That started me thinking (very dangerous) about the various sized “film grains” of the emulsion, that might hinder your idealized points (would you weight it’s size, which itself is the average of light that originally exposed it?). Those grains are large enough to be on pixel boundaries to have influence on multiple pixels, too. Also, the emulsion is thick enough to have multiple planes of unique clouds that might hide other clouds among the layers. (It quickly becomes complicated.)
I expect you saw this (or something like it), which contains quotes from the originating KODAK “H-1” tech publication:
Film Grain Resolution & Fundamental Film Particles 200704xx Tim Vitale states:
The Kodak publication itself is now only at Internet Archive – Internet Archive - KODAK Motion Picture Film: H-1. PDF files also have been saved by IA but one is missing - pp.80-85.