BT.1886 Shorthand Is A Trap

In a technical talk from SIGGRAPH Asia 2018 on Gran Turismo SPORT, there’s a slide that reads:

“ITU-R Recommendation BT.709 = Rec.709 = BT.1886 = sRGB”

“Different names, same gamut.”

Only BT.1886 is not a gamut.

A gamut defines the range of colors an imaging device can detect or produce—using specific xy coordinates for red, green, blue, and white.

A gamma/EOTF is a formula that tells a display how much light to produce for a given electronic signal value. It has no color primaries. It has no white point.

The table of coordinates belongs only to the Rec.709 (and sRGB) color primaries. BT.1886 is just the widely adopted display curve (gamma) designed to be used in conjunction with those Rec.709 primaries for HDTV content.

Don’t let the “equals sign” fool you. Use the slide’s table exclusively for identifying the gamut, not the gamma (which is BT.1886). Keep your primaries and your transfer functions separate in your mind, and you’ll keep your colors accurate.

Hajime Uchimura, Kentaro Suzuki, Practical HDR and Wide Color Techniques in Gran Turismo SPORT, SIGGRAPH ASIA 2018