Rebate

An FFGL effect for Resolume Arena and Avenue. A film look is usually a lookup table, and this one runs the process instead. Your clip is the scene, and it exposes the three dye layers of a colour negative through the overlap of their spectral sensitivities. Each layer is developed along a characteristic curve (a toe, a straight line of slope γ, a shoulder) into dye. The dyes aren't pure, so the film carries masking couplers to cancel their impurities, which is why a negative is orange. Then the flat orange negative is scanned and inverted: divide by the base, set the levels, invert. View Negative shows you the film on a light box before the scanner gets to it.

The grain is a count. Each cell holds N sites a dye cloud can land on, so the covered fraction's variance is c(1 − c)/N: loudest in the mid-tones, gone in clear shadows and blocked highlights, and nobody tuned it to go there. Stock sets N, and Grain Size sets the cell. Push steepens the curve and lifts the fog. Age fog is an exposure, so it goes through the curve and the blue-sensitive top layer takes most of it, which is why expired stock scanned with the normal profile goes blue in the shadows and warm in the highlights. Auto Levels, the lab re-measuring the roll, takes most of that back out.

A light leak is light coming through the base, which reaches the red-sensitive layer first, so it's warm. It's also an exposure, so it saturates on the shoulder instead of piling up forever, and it fogs the rebate along with the picture. Cross-processing is reversal film through C-41: no mask, a steep curve, and a scanner dividing by a mask that isn't there, so the positive goes warm, most of all in the shadows. Round the frame, in Full, 6x6 or 35 mm, is the rebate: unexposed film that prints black, a latent edge print that prints light, and clear sprocket holes that clip to black. The stock codes and frame numbers are made up, and no real manufacturer's name or mark appears.

The model is three layers sharing one curve shape, a 3×3 spectral crossover and a 3×3 dye-impurity matrix. That's enough for every mechanism above, but it isn't a spectral simulation of any real stock. The five stocks are invented and described by their parameters.

Also available as an OpenFX plugin for DaVinci Resolve, Vegas Pro, Nuke and Natron, with the same film and scan in float from end to end. Auto Levels measures each frame on its own there, and an Encoding control takes a clip that's already linear light, the way Nuke and Natron work, as well as display-encoded picture.