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From: Margus Ramst
Subject: Re: Are angle dependent reflections based upon actual lighting effects?
Date: 10 Aug 1999 22:28:24
Message: <37B0DFCB.4BB5598C@peak.edu.ee>
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I believe Ken means light only enters the medium and is refracted if it is not
reflected. Light can be partially reflected or refracted, but only one of the
two can happen on a photon by photon basis.
Margus
"Jerome M. BERGER" wrote:
>
> ??? What do you mean "mutually exclusive"? In most cases, both occur
> simultaneously (each time you change medium: air/water, air/glass, ...).
> The only cases I can think of where you can have one without the other
> is the mirage (or anytime the IOR changes continuously) where you only
> have refraction and the metallic surface where you have no transmitted
> light (and therefore no refraction...)
>
> Jerome
>
> --
> *******************************
> * they'll tell you what can't * mailto:ber### [at] iname com
> * be done and why... * http://www.enst.fr/~jberger
> * Then do it. *
> *******************************
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From: Ken
Subject: Re: Are angle dependent reflections based upon actual lighting effects?
Date: 10 Aug 1999 23:17:36
Message: <37B0EB0B.2ABCB1BF@pacbell.net>
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Margus Ramst wrote:
>
> I believe Ken means light only enters the medium and is refracted if it is not
> reflected. Light can be partially reflected or refracted, but only one of the
> two can happen on a photon by photon basis.
>
> Margus
Ior is a property of a material. Reflection is a property of a surface. At least
this was the rational for moving ior into it's own property wrapper i.e. interior.
I know that surfaces can be considered to have an ior value but this is generaly
a very minor property where roughness and color have a much greater impact than
does a surfaces ior value will.
To really clarify my point air does not generaly reflect light. It will transmit
and refract light in varying amounts however. Shiny steel will reflect light redily
but has extremely poor light transmittance.
--
Ken Tyler
See my 700+ Povray and 3D Rendering and Raytracing Links at:
http://home.pacbell.net/tylereng/index.html
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From: Mark Wagner
Subject: Re: Are angle dependent reflections based upon actual lighting effects?
Date: 11 Aug 1999 02:22:38
Message: <37b116ae@news.povray.org>
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Margus Ramst wrote in message <37B0DFCB.4BB5598C@peak.edu.ee>...
>I believe Ken means light only enters the medium and is refracted if it is
not
>reflected. Light can be partially reflected or refracted, but only one of
the
>two can happen on a photon by photon basis.
Take this one up with the quantum physicists -- they will tell you that a
photon can be simultaneously reflected and refracted. :-)
Mark
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>Ior is a property of a material. Reflection is a property of a
surface.<
Hmm, actually, they can both be considered properties of the boundaries
between two materials(and the same substance at a different temperature
could be considered a different material.) And gaseous materials do
reflect light, although usually in small amounts.(although clouds, fog,
etc are not examples of this because they are droplets of liquid
suspended in the air.)
Of course, this has nothing to do with the way POV considers it...
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From: Jerome M BERGER
Subject: Re: Are angle dependent reflections based upon actual lighting effects?
Date: 11 Aug 1999 13:17:03
Message: <37B1B00E.630124BA@enst.fr>
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Ken wrote:
>
> Margus Ramst wrote:
> >
> > I believe Ken means light only enters the medium and is refracted if it is not
> > reflected. Light can be partially reflected or refracted, but only one of the
> > two can happen on a photon by photon basis.
> >
> > Margus
>
> Ior is a property of a material. Reflection is a property of a surface. At least
> this was the rational for moving ior into it's own property wrapper i.e. interior.
> I know that surfaces can be considered to have an ior value but this is generaly
> a very minor property where roughness and color have a much greater impact than
> does a surfaces ior value will.
>
> To really clarify my point air does not generaly reflect light. It will transmit
> and refract light in varying amounts however. Shiny steel will reflect light redily
> but has extremely poor light transmittance.
>
> --
> Ken Tyler
>
> See my 700+ Povray and 3D Rendering and Raytracing Links at:
> http://home.pacbell.net/tylereng/index.html
Well, actually I think that reflection depends on the ior (or rather on
the difference of iors between two materials) which in turn depends on
its electrical conductivity (is that the right word?). At least, that's
what happens when an electromagnetic wave hits a metal (please don't
think in photons as they are governed by quantic laws, which I'm not
familiar with): the electric field in the wave agitates the metal's
surface electrons creating an eletric current (since the metal is a
conductor) which in turn generates a new electromagnetic wave perfectly
in sync with the incoming one but of opposite sign. This wave is of
course emitted in all directions which means it *cancels* the incoming
wave inside the metal and creates what we call "reflection" outside.
When the material isn't as good an electrical conductor, the new wave
isn't as strong as the incoming one and that's what causes partial
reflection and refraction. Moreover the exact effect depends on the
angle between the *eletrical field* (not the direction of travel) and
the surface, therefore: angle dependant effects and polarization
dependant effects. This same effect causes absorption and scattering: as
the wave travels through a slightly conductive material, it will agitate
more and more electrons along the way and each time a small fraction of
the wave gets cancelled out and reemitted in other directions.
Okay, there's just one problem with this model: I don't remember how it
accounts for materials like wood that neither reflect nor transmit any
light...
Just my 2c,
Jerome
--
*******************************
* they'll tell you what can't * mailto:ber### [at] iname com
* be done and why... * http://www.enst.fr/~jberger
* Then do it. *
*******************************
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From: Nieminen Mika
Subject: Re: Are angle dependent reflections based upon actual lighting effects?
Date: 11 Aug 1999 13:52:41
Message: <37b1b869@news.povray.org>
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Jerome M. BERGER <jbe### [at] enst fr> wrote:
: Okay, there's just one problem with this model: I don't remember how it
: accounts for materials like wood that neither reflect nor transmit any
: light...
Actually wood reflects light. If it didn't, you would see it as black.
And a white object in a room with wooden walls will certainly be colored
differently than in a room with white walls.
I think that the color of the wood (or any material) depends on the
frequency of the electrons the light affects.
--
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/
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From: Ken
Subject: Re: Are angle dependent reflections based upon actual lighting effects?
Date: 11 Aug 1999 14:01:51
Message: <37B1BA77.D6B2DFEB@pacbell.net>
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Nieminen Mika wrote:
>
> Jerome M. BERGER <jbe### [at] enst fr> wrote:
> : Okay, there's just one problem with this model: I don't remember how it
> : accounts for materials like wood that neither reflect nor transmit any
> : light...
>
> Actually wood reflects light. If it didn't, you would see it as black.
> And a white object in a room with wooden walls will certainly be colored
> differently than in a room with white walls.
> I think that the color of the wood (or any material) depends on the
> frequency of the electrons the light affects.
Yeah don't get me started on the properties of "blackbody" objects. I got
into a lengthy argument not to long ago in one of sci.electronics groups
about the thermal radiation and emmisivity characteristics of variously
colored heat sink materials and don't want to relive that again for a while.
I was right of course but they just wouldn't listen to my common sense:)
--
Ken Tyler
See my 700+ Povray and 3D Rendering and Raytracing Links at:
http://home.pacbell.net/tylereng/index.html
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From: Margus Ramst
Subject: Re: Are angle dependent reflections based upon actual lighting effects?
Date: 11 Aug 1999 14:50:18
Message: <37B1C5EA.DE67AE8E@peak.edu.ee>
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No, thanks. They could well be BS-ing and I'd have no way of finding out :)
Margus
Mark Wagner wrote:
>
> Margus Ramst wrote in message <37B0DFCB.4BB5598C@peak.edu.ee>...
> >I believe Ken means light only enters the medium and is refracted if it is
> not
> >reflected. Light can be partially reflected or refracted, but only one of
> the
> >two can happen on a photon by photon basis.
>
> Take this one up with the quantum physicists -- they will tell you that a
> photon can be simultaneously reflected and refracted. :-)
>
> Mark
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From: Jerome M BERGER
Subject: Re: Are angle dependent reflections based upon actual lighting effects?
Date: 11 Aug 1999 14:53:12
Message: <37B1C697.D650D44C@enst.fr>
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Nieminen Mika wrote:
>
> Jerome M. BERGER <jbe### [at] enst fr> wrote:
> : Okay, there's just one problem with this model: I don't remember how it
> : accounts for materials like wood that neither reflect nor transmit any
> : light...
>
> Actually wood reflects light. If it didn't, you would see it as black.
> And a white object in a room with wooden walls will certainly be colored
> differently than in a room with white walls.
> I think that the color of the wood (or any material) depends on the
> frequency of the electrons the light affects.
>
> --
> main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
> ):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/
Yes, what I meant was that you can't see any reflections on a wood
surface (unless it is higly polished and varnished). The effect that
causes wood to become visible is probably different from the one I
described since it is independant on the viewing direction...
Jerome
--
*******************************
* they'll tell you what can't * mailto:ber### [at] iname com
* be done and why... * http://www.enst.fr/~jberger
* Then do it. *
*******************************
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From: Ken
Subject: Re: Are angle dependent reflections based upon actual lighting effects?
Date: 11 Aug 1999 15:09:52
Message: <37B1CA6E.C84ECD22@pacbell.net>
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"Jerome M. BERGER" wrote:
>
> Nieminen Mika wrote:
>
> Yes, what I meant was that you can't see any reflections on a wood
> surface (unless it is higly polished and varnished). The effect that
> causes wood to become visible is probably different from the one I
> described since it is independant on the viewing direction...
>
> Jerome
Actually wood cellulose is highly reflective. This cam be seen when
viewed with a simple magnifying glass. It's surface properties are so
porous and broken into so many angles that it is not redily apparent
from casual inspection.
--
Ken Tyler
See my 700+ Povray and 3D Rendering and Raytracing Links at:
http://home.pacbell.net/tylereng/index.html
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