HDfury Diva

HDMI signals

Colour gamut

BT.709, DCI-P3 and colour primaries

In short

The range of colours a signal can describe, fixed by the red, green and blue primaries a standard nominates, such as BT.709, DCI-P3 or BT.2020.

Gamut is the palette, not the brightness. It is declared rather than measured, which is why the Diva can change what a display believes it is receiving without touching a single pixel.

A colour gamut is the range of colours a signal can describe. It is fixed by three primaries, the exact red, green and blue a standard nominates, plus a white point. Everything the format can encode lies inside the triangle those points make, and anything outside it cannot be represented at all.

BT.709 is the gamut of HD and of effectively everything broadcast since the 1990s. DCI-P3 came from digital cinema and is roughly what a good modern panel can actually reproduce. ITU-R BT.2020, published in 2012 for UHD, is larger than any consumer display can show, so it works as a container: content is mastered within P3 and carried in BT.2020 coordinates.

None of this lives in the pixels. The gamut in use is declared in the colorimetry field of the AVI infoframe and, for HDR, in the primaries of the HDR metadata, while what a display will accept is declared in its EDID. Get the declaration wrong and colours shift: BT.2020 content decoded as BT.709 looks oversaturated, and the reverse looks flat.

Colour gamut on the HDfury Diva

Three sections touch it. In the HDR/DV section, the custom HDR metadata generator has a Primaries field offering DCI P3, ITU-R BT 709-5 and ITU-R BT2020-2, and that value is written into the metadata you build with Create IF. The custom AVI infoframe generator alongside it has its own Primaries selector, and the usual reason to reach for it is activating the BT.2020 mode of a television whose content is not sending the correct infoframe.

In the SCALER section, Custom Scaling sets the colour space explicitly for the TX0 output: RGB FULL, RGB BT2020, 4:4:4 BT.709, 4:4:4 BT2020, 4:2:2 BT.709, 4:2:2 BT2020, 4:2:0 BT.709 or 4:2:0 BT2020, with Follow Input as the default. Nothing takes effect until you click SEND.

In AUTOMIX, the 2020/xvYCC flag forces the mixed EDID to present BT.2020 and xvYCC support, so a source that would otherwise be told the chain is BT.709 only will send wide gamut. Over RS232 or IP that is set edid bt2020 on, and it only adds the capability where it is missing rather than removing it from a sink that already claims it.

Forcing BT.2020 by hand

If a television has a BT.2020 mode that the content never triggers, a custom AVI infoframe is the direct route. These starting values are published with the manual:

  • BT.2020 RGB is 00:E8:64:5D:00
  • BT.2020 YCbCr 4:2:2 is 20:E8:64:5D:00
  • BT.2020 YCbCr 4:4:4 is 40:E8:64:5D:00
  • BT.2020 YCbCr 4:2:0 is 60:E8:64:5D:00

Related terms

BT.2020The ITU recommendation that defines the wide colour gamut and the formats used for ultra high definition television.Colour spaceThe way colour is encoded in a video signal: RGB or YCbCr, at full or limited range, measured against a defined set of primaries.HDRVideo carrying a far wider range of brightness than the older standard, described to the display by metadata sent alongside the picture.EOTFElectro-Optical Transfer Function: the curve that maps a digital code value to the amount of light a display emits.

In the manual

The pages of the HDfury Diva manual where this comes up.

All glossary terms