Displays quantize color into steps, and slow gradients expose the steps as banding: contour lines across what should be a smooth glow. Dithering trades that structured error for noise, jittering each pixel’s rounding so the average is right and the bands dissolve.
The technique is old and everywhere: newspaper halftones, GIF color reduction, audio’s equivalent at the bit level, and the ordered Bayer patterns of retro graphics, now a deliberate aesthetic of their own.
Dark moody visuals, exactly the palette-driven kind Photism renders, live or die by it, since banding thrives in dim gradients. A whisper of blue noise before output is the difference between glass and topography.