Upcoming HDMI 2.1a spec to add source-based tone mapping for HDR content

HDMI Forum, the entity responsible for issuing and licensing HDMI standards, will be announcing HDMI 2.1a at CES 2022. This is the next version of the latest HDMI 2.1 standard that is currently available, and will bring with it source-based tone mapping or SBTM.

According to The Verge, SBTM enables tone mapping of HDR content on the source device rather than the display. This means, if you have a Blu-ray player plugged into a TV and playing HDR content, the tone mapping for the HDR content will be done on the Blu-ray player rather than the television.

While the article does not provide any further details, SBTM does sound remarkably similar to the TV-led or Player-led tone mapping supported by Dolby Vision. TV-led tone mapping is usually the default option as it allows the TV or monitor to tone map the incoming signal to the characteristics of the display resulting in the best image quality.

However, some devices and television models, most notably the Xbox Series consoles and older Sony televisions, support Player-led tone mapping for Dolby Vision, which does the tone mapping on the source device in an effort to reduce latency and input lag but generally provides inferior image quality.

It seems SBTM in HDMI 2.1a will work similarly and will likely have similar outcome. By being made part of the HDMI spec, it should become accessible to all HDR standards, including HDR10 and HDR10+ without having to rely on Dolby Vision's proprietary implementation. However, it remains to be seen if the feature has any notable upsides over existing display-based tone mapping technique.

If you want to learn more about HDR, click here.

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