Resources
HDR Video Glossary
Plain definitions for the terms that decide whether a file is really HDR: PQ, BT.2020, MaxCLL, 10-bit, tone mapping, and the rest, each with how to check it in a real file.
- 10-bit colour10-bit video stores 1,024 brightness levels per colour channel, against 256 for 8-bit. Across three channels that is roughly 1.07 billion possible colours rather than 16.7 million. HDR requires it because the PQ curve spreads a far larger brightness range across the same code values.
- BandingBanding, sometimes called contouring, is the visible stepping that appears in what should be a smooth gradient. It happens when a gradient spans too few distinct code values, so the eye sees discrete bands instead of a continuous ramp. Skies, studio backdrops and lens flares show it first.
- BT.2020ITU-R BT.2020 is the wide colour gamut specified for ultra-high-definition and HDR video. Its three primaries are monochromatic wavelengths, and the triangle they define covers roughly 75.8% of the CIE 1931 chromaticity diagram, against about 35.9% for the BT.709 gamut used by SDR.
- BT.709ITU-R BT.709 is the colour standard for high-definition television and the colour space almost all SDR video lives in. It defines a gamut covering about 35.9% of CIE 1931, a transfer curve corresponding to roughly 2.4 display gamma, and a reference white of 100 cd/m².
- Chroma subsamplingChroma subsampling stores colour information at a lower resolution than brightness information, exploiting the fact that human vision resolves luminance detail far better than colour detail. The notation 4:4:4, 4:2:2 and 4:2:0 describes how much colour resolution is kept.
- Dolby VisionDolby Vision is a proprietary HDR format that carries dynamic, per-frame metadata instead of one static set of values for a whole clip. It supports signals up to 12-bit and requires a licence for both encoding and playback, which is why device support is narrower than HDR10's.
- Dynamic rangeDynamic range is the ratio between the brightest and darkest values a system can capture or reproduce. It is usually counted in stops, where each stop is a doubling of light. SDR delivery covers roughly 6 stops of usable range; HDR delivery formats extend that substantially.
- EOTF and OETFAn OETF, or opto-electronic transfer function, converts scene light into code values at the camera. An EOTF, or electro-optical transfer function, converts code values back into emitted light at the display. They are the two halves of a video signal's brightness encoding and they are not inverses of each other.
- Gamut mappingGamut mapping fits colours from a wider colour space into a narrower one that cannot reproduce them. It is the colour counterpart of tone mapping, which handles brightness, and it is required whenever BT.2020 content is shown on a display covering only BT.709 or DCI-P3.
- HDR10HDR10 is the baseline high-dynamic-range video format. It combines ITU-R BT.2020 colour primaries, the SMPTE ST 2084 perceptual quantizer transfer curve, 10-bit depth, and static metadata describing the mastering display. It is royalty-free, which is why every HDR TV supports it and why it is the safe delivery target.
- HDR10+HDR10+ adds dynamic, scene-by-scene metadata to an ordinary HDR10 stream, using the SMPTE ST 2094-40 specification. Because the base layer is plain HDR10, a display that does not understand the extra metadata ignores it and plays the file as HDR10 with no fallback logic required.
- HEVC (H.265)HEVC, also called H.265, is a video compression standard and the codec HDR10 delivery normally uses. Its Main 10 profile supports 10-bit encoding, which HDR requires, and its SEI messages are where HDR static metadata is physically carried.
- HLGHLG, or Hybrid Log-Gamma, is an HDR transfer curve that needs no metadata. Standardised as ARIB STD-B67 and included in ITU-R BT.2100, it uses a conventional gamma curve for the lower half of the signal and a logarithmic curve above it, so an SDR display shows something reasonable without any conversion.
- LUTA LUT, or lookup table, maps input colour values to output colour values. A 3D LUT samples the whole RGB cube at a fixed grid, commonly 33 points per axis, and interpolates between the samples. It applies a fixed colour transform without needing the software to implement that transform itself.
- Mastering display metadataMastering display metadata, specified in SMPTE ST 2086, records the colour primaries, white point and minimum and maximum luminance of the reference monitor a piece of HDR content was graded on. It describes the grading environment rather than the picture, so a different display can work out how far its own capabilities diverge.
- MaxCLLMaxCLL, or Maximum Content Light Level, is the brightness in nits of the single brightest pixel anywhere in a piece of content. It is one of the two static metadata values defined in CTA-861.3 and is sent once for the whole file, telling a display the highest value it will ever have to render.
- MaxFALLMaxFALL, or Maximum Frame-Average Light Level, is the highest average brightness of any single frame in a piece of content, measured in nits. Where MaxCLL reports the brightest pixel, MaxFALL reports the brightest whole frame, and displays need both to tone-map safely.
- Nits (cd/m²)A nit is one candela per square metre (cd/m²), the standard unit for how much light a display emits. SDR reference white is defined at 100 nits. HDR content is typically mastered on a display capable of 1,000 or 4,000 nits, and consumer HDR televisions peak somewhere between about 400 and 2,000.
- PQ (SMPTE ST 2084)PQ, the perceptual quantizer, is the transfer function behind HDR10 and Dolby Vision, standardised as SMPTE ST 2084. It maps code values to absolute luminance from 0 to 10,000 cd/m², so a given code means a specific brightness on any display rather than a proportion of that display's maximum.
- SDRSDR, or standard dynamic range, is the conventional video encoding almost all existing footage uses. In practice it means BT.709 colour primaries, a transfer curve around 2.4 display gamma, 8-bit depth, and a reference white of 100 cd/m². Its defining constraint is that nothing can be brighter than diffuse white.
- Tone mappingTone mapping is the process of compressing a wider brightness range into a narrower one so it can be shown on a display that cannot reach the original peak. It is applied whenever HDR content meets a display with less headroom than the content was graded for, which is most displays.
Questions people ask
Which terms should I read first?
SDR and HDR10 settle what the two things are. PQ and 10-bit explain why the encoding needs both. Everything else is detail you can reach for when a specific field or number comes up.
How do I check what my own file is?
Run `ffprobe -v error -select_streams v:0 -show_entries stream=color_transfer,color_primaries,pix_fmt -of default=nw=1 input.mp4`. `smpte2084` with `bt2020` and a `10le` pixel format is HDR10. `bt709`, or an empty transfer field, is SDR.
Why does each entry include an ffprobe field?
Because a definition you cannot check is not much use. Every term here that appears in a file has the field name and the value to look for, so you can settle the question about your own footage rather than reasoning about what a camera probably did.
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