What is HDMI 2.1a and why did people suddenly start talking about it?

The HDMI Licensing Administration recently announced an update to HDMI 2.1 called HDMI 2.1a, which aims to improve image quality for a wide variety of content. In this context, some common players and users had questions about the new version.

Since the numbers, tables and graphs are more likely to be misleading, let’s understand in simple terms what kind of HDMI 2.1a is and why it is important.

What is HDMI 2.1a?

In short, this is still the same HDMI 2.1 interface, but its new feature is called Source-Based Tone Mapping.

So what is source-based tone mapping?

This can be translated as “source-based tone mapping”. Tonal mapping is a technique used in image processing where digital signals match the brightness and color gamut of a television. Thus, you can take an HDR image and display it on a monitor with limited dynamic range while maintaining detail, contrast, and color.

With HDMI 2.1, processing can be done by the source, for example a TV box, PC or console, in addition to processing on the screen side.

Why does that matter?

The source can send a signal that will take advantage of the HDR rendering of the screen itself.

When it comes to still images and HDR video, the display usually does some processing to match the content to its capabilities. Sometimes a piece of content can include different levels of HDR. For example, an SDR image and an HDR item can be displayed on the screen at the same time, for example, in picture-in-picture mode.

Typically, in this case, the screen receives a predefined brightness and color gamut. With source-based tone mapping, the signal source can be adapted to the screen by sending a signal optimized for the HDR capabilities of a particular screen.

The main idea is that the new technology will not require the user to manually adjust the signal source, always obtaining an image suitable for a particular model of TV or screen.

And what does all this mean?

The fact that TV and monitor manufacturers will have to do software updates. However, the first shipments of devices with HDMI 2.1a support are scheduled for the first quarter of 2022, so more details will be available at a later date.