POV-Ray : Newsgroups : povray.general : media tester scene Server Time: 19 Oct 2017 10:51:50 GMT
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From: omniverse
Subject: Re: media tester scene
Date: 11 Sep 2017 12:25:01
Message: <web.59b67f86252f876e9c5d6c810@news.povray.org>
"Kenneth" <kdw### [at] gmailcom> wrote:
> I made this in version 3.7 (actually 3.7.1 beta 9). I haven't tested it in v3.6,
> but I think it should work there as well.

No idea why but v3.6 makes the scattering media overly bright. Either the
extinction value must be doubled (2.0) or light_source halved (0.5) to get
something similar to v3.7.
Changing to #version 3.6 within v3.7 doesn't matter, and gamma apparently isn't
the reason either.

Thanks for the test scene!


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From: clipka
Subject: Re: media tester scene
Date: 11 Sep 2017 13:19:32
Message: <59b68d64$1@news.povray.org>
Am 11.09.2017 um 14:20 schrieb omniverse:
> "Kenneth" <kdw### [at] gmailcom> wrote:
>> I made this in version 3.7 (actually 3.7.1 beta 9). I haven't tested it in v3.6,
>> but I think it should work there as well.
> 
> No idea why but v3.6 makes the scattering media overly bright. Either the
> extinction value must be doubled (2.0) or light_source halved (0.5) to get
> something similar to v3.7.
> Changing to #version 3.6 within v3.7 doesn't matter, and gamma apparently isn't
> the reason either.

Does the media brightness in v3.6 change when using different media
sampling parameters (sampling method, intervals, samples etc.)?


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From: Kenneth
Subject: Re: media tester scene
Date: 11 Sep 2017 17:15:00
Message: <web.59b6c36e252f876e883fb31c0@news.povray.org>
"Bald Eagle" <cre### [at] netscapenet> wrote:
>
> Some combinations might benefit from a ternary plot.
> https://en.wikipedia.org/wiki/Ternary_plot
>
I had to look up that term (I already knew the concept, but not the name; thanks
for the tip.)  It's an interesting idea; but here's what Wikipedia says...

"In a ternary plot, the proportions of the three variables a, b, and c must sum
to some constant, K. Usually, this constant is represented as 1.0 or 100%."
Meaning, the useful result is represented by some proportion of 'overlapping
area' within the triangle graph, where all 3 variables can still produce the
desired outcome.

To do adequate justice to media-- its many possible variables--a ternary plot
would not be adequate; it would need a 5,6 or 7-variable plot! ;-) Not simple
variables like media method or number of samples, but color, density, color-map
entries, etc.

But here's a simpler 3-variable example, with the sole purpose of making a
decent-looking puffy 'sky cloud.' For the three variables, I'll choose only
COLOR, DENSITY and TURBULENCE. Yet even with this 3-variable restriction, the
resulting ternary plot would have only a tiny circular area somewhere within the
triangle, representing 'a decent puffy cloud'. All other combinations of the 3
variables would indeed produce *something*--but it wouldn't really look like a
sky cloud.

Making a good media object or effect is a tricky business-- because we are so
attuned to real-life examples.


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From: Kenneth
Subject: Re: media tester scene
Date: 11 Sep 2017 18:00:06
Message: <web.59b6cd92252f876e883fb31c0@news.povray.org>
"Kenneth" <kdw### [at] gmailcom> wrote:
>
> As far as filter/transmit goes, color-filtering can be done in the
> density-statement's color_map. I.e., instead of using a single red-ish
> media like
>          emission 1.5*<.3,1,.5>

Sorry, that's not 'red-ish' at all; I meant 1.5*<1,.5,.3> (and <1,.5,.3> in the
color_map example).


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From: Bald Eagle
Subject: Re: media tester scene
Date: 11 Sep 2017 19:20:00
Message: <web.59b6e1c3252f876ec437ac910@news.povray.org>
"Kenneth" <kdw### [at] gmailcom> wrote:

> I had to look up that term (I already knew the concept, but not the name; thanks
> for the tip.)
I remember them from an HPLC course I took circa 1993.
They used them to plot mobile phase composition.

> To do adequate justice to media-- its many possible variables--a ternary plot
> would not be adequate; it would need a 5,6 or 7-variable plot! ;-) Not simple
> variables like media method or number of samples, but color, density, color-map
> entries, etc.

Yes, obviously the ternary plot is only good for certain instances, but it might
be the best way to communicate the data in those specific instances.

Here's a 4-variable plot  :D  :D  :D
http://udav.sourceforge.net/mgl_en.html/mgl_en_3.html
(scroll down to 3.6.9 Quaternary plot sample)
(I love all those cool-looking unusual types of graphing)

> But here's a simpler 3-variable example, with the sole purpose of making a
> decent-looking puffy 'sky cloud.' For the three variables, I'll choose only
> COLOR, DENSITY and TURBULENCE. Yet even with this 3-variable restriction, the
> resulting ternary plot would have only a tiny circular area somewhere within the
> triangle, representing 'a decent puffy cloud'. All other combinations of the 3
> variables would indeed produce *something*--but it wouldn't really look like a
> sky cloud.

Yes, but think about it this way - sometimes information on what NOT to do is
just as valuable as what to do.
"I want to experiment with media.  Oh, look, Kenneth made a pretty graph of
different combinations ---- oh, all the combinations outside of that one little
region all suck.   I won't bother wasting my time experimenting with those...."

[And I could _swear_ that someone once showed me a way to plot multiple
variables on 2d-graphs, much like the ternary plot, but I can't find any mention
of this or examples...   Oh, brain, why do you invent these tantalizing false
memories....]


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From: Kenneth
Subject: Re: media tester scene
Date: 11 Sep 2017 20:45:01
Message: <web.59b6f418252f876e883fb31c0@news.povray.org>
"Bald Eagle" <cre### [at] netscapenet> wrote:
> "Kenneth" <kdw### [at] gmailcom> wrote:


> > ... the resulting ternary plot would have only a tiny circular area
> > somewhere within the triangle, representing 'a decent puffy cloud'. All
> > other combinations of the 3 variables would indeed produce *something*--but
> > it wouldn't really look like a sky cloud.
>
> Yes, but think about it this way - sometimes information on what NOT to do is
> just as valuable as what to do.
> "I want to experiment with media.  Oh, look, Kenneth made a pretty graph of
> different combinations ---- oh, all the combinations outside of that one little
> region all suck.   I won't bother wasting my time experimenting with those...."
>
Good point. I remember my very first try at making a cloud; I spent HOURS
fiddling with the various parameters (and every experiment led to another even
more-interesting experiment!) I think it was several days later that I finally
settled on what I thought were the best(??) parameters for a decent 'cloud'. But
every time I make one now, I always change *something*, to tweak it a little
better (or to re-learn something that I've forgotten!)


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From: Bald Eagle
Subject: Re: media tester scene
Date: 11 Sep 2017 20:50:00
Message: <web.59b6f64a252f876ec437ac910@news.povray.org>
"Bald Eagle" <cre### [at] netscapenet> wrote:

> [And I could _swear_ that someone once showed me a way to plot multiple
> variables on 2d-graphs, much like the ternary plot, but I can't find any mention
> of this or examples...   Oh, brain, why do you invent these tantalizing false
> memories....]

....and the best I could find so far is:
https://en.wikipedia.org/wiki/Radar_chart

Maybe connect the points with media-filled cylinders...


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From: Stephen
Subject: Re: media tester scene
Date: 11 Sep 2017 21:09:58
Message: <59b6fba6@news.povray.org>
On 11/09/2017 21:40, Kenneth wrote:
> (or to re-learn something that I've forgotten!)

Now that sounds like me every time I use media. :-)

-- 

Regards
     Stephen


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From: omniverse
Subject: Re: media tester scene
Date: 12 Sep 2017 01:35:00
Message: <web.59b7399c252f876e9c5d6c810@news.povray.org>
clipka <ano### [at] anonymousorg> wrote:
> Am 11.09.2017 um 14:20 schrieb omniverse:
> > "Kenneth" <kdw### [at] gmailcom> wrote:
> >> I made this in version 3.7 (actually 3.7.1 beta 9). I haven't tested it in v3.6,
> >> but I think it should work there as well.
> >
> > No idea why but v3.6 makes the scattering media overly bright. Either the
> > extinction value must be doubled (2.0) or light_source halved (0.5) to get
> > something similar to v3.7.
> > Changing to #version 3.6 within v3.7 doesn't matter, and gamma apparently isn't
> > the reason either.
>
> Does the media brightness in v3.6 change when using different media
> sampling parameters (sampling method, intervals, samples etc.)?

Yes. In a way.
I couldn't get good results unless the "complementary color" was used along with
scattering, because otherwise it always remained transparent. Which I think is
where the self-shadowing would have been if rendered in v3.7.

method 2 intervals 2 and a sufficiently high samples (50) was best I could find
for it. That's for both scattering and absorption (complementary color) while
leaving light_source color <1,1,1> and extinction 1.0.

Not much luck using method 1, while method 3 just kept over-brightening in the
directly lit outer portions. However, using commenting out intervals or raising
its value above 1 was better than if left at 1.


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From: omniverse
Subject: Re: media tester scene
Date: 12 Sep 2017 11:35:00
Message: <web.59b7c5ed252f876e9c5d6c810@news.povray.org>
"omniverse" <omn### [at] charternet> wrote:
> clipka <ano### [at] anonymousorg> wrote:
> >
> > Does the media brightness in v3.6 change when using different media
> > sampling parameters (sampling method, intervals, samples etc.)?

Going to revoke my findings from before, think I was confusing what I was trying
to do. In going back over it all again to make sure I was beginning with
original test scene file.

Rendering with v3.6 and using media method 3 and intervals 3 helps get closer to
v3.7.0, while doubling samples too (slow!), but I haven't succeeded equal
appearances at all.

Sorry for spreading any of my own confusion to others here!


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