Tone mapping adapts an image’s brightness relationships to the range that a destination can reproduce. It is central when HDR content is shown on a display with lower peak brightness or converted for an SDR output. Rather than simply lowering every value equally, a mapping can compress highlights while preserving useful separation in midtones and shadows. Different methods make different compromises. The term describes a transformation of the picture, not an HDR format, and it does not guarantee that an application or television performs the transformation well.
Tone mapping and Color calibration
Tone mapping adapts signal range; calibration aligns display behavior to a chosen target.
Fitting a larger range
Suppose a master contains highlights beyond a television’s capability. Directly clipping them would turn several distinct bright details into the same maximum value. A tone curve can roll those values into the available range instead. Depending on the implementation, the curve may use mastering information, scene analysis or a fixed policy; the resulting image can therefore vary between devices.
Brightness and colour interact
Compressing highlights affects perceived contrast and can also require careful colour handling. A bright saturated sign may lose colour or change hue if conversion is careless. Gamut mapping concerns colours outside the destination’s colour range, while tone mapping concerns brightness relationships. The operations are related in a complete conversion but should not be treated as interchangeable settings.
Find the conversion stage
Determine whether the source, player or television is performing the mapping. Multiple conversion stages can make diagnosis difficult. Compare the same scene with one documented path at a time, looking at bright detail, faces and shadow separation. A picture that looks brighter overall may still have less useful highlight detail or a less faithful midtone balance.
An illustrative example
A bright cloud contains texture in an HDR master. On an SDR output, a suitable conversion compresses the cloud’s brightest values so that texture remains visible. A simple hard cut instead produces a flat white patch even though the rest of the scene still appears normally exposed.
Practical actions
- Identify where HDR-to-SDR or display adaptation occurs.
- Compare highlights and faces in the same scene.
- Avoid stacking undocumented conversion modes.