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On 19-3-2018 18:31, William F Pokorny wrote:
> On 03/15/2018 06:01 PM, Norbert Kern wrote:
>> William F Pokorny <ano### [at] anonymous org> wrote:
> ...
>>>
>>> I got a couple small renders done yesterday - with and without the
>>> emission - and compared them. At a high level adding in emission the
>>> color of the background sky makes the clouds look as if they are sitting
>>> in a hazy atmosphere without having modeled the hazy atmosphere. See the
>>> attached image.
>>>
>>> The difference image on the right shows an aspect or pitfall of the
>>> method - depending on one's goal I suppose. Once one or more color
>>> channels for the media 'interval' being sampled is maxed out (Red here),
>>> you get a 'disjoint' color-hue change in the media due the emission
>>> adder.
>>>
> ...
>>
>> Interesting. I wouldn't have thought the effect of small emission
>> value is that
>> strong. I've to do more tests...
>>
>> Norbert
>>
>>
> Sorry slow - busy with real life.
>
> Emission is stronger by nature because the emission intensity increases
> with depth of media. If you want to 'sort of' match a scattering
> intensity with an emission media, you have to add absorption at about
> the same value as the emissive value (1).
>
> I've always used scattering+absorption, emission+absorption or
> emission+scattering. Never all three - intentionally at least - as
> Gilles did here (2).
>
> Bill P.
>
> (1) - An idea on my to play with list is some method to pre-render or
> pre-calculate scattering with attenuation media so as to be able to
> create a faster emission+absorption or a scattering without attenuation
> + absorption media model for use in follow-on renders.
>
> (2) - I've wondered some recently about whether POV-Ray should support
> two absorption specifications given Gilles technique looks useful.
Aha! This is an interesting notion I was not aware of. I am going to
follow that up. Thanks!
--
Thomas
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