AV1 Color Spaces and Transfer Characteristics

The AOMedia Video 1 (AV1) specification standardizes color representations by adopting the ITU-T H.273 and ISO/IEC 23091-2 Coding-Independent Code Points (CICP) system. Through this architecture, AV1 officially supports a broad spectrum of color spaces, color primaries, transfer characteristics (gamma and HDR curves), and matrix coefficients, allowing seamless delivery of Standard Dynamic Range (SDR), Wide Color Gamut (WCG), and High Dynamic Range (HDR) content.

How AV1 Signals Color Metadata

AV1 signals color parameters directly in the sequence header within the color_config() syntax structure. It defines three primary 8-bit integer parameters corresponding directly to ITU-T H.273:

• Color Primaries: Defines the chromaticity coordinates of the source color gamut.
• Transfer Characteristics: Specifies the opto-electronic or electro-optical transfer function (OETF/EOTF).
• Matrix Coefficients: Defines the transformation matrix used to derive luma and chroma signals from red, green, and blue primaries.

Standardized Color Primaries

AV1 supports the following standardized color primaries (CICP values):

• BT.709 (Value 1): Standard gamut for HDTV, sRGB, and web SDR video.
• BT.470 System M (Value 4): Historical NTSC standard.
• BT.470 System B, G (Value 5): Historical PAL/SECAM standard.
• BT.601 / SMPTE 170M (Value 6): Standard definition NTSC.
• SMPTE 240M (Value 7): Early HDTV standard.
• Generic Film (Value 8): Traditional color film using standard illuminant C.
• BT.2020 / BT.2100 (Value 9): Ultra HD and Wide Color Gamut (WCG) standard.
• SMPTE ST 428-1 (Value 10): CIE 1931 XYZ standard.
• SMPTE ST 431-2 / DCI-P3 (Value 11): Digital Cinema Initiatives P3 with DCI white point.
• SMPTE ST 432-1 / Display P3 (Value 12): DCI-P3 primaries with a D65 white point, widely used on modern mobile and computer displays.
• EBU Tech. 3213-E (Value 22): Standard European broadcasting monitor phosphors.

Standardized Transfer Characteristics

The AV1 specification standardizes electro-optical and opto-electronic curves across legacy and modern HDR workflows:

• BT.709 (Value 1): Standard SDR curve for HDTV broadcasts.
• BT.470 System M (Value 4): Assumed gamma 2.2 curve.
• BT.470 System B, G (Value 5): Assumed gamma 2.8 curve.
• BT.601 / SMPTE 170M (Value 6): Standard SDR OETF for SDTV.
• SMPTE 240M (Value 7): Interim HDTV transfer characteristic.
• Linear (Value 8): Linear transfer function (gamma 1.0), used in raw VFX and computer-generated imagery.
• Logarithmic (Values 9 & 10): Log 100:1 and Log 100*Sqrt(10):1 dynamic range curves.
• IEC 61966-2-4 / xvYCC (Value 11): Extended gamut SDR function.
• BT.1361 (Value 12): Extended color gamut OETF.
• IEC 61966-2-1 / sRGB (Value 13): Standard transfer function for web and computer graphics.
• BT.2020 10-bit and 12-bit (Values 14 & 15): Standard SDR functions designed for UHDTV broadcast pipelines.
• SMPTE ST 2084 / PQ (Value 16): Perceptual Quantizer curve designed for HDR displays mastering up to 10,000 nits (standard for HDR10 and Dolby Vision).
• SMPTE ST 428-1 (Value 17): D-Cinema transfer function.
• BT.2100 / ARIB STD-B67 / HLG (Value 18): Hybrid Log-Gamma function, standard for HDR broadcast television.

Standardized Matrix Coefficients

To convert RGB image data into YCbCr or other representations, AV1 standardizes the following matrix coefficients:

• Identity (Value 0): Full-range RGB or GBR color representations.
• BT.709 (Value 1): Standard HD YCbCr conversion.
• FCC (Value 4): Historical broadcast standard.
• BT.601 / SMPTE 170M (Value 5 & 6): Standard definition YCbCr.
• SMPTE 240M (Value 7): Early HD luma conversion.
• YCgCo (Value 8): Highly efficient, lossless integer-reversible color model.
• BT.2020 Non-Constant Luminance (Value 9): Standard YCbCr conversion for UHD, HDR10, and HLG workflows.
• BT.2020 Constant Luminance (Value 10): Alternative broadcast model preserving luminance fidelity across chroma subsampling.
• SMPTE ST 2085 (Value 11): Specific matrix used with D-Cinema setups.
• BT.2100 ICtCp (Value 14): Constant luminance color representation optimized for HDR and Wide Color Gamut encoding.