Film grain
Fine noise laid over an image so it reads as shot on film, regenerating every frame once the footage starts moving.
See it
What it is
On real film the picture is made of silver halide crystals, and their clumping is visible as grain. Faster stocks grain harder, and grain shows most in shadows and midtones while blown highlights stay smooth. Digital film grain is a noise layer that imitates that. On moving footage the thing that sells it is regenerating every frame, because every frame of real film is a fresh sheet of crystals. Hold one grain pattern still under motion and it reads as dirt on the lens instead of film. On a single still photograph the opposite is true: one fixed grain pattern is exactly what a frame of film looks like, so there is nothing to animate.
Reach for it when digital video or a 3D render feels too clean and clinical, when dark gradients are banding, or when you want a period feel. It rarely works alone: grain plus a slight warm halation around highlights plus a soft color grade is the combination that reads as 'shot', and A24 trailers, Kodak-emulation LUTs, and most indie title sequences use exactly that stack.
Gotcha: grain and video codecs are enemies. Every frame of noise is new detail, so the encoder spends its bitrate on randomness and smears the actual picture, which is why grainy films look mushy when streamed. Apply grain last, after grading, keep it finer than you think, and consider a lighter pass for web delivery than for the master.
Ask AI for it
Overlay animated film grain on this video: generate monochrome noise that regenerates every frame at about 24fps (not a static texture), blend it with soft-light at 6 to 10 percent opacity, weight it toward shadows and midtones so highlights stay cleaner, and add a faint warm halation glow around bright edges. Target fine 35mm grain, not chunky video static, and apply it after color grading, as the last pass.