Tutorial: What is Hybrid Log-Gamma (HLG)?

Discussion in 'General TV Discussions Forum' started by Steve Withers, Nov 14, 2016.


    1. Steve Withers

      Steve Withers
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    2. Dutch

      Dutch
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      Very informative article. Thanks .
       
    3. connect

      connect
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      Agreed, these articles are great for reference. I'm hoping to get an OLED in the Black Friday discounts. Either a C6 or E6 depending on price. I hope LG update these sets in the future and don't forget about them once the 2017 sets are out.

      Edit - Saying that though, don't the OLED TV's have faux HDR mode for SDR content? So worst case if they were not to be updated we still have that option.
       
    4. zubeir

      zubeir
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      HLG, HDMI 2.1, it will never stop. But manufacturers should provide firmware updates to the early investors. In reality its about the ££$$$
       
    5. Kyle009

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      Great article, I'd be very interested to see if any manufacturers do provide a HLG update via firmware. As zubeir suggests it's all about $$$ so if your TV can't support HLG, you're going to buy another!
       
    6. couto27

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      Sony Projectors will support HGL

      2016 Models
      VPL-VW675ES
      VPL-VW550ES

      2015 Models
      VPL-VW500S
      VPL-VW320ES

      Sigma SOCs will support HGL
      STV7804 (this one supports 100Hz/120Hz frame rate converter)
      SMP8980
      SMP8758

      Android Nougat 7.0 Already support HGL

      More to come..
       
    7. BRAKKUS1

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      I think it should absolutely be a priority to upgrade a previous years set, it isn't acceptable to sell a £2k TV say, and not update it if it were possible, because in reality most people won't upgrade to another, in many cases way less than 12 months, especially with the flux that HDR is in at the moment.

      It does happen though, we've seen it with last year's HDR sets receiving 2.0a upgrades, and I remember Sony updating their first 4K set from 1.4 to 2.0 60Hz, and their previous 2 AV receivers from 1.4 to 2.0 4K 60Hz, I'm hopeful.
       
      Last edited: Nov 14, 2016
    8. Toon Army

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      Thanks Steve for another good " reference "article. I recently asked a salesman at a well known technology store about HLG and he did not have a clue about it. I suggested he started to read and listen to AV Forums.
      Any thoughts about creating a page on the website that summarises what every TV can deal with. This would be an ideal starting point for prospective buyers as we attempt to future proof our purchases.
       
    9. Roohster

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      Anyone else feel like this while shopping for new kit at the moment?

      Not The Nine O'Clock News - HiFi Shop
       
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    10. Kyle009

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      I completely agree with you, it should be a priority but that doesn't necessarily work out to be the case.

      Although you make a very good second point, Sony (and others) have rolled out things like HDR via updates to sets so maybe they can (and will!) roll out updates for HLG.
       
    11. kingofscotland

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      Having spent over 2k for LG B6 OLED and there is already doubt whether they will update HDR for Game Mode, if HLG is not updated with a patch I'm out of the TV arms race its becomming a very expensive hobby to keep up
       
    12. Garioch

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      Sorry for the extremely novice question but would HLG be received using a standard TV antenna or satellite dish? Or would some kind of special equipment be required (other than an HDR-10/DV TV of course)? Many thanks.
       
    13. NickInWiltshire

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      Yes - HLG is intended to be the broadcast standard for HDR and it is included in the spec for the next iteration of the Freeview Standard but I'm not sure when any transmissions that use the new features will start.
       
    14. Navvie

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      A databse that lists TV and their supported standards would be worth invaluable. Number of HDMI ports and what version, HDCP, HDR, HLG, panel depth etc, links to AVF reviews.

      Big task keeping that up to date though.
       
    15. daviboy88

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      The views in this discussion about upgrading / manufacturer responsibility for updates are interesting. Would you expect a new car to be updated after a year or two when a more economical engine is available or a new technology is developed by the car manufacturer?

      @Steve Withers - great article. Forgive my naive question but is there any implication for camera equipment to be able to record content for HDR/HLG or are the cameras already way ahead of the resolution and dynamic range that is actually broadcast - i.e. if the broadcast element is resolved then all major channels could start transmitting HLG?
       
    16. Mr.D

      Mr.D
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      so this is almost the same as Cineon log invented by Kodak (or rather standardised) circa 1993.
      Essentially a 10.5 stop range nonlinear format with a notional white ref close to its mid point in terms of the distribution curve.

      I suspect HLG modifies the "straight line portion" of the curve below the ref white to be around 0.44 instead of Kodak's 0.6 target. Probably loses the Dmin ref (95 code values) and sets up at 0 black. And probably loses maybe 1.5 stops in the superwhite range relative to Cineon log.

      Individual displays then impliment a soft clip depending on their capabilities but the range from white to mid gray is probably consistent from display to displa ( at least proportionally in terms of the stops increasing)

      This is a much better way of handling HDR and should also allow each display to still range as high as it maximal white level will go.

      Its also very similar to how actual post production chains move images around and maintain a consistent visual intensity range with different dynamic range material.
       
    17. Mr.D

      Mr.D
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      The common motion pictures cameras are more than sufficient in terms of dynamic range.

      Even nominally exposed negative film from decades ago is more than sufficient.

      There is a bit of a white elephant in the room with HDR.

      Most nominally exposed scenes in a naturally lit location contain about 9 stops of useful information from shadows to usuallybeyond the point where extra highlight information becomes detectable to a human being.

      Negative film captures about 10.5 stops max.

      The common digital motion picture cameras capture a "claimed" 14stops. And at least one of them tops out about 12stops in reality.

      I have NEVER seen an image that contained more than 9.5stops and most rarely get higher than 9. Whether its artificially lit , naturally lit... whatever.

      If you were to view the full range of a captured 9stop image whilst maintaining the stop relationship back to luminance , it will look flat and washed out.

      To make it pleasing you need to bend around the contrast. Compress and even softclip the whites and shadows to get a nice visually pleasing range. You actually have to throw away dynamic range to make the image pleasing to the eye.

      This is regardless of the dynamic range the display is capable off.

      Most imagery regardless of its inherent dynamic range benifits from being displayed with as much dynamic range as possible assuming its been mapped properly ( again this mapping is also part of grading , its effectively the same thing or ends up having the same impact as "rendering intent".

      By the time its graded to look pleasing its essentially no more than about 7 stops of representational range.

      So the issue with HDR isn't how much range the camera shoots . Its not even really the range left in your graded image as long as it looks visually the way it should according to the creators.
       
    18. geogan

      geogan
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      I would be very impressed if I actually found an electrical store salesman with as much technical knowledge as the salesman in this sketch. If I did I would be much happier. Most sales guys in the AV departments of so called mainstream electrical retailers haven't a clue of the technical details of what they are selling. Their only job is to shift merchandise to customers who have even less idea than they do. If someone with AV knowledge comes in, they don't ask the salesmen or ignore the bull they are spouting, so the salesman walks away.
       
    19. Captain Ron

      Captain Ron
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      So, in simple terms, is HLG more like Dolby Vision in action and describes the image content dynamically or is it a one shot static description like HDR10? If it's the former and works over current HDMI2.0a then it would seem to make sense to use HLG encoding on UHD disc rather than wait for the industry to foist dynamic HDR10 upon us requiring us all to upgrade to HDMI2.1. That's of course if HLG is royalty free. I'm assuming it is.
       
    20. fxv300

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      Are Samsung updating their SUHD range to support HLG ?
       
    21. suki basi

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    22. fxv300

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      Does anyone know ?
       
    23. AlanX

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      What exactly is meant by "TVs and projectors won't be able to automatically detect the HLG signal and engage the HDR mode, you'll need to do that manually"? How will you know when to manually engage HLG? If there is something in the signal that says HLG, that could be used to do the switch. If there is nothing in the signal, do you just 'suck it and see' for each broadcast?
       
    24. Steve Withers

      Steve Withers
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      When I originally wrote this article, JVC projectors required the user to manually select the HLG curve when watching HLG content over HDMI, presumably because it lacked any metadata flags. However now that the BBC has begun to offer HLG content on the iPlayer it appears that TVs at least can automatically select the HLG curve when playing HLG content using their built-in apps. I'm still not sure what will happen when HLG content is delivered over HDMI but I've updated the article to reflect recent developments.
       

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