The one-page reference for compositing and VFX. Screenshot it before a green-screen shoot or a key. The governing idea, in one line: a visual effect should be invisible and motivated — and a clean composite is lit and shot on set, not fixed in post.
The terms, fast
Term
In one line
Compositing
Combining two or more image layers into one seamless shot.
VFX
Any imagery created/altered outside the live moment of filming. Best when invisible.
Alpha channel
A per-pixel transparency map, alongside R/G/B.
Matte
The alpha viewed as black-and-white: white = keep, black = drop, grey = soft edge.
Green screen / chroma key
An evenly-lit colored backdrop shot so its color can be made transparent in post.
Keying
Generating a matte from footage (usually by color) and refining its edges.
Despill
Removing the green light contaminating the subject's edges.
Mask
A drawn shape isolating a region of the frame.
Roto (rotoscoping)
Animating a mask frame-by-frame to follow a moving subject you can't key.
Stock elements
Licensed pre-made assets (skies, fire, flares, light leaks) composited in.
Screen replacement
Replacing a phone/monitor screen in-shot via a corner-pin track.
Synthetic media / deepfake
Software-generated/altered likeness or voice; a deepfake convincingly fakes a real person.
The two composite laws
Law
What it means
The greys are the game
Black and white in a matte are trivial; hair, motion blur, and soft edges (the greys) make or break the seam.
A composite must agree with itself
Foreground + background must share one light, lens/DoF, camera angle, motion, grade, and grain. The eye reads light before edges.
Green-screen lighting checklist (light TWO things, separately)
#
On set
Why
1
Screen taut and wrinkle-free (steam/clamp/paint)
every wrinkle = a shadow = a second green value
2
Screen lit flat and even — two soft sources, ~45° each, equal power
the keyer needs one color to find
3
Subject 6–10 ft in front of the screen
kills spill; drops the subject's shadow off the screen
4
Subject lit to match the background plate (key direction/color/hardness, contrast ratio)
so they belong in the new world
5
Add a rim/back light on the subject
overpowers green spill; separates the edge
6
Keep screen light off the subject, subject light off the screen
contamination in either direction wrecks the key
7
Expose the screen to a clean, even mid-green (not blown)
overexposed/uneven greens key worse
8
Capture the least-compressed, highest-chroma format (4:2:2 > 4:2:0)
color edges key clean; you can't add it back later
9
Lock white balance; shoot 1/50 s at 24 fps (180°)
no color drift; motion blur matches the plate
10
Grab a clean plate, a still reference, and room tone
the safety shots post will beg for
Green vs. blue: green is default (far from skin; best-resolved channel; needs less light). Switch to blue when the subject is/wears green.
The keying order (and what each step fixes)
Step
Do
Watch for
1. Pull
sample the green → make a matte
judge the matte in black-and-white, not color
2. Read
background pure black? subject pure white? edges thin grey?
grey "black" = uneven screen; holes in white = key grabbed subject
rolling-shutter flicker/banding (Ch.2), moiré, too dim, glare, or UI wasn't ready on set
Any stock element
license it — "found it online" is not a license; keep records (Ch.38)
When NOT to use VFX (decision aid)
Ask
If the answer is…
Then
Can the story be told without it?
yes
don't add it — decoration is how finishing goes wrong
Can I say in one sentence why the story needs it?
no
don't add it
Can I do it for real (practical) instead?
yes, and it's affordable
do it for real — real beats faked
Will anyone notice the effect?
yes
either make it invisible or cut it
Can I match the plate (light, grade, grain, motion)?
no
don't — an unmatched effect is worse than none
Is every stock element licensed?
no
stop — license it first (Ch.38)
Does it involve a real person's likeness/voice?
yes
go to the ethics gate below before anything else
The rule: an effect you can justify in one sentence and no one can spot is craft. An effect you added because it looked cool, or that anyone can point to, is decoration.
Synthetic-media ethics (non-negotiable)
Gate
Question
Rule
Consent
Do you have informed, specific consent for a real person's likeness/voice?
No → STOP. Never make a real person appear to say/do what they didn't.
Impersonation
Could it deceive an audience into thinking it's genuinely them?
Deceptive impersonation without consent is forbidden (Ch.21 ethics).
Disclosure
Could a viewer mistake it for real/unaltered?
If yes, disclose it. In documentary/journalism the duty is absolute.
Extra care: minors, vulnerable people, the dead. Legitimate uses (consented de-aging, licensed voice, disclosed AI narration, accessibility voices) are fine; the harm is in the non-consensual, deceptive use. Get releases (Ch.38); laws vary and this isn't legal advice.
♿ Also: keep flashing/strobing effects (flares, glitches) gentle — photosensitivity risk (Ch.34). Disclosure is an accessibility act: the audience has a right to know what's real.
Top mistakes → fixes
Mistake
Fix
Subject too close to the screen
move them 6–10 ft forward (spill + shadow gone)
Overexposing the screen
expose to a clean, even mid-green
Heavily compressed codec for a key
shoot 4:2:2 / higher bit depth (Ch.3)
Judging the key in color
judge the matte in black-and-white first
Leaving green spill
despill — the decisive step
Over-cleaning the matte
stop before the hair turns to a helmet
Unmatched stock/screen element
grade, grain, motion-blur, and light-match it to the plate
Ungraded composite
grade the stack as one; protect skin; add grain + light wrap
Unlicensed stock
license everything; keep records (Ch.38)
Faking a real person without consent
don't — consent, no impersonation, disclose
The principle, and the project
Story governs the effect. Motivate every composite; if you can't say why in a sentence, cut it.
The finish begins on set. An even screen, separation, matched light, and a good codec make the key easy. Careless shooting can't be plugin'd away.
Invisible is the goal. The best VFX is the one no one notices — a disappearance, not a spectacle.
The craft and the responsibility are inseparable. With synthetic media: consent, no impersonation, disclosure.
Production Checkpoint (Project 3): add one composited element — a green-screen key, a screen replacement, or a clean graphic composite/clean-up — motivated by the story, matched so it's invisible, and (if a real person is synthesized) consented and disclosed. Every stock element licensed. This is the last creative layer before delivery (Chapter 36).