>>3426156I mean, most of these tutorials make a very strong basis assumption, which seems natural and logical, but is false nonetheless.
They assume that the orange mask is like a filter, so once you figure it's hue and density - by clicking on blank and burnt parts of the film - you can just cancel it out by applying the reverse.
But the orange mask is an integral mask of variable hue and density, which depends on subject brightness and subject colour. The same subject taken at different exposures, will have different densities of orange mask (more exposure=heavier mask).
Also, at the same exposure level, the same subject but painted a different colour, will have a different hue in its orange mask (blue=most neutral, green=most shifted). So the mask depends *both* on the brightness and the colour of the subject, at the same time.
The way to make it work with this methods is not just sampling the whites and blacks, but shooting a colour checker across the exposure range (say 8-10 stops), and sampling the three primary colours on the colour checker, for every exposure. This way you can create a pretty accurate profile for a film. It's essentially what every scanning software has been doing since the late '80's.
