Tone mapping is the process of converting an HDR signal to fit a display that can't show the full HDR range. An HDR film might be mastered for peaks up to 1000 or 4000 nits, but a typical mid-range TV maxes out at 600 nits, a budget LED might do 300, a phone screen might do 800 in HDR mode. Tone mapping is what the TV does behind the scenes to squash that wider range into what it can physically display without losing the look the colourist intended.
Done well, it preserves both the dark detail and the highlight detail proportionally — a bright sky stays bright relative to a shadow but doesn't get clipped to pure white. Done badly, three things go wrong: highlights get crushed to flat white (sky becomes paper), shadows get crushed to flat black (faces disappear), or the whole image looks dim because the TV is trying too hard to preserve highlights it can't show anyway. Premium TVs have dedicated tone-mapping silicon and fine-tuned algorithms; budget TVs do a generic curve and hope for the best.
For a streaming product, tone mapping is where dynamic HDR metadata pays off. hdr10 uses one tone-mapping strategy for the entire film — same approach on a dark cathedral scene as on a noonday explosion. dolby-vision and hdr10-plus ship per-scene instructions telling the TV exactly how to tone-map each scene optimally. The visible difference: on a 600-nit budget HDR TV, an HDR10 master often looks acceptable, while the same content as Dolby Vision looks noticeably better because each scene gets bespoke treatment. The takeaway: tone mapping is the link between "what was mastered" and "what the viewer actually sees", and HDR delivery decisions are really decisions about how much control you give the TV's tone mapper.
