attached to an actor’s body → matchmove plus rotomation.
- 2D elements (screen inserts, signs) on a moving surface → a 2D planar or point track is often enough; full matchmove is needed when perspective or parallax changes significantly.
- Something to remove, such as a wire, rig or marker → paint and cleanup, often with roto to protect the foreground and a track to place the patch.
- Several layers to bring together into a final image → compositing, which uses the outputs of all of the above.
Roto and keying answer “what is in front?”. Matchmove answers “where was the camera?”. Rotomation answers “where exactly was the body?”. Most VFX shots need at least two of those answers.
How the techniques combine on one shot
On real productions these techniques are rarely used alone. Three common combinations:
Key plus roto for hair against a poor screen
An actor with loose hair is shot against a green screen that doesn’t quite reach the top of frame and has a shadow across one side. The keyer handles the hair detail where the screen is clean. Roto provides a core matte for the body, a garbage matte for everything outside the screen, and hand-drawn shapes where the key fails. The compositor combines them so the edge comes from the key and the solid interior comes from the roto.
Matchmove plus rotomation for CG armour
A character wears a practical tracking suit; in the final shot they wear CG armour. Matchmove solves the camera first, so the 3D scene matches the plate. Rotomation then matches a rig to the actor’s body frame by frame. The armour is rendered on that animated rig, and roto of the actor’s head, hands and any foreground objects lets the compositor layer the armour correctly.
Roto plus paint for wire removal
A stunt performer is held by a wire that crosses their arm and the background. Roto isolates the performer so the background behind the wire can be rebuilt without touching the actor. Paint removes the wire from the background with a tracked clean patch, then a separate paint pass handles the section where the wire crosses the arm. See our wire and rig removal service for this type of work.
On-set tips that reduce cost later
Most of the cost of these techniques is decided on the shoot day. If you can influence the shoot, these habits pay for themselves.
For keying
- Light the screen evenly and separately from the subject, and expose it correctly rather than hot.
- Keep the subject as far from the screen as the space allows, to reduce spill.
- Avoid costume, props and hair products close to the screen colour, and fix creases and tears in the screen.
For roto
- Where possible, choose backgrounds with contrast against the subject’s hair and costume.
- Shoot a clean plate — the same move without actors — whenever you can. It helps roto, paint and comp.
- Remember that higher shutter speeds reduce motion blur, but can change the look of the shot; agree this with the DP.
For matchmove and rotomation
- Record lens, focal length, sensor/format and focus distance for every take, and shoot lens distortion grids.
- Place tracking markers where the camera will see them, but avoid putting them on hair or faces unless the job needs it; each marker must be painted out later.
- Take set measurements, photographs or survey scans, and photograph actors in their tracking suits from several angles for rotomation.
For a full list of what to send a vendor after the shoot, see how to prepare plates and briefs for a VFX vendor. For definitions of the terms used here, see our VFX glossary.
What to ask for in the delivery
Each technique has its own deliverable, and the downstream artist needs it in a particular form. Agree these details before work starts, because changing them after delivery often means redoing the work.
Roto deliverables
Ask whether you need the mattes rendered as image sequences, the shapes themselves (so your compositors can adjust them), or both. Specify how elements are split: one matte per character, separate mattes for hair, limbs or props, or depth layers for stereo. Say whether motion blur should be built into the matte or added in comp, and whether the matte should be premultiplied or straight. A QC render — the matte overlaid on the plate in a contrasting colour — makes review much faster.
Keying deliverables
A key can be delivered as a matte only, as a despilled and premultiplied foreground, or as a full comp over a temporary background for review. Ask for the edge and core mattes separately if your compositors will want to rebalance them, and say whether the despill should be neutral or matched to the intended background.
Matchmove deliverables
Matchmove output needs to load cleanly in your 3D and comp packages. Agree the scene scale and units, the up axis, the frame offset, how lens distortion is delivered (undistorted plates, distortion nodes, or STMaps), and whether you need a point cloud, proxy geometry or a ground plane. A tracking QC render — a grid or test geometry rendered through the solved camera over the plate — shows quickly whether the solve holds.
Rotomation deliverables
For rotomation, agree which rig or model the artist will animate, the level of accuracy needed (silhouette match for a wide shot, or contact-accurate for a close-up), and the export format your lighting and FX teams use. Ask for a QC render of the matched geometry over the plate, viewed in wireframe or shaded, so you can check fit frame by frame.
Whatever the technique, ask for consistent naming and versioning, so each delivery can be traced back to the brief and the notes that produced it.
Briefing the right technique
The most expensive brief is the one that asks for the wrong technique. A request for “roto” on a well-lit green screen shot wastes artist time on edges a keyer would have pulled in minutes; a request for a “key” on a shot with no usable screen produces a matte nobody can use. Equally, a 2D track may be enough for one screen insert, while a similar shot with a moving camera and a reflective surface needs a full matchmove.
When you are not sure which technique a shot needs, describe the result you want rather than the method: “replace the sky behind the actor”, “add CG armour to the hero”, “remove the safety wire”. A good vendor will propose the technique, or combination, and explain why. At RotoEdge we review the footage during shot preparation and suggest the most efficient approach before production starts.