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post #1 of 6 Old 09-26-2017, 05:17 PM - Thread Starter
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HDR Deep Dive

Color-imaging scientist Jack Holm digs deep into high dynamic range. Topics include color volume, what artists might do with an expanded palette of colors and brightness, the actual dynamic range of most images, accurate versus preferred images, the difference between PQ and HLG HDR formats, the "look" of HLG, HLG's backward compatibility with SDR displays, the problems of delivering SDR and HDR streams, expanding SDR for HDR displays versus compressing HDR for SDR displays, the importance of the viewing environment, answers to chat-room questions, and more.

https://www.avsforum.com/hdr-deep-dive/
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post #2 of 6 Old 09-28-2017, 01:51 PM
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One can only hope that cinematographers do the sanity check regarding HDR technology. Were it for manufacturers and technology developers we have to have 10,000 nits (full screen) 16k TVs.

Watching this podcast, there were so many things I wanted to make a footnote about; I will choose just two because they are some of the biggest misconceptions about HDR:

1) Those so-called HDR images where there is a full tonal range indoor-scene and a window where you can see the outside landscape and not a burned-out area are not dependent on HDR monitors, they are produced by HDR __CAMERAS__ (or techniques). HDR cameras allow to have a capture where the burned-out area, even if it looks burned out --you have already exposed for diffuse white (Zone X) inside the room so the outside scene is then brighter and burns out-- STILL can be graded/tone-mapped to a regular tone-range because the numbers are there, the color/light values are not clipped even if the image looks so. If you do the grading (to you artistic vision's desire) the image can be displayed in a regular monitor, you don't need a HDR monitor to display it.

2) HDR does not affect the black level limit of a monitor; that is dependent on the TV technology (and the room).

This paper is the most sensible thing I have read about HDR:

UHDTV - HDR, HLG and WCG

A few more items:

What finally, finally was said (kudos to the guest) is that if the reference level is kept at 100 nits for diffuse white (the standard) then a, say, 800 nits peak display would have a range of 3 stops to show highlights beyond diffuse white (Zone X), which should be enough for "normal" cinematographers. That capability would be needed just in small areas (highlights).

It is quite a stretch to say that it is important that people that watch TV in a bright room should enjoy the same reference dynamic range, so 10,000 nits is a necessity: to mention one factor, some blacks will look gray no matter what because of reflections. Another stretch is to say that the same people would notice or care about faint color tints in highlights.

It is impossible to do HDR with film: Diffuse white is the lowest density film can have (clear film), and it is in the regular tone range (Zone 0-Zone X). No way to do additional zones.

Manufacturers took two important improvements, more bits and better highlights, and turned them into a mon$ter.

Last edited by proufo; 09-28-2017 at 02:02 PM.
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post #3 of 6 Old 09-29-2017, 03:45 AM
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Originally Posted by proufo View Post
What finally, finally was said (kudos to the guest) is that if the reference level is kept at 100 nits for diffuse white (the standard) then a, say, 800 nits peak display would have a range of 3 stops to show highlights beyond diffuse white (Zone X), which should be enough for "normal" cinematographers. That capability would be needed just in small areas (highlights).

It is impossible to do HDR with film: Diffuse white is the lowest density film can have (clear film), and it is in the regular tone range (Zone 0-Zone X). No way to do additional zones.
The zone system was developed as a sort of rule of thumb based upon the capabilities of film and printing in the 1930's. Each zone corresponds to a one stop change, and the usable range of the zone system only spanned 11 stops. However, Adams actually noted that the zone system does not end at X on a negative. Even those older negatives could capture beyond X, but it was technically impractical to try to get details from XI and beyond to reproduce in the limited dynamic range of a print. Today, 0-X zone system is out of date. Modern camera negatives can capture 14 stops when properly exposed and are absolutely capable of recording HDR images that can finally be reproduced thanks to HDR displays.

You also have film density flipped around. When capturing on film you are recording a negative, so the more light in the scene the higher the density (further away from clear base) on film. Density can continue to increase beyond diffuse white up to the limit where the film is fully exposed. And that's what really matters since we are scanning negatives, and skipping the print.
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post #4 of 6 Old 09-29-2017, 07:05 AM
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Illuminating.
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post #5 of 6 Old 09-29-2017, 08:25 AM
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You also have film density flipped around.
No. I am referring to the film print (positive).

Somehow when you mention density everybody thinks negative (no pun intended).
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post #6 of 6 Old 09-29-2017, 01:06 PM
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No. I am referring to the film print (positive).

Somehow when you mention density everybody thinks negative (no pun intended).
Haha @ that unintentional pun.

Yeah, the reason we all think about density on the negative is because that's the foundation of the image. When a film is scanned for restoration or any digital intermediate process, you pretty much always work from a scan of the negative. You'd never work from the print unless it's an old movie and the only thing that exists anymore is that print.
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