BT601BT709

BT.601 and BT.709 are ITU-R recommendations that define two related color encoding systems used for video signals. They specify how color information is represented digitally and how it maps to displayed images. Both standards use the Y'CbCr color space, define a transfer characteristic, specify prime colors and a white point, and describe acceptable sampling formats for digital video in their respective domains.

BT.601, the standard for standard-definition television, was established for SD formats such as 625-line (PAL) and 525-line (NTSC). It uses Rec.601 primaries and a white point of D65, a Y'CbCr matrix for converting from RGB, and a limited-range digital representation with Y' typically in 16–235 and Cb/Cr in 16–240. The typical SD matrix for RGB to Y'CbCr in BT.601 is Y' = 0.299R' + 0.587G' + 0.114B', Cb' = -0.168736R' - 0.331264G' + 0.5B', Cr' = 0.5R' - 0.418688G' - 0.081312B'.

BT.709, the standard for high-definition television, covers HD formats such as 720p and 1080i/p. It uses Rec.709 primaries and the same D65 white point, but with a different Y'CbCr matrix to reflect HD colorimetry. The BT.709 luma coefficients are Y' = 0.2126R' + 0.7152G' + 0.0722B', with corresponding Cb and Cr equations that differ from BT.601.

In practice, converters between BT.601 and BT.709 are routine in post-production and broadcasting workflows, reflecting the transition from SD to HD and the need for consistent color reproduction across formats.