An upcoming revision of HDMI 2.1, labeled HDMI 2.1a, will add support for a new feature; Source-Based Tone Mapping (SBTM). Many devices can firmware-upgraded to support it.

HDMI 2.1a revision
Like HGIG (HDR Gaming Interest Group), a new HDMI 2.1 feature will let a source device adapt its HDR output to match a specific display or TV.

The HDMI organization explains:

In today’s environment, not all displays have the same HDR capability; some have different ranges of color and brightness levels than others. This is fine when HDR video such as HDR10 and HLG are sent, because the television will typically map HDR content beyond the display’s capabilities to the brightness and color ranges available. But sometimes, a source device needs to combine different types of content (HDR, SDR, dynamic HDR, graphics) together 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. To optimize the quality of the combined content, processing is needed in the Source device that cannot be performed inside the display.

Source-Based Tone Mapping (SBTM) enables the source to send a video signal that takes full advantage of a specific display’s HDR capability by adjusting its output to take better advantage of each display’s potential. As with other HDR technologies, rather than adopt a fixed set of color and brightness ranges, SBTM allows the Source to adapt to a specific display. SBTM can also be used by PCs and gaming devices to eliminate manual user optimization for HDR.
SBTM is not a new HDR format and it does not replace technologies such as HDR10, HDR10+, HLG or Dolby Vision. Instead, it is a more intelligent link to let the source device and display communicate. There is no manual 'SBTM Mode' just like there is no manual 'HGIG Mode'.

 Also read: Sony X900H/XH90: New firmware with official VRR mode & HGiG rolling out


 HDMI Source-Based Tone Mapping (SBTM). Illustration: HDMI organization

The HDMI organization said that many devices can be firmware-upgraded to support SBTM. It can work with media players, PCs, game consoles, set-top boxes, and other types of players.

Both the transmitting and receiving device must support SBTM for it to work. It will work with any HDMI cable.

 Also read: HDMI 2.0 devices are now HDMI 2.1 devices: "HDMI 2.0 no longer exists"

Manufacturers of TVs, monitors, players and other devices can advertise 'HDMI SBTM' as a supported feature under HDMI 2.1. We will be chasing more information at CES 2022.

- Source: HDMI.org