HDMI 2.1 spec adds Source-Based Tone Mapping feature

Mike Wheatley

The HDMI Licensing Administrator has announced it’s updating the HDMI 2.1 standard. The new revision is to be known as HDMI 2.1a, and will add support for a brand new feature called Source-Based Tone Mapping.


It’s said that it will allow a source device to adapt its HDR output to match a specific TV or display.

The organization explained on its website that today’s displays innumerable consumer displays do not all have the same HDR capability. The reality is that some TVs cover a much wider range of colour and brightness than others. That’s not a problem when a HDR video such as HDR10 or HLG is sent to the display, because in that case it just maps the content beyond its capabilities to whatever brightness and colour range is available.

The problem is that sometimes, source devices need to combine different kinds of content – for example HDR, SDR, dynamic HDR and graphics – and send it at the same time.

“For example, when you view a menu of video thumbnails from a streaming video service, some of the thumbnails might be HDR and others might be SDR, and the menu is rendered using graphics,” the HDMI Licensing Administrator explained. “To optimize the quality of the combined content, processing is needed in the Source device that cannot be performed in the display.”

That’s where Source-Based Tone Mapping (SBTM) will come in handy. The new feature will make it possible for the source device to send a video signal that takes full advantage of a display’s HDR capabilities by adjusting its output. As with other HDR technologies that defer from adopting a fixed set of colour and brightness ranges, the SBTM feature will allow the source to instead adapt to each display. One example of its use might be in PCs and gaming devices, where it can eliminate the need for manual user optimization when playing games in HDR.

HDMI SBTM can be thought of as a kind of intelligent link for various HDR formats that lets the source device and the display communicate. So it is not a replacement for HDR10, HDR10+, Dolby Vision etc.

The best thing about SBTM is that most existing devices should be able to support it via a firmware update. The HDMI Licensing Administrator explained that it should work with most PCs, games consoles, media players, set-top boxes and other devices.

For SBTM to work, both the TV and the source device must support the feature. In which case, it will work with any standard HDMI cable.

If the SBTM feature sounds like something you’re interested in having, keep an eye out for new devices advertising a “HDMI SBTM” capability in their new products, starting at CES 2022.