02 Dec 2018

HEVC/H.265: Everything you need to know

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HEVC - H.265 HEVC - H.265 RedShark


Optimised for multiple core processing

There are other changes in HEVC, mainly aimed at  making it easier to implement in a parallel processing environment (effectively, one where many CPU cores are available to do work simultaneously). These, however, aren’t aimed at improving image quality (in fact, a couple of them may fractionally decrease it) and are mainly intended to make it possible to divide up the work of decoding HEVC on a finer level than was possible with h.264.

So, that’s an overview, albeit a very broad one, of what HEVC is about. The question of whether it achieves its fifty per cent bitrate reduction goal for the same picture quality is a difficult one because objectively measuring video quality as perceived by humans is strictly speaking impossible. The industry has been trying to move away from a simple ratio of signal to noise, as it has been recognised that it can suggest unreasonably good results in some circumstances. Wavelet codecs, such as the JPEG-2000 algorithm used by Red in their cameras, are notorious for producing great signal to noise figures while simultaneously not necessarily looking as good as the S/N statistic would suggest. Real world tests of image quality tend to involve both widely-agreed mathematical algorithms and the results of subjective analysis by real humans, averaged in an attempt to remove individual bias.

Does it succeed?

In reasonable tests, then, HEVC does approach its goal of 50% bitrate reduction. At half the bitrate, individual HEVC frames may look less sharp than h.264 frames, but HEVC moving image sequences tend to do better in human-observer tests as it produces much reduced temporal artefacts. Video compressed with HEVC flickers less, suffers less from trembling blocks of image, and generally looks better on the move.

When we’ll start to see it deployed in acquisition devices - cameras - is anyone’s guess, but software products and hardware encoders for the mobile content market are already available. To put this in perspective,  digital terrestrial TV in the UK (for example) is still mainly MPEG-2!

Read our article on Video Data Rates if you want to understand why we really do need compression!

Phil Rhodes

Phil Rhodes is a Cinematographer, Technologist, Writer and above all Communicator. Never afraid to speak his mind, and always worth listening to, he's a frequent contributor to RedShark.

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