id: film_sim
order: 25
attributes: [tone, colour]
rust: FilmSim

why_rust: |
  It carries a stock's measured tables — an exposure matrix, three
  characteristic curves and a density lookup — which are not parameters and
  which no `uniforms:` expression could produce. Its neutral is "no stock
  loaded" rather than a set of values, and it is the one node that declares
  `Operation::renders`, so the composer omits the camera profile's base curve
  and the conversion out of camera space on its behalf.

placement: |
  After white balance and exposure, and before everything else.

  Those two are what the camera did — interpreting the sensor, and correcting
  the amount of light that reached it — and they are only meaningful on
  scene-linear values, which is what a film has to be handed. Everything below
  is a decision about the picture, and a decision about the picture belongs
  after the film has rendered it, exactly as it does when you scan a frame and
  then work on the scan.