Film Grain
Add deterministic, luminance-weighted grain that clumps like the real thing.
All processing runs in your browser. No file leaves this device.
Amplitude is weighted by luminance because real silver halide grain is most visible in the midtones and nearly invisible in deep shadows and blown highlights. Adding noise uniformly across the range is what immediately reads as digital.
Size works by lowering the sampling frequency of the noise field and interpolating up, producing grain that clumps rather than sitting one pixel at a time. The generator is seeded, so the same seed always reproduces the same grain.