Tone mapping
Also known as: range compression, highlight roll-off
Fitting a wide range of brightness into a narrower one, deciding what happens to highlights that have nowhere left to go.
Updated
What it means
Tone mapping is a compromise made visible. A camera records more Dynamic range than a standard display can show, so something has to give, and the mapping decides what. There is no lossless answer.
The alternative is clipping. Without a mapping the highlights simply stop at the top of the range, which is why a hard conversion produces white skies. Nothing above the ceiling survives it.
A good curve rolls off instead. Highlights compress gradually rather than hitting a wall, which is the behaviour film had and digital has to be asked for explicitly in the conversion.
How it works in practice
It is part of the conversion rather than a separate step. A Technical LUT contains a mapping, and the differences between tables are mostly differences at the top end of the range.
Scopes are how it gets judged. A Waveform shows whether highlights are rolling or clipping, which a bright screen hides completely, because the eye adapts and the scope does not adapt to anything.
Shooting with headroom makes it work. Exposing so that a Highlight clipping warning stays quiet leaves information for the mapping to compress rather than invent. Headroom cannot be added afterwards.
What to watch out for
Aggressive mapping flattens the image. Compressing everything to keep the highlights produces a clip with no brightness anywhere, which reads as unfinished. Range is not the same thing as brightness.
Automatic conversion on upload is unpredictable. A platform converting an HDR video file for standard viewers applies its own mapping, and the result is frequently worse than any deliberate choice made in advance.
Mixed delivery breaks matching. One clip mapped and another clipped read as two different cameras, so the decision belongs to the whole sequence rather than to the individual shots inside it.
How RawClip handles it
Highlight handling is applied consistently across the assembled sequence rather than left to a platform, which keeps a bright sky from turning into a flat white area at one cut and not another. Material with headroom gives that step something real to work with.