It is often said that the film response curve is S-shaped, without stressing or even mentioning the role of film processing. Here is an example from Wiki:
"The relationship between density and log exposure is linear for photographic films except at the extreme ranges of maximum exposure (D-max) and minimum exposure (D-min) on an H&D curve, so the curve is characteristically S-shaped (as opposed to digital camera sensors which have a linear response through the effective exposure range)." - en.wikipedia.org/wiki/Photographic_film#Film_basics
First, it's S-shaped in log-log coordinates; second, comparing developed film to raw data is inadequate; third, film latent image is rather linear above the low intensity reciprocity failure and up to high intensity reciprocity failure, and before degradation starts to really hit.
April 3, 2023