Bloom
Bright areas spilling soft light onto everything near them, the way a real lens smears a highlight.
See it
What it is
Bloom is the light spill around things that are genuinely bright: streetlights, a screen in a dark room, sun through a window. The recipe is always the same three steps. Isolate the pixels above a brightness threshold, blur that isolate at several sizes, add it back on top of the original.
Reach for it when something needs to read as emitting light rather than just being painted a light color. Neon signage, HDR game lighting, night scenes, a glowing CTA. It differs from glow, which is a halo an artist attaches to one chosen element, and from halation, which is warm-only and comes from film stock.
Gotcha: bloom computed on ordinary 0 to 1 sRGB values turns the whole frame milky, because mid-tones leak into the blur and grey out your contrast. Do it in linear light with a threshold above the display white point, so only the actual highlights bloom. Combine two or three blur radii instead of one huge one: stacked scales give a falloff that behaves like real scattered light, hot and tight near the source and fading out wide, where a single enormous blur just lays down one flat, oversized haze.
Ask AI for it
Add a bloom pass to this scene, working in linear light: take the scene-linear pixels above display white (values over 1.0) as the bright pass, blur that pass at three radii (4px, 16px, 48px), and composite it back additively over the source at roughly 40 percent strength. If the source is SDR and has nothing above white, drive it from an explicit mask of the emissive lights and highlights instead of a global luminance cutoff, which would bloom ordinary white surfaces and bright midtones. Leave normal whites and midtones crisp. The look: neon and light sources glowing outward, highlights bleeding, everything else still sharp.