The HDMI 2.1 Specification is Getting Updated, Again

(Image: D-Kuru, Own work. Wikipedia.) Even though the ink hasn’t even dried on the last round of confusing news regarding the HDMI 2.1 specification, a new edition to the spec has been announced by the HDMI forum. It is likely to make things more confusing for people. Drum roll: say hello to HDMI 2.1a! This small-ish update, denoted by the letter a, obviously, will be on-display at CES 2022, pardon the pun, and contains just one addition to the bewildering specification stack: the addition of Source-Based Tone Mapping, or SBTM.

This addition to the spec is being offered as a feature to improve HDR on TVs, as it will allow the source of the content, such as your cable box, to do some of the tone mapping on content before it arrives on your television. As The Verge points out, this is not a new HDR standard, but rather a way to make HDR content look good on any TV without requiring the user to specifically calibrate their display for it. So for example, if you found that SDR content looked fine, but you had to adjust your TV for HDR content, this update should allow you to just sit on your couch and enjoy both types of content without having to fiddle with anything. As the HDMI website notes, “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.” This new feature will also allow content that has both SDR and HDR qualities to be displayed together without looking weird.

Some of you may recall the concept of source-based tone mapping from AMD’s FreeSync 2 / FreeSync Premium Pro standard. The application here is identical — it’s a way for color data to be passed directly from GPU to device (or player to device). The difference is that the capability is being baked into the HDMI 2.1a standard rather than supported in an AMD-specific product.

AMD discussed FreeSync 2 (later FreeSync Premium Pro) in terms of gaming, but the HDMI 2.1a feature can be used for video as well.

This new update to the spec adds to what is widely considered to be a messy situation, as the rollout of the HDMI 2.1 specification has caused head-scratching on a global scale. Though the list of features being included in the 2.1 update is indeed impressive — support for 8K displays at 60Hz, and 4K at 120Hz among many welcome upgrades — precisely none of the new features need to be supported by an HDMI 2.1 compatible device, and that includes this new feature as well. Since HDMI 2.1 is replacing HDMI 2.0, and all the new features are optional, you could find yourself with a brand-new HDMI 2.1 compatible device, that actually delivers zero new features over the previous spec.

HDMI 2.1 will require a new, high-speed cable, so even choosing the right cable will require reading carefully.

Toss SBTM on the pile of confusing and optional features that may or may not be supported by the new TV you will buy in the future. And if you are in the market for some new hardware, be sure to pay very close attention to the fine print that accompanies it, because just being “HDMI 2.1”-compatible means absolutely nothing.

Now Read:

• HDMI 2.1 Devices Are Not Required to Support Any New HDMI 2.1 Features
• HDMI 2.1 Spec Released With Better Color, Faster Refresh Rates, 10K Video
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