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29 Mar 2024 02:52:48 EDT (-0400)
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From: omniverse
Subject: Re: Emitting media
Date: 2 Sep 2017 00:35:00
Message: <web.59aa341da4b127e99c5d6c810@news.povray.org>
Alain <kua### [at] videotronca> wrote:
> Le 17-08-31 à 18:58, Loren a écrit :
> >         media{ emission Red intervals 30 samples 100,100 }
> Yuck! That WAS ok in version 3.5 and older that used sampling method 2
> as the default. As of version 3.6, the sampling method is method 3 and
> it must use intervals 1 (the default value).
> Using method 3, more intervals only dramatically slow you down. It can
> also cause some artefacts.
> Also :
> 1) It only use a single value for samples. If a second value is used,
> it's silently ignored.
> 2) confidance and variance are also silently ignored as they are
> meaningless when you have only a single interval.
>
> Defaults for media in version 3.6+
> method 3
> samples 10
> confidance Not Applicable
> variance N/A
> intervals 1
> jitter 1
>
> Alain

Well I'm learning something, again, because I had thought

 samples LesserInteger, GreaterInteger

was valid for method 3. And I also thought samples 1,1 was the default.
Reading the 3.7 doc I don't find it saying the above you tell of, not that I
don't believe you Alain, but I refer to the docs a lot and try to believe what I
read there. :)


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From: Stephen
Subject: Re: Emitting media
Date: 2 Sep 2017 02:42:18
Message: <59aa52ca$1@news.povray.org>
On 02/09/2017 05:31, omniverse wrote:
> Alain <kua### [at] videotronca> wrote:
>> Le 17-08-31 à 18:58, Loren a écrit :
>>>          media{ emission Red intervals 30 samples 100,100 }
>> Yuck! That WAS ok in version 3.5 and older that used sampling method 2
>> as the default. As of version 3.6, the sampling method is method 3 and
>> it must use intervals 1 (the default value).
>> Using method 3, more intervals only dramatically slow you down. It can
>> also cause some artefacts.
>> Also :
>> 1) It only use a single value for samples. If a second value is used,
>> it's silently ignored.
>> 2) confidance and variance are also silently ignored as they are
>> meaningless when you have only a single interval.
>>
>> Defaults for media in version 3.6+
>> method 3
>> samples 10
>> confidance Not Applicable
>> variance N/A
>> intervals 1
>> jitter 1
>>
>> Alain
> 
> Well I'm learning something, again, because I had thought
> 
>   samples LesserInteger, GreaterInteger
> 
> was valid for method 3. And I also thought samples 1,1 was the default.
> Reading the 3.7 doc I don't find it saying the above you tell of, not that I
> don't believe you Alain, but I refer to the docs a lot and try to believe what I
> read there. :)
> 
> 
> 
> 

Did you look at the online version?
http://www.povray.org/documentation/3.7.0/r3_4.html#r3_4_8_3

The distributed copies of the Help are not the best.

-- 

Regards
     Stephen


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From: Thomas de Groot
Subject: Re: Emitting media
Date: 2 Sep 2017 03:03:18
Message: <59aa57b6$1@news.povray.org>
On 2-9-2017 6:31, omniverse wrote:
> Alain <kua### [at] videotronca> wrote:
>> Le 17-08-31 à 18:58, Loren a écrit :
>>>          media{ emission Red intervals 30 samples 100,100 }
>> Yuck! That WAS ok in version 3.5 and older that used sampling method 2
>> as the default. As of version 3.6, the sampling method is method 3 and
>> it must use intervals 1 (the default value).
>> Using method 3, more intervals only dramatically slow you down. It can
>> also cause some artefacts.
>> Also :
>> 1) It only use a single value for samples. If a second value is used,
>> it's silently ignored.
>> 2) confidance and variance are also silently ignored as they are
>> meaningless when you have only a single interval.
>>
>> Defaults for media in version 3.6+
>> method 3
>> samples 10
>> confidance Not Applicable
>> variance N/A
>> intervals 1
>> jitter 1
>>
>> Alain
> 
> Well I'm learning something, again, because I had thought
> 
>   samples LesserInteger, GreaterInteger
> 
> was valid for method 3. And I also thought samples 1,1 was the default.
> Reading the 3.7 doc I don't find it saying the above you tell of, not that I
> don't believe you Alain, but I refer to the docs a lot and try to believe what I
> read there. :)
> 

Alain is absolutely right. He is the one person warning us, again and 
again, for the method/intervals/samples misconception cropping up 
regularly in these ng's. Hail to the chief! ;-)

As for the docs, samples LesserInteger, GreaterInteger, is only valid 
for method 1 and 2. I agree that there is an ambiguity where method 3 is 
concerned: paragraph 2.7.2.3 Sampling Parameters & Methods in the wiki ( 
http://wiki.povray.org/content/Reference:Sampling_Parameters_%26_Methods 
) does not state clearly that the second term is ignored when using 
method 3. This should be changed.


-- 
Thomas


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From: Kenneth
Subject: Re: Emitting media
Date: 2 Sep 2017 03:30:00
Message: <web.59aa5d0ba4b127e9883fb31c0@news.povray.org>
"omniverse" <omn### [at] charternet> wrote:
>
> Well, let's think about it here.
>
[snip]
> Or so I believe. Seems the more I talk the less sense I make to myself, possibly
> everyone else too!
>

Ha! No worries; your comments are definitely helping me to think more deeply
about this phenomenon. And to modify my own theories ;-)

In your laser code, I'm now using   absorption 2*<0,1,1>  instead of emission,
to see the effect more clearly. I think I understand what you're getting at, re:
the media 'filtering' the hexagonal background colors. What I see is that green
and blue are now BLACK (as would be expected from 'absorbing' those colors),
whereas the RED hexagons are unaffected, and show though the media-- because
there's a zero in the media's red color vector (no absorption there.)

I'm still a bit unconvinced as to whether the 'black' in this example can be
thought of as actual *opacity*, or whether it is solely a filtering effect of
the background. I think it's the latter-- but the end result *looks* the same
regardless, 'cause black is black!

I'm still formulating my theory... ;-)

> Where I get most confused is that factoring in of background colors, which I
> think always remain additive (emitting) or subtractive (absorbing)
> regardless of the media itself.

I think that's true, when using a SINGLE media. But when two types of media are
used (like emission + absorption), it gets a bit trickier-- and seems to depend
on their own respective colors.


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From: Kenneth
Subject: Re: Emitting media
Date: 2 Sep 2017 03:55:00
Message: <web.59aa6355a4b127e9883fb31c0@news.povray.org>
Alain <kua### [at] videotronca> wrote:
>
> 2) confidance and variance are also silently ignored as they are
> meaningless when you have only a single interval.
>

However, the online documentation for method 3 does mention that "if more
intervals are needed, POV-Ray will create them", or something to that effect. I
honestly don't know what the *visual* difference is between more SAMPLES and
more INTERVALS, or how they differ in meaning, but I'm wondering if 'confidence'
and 'variance' are truly ignored, if more intervals are created. The
documentation doesn't explain this well; perhaps the underlying algorithm is too
technical to do so.

Personally, I've never been able to see much (if any) difference when varying
confidence and variance, using method 3. So I ignore them too.


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From: omniverse
Subject: Re: Emitting media
Date: 2 Sep 2017 08:15:00
Message: <web.59aaa08ca4b127e99c5d6c810@news.povray.org>
Stephen <mca### [at] aolcom> wrote:
>
> Did you look at the online version?
> http://www.povray.org/documentation/3.7.0/r3_4.html#r3_4_8_3

Yep, that was it. Thanks for putting it here.

I knew about method 3 being "adaptive sampling", so I guess that implies only
one sample parameter is used, I'm just not finding that written in the doc.
Likewise the defaults list doesn't mention what Alain tells of.

Note to everyone: Clicking a link like that one, the long jump down the page
might not make it all the way to the target section. If that happens you should
be able to locate the section by name via the left side list, or maybe a
refresh.


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From: Alain
Subject: Re: Emitting media
Date: 2 Sep 2017 09:13:32
Message: <59aaae7c@news.povray.org>
Le 17-09-02 à 03:03, Thomas de Groot a écrit :
> On 2-9-2017 6:31, omniverse wrote:
>> Alain <kua### [at] videotronca> wrote:
>>> Le 17-08-31 à 18:58, Loren a écrit :
>>>>          media{ emission Red intervals 30 samples 100,100 }
>>> Yuck! That WAS ok in version 3.5 and older that used sampling method 2
>>> as the default. As of version 3.6, the sampling method is method 3 and
>>> it must use intervals 1 (the default value).
>>> Using method 3, more intervals only dramatically slow you down. It can
>>> also cause some artefacts.
>>> Also :
>>> 1) It only use a single value for samples. If a second value is used,
>>> it's silently ignored.
>>> 2) confidance and variance are also silently ignored as they are
>>> meaningless when you have only a single interval.
>>>
>>> Defaults for media in version 3.6+
>>> method 3
>>> samples 10
>>> confidance Not Applicable
>>> variance N/A
>>> intervals 1
>>> jitter 1
>>>
>>> Alain
>>
>> Well I'm learning something, again, because I had thought
>>
>>   samples LesserInteger, GreaterInteger
>>
>> was valid for method 3. And I also thought samples 1,1 was the default.
>> Reading the 3.7 doc I don't find it saying the above you tell of, not 
>> that I
>> don't believe you Alain, but I refer to the docs a lot and try to 
>> believe what I
>> read there. :)
>>
> 
> Alain is absolutely right. He is the one person warning us, again and 
> again, for the method/intervals/samples misconception cropping up 
> regularly in these ng's. Hail to the chief! ;-)
> 
> As for the docs, samples LesserInteger, GreaterInteger, is only valid 
> for method 1 and 2. I agree that there is an ambiguity where method 3 is 
> concerned: paragraph 2.7.2.3 Sampling Parameters & Methods in the wiki ( 
> http://wiki.povray.org/content/Reference:Sampling_Parameters_%26_Methods 
> ) does not state clearly that the second term is ignored when using 
> method 3. This should be changed.
> 
> 

For the massive slowdown when using intervals >1, I've found out by 
testings.
For the possibility of artefacts, it's writen in the docs.


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From: Stephen
Subject: Re: Emitting media
Date: 2 Sep 2017 13:53:42
Message: <59aaf026@news.povray.org>
On 02/09/2017 13:14, omniverse wrote:
> Note to everyone: Clicking a link like that one, the long jump down the page
> might not make it all the way to the target section. If that happens you should
> be able to locate the section by name via the left side list, or maybe a
> refresh.

Yes my browser hiccuped loading it.

-- 

Regards
     Stephen


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From: Kenneth
Subject: Re: Emitting media
Date: 2 Sep 2017 17:50:00
Message: <web.59ab250fa4b127e9883fb31c0@news.povray.org>
"Kenneth" <kdw### [at] gmailcom> wrote:
> "omniverse" <omn### [at] charternet> wrote:
> >
> > Where I get most confused is that factoring in of background colors, which I
> > think always remain additive (emitting) or subtractive (absorbing)
> > regardless of the media itself.
>
> I think that's true, when using a SINGLE media. But when two types of media are
> used (like emission + absorption), it gets a bit trickier-- and seems to depend
> on their own respective colors.

Actually, I'm starting to come around to your idea ;-)-- that at least emission
and absorption media effects depend (solely??) on what the background colors
are, for their final 'filtered' media-color. The use of a pure-color
media-- with one or more zeros in the color vector-- seems to confirm this. And,
that using multiple medias (well, emission + absorption) of COMPLEMENTARY pure
colors serves to filter *all* of the background color to some extent-- because
there are no longer any zeros in the 'combined' color-filtering vector-- with
the result *looking like* actual opacity.

This is a paradigm shift for me: I used to think that volumetric media was a
'thing unto itself', more or less, with its effects only modifying the colors
of objects WITHIN the media object-- and having nothing at all to do with
filtering the background and *its* colors. I guess I never really noticed the
background-color effects, because I've only lately tried creating a PURE-color
media (where there's a zero in one or more of the components, showing the
obvious filtering that's going on-- and showing NO so-called 'opacity' for those
colors.)  My previous uses of a single media never had a zero in the color
vector-- so I took the resulting 'all-color filtering' to mean 'opacity.'

This is my latest theory, anyway ;-)

HOWEVER... Scattering media might be a different animal (or not?) The current
way that I think about scattering (and its 'extinction' value) is that it's
basically emission and absorption media combined (while also showing effects
from lighting, of course.) That's probably a too-simplistic description, but it
will do for now.

But PURE-color scattering used as a SINGLE media also shows
the background filtering (no 'opacity' or filtering for certain colors) , even
with a very high extinction value. For example,
        scattering{1, <1,0,0> extinction 300}
Using this in your laser code, it completely extinguishes the red background
hexagons (i.e., makes them black)-- but leaves the green and blue hexagons
unaltered.  So extinction 300 is actually   300*<1,0,0>   in this case (or can
be thought of that way) -- the SAME color as the media color itself-- but
'extinguishes' that red color. So scattering media-- when used with extinction--
is a 'complementary-color' filter for the background, and for the impinging
light source. (Interestingly, scattering with extinction 0-- and no light
source--shows NO media effect at all, as if the media wasn't there.)

Currently, scattering's extinction allows just a single float value. I have a
dim and fuzzy memory, from v3.6xx days, that extinction could actually take a
color vector (but I might be confusing that with an added absorption media.) It
would be a nice feature addition to allow a color there-- so that a
'complementary' color could be used for the color extinction. For example,
        scattering{1, <.2,1,.2>, extinction 1}
produces a green-ish cloud-- but the 'complementary' color is filtered out of
the incoming light, resulting in purple self-shadowing. With extinction
<.8,0,.8>, the self-shadowing color would match the main green media, and the
cloud would look nice and green throughout. That's not physically accurate, of
course, but it would be more visually appealing ;-)


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From: Kenneth
Subject: Re: Emitting media
Date: 2 Sep 2017 18:00:01
Message: <web.59ab293aa4b127e9883fb31c0@news.povray.org>
"Kenneth" <kdw### [at] gmailcom> wrote:
>
>(Interestingly, scattering with extinction 0-- and no light
> source--shows NO media effect at all, as if the media wasn't there.)
>
Correction:
PURE-color scattering media, with extinction 0-- and no light source--shows NO
media effect at all, as if the media wasn't there.

Something like scattering {1,<.2,1,.2> extinction 0} does show some effects.


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