Merge, premult, cameras, blacks and whites, explained with pictures you can move in your browser. Try it now without signing up, at your own pace.
1 How two images stack
Every time you put CG over a plate, Nuke does one line of maths: A + B·(1−α). The covered part of the plate fades by alpha, then the image on top is added. It sounds simple, yet almost every edge problem starts on this line.
2 Try one question
Nothing to sign up for. A wrong answer is fine; the picture shows why.
An orange shape merged over sky three ways. Which one is premultiplied correctly?
3 Beliefs to unlearn
Many people believe these. Open one to see why it isn’t true.
“A key is a mask, so more contrast is always better”
Crushing a key to pure black and white eats soft edges like hair and motion blur. Keep a soft key for the edge, a separate hard core key inside, and combine them with max.
“Screen is the best way to add light”
Nuke’s screen gives A+B−AB only when values are ≤ 1; above 1 it returns max(A,B), which clips HDR. For light, use plus.
“Matching blacks = raising lift in a Grade”
Grade lift pivots at 1, so it also pulls highlights down (lift 0.1 turns 4.5 into 4.15). Use a toe that only touches the darks.
“Add grain to every element along the way”
Grain goes on once, as the last node, per channel, blacks first; blue is usually the strongest.
“Any grade works fine on a premultiplied image”
Only pure multiplies are safe on premultiplied images. Lift, gamma and offset need unpremult → grade → premult, or the edges go wrong.
“CG needs pure black to look punchy”
Almost nothing in a real plate reaches 0. CG blacks follow depth: far things sit in haze, so their black is lifted and tinted.
4 Keep reading
This essay continues as 10 lessons. The first three are free and fully playable; the rest say plainly how far along they are.
Edges and alpha
01 · Merge over and premultFree · 6 min- 04 · Two-layer keys: soft + core🔒 Nuke Keying Masterclass · Being recorded · no opening date yet
- 05 · Despill: limit, then replace🔒 Nuke Keying Masterclass · Being recorded · no opening date yet
- 06 · Fixing halos in the right order🔒 Nuke Keying Masterclass · Being recorded · no opening date yet
Camera and space
Colour and air
AI in comp
5 Talk to us
Questions about lessons, team use, or which lesson to make next. LINE is the main channel. (This button is not linked to a real LINE account yet)
Not sure? Just tell us first — Sky