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Color Primaries

This section details the first of three settings that are important for retaining accurate color when encoding videos, those settings being primaries, color matrix, and transfer characteristics.

Color primaries are used to indicate the correct coordinates for the red, blue, and green colors. There are historical reasons for why so many standards exist, and this guide will not go in depth into history lessons, but will explain what primaries are available and when to use each one.

Note that for primaries, matrices, and transfer, you can view the values that are set on a video using a tool like MediaInfo. If there are no values set, the player will need to guess which values to use. A safe default assumption for most modern videos is BT.709, although this may vary depending on source and resolution for the video. It is strongly recommended to set the correct values when encoding.

Each setting has at least one name and exactly one integer value representing it--most encoder softwares will accept one or more of the names, but some tooling such as Vapoursynth and MKVToolnix accepts the integer values instead. The integer values are defined within universal specifications, and as such they will be the same across all encoding and playback tools.

1: BT.709​

BT.709 is the standard used for modern high-definition video, and is a safe default assumption.

This color primary setting is used in the following standards:

  • Rec. ITU-R BT.709-6
  • Rec. ITU-R BT.1361-0 conventional colour gamut system and extended colour gamut system (historical)
  • IEC 61966-2-1 sRGB or sYCC
  • IEC 61966-2-4
  • Society of Motion Picture and Television Engineers (SMPTE) RP 177 (1993) Annex B

2: Unspecified​

This value indicates that no color primary is set for the video, and the player must decide which value to use.

mpv will use the following heuristics in this case:

if matrix == "BT.2020" {
    "BT.2020"
} else if matrix == "BT.709" {
    "BT.709"
} else if width >= 1280 || height > 576 {
    "BT.709"
} else if height == 576 {
    "BT.470BG"
} else if height == 480 || height == 488 {
    "SMPTE 170M"
} else {
    "BT.709"
}

4: BT.470M​

BT.470M is a standard that was used in analog television systems in the United States.

This color primary setting is used in the following standards:

  • Rec. ITU-R BT.470-6 System M (historical)
  • United States National Television System Committee 1953 Recommendation for transmission standards for color television
  • United States Federal Communications Commission (2003) Title 47 Code of Federal Regulations 73.682 (a) (20)

5: BT.470BG​

BT.470BG is a standard that was used for European (PAL) television systems and DVDs.

This color primary setting is used in the following standards:

  • Rec. ITU-R BT.470-6 System B, G (historical)
  • Rec. ITU-R BT.601-7 625
  • Rec. ITU-R BT.1358-0 625 (historical)
  • Rec. ITU-R BT.1700-0 625 PAL and 625 SECAM

6: SMPTE 170M​

SMPTE 170M is a standard that was used for NTSC television systems and DVDs.

  • Rec. ITU-R BT.601-7 525
  • Rec. ITU-R BT.1358-1 525 or 625 (historical)
  • Rec. ITU-R BT.1700-0 NTSC
  • SMPTE ST 170 (2004)

7: SMPTE 240M​

SMPTE 240M was an interim standard used during the early days of HDTV (1988-1998). Its primaries are equivalent to SMPTE 170M.

8: Film​

This represents generic film using Illuminant C.

9: BT.2020​

BT.2020 is a standard used for ultra-high-definition video, i.e. 4K and higher. It may be used with or without HDR, as HDR is defined by the transfer characteristics.

This color primary setting is used in the following standards:

  • Rec. ITU-R BT.2020-2
  • Rec. ITU-R BT.2100-2

10: SMPTE 428​

SMPTE 428 is used for D-Cinema Distribution Masters, aka DCDM.

This color primary setting is used in the following standards:

  • SMPTE ST 428-1 (2019)
  • (CIE 1931 XYZ as in ISO 11664-1)

11: DCI-P3​

DCI-P3 is a wide-gamut colorspace used alongside RGB. It is used internally by most HDR monitors on the market.

12: Display-P3​

Display-P3 is a variant of DCI-P3 developed by Apple because they wanted to be different.

22: EBU Tech 3213​

Nobody really knows what this is.