Bloom
Soft glow around bright pixels
Definition
Bloom is a post-processing effect that simulates how very bright light sources bleed and glow in real cameras and human vision. The renderer extracts pixels above a brightness threshold, blurs them, and adds the blur back over the scene. Used subtly, bloom adds physical realism — neon signs, sun reflections, character magic effects. Overused, it produces the infamous "2007 game" look where everything bright is wrapped in a fog of glow.
In production
Tune bloom threshold (where it starts, typically around 1.0 in linear HDR value), intensity (how strong), and radius (how wide the glow) in the engine's post-processing settings — in Unreal Engine 5 these live in the Post Process Volume's Bloom category, while Unity's URP/HDRP expose them in the Volume Profile's Bloom override. Most stylized games use higher intensity for visual punch; photoreal games stay restrained, often keeping bloom subtle enough that players only notice it on direct light sources. Bloom is typically computed from a downsampled mip chain of the HDR framebuffer, blurred at multiple resolutions and composited back together, which is why cheap implementations can look blocky at the edges of bright objects if the downsample chain is too short. A frequent art-direction mistake is leaving bloom's default intensity untouched after lighting changes, causing every added light source to bloom unpredictably — the fix is re-tuning the threshold after major lighting milestones rather than at the very end.