HDfury Diva

HDR and Dolby Vision

STM profile

The HDfury Diva HDR to SDR tone mapping profiles

In short

A fixed tone mapping curve, chosen once in advance, that fits high dynamic range content into what a standard dynamic range display can show.

When HDR is converted to SDR something has to be done with highlights brighter than the display can produce. On the Diva that decision is one dropdown, and it has a default worth knowing.

Tone mapping is the compression of a wide brightness range into a narrower one. HDR10 content is mastered for a peak of 1000 nits or more, while a standard dynamic range display works to something near 100 nits, so the highlights have to go somewhere. Clip them all to white and clouds turn into flat paper. Roll them off gently and you keep the detail but lose contrast further down. A tone mapping curve is where that compromise is fixed.

The initials stand for static tone mapping: one curve chosen in advance and applied to everything, as opposed to dynamic tone mapping, which recalculates scene by scene from metadata the content carries. Static is predictable and costs no latency, which is why hardware sitting in the signal path tends to use it. What differs between profiles is the shape of the roll-off, and which shape looks best depends on your display's own behaviour more than on the content.

The STM profile on the HDfury Diva

The control is PROFILE, at the top of the TOOLS section of the web server, above the ambient light effects and the lag tester. There are six positions. Profile 0-OFF turns the conversion off, and the manual's advice for the rest is that most people get the best result from Profile 2, with some displays rendering slightly better colours on a neighbouring profile, so it is worth trying the ones either side on real content before settling. Over IP or RS232 the command is set hdrprofile 2, taking a value from 0 to 5.

Two documented details are worth having. The conversion applies only when the input is HDR10, so a source sending HLG or Dolby Vision looks unchanged whatever you select here. And TX1 is the HDR to SDR 1080p output, the one that exists so that older or 1080p-only equipment gets a picture it can lock onto, which is where the conversion normally earns its keep.

When to set it to zero

The lag tester instructions tell you to disable HDR to SDR conversion for the TX0 output by setting Profile 0-OFF before measuring, along with AUTOSCALING enabled and the presets left at AUTOSENSE with UPSCALING enabled. The same reasoning applies to any measurement or comparison: with a profile running you are looking at the Diva's curve as well as the display's, so start from 0-OFF when you want to see what your display does on its own.

Related terms

Tone mappingThe process of fitting a picture graded for a high brightness range into the smaller range a particular display can actually reproduce.SDRStandard Dynamic Range: conventional gamma-based video with a reference white of around 100 nits, the way everything looked before HDR arrived.DownscalingConverting a signal to a lower resolution, and often a lower dynamic range, so that equipment which cannot accept the original can display it.Ambient lightA strip of LEDs behind a display, driven from the picture, so the wall around the screen carries the colours at the edges of the image.

In the manual

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

All glossary terms