Tone mapping adapts an image's brightness representation to the capabilities or intended range of the output display. It is important when an HDR source contains levels a particular screen cannot reproduce directly. The process involves trade-offs in highlights, overall brightness and detail; different implementations can therefore present the same source differently to the viewer.
A practical example
A television may compress very bright highlight information so that clouds or reflections remain distinguishable on its panel. Another supported picture mode may favour a brighter overall image, changing the balance even though the underlying programme is the same.
A common misunderstanding
A darker HDR picture is not automatically a network or subscription fault. Viewing conditions, source grading, display brightness and tone-mapping choices can all affect what appears on the screen.
Related terms
Stable technical definition. Editorial approach