We recently reported that the HDMI Licensing Administrator stopped labeling newer HDMI displays with the 2.0 version, and allowed manufacturers the ability to utilize the HDMI 2.1 moniker, as long as it fits the standards already set. This potentially can cause a manufacturer to label an HDMI 2.0 display as the 2.1 version to falsify claims to consumers and was seen by a Chinese seller practicing that exact scenario.
Now, there is a new HDMI 2.1 variant about to be released at some point in the future with the moniker of "HDMI 2.1a."
The HDMI Licensing Administrator confirms new standards for HDMI 2.1 with the addition of SBTM
What is currently odd is the information about HDMI 2.1a, as it will be soon called, was appearing on the Licensing Administration's page but has since mysteriously disappeared with no explanations. It is possible that there are a few last-minute decisions to finalize the new standard for use, but that in and of itself is pure speculation. VideoCardz has mentioned that the information can be found via Google Cache. One of the newest additions to the HDMI 2.1a is the use of Source-Based Tone Mapping or SBTM.
Source-Based Tone Mapping (SBTM) is a new HDR feature that allows a portion of the HDR mapping to be performed by the Source device instead of the Display device. SBTM is especially useful in cases where HDR and SDR video or graphics are combined together into a single picture, such as picture-in-picture or a program guide with an integrated video window. SBTM also enables PCs and gaming devices to automatically produce an optimized HDR signal in order to maximize the utilization of the display’s HDR capabilities without manual user configuration of the Source device.
Gamers and PC enthusiasts will see the most use of the new technology, due to the ability for multiwindowed environments. The source device, in essence, controls the tone mapping. This process allows separate windows to display either SDR or HDR optimized content simultaneously. TFTCentral states that the new SBTM is not a replacement for the current HDR technology (HDR10 and HLG, as well as other offerings). SBTM is set to deepen the HDR experience by offering more capability for optimization with HDR-capable devices.