BT2020

ITU-R Recommendation BT.2020, also known as Rec.2020, is a standard defining the color space, sampling, and related parameters for ultra high definition television (UHDTV). It establishes a wide color gamut, support for 4K and 8K resolutions, and modern bit depths and chroma subsampling schemes used in contemporary video and broadcast systems.

The color space of BT.2020 uses the Rec.2020 primaries with white point D65, resulting in a substantially larger gamut than the older Rec.709 used for standard HDTV. The primaries are defined by specific CIE 1931 chromaticity coordinates, and the standard supports a range of color representations through the luma Y' and chroma Cb and Cr signals.

Resolution and scan format defined by BT.2020 include 3840x2160 (4K) and 7680x4320 (8K) with progressive scanning as the default. The standard allows multiple chroma subsampling options, including 4:4:4, 4:2:2, and 4:2:0, and supports bit depths up to 10 or 12 bits per sample (8-bit is technically allowed but not typical for UHD content).

Transfer characteristics in BT.2020 are not fixed to a single curve; SDR content commonly uses gamma-based approximations similar to Rec.709, while HDR implementations rely on separate HDR transfer functions defined in related ITU-R BT.2100 standards, such as ST 2084 (PQ) or Hybrid Log-Gamma (HLG). BT.2020 is widely used in UHD Blu-ray, streaming, and broadcast to realize wide-gamut video with high resolution and depth.

Overall, BT.2020 specifies the color and sampling framework that enables modern UHD content to display with a broader color range and higher fidelity than previous standards.