[x3d-public] ambientIntensity [0, 1] or unbounded [0, infinity) ?

[Michalis Kamburelis]

You can do HDR with X3D, nothing special about it :)

The lighting intensity has a physical interpretation (that is also why
it is unbounded now) and PBR equations are closer to physics. You can
calculate colors that make sense for physics. You can then process
them in any way to "fit" and display in non-HDR monitors. Remember to
apply gamma correction properly (convert from linear space to monitor
space, sRGB) at proper place.

Regards,
Michalis

pt., 29 kwi 2022 o 19:51 John Carlson <yottzumm at gmail.com> napisał(a):
>
> After reading through Michalis’ arguments, I am reminded of High Dynamic Range (HDR), but I don’t know of any applicability to X3D (anyone?).
>
> John
>
> On Fri, Apr 29, 2022 at 5:49 AM Michalis Kamburelis <michalis.kambi at gmail.com> wrote:
>>
>> Hm, good point. To be honest we can go either way for me.
>>
>> It doesn't matter that much because
>>
>> A. ambientIntensity is ignored by PBR model (PhysicalMaterial) that
>> doesn't have a concept of "ambient" at all. (This is stated explicitly
>> in spec, """In the physical lighting model, the ambientIntensity value
>> is unused. """)
>>
>> B. In most practical cases, even with Phong (Material), people should
>> not use too large ambientIntensity values. The ambient and
>> ambientIntensity in Phong are already somewhat "unrealistic cheat"
>> (that is, you just bump the final color to simulate global
>> illumination; that's as naive implementation of "global illumination"
>> as you can get :) ).
>>
>> So likely authors don't need to use values for ambientIntensity > 1.
>> But then, there's nothing in Phong lighting equations that really
>> prevents bigger ambientIntensity values.
>>
>> So, ways to go:
>>
>> 1. Ignore, i.e. leave ambientIntensity in [0,1]. Just because there's
>> no practical reason to change it.
>>
>> 2. Or make ambientIntensity unbounded like intensity, i.e. allow [0,infinity].
>>
>> For me, the only real advantage of AD 2 solution is that it will make
>> ambientintensity consistent with intensity. But that's not a big gain
>> -- ultimately ambientIntensity and intensity are just completely
>> different concepts, they just happen to share a common name. The
>> "intensity" has a physical interpretation (that we put in spec) and
>> works with all lighting models. "ambientIntensity" is a "cheat' and
>> only available in Phong lighting model.
>>
>> So I would choose solution AD 1 (do nothing) just because there's no
>> real need (from authors' perspective) to remove the limit, from what I
>> know. But both AD 1 and AD 2 resolutions are acceptable for me.
>>
>> Regards,
>> Michalis
>>
>> pt., 29 kwi 2022 o 02:53 Brutzman, Donald (Don) (CIV)
>> <brutzman at nps.edu> napisał(a):
>> >
>> > Hi Michalis.  We’re looking at
>> >
>> >
>> >
>> > Mantis 130: 17.2.2: Lighting Max Values
>> > https://www.web3d.org/member-only/mantis/view.php?id=130
>> >
>> >
>> >
>> > Most light intensity-related fields (but not all) are now unbounded.  The intensity field is [0,infinity)
>> >
>> > Not quite sure about ambientIntensity bounds, which are currently [0,1] and thus not unconstrained like intensity.
>> >
>> >
>> >
>> > Please advise what you think, TIA.
>> >
>> >
>> >
>> > all the best, Don
>> >
>> > --
>> >
>> > Don Brutzman  Naval Postgraduate School, Code USW/Br        brutzman at nps.edu
>> >
>> > Watkins 270,  MOVES Institute, Monterey CA 93943-5000 USA    +1.831.656.2149
>> >
>> > X3D graphics, virtual worlds, Navy robotics https:// faculty.nps.edu/brutzman
>> >
>> >
>>
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