Visual effects
The vocabulary of visual effects
Keying, roto, tracking and compositing, and the lens, film and digital effects that finish a shot. Press a term to watch it done to one actor on a green screen and a street at dusk.
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One actor on a green screen, one street at dusk. Press a term to key, track, composite or finish the shot and see what it is called; where there is one, the compare button shows the shot without the effect.
Keying and mattes
Pulling the actor off a coloured screen. The key makes a matte: a black and white image that says what stays.
Roto and tracking
When there is no screen, mattes are drawn by hand; when the camera moves, every added element has to follow it.
Compositing
Layering plates, mattes and CG into one picture that looks like it was shot in a single take.
Lens effects
What real glass does to light. Added in the comp to make CG look photographed, or as a look of its own.
Film and texture
The marks of a film camera and stock: added over clean digital images for warmth and age.
Digital effects
Effects made in the computer: generated particles and CG, and the look of broken video.
All terms
Keying and mattes
- Green screenalso: Greenscreen, Green screen effect
- The actor is filmed in front of a bright, evenly lit green backdrop, and the green is swapped for another picture later. Green because it is far from skin tones and cameras record it with the least noise.
- Chroma keyalso: Keying, Colour key, Key
- Making one colour transparent. You pick the screen colour, then raise the tolerance until the whole screen goes, including its darker, unevenly lit corners, without eating into the actor.
- Blue screenalso: Bluescreen
- The same trick with a blue backdrop. It spills less light onto the actor and suits night scenes and anything green in the shot, but needs more light, since cameras are less sensitive to blue.
- Spillalso: Green spill, Despill, Spill suppression
- Green light bouncing off the screen onto the actor, seen as a green fringe on hair and edges. Spill suppression pulls the green back to neutral after the key.
- Mattealso: Alpha channel, Alpha matte, Mask
- A black and white image that says which pixels to keep: white is solid, black is see-through, greys are partly see-through, like soft hair. A key, a roto or a painted shape all make one.
- Garbage mattealso: Junk matte
- A rough shape drawn around the actor that throws away everything outside it: light stands, studio walls, the edges of the screen. The key then only has to work on what is left.
- Luma keyalso: Luminance key
- A key made from brightness instead of colour: dark pixels go, bright ones stay. Used for fire, sparks, smoke and fireworks shot on black.
- Light wrapalso: Edge wrap
- A little of the background's light blended onto the actor's edges, as if the bright sky behind were wrapping around them. Without it a keyed actor looks cut out and pasted on.
Roto and tracking
- Rotoscopingalso: Roto
- Tracing a shape around something by hand, frame by frame, to make a matte when there is no green screen. The shape's points are moved as the subject moves. Named after the device animators used to trace live action.
- Tracking markersalso: Track markers, Tracking dots
- Small crosses or dots taped onto a green screen or set. A plain screen has nothing to lock onto, so markers give the tracker points to follow; they are keyed or painted out after.
- Motion trackingalso: Point tracking, 2D tracking
- Following a point through the shot so something can be stuck to it. The tracker searches each frame for the same small patch of pixels; anything attached to the track then moves with the camera.
- Planar trackingalso: Corner pin, Screen replacement
- Tracking a whole flat surface, like a sign, a phone screen or a wall, instead of one point. It follows its position, rotation, scale and perspective, so a new image can be corner-pinned onto it.
- Match movealso: Camera tracking, 3D tracking, Camera solve
- Working out the real camera's path in 3D from the footage, by tracking many points at different depths. A virtual camera then moves the same way, so CG objects sit in the scene.
- Stabilisationalso: Stabilization, Stabilize, Warp stabilizer
- Tracking the shake in handheld footage and moving the frame the opposite way to cancel it. The frame's edges then wander, so the picture is scaled up a little to hide them.
- Wire removalalso: Paint out, Rig removal, Clean-up
- Painting out the safety wires, rigs and markers that held up a stunt, using a clean plate or nearby pixels. The actor appears to float on their own.
Compositing
- VFXalso: Visual effects, Special effects
- Any image made or changed after the shoot: keying, CG, matte paintings, tracking, compositing and lens effects. (Special effects, SFX, are the practical ones done on set, like explosions and rain.)
- Compositingalso: Comp, Digital compositing
- Combining separate layers (background plate, keyed actor, CG, effects) into one image, back to front. A compositor also matches their colour, light, focus and grain so the seams vanish.
- Platealso: Background plate, BG plate, Foreground plate
- A piece of footage shot to be used in a composite. The background plate is the scene with no actor in it; the foreground plate is the actor shot on a screen.
- Clean platealso: Clean pass
- The same shot filmed again with the actor, rigs or crew out of frame. It is what the compositor paints back in to remove anything from the picture.
- Matte paintingalso: Digital matte painting, DMP
- A painted landscape or building that replaces part of the frame, like a castle on the far hills. Once painted on glass, now painted digitally, often over photos and 3D.
- Set extensionalso: Digital set extension
- Only the part of the set the actors touch is built; the rest, here the top of a city wall and its towers, is added digitally. Green above the build tells the comp where to put it.
- Blend modesalso: Transfer modes, Screen, Multiply, Add
- How a layer's pixels mix with the ones below. Screen and Add only brighten, so a glow shot on black drops in with no matte; Multiply only darkens, for shadows and dirt.
- Depth passalso: Z-depth, Depth map, Atmospheric haze, Fog
- A grey image of how far away each pixel is, near white and far black. The comp uses it to add haze and fog that thicken with distance, or depth of field.
Lens effects
- Lens flarealso: Flare
- Bright light bouncing between the glass elements inside a lens: a glow, streaks, and a line of rings and shapes across the frame. The rings move opposite the light as the camera pans.
- Chromatic aberrationalso: Colour fringing, RGB split, CA
- A lens bends red, green and blue light by different amounts, so they do not quite line up: coloured fringes on edges, strongest at the corners. Added to CG to make it look shot, or pushed as a style.
- Vignettealso: Vignetting, Light falloff
- The corners of the frame fall darker than the centre. Lenses do it naturally; colourists add it to pull the eye to the middle.
- Bokehalso: Out-of-focus highlights
- The quality of the out-of-focus parts of an image. Small lights behind the subject spread into soft discs shaped by the lens's aperture. Shallow focus and a wide aperture make more of it.
- Anamorphic flarealso: Anamorphic streak, Horizontal lens flare
- A long horizontal line of light, often blue, through bright lights. It comes from anamorphic lenses, which squeeze a wide picture onto the sensor; now added for a widescreen sci-fi look.
- Lens distortionalso: Barrel distortion, Pincushion, Fisheye
- Straight lines bending near the edges. Wide lenses bow them outward (barrel), long zooms pinch them in (pincushion). Removed before compositing so CG lines up, then added back.
Film and texture
- Film grainalso: Grain, Noise
- The fine, random texture of film, from the silver crystals that capture the image. It changes every frame, so it shimmers. Added to digital and CG to match film or soften a too-clean look.
- Light leakalso: Light leaks, Film leak
- Warm orange and red light washing in from the edge of the frame, from light getting into a camera body or film can. Used as a nostalgic look or a transition.
- Film burnalso: Burn transition
- The frame melting and blooming into white, as when a projector's lamp burns through a stuck frame. Used as a transition between shots or a retro accent.
- Halationalso: Film halation
- A red-orange glow around bright lights and edges on film, from light bouncing off the back of the film stock. Its warm colour is what tells it apart from a plain glow.
- Gate weavealso: Film weave, Jitter
- The picture drifting and jumping slightly, because film never sits in exactly the same place in the camera or projector gate. The cross stays still, so you can see the frame move.
- Dust and scratchesalso: Film damage, Film scratches
- Specks, hairs and long vertical lines on a worn film print, flashing for a frame at a time. Added for an old-film look; removed when restoring.
Digital effects
- Glitch effectalso: Glitch, Digital distortion
- The look of broken digital video: slices of picture jumping sideways, colour channels splitting, blocks of wrong colour, in short bursts. Used for tech, horror and music videos.
- Datamoshalso: Datamoshing, Pixel bleed
- Deleting the keyframe at a cut, so the next shot's motion drags the last shot's pixels around instead of replacing them. Melting, smeared colour, as in music videos.
- VHS effectalso: VHS, Retro VHS, Tape effect
- Videotape's flaws: soft colour bleeding sideways, scan lines, a rolling band of tracking noise and a timestamp. Used for 80s and 90s nostalgia and found footage.
- Particle effectsalso: Particles, Particle system
- Thousands of tiny generated points, each with its own speed, life and fade, for sparks, embers, dust, snow, rain and magic. An emitter spawns them and forces like wind and gravity move them.
- Glowalso: Bloom, Glow effect
- Bright parts of the picture bleeding soft light into their surroundings. Bloom is the name in games and CG; glow in compositing and motion graphics.
- CGIalso: CG, Computer-generated imagery, 3D render
- Anything made in 3D software: modelled, textured, lit to match the plate and rendered, then composited in. Here a crystal goes from wireframe to lit object with a shadow on the ground.