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Aphelion

Chroma keying and matte work in Aphelion Editor

Keying is a pipeline, not a button. Aphelion splits it into nodes that each do one thing — pull the matte, refine it, clean the spill, combine it with another — so you can see and control each stage instead of tuning a single opaque control.

The keying pipeline

  1. 1KeyPick the screen colour and the keyer separates foreground from background. Because the keyer is a node, the signal it sees is whatever is wired into it — you can grade the plate before keying rather than after.
  2. 2Refine the matteChoke pulls the matte in to remove a fringe; feather softens it to sit against motion blur. Both act on the matte, not the image, so you can see the alpha on its own while you tune it.
  3. 3Suppress spillGreen or blue bounced onto the subject is desaturated toward neutral without desaturating the rest of the frame, which is the difference between a key that holds on hair and one that does not.
  4. 4CombineA second matte — a garbage matte from a roto shape, or a second key — is merged with the first by add, subtract, intersect or maximum, so one matte can clean up what the other could not.
  5. 5PremultiplyPremultiply and unpremultiply nodes are available for the points in a graph where an element's RGB has to be consistent with its alpha, such as before a blur.

Masks are first-class, not an afterthought

A matte node outputs a mask on its own socket, separate from the frame. That means a mask can be routed independently of the image it came from: into an effect's mask input to limit where it applies, into a combine node to be merged with another matte, or into a Viewer to be inspected as a greyscale image.

This is why a chroma key rarely needs to be perfect on its own. A key that holds everywhere except a shadow on the floor can be combined with a hand-drawn roto matte that covers that region, and the result is one clean mask without re-tuning the key.

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