New technical term - HLG

[Dave2002]

I just came across a technical term new to me - HLG. That stands for Hybrid Log Gamma.

https://www.whathifi.com/advice/hybrid-log-gamma-explained-new-hdr-tv-broadcast-format

There's also more here

https://en.wikipedia.org/wiki/Hybrid_Log-Gamma

HLG is a new "standard" for HD video, developed jointly by the BBC and NRK.

This will presumably start to have an impact on the consumer market for TVs and other visual entertainment forms soon - if it hasn't already.
It will also impact content producers, and others - such as video editors and video editing tools..

[Stunsworth]

It’s one of the High dynamic range (HDR) formats for TV. The others being HDR 10, HDR 10+ and Dolby Vision. All these formats work differently, but allow the programme producer to show programmes with a broader colour palet and a higher visual dynamic range (so darks can be darker and highlights brighter). It’s not to be confused with HDR in the photographic world, that tries to cram a wide dynamic range into a smaller number of digital bits, HDR on a TV allows a greater dynamic range than in a standard TV.

At the moment the prime source of HDR material is either streaming (Netflix/Amazon) or HDR Blu-Ray. The latter will not play in ‘standard’ player, so you need a HDR machine or an XBOX 1S to replay them - an HDR player will also replay standard discs.

Visually HDR looks very good, and is an obvious improvement on standard dynamic range. The BBC Life on Earth set looks stunning - as do the Netflix offerings such as Godless.

[Dave2002]

It’s not to be confused with HDR in the photographic world, that tries to cram a wide dynamic range into a smaller number of digital bits, HDR on a TV allows a greater dynamic range than in a standard TV.

Although the technical details are different from the photographic world, surely the HDR issues are the same. The dynamic range of the output device is smaller than the "natural" dynamic range which the recording equipment is trying to capture. Perhaps what you are saying is that a TV with HLG or one of the other HDR formats you mention is actually capable of delivering a wider dynamic range than one of the current "standard" TVs.

[Stunsworth]

Dave, yes, that’s what I meant. Neither HDR photo or video can capture the full dynamic range, but where as HDR photography compresses the dynamic range into an existing container, HDR TV has a ‘larger container’ than standard TV.

[Dave2002]

Steve

Thanks for the clarification. We seem to be in agreement. HDR as it exists currently in photography appears to rely on taking multiple photos, then stacking them, and then performing operations on them to give a perceived effect of higher dynamic range. It is also possible to give an impression of wider DR even with a single photo by adjusting the levels within the photo selectively. The output range remains the same whatever is done, but input data can be used to capture more detail.

This is achieved in several ways - including:

modify the global contrast - but selectively - often using something like an S curve in an adjustment layer. This method effectively squashes the dynamic range in some parts of the image - as determined by luminance levels, and increases the contrast where there is detail in the image - again as determined by luminance levels.

modify the local contrast - but selectively - often using something like an S curve in an adjustment layer. This method effectively squashes the dynamic range in some parts of the image - as determined by luminance levels, and increases the contrast where there is detail in the image - again as determined by luminance levels. However, this method also takes into acount the position of areas of detail within images. I don't know whether there are automated algorithms to do this (possibly) but some HDR photography work is done by manual tweaking of each photo. This can be done because of the way our eyes work - as shown in this set of optical illusions - https://www.washingtonpost.com/news/...=.2fc34fe9b4e0

The 2nd one down - the gray bar on the background - shows that it's possible to trick the eye about absolute levels, and this is (at least one of) the way that an HDR photograph can give the impression of high dynamic range within what is actually limited, as attention is drawn away from the transitions between different parts of the image. Without that it would be very obvious that different parts of the image are treated differently.

The stacking methods use different parts of each similar image to "improve" the perceived result.