HDR and Dolby Vision

SDR

Standard Dynamic Range

SDR is the name given to ordinary video once HDR existed to contrast it with. On the Diva it also describes an output, because TX1 turns what arrives into 1080p SDR for equipment that cannot take more.

SDR, Standard Dynamic Range, is conventional video: a gamma curve, a reference white of around 100 nits and a BT.709 gamut. The term was invented in retrospect. Nobody called it SDR until HDR arrived and something was needed for everything that had gone before.

The real difference is what the code values mean. In SDR the curve is relative, so a display maps the brightest code to whatever its own peak happens to be. HDR uses an absolute curve plus metadata describing the mastering display, which is why HDR content shown as SDR looks flat and grey: the receiving end applies the wrong transfer function.

Converting HDR to SDR is therefore not a matter of dropping the metadata. The picture has to be tone mapped, its highlights compressed into the range an SDR display expects, or the result is a dull image with washed out colour.

SDR on the HDfury Diva

TX1 is the HDR to SDR 1080p output. Equipment that is only capable of 1080p, in HDR or SDR, connects there and gets full HDMI sound and video, with the Diva tone mapping and downscaling the channel and encrypting it to the level that sink expects. The conversion follows what the connected sink says it accepts, so a 1080p display that genuinely claims HDR is not forced down to SDR.

The tone mapping itself is chosen in the TOOLS section. PROFILE selects the profile that suits your display; most people get the best result from Profile 2, and the neighbouring ones are worth trying on real content because some displays render slightly better colours on another. Over RS232 or IP it is set hdrprofile 2, where 0 is OFF, and it applies only when the input is HDR10.

To confirm what happened, read the IN row and the VIDEO row for that output together in the INFO section. If they differ, the Diva did something, and the SCALER and HDR/DV sections between them explain what.

Reaching SDR without the scaler

The HDR/DV section can also stop a display entering HDR mode at all. Disable all output HDR makes the Diva intercept and cancel all incoming HDR metadata and send nothing, with narrower versions for HDR10 only and for HLG only. The RS232 form is set hdrdisable on. The picture still leaves in whatever colour space and bit depth it arrived in; only the metadata is removed.

In the MACROS section, SDR BT.709 and SDR BT.2020 are two of the content types you can attach an RS232 command to, so a projector changes picture mode by itself when SDR content starts.

All glossary terms