All about HLG: What Hybrid log gamma means for your TV


‘Hybrid log gamma’ is yet another a new video format that promises better picture quality for broadcast and live TV. So how is it different from Dolby Vision and HDR10?

Hybrid log gamma, or HLG, is another kind of high dynamic range (HDR), similar to HDR10 and Dolby Vision. All three promise better picture quality for compatible TVs than standard dynamic range material — aka the TV shows and movies you’re probably watching now. HDR images on good HDR TVs have brighter highlights, more impact and improved color.

So how is it different? While HDR10 and Dolby Vision are restricted to streaming (Netflix, Amazon Video, etc.), disc (4K Blu-ray) or video games, HLG is designed for broadcast cable, satellite and live TV.

What is HDR for TVs?
At this point you’re probably muttering, “Great, another HDR format. Something else to worry about when I buy a new TV.” Relax.
Unlike the other HDR formats, no HLG TV shows or movies are available yet, and given the slow pace of broadcast innovations, I’m not holding my breath. Still, many new HDR TVs either have HLG built in already, or the ability to add it via a firmware update. It’s even backward compatible with SDR TVs!
So while it’s possible you’ll be hearing more about HLG in the future, it’s not something you’ll need to worry about now — or regret missing if you recently bought a TV that lacks HLG..
H-L-G could be B-I-G (eventually)
Hybrid log gamma was co-developed by the BBC in Britain and NHK in Japan. At issue was how the two currently available HDR formats, HDR10 and Dolby Vision, were difficult to broadcast. Essentially, the metadata is a problem. Metadata is the additional information that travels alongside the visible video signal, and an HDR TV requires metadata to make HDR look like HDR.
It’s also possible that those of you watching on SDR displays will get a little better image, since the HLG is sending more brightness detail. Your TV will show this detail (textures in clouds on a bright day, for example), it just won’t show it as brighter since you’d need an HDR TV for that.
HDR is the future of TV, as the vast majority of people on both sides of the screen are excited about it (unlike, say, 3D, which most hated). With hybrid log gamma, the amount of HDR content will grow considerably, and that’s always a good thing.