Grain's Anatomy

Film grain has complex characteristics, both in spatial structure and in value/intensity. Many understand the basic principle behind how film works (in simple terms, light sensitive crystals - or grains - causing variations in density depending on the amount of exposure to light), and therefore why grain exists and why it tends to have the shape it does (lots of overlapping crystals/grains). What isn't immediately obvious to many is how the intensity of the grain is influenced by the nature of film.