ITU-R BT.2100
ITU-R BT.2100 specifies HDR television image parameters for PQ and HLG systems.
BT.2100 is the HDR television system specification that joins image geometry, wide color, signal precision, and HDR transfer relationships. A file usually exposes those pieces in separate fields rather than carrying a single “BT.2100” badge.
| System part | Defined relationship |
|---|---|
| Primaries | The wide-gamut coordinates also used by BT.2020 |
| HDR transfer systems | PQ and HLG |
| Image sizes | 1920 × 1080, 3840 × 2160, 7680 × 4320 |
| Scanning | Progressive |
| Precision | 10 or 12 bits per component |
The current recommendation is BT.2100-3, approved in February 2025. Its transfer-system definitions connect scene light, the encoded signal, reference display light, and viewing conditions.
Recognize the system in a media report
An HDR recording can identify BT.2020 primaries, a PQ transfer characteristic, and a compatible component matrix. Those fields provide the instructions for interpreting the decoded pictures. A different recording can use the same primaries with HLG, changing the light relationship while retaining the color coordinates.
The decoder first reconstructs samples from the compressed video. HDR-aware presentation then interprets those samples and prepares the picture for the output. Being able to decode HEVC, for example, answers a coding question; handling the resulting HDR signal answers a rendering question. Emby playback needs both parts of the selected path to work.
Can 1080p be HDR?
Yes. HD geometry is part of the BT.2100 system. A 1920 × 1080 HDR picture has fewer spatial samples than UHD, while its brightness and color interpretation can still require HDR-aware presentation.
Reducing the grid to a smaller delivery size changes spatial detail. It does not automatically replace the transfer function. An SDR destination needs an actual HDR-to-SDR conversion, including the appropriate brightness and color operations, rather than a resolution change alone.
Where do HDR formats fit?
Formats such as HDR10 combine defined signal characteristics with delivery conventions and metadata. BT.2100 supplies the underlying television image parameters; the format describes how a particular presentation is carried and identified.
Reading an HDR label becomes more useful when those layers are kept visible: compressed coding, television signal interpretation, format metadata, and the intended display output.