"Kenneth" <kdw### [at] gmailcom> wrote:

> Here's an example scene that shows the lack of opacity that I was talking
> about...
>
Forgot to mention: The light source in the code is in case you want to change my
absorption media to scattering{...}

Post a reply to this message

"omniverse" <omn### [at] charternet> wrote:
> "Kenneth" <kdw### [at] gmailcom> wrote:

> >
> > Adding an identical pure-color ABSORPTION media (or even its complementary
> > color)-- to try and *force* some opacity-- doesn't work either.
> >
>
> Trying things the following scene looks like it works okay, except for edges
> where I attempted to keep it from being like a solid object... In this case
> density rgb 5, instead of only 1, could be good enough.
>
> // test laser beam

I just discovered that you're right (and I was wrong, about this particular
case): A pure-color emitting media like <1,0,0>, along with an additional
absorption media of the COMPLEMENTARY color (<0,1,1>) and same density, does
indeed show true opacity, when both densities are made high enough. I guess I
didn't crank up the density enough in my original experiment(?). I see that the
same also applies to absorption + absorption (!), and
scattering + absorption, when using the complementary color. Thanks for your
scene code; I probably wouldn't have noticed this otherwise, in my own test
code.

Perhaps the 1's and 0's in both medias serve to 'cancel' any 'zero effect', when
used together.

So, the 'transparent color' effect (no opacity) is apparent only when using a
SINGLE pure-color media (or when adding the *same*-color absorption media to
it.)

But I'm still curious about the effect of zero(s) in a single media... ;-)

Post a reply to this message

Le 17-08-31 à 18:58, Loren a écrit :
> Hello,
> 
> I'm having great difficult getting emitting media (glowing red media, as in a
> laser), in my scenes. First, a simple example which doesn't work:
> 
> 
> -------------
> // #include "shapes.inc"
> // #include "colors.inc"
> //
> // camera {
> // location 10
> // look_at 0
> //  angle 45
> // }
> // light_source { 10
> //  color rgb<1, 1, 1> }
> // sphere { 0, 1 color rgb<1,0,0> }
> 
> #include "colors.inc"
> 
> background { color White }
Emissive media can't show against a white background. Try something MUCH 
darker.
background { Cyant/5 }
or
background { Black }

> 
> camera {
>    location <0, 2, -3>
>    look_at <0, 1, 2>
> }
> 
> sphere {
>    <0, 1, 2>, 2
>    texture {
>      pigment { color rgbf 1 }
>    }
>    hollow
>    interior{
>         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.

Use :
media{ emission Red samples 100 }

>    }
> }
> 
> light_source { <2, 4, -3> color White}
> 

Defaults for media in version 3.6+
method 3
samples 10
confidance Not Applicable
variance N/A
intervals 1
jitter 1

Alain

Post a reply to this message

"Kenneth" <kdw### [at] gmailcom> wrote:
> "omniverse" <omn### [at] charternet> wrote:
> > "Kenneth" <kdw### [at] gmailcom> wrote:
>
> > >
> > > Adding an identical pure-color ABSORPTION media (or even its complementary
> > > color)-- to try and *force* some opacity-- doesn't work either.
> > >
> >
> > Trying things the following scene looks like it works okay, except for edges
> > where I attempted to keep it from being like a solid object... In this case
> > density rgb 5, instead of only 1, could be good enough.
> >
> > // test laser beam
>
> I just discovered that you're right (and I was wrong, about this particular
> case): A pure-color emitting media like <1,0,0>, along with an additional
> absorption media of the COMPLEMENTARY color (<0,1,1>) and same density, does
> indeed show true opacity, when both densities are made high enough. I guess I
> didn't crank up the density enough in my original experiment(?). I see that the
> same also applies to absorption + absorption (!), and
> scattering + absorption, when using the complementary color. Thanks for your
> scene code; I probably wouldn't have noticed this otherwise, in my own test
> code.
>
> Perhaps the 1's and 0's in both medias serve to 'cancel' any 'zero effect', when
> used together.
>
> So, the 'transparent color' effect (no opacity) is apparent only when using a
> SINGLE pure-color media (or when adding the *same*-color absorption media to
> it.)
>
> But I'm still curious about the effect of zero(s) in a single media... ;-)

Well, let's think about it here.

Additive only if singular densities exist in the singular media, so zero plus
whatever other color equals the other color(s).
Yet pair up density statements in the single media and those
colors(density*absorption, or emission or both) multiply densities, therefore
zero anywhere makes same color 0. Or rather factored by that, depending on type
of media.

Or so I believe. Seems the more I talk the less sense I make to myself, possibly
everyone else too!

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.

Post a reply to this message

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. :)

Post a reply to this message

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

Post a reply to this message

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

Post a reply to this message

"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.

Post a reply to this message

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.

Post a reply to this message

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.

Post a reply to this message