HDR and Dolby Vision

Tone mapping

Fitting HDR into what a display can show

Every HDR picture is tone mapped by something before you see it. On the Diva you choose the profile, and on the TX1 output the conversion goes all the way to SDR.

Tone mapping is the business of fitting a picture graded for one brightness range into what a display can actually produce. HDR is mastered against an absolute curve, PQ as defined in SMPTE ST 2084, which runs to 10,000 nits, and content is typically graded at 1000 or 4000. Almost nothing in a living room reaches those numbers, so something in the chain has to decide what becomes of the highlights.

There are two ways to decide. Clipping throws away everything above what the panel can show, which keeps the rest of the image at the right brightness but flattens bright detail into a single white. Rolling the top of the range off gradually keeps that detail but darkens or desaturates the picture below it. Converting HDR to SDR is the same job carried further: the PQ curve and BT.2020 primaries have to become a gamma curve and BT.709 primaries, and a good conversion looks like a properly graded SDR picture rather than a washed out one.

There is no single correct answer, which is why equipment offers profiles rather than a switch. A curve that suits a bright television clips a projector, and the reverse.

Tone mapping on the HDfury Diva

TX1 is where it matters most. That output exists for older or 1080p-only equipment: the Diva tone maps and downscales the channel to 1080p SDR and encrypts it to the level that sink expects, so a first generation display or an older AVR receives something it can lock onto instead of a black screen or an HDCP error.

The strength of the conversion is chosen in the TOOLS section. PROFILE selects the tone-mapping profile that works best for your display. Most people get the best result from Profile 2, but some displays render slightly better colours on a neighbouring profile, so it is worth comparing them on real content before settling. Over RS232 or IP the command is set hdrprofile x, where x is 0 to 5 and 0 is off.

Where the profile does and does not apply

The profile acts on HDR10 input only, so HLG and Dolby Vision material is not passed through it. It also reaches TX0, which is easy to miss until it interferes with a measurement: the input lag tester instructions ask you to disable HDR to SDR conversion for the TX0 output by setting Profile 0-OFF in TOOLS, with scaling left at its defaults and AUTOSENSE and UPSCALING enabled, so that the number you get describes the display rather than your own processing.

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