On its website, the HDMI Licensing Administrator announces an optional addition to the protocol for HDMI 2.1. It's about Source-Based Tone Mapping. This will come as an option in an update to HDMI 2.1a, but what's the point?
Source-Based Tone Mapping with HDMI 2.1a
We have known the term HDR (and many variants of it) for a while. It stands for High Dynamic Range and offers the possibility to show very contrasting images. This comes in handy especially in cases of backlighting, but HDR technology also provides a better photo or video for everyday photos. The Apple TV 4K supports this technology, but your television must also be suitable for it.
With Source-Based Tone Mapping (SBTM), HDR goes one step further. The ‘problem’ with ordinary HDR content, the image shown on television does not always consist of a 100% HDR image. For example, only a quarter of the image you see at one moment is shot in HDR. Think of YouTube videos where you also see all kinds of other images at the same time. At the moment, the entire image is still being adjusted for HDR, while that is actually not necessary. It can cause a distorted image with certain content.
Thanks to SBTM, source devices such as Apple TVs and gaming consoles as well as screens (such as televisions) can show better images. This new technology allows devices to decide for themselves which part of the image should be seen as HDR and which part as SDR (Standard Dynamic Range). All the image is then shown in the best possible way. Furthermore, SBTM can optimize the image for a display's specifications, rather than sending a generic signal over the HDMI cable. In short: your HDR image will be more beautiful.
A simulated indication of the difference between HDR content without SBTM (left) and with SBTM (right). Results vary by display.
Is Source-Based Tone Mapping coming to the Apple TV 4K?
As indicated, SBTM is part of an update to HDMI 2.1a. According to the HDMI Licensing Administrator, a software update will allow devices to move to HDMI 2.1a. At the moment, the Apple TV 4K uses HDMI 2.1 and therefore the device has the right hardware. This only concerns the 2021 model, so the first-generation Apple TV 4K is excluded. It uses older hardware that is not HDMI 2.1 or HDMI 2.1a capable. Other devices such as game consoles can also use SBTM.
