Tone mapping is the process of compressing the wide brightness range of a high-dynamic-range (HDR) rendered image into the narrower range that a standard display or print can show. Without tone mapping, an HDR render would either blow out highlights (the bright window becomes solid white) or crush shadows (the dark corner becomes solid black) when displayed on a standard 8-bit-per-channel monitor.
Different tone-mapping curves produce different visual character. Linear tone mapping preserves brightness relationships but tends to lose highlight detail. Filmic tone mapping (used in modern game engines and rendering software) gives soft rolled-off highlights similar to film photography. Reinhard tone mapping is mathematically simple and produces somewhat washed-out results. Production renderers usually offer a choice and let the artist pick.
AI rendering performs the equivalent of tone mapping automatically as part of producing display-ready output. The model has learned what filmically-tone-mapped HDR scenes look like and produces output that's already 'cooked' for standard display. You don't usually need to think about tone mapping in an AI prompt, but if your output is looking too contrasty or washed out, asking for 'preserved highlight detail' or 'naturalistic contrast' nudges the AI toward more balanced rendering.
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