Wow, we sure did stir up the hornet's nest.
Here's an update.
- I checked with Patrick, and it turns out that that HLG does not yet support Dynamic Tone Mapping. We will implement HLG Dynamic Tone Mapping, but it might be a bit before we can get it in the code.
- Currently for Dynamic Tone Mapping the "Low-Set" Shape and Transition parameters do not affect the Dynamic Tone Mapping. Thrang was first to point this out (that I saw). Turns out to be that the "Low" curve is lower than his setting for Display Max Light of 400. Without getting into too many details, if you are doing HDR and the "display" says it has more range then the source needs (this case) then no Tone Mapping is needed since the "display" can render the entire range of the source. As an example if you have a 1000 nit TV and a 1000 nit source you can render the source without tone mapping, but for a 4000 nit source you would need tone mapping.
- So while this is *not* a bug, it is a choice we are reconsidering. Based on feedback the current choice works very well, other than the Low-Set Shape and Transition do not change the transfer function.
- I actually designed the low to high Tone Mapping Blend equations to allow the current Frame MaxCLL to be well below the low-curve-nit-point, and to also be able to be well above the high-curve-nit-point. This is because originally I planned on the low curve being higher than we ended up with, and just plain did not consider the effect using a much lower nit curve would have on using Shape and Transition.
- We are now planning to raise the "nit point" of the low-nit curve up so that for devices in the <700 nits range Shape and Transition will have some effect on the transfer function. This should give extra control for Dynamic Tone Mapping and *may* help tune the scenes referenced in the various posts.
Some general comments on Dynamic Tone Mapping:
It is not possible to get perfect results for every scene using Dynamic Tone Mapping. Also, Dynamic Tone Mapping results will be different than Static to some degree. For almost all scenes the Dynamic Tone Mapping results should be better than Static Tone Mapping.
Tone Mapping is all about trade-offs. If you are trying to reproduce Mad Max Fury Road with a MaxCLL of 9919-ish nits on a 100 nit projector, something's gotta give. In general we believe allocating more of the range to low and mid-tones and allowing highlights to show some clamping looks the best. You may not agree (and you have controls to change this if you wish).
I think saying that having more controls means the job is not done ignores that different producers do things differently, and every person has their personal preferences. The only way to deal with this is enough controls to tune the image to personal taste and compensate for differences in the content. I don't get that people say there are too many controls when they do not have to use them since the default settings are extremely good.
We spent a great deal of effort on tuning Static HDR Mapping. I want to thank everyone who gave us feedback on optimal settings for Static Tone Mapping. A special thanks to Kris Deering who's feedback and parameter settings were instrumental in getting the Static Tone Mapping tuned and selecting the current parameter defaults we use for Static Tone Mapping.
If a scene "looks better" with static as compared to Dynamic Tone Mapping, then it likely means that the Static MaxCLL number was "wrong," but happily so in that it improved the scene slightly. Of course as people point scenes where they think Static Tone Mapping looks better we can investigate and see if there is a way to improve Dynamic Tone Mapping.