Bloom isolates the brightest parts of the frame, blurs them, and adds them back, imitating how real lenses and eyes scatter strong light. A neon line gains a halo; a flash swallows the screen for a frame.
Because it only touches what is already bright, bloom is an intensity amplifier: quiet scenes stay clean while peaks luminesce. That makes it a natural audio target, with energy driving threshold or strength so the music literally makes the image radiate.
It is also the most abused effect in real-time graphics; over-bloomed everything reads as haze. The craft is a high threshold and restraint, glow as punctuation rather than climate. Photism’s HEAT control rides exactly this line.