Understanding HDR

By Jérôme Blanc, EVP Compression Products

Did you know that soon – very soon, in fact – the images you watch on your TV could be of better quality than those you see at the cinema? That’s thanks to HDR. This stands for “High Dynamic Range” and improves the viewing experience thanks to more vivid colour and greater detail.

It’s not just a technical thing. HDR actually improves how viewers perceive the images. In fact, studies show that viewers prefer HDR to 4K. When moving from HD to 4K, the perceived improvement is not as great as it is when just adding HDR to HD. So HDR beats anything that you have seen before. And even HD content can benefit from it – which is significant, because not everyone has access to 4K.

HDR – What’s that?

This keyword combines several video technologies that offer substantial video-quality improvements for both live TV and VOD. The improvements are both in the contrast and in the colours. And anything that does not have HDR goes by the name of SDR, or “Standard Dynamic Range”.

The technology for HDR is already in most viewers’ hands. While viewers might not have access to 4K, most display devices and TV sets today are HDR-capable. So, if a viewer owns one of these, all she has to do is make sure her set-top box or decoder is HDR-capable, get access to HDR content, and then sit back to enjoy a new viewing experience.

How we got here

First came analogue TVs, which some of us still remember. These were built on brightness and colour standards designed to match the physical responses of technologies of the time. They were based on Cathod Ray Tubes (CRT), electron guns and phosphors. For example, a given electrical value of (R, G, B) had to produce a standardised and well-defined colour and light.

Then came digital TV. Not much changed at first in terms of colours. They were based on the same standards as analogue – just the digital version of them. A given numerical value of (R, G, B) had to produce the same colour and light as it would in analogue TV.

But CRT is long gone, and Plasma, LCD, and OLED screens can now render a much wider contrast and colour range than what CRT could. The green colour, for example, can now be rendered in a way that matches human vision much more closely.

To support this wider range, we need to digitise the electrical values with higher precision. This means that they require 10 bits instead of 8. Furthermore, the processing chain has to generate the right meta-data and carry it to the screen, so that it knows how to interpret these values to light up the pixels correctly. This process is known as “HDR signalling“.

I’m a content owner, a broadcaster, an operator… How do I implement HDR?

The main change is for your encoders and decoders, because the video-processing chain now has to work in 10 bits instead of 8, from capture to display. So you need to change your codec – possibly to HEVC. Other options are available to enable 10-bit processing, but you will most commonly find HEVC in TV displays today.

But activating HEVC 10-bit encoding is not enough. You will also need to make sure that the encoder, and potentially the OTT packager, create and carry the right metadata for HDR signalling, right down to the display.

And that’s exactly what Anevia’s video encoders and packagers do – supporting HDR with both 10-bit HEVC encoding and metadata signalling. So that your viewers can enjoy a better-than-cinema experience – wherever they may be.

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