Severi Salminen wrote:
> Do you know if
> "normal" reflections happen (about) equally when going from less dense
> medium to denser medium when compared to opposite situation?

  Sorry, I'm not too acquainted with the specifics of the physics
involved...

> And my renderer
> still misses many important features that make the image look realistic.

  Speaking of which, does it handle total internal reflection properly?

  (OTOH, that would also be something which should be specified with a
physically accurate BRDF instead of being hard-coded into the renderer...)

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> Do you know if
> "normal" reflections happen (about) equally when going from less dense
> medium to denser medium when compared to opposite situation?

Yes, the inside of a RL glass surface reflects about the same as
the outside, sometimes a bit more reflective, since grime can
build up on the outside, but not on the inside.

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> I don't know what you mean by uneven fading. Is it still present in this
> higher quality render attached?

Yes, the first couple reflective bounces are colored darker,
(which is correct) but as the reflections continue on they
are close to the same color instead of darker, probably a
saturation issue?

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Attachments:
Download 'kuva9a.jpg' (15 KB)

Preview of image 'kuva9a.jpg'

"Tim Attwood" <tim### [at] comcastnet> wrote in message 
news:47c34a7b$1@news.povray.org...
>> Do you know if
>> "normal" reflections happen (about) equally when going from less dense
>> medium to denser medium when compared to opposite situation?
>
> Yes, the inside of a RL glass surface reflects about the same as
> the outside, sometimes a bit more reflective, since grime can
> build up on the outside, but not on the inside.

Are you sure?  A watersurface seems a lot more reflective from underneath 
the water than from above the water. Could be an optical illusion though.

cu!
-- 
#macro G(b,e)b+(e-b)*C/50#end#macro _(b,e,k,l)#local C=0;#while(C<50)
sphere{G(b,e)+3*z.1pigment{rgb G(k,l)}finish{ambient 1}}#local C=C+1;
#end#end _(y-x,y,x,x+y)_(y,-x-y,x+y,y)_(-x-y,-y,y,y+z)_(-y,y,y+z,x+y)
_(0x+y.5+y/2x)_(0x-y.5+y/2x)            // ZK http://www.povplace.com

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> Are you sure?  A watersurface seems a lot more reflective from underneath 
> the water than from above the water. Could be an optical illusion though.

Look up some lake reflections... it's just that sometimes the
surface of water doesn't have much to reflect, just empty sky.

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Tim Attwood wrote:
>> I don't know what you mean by uneven fading. Is it still present in this
>> higher quality render attached?
> 
> Yes, the first couple reflective bounces are colored darker,
> (which is correct) but as the reflections continue on they
> are close to the same color instead of darker, probably a
> saturation issue?

Yeah, it is simply because the spheres are very reflective and the light
source is very intensive. So the red components remains strong even
after many bounces. It takes many reflections to get the value go down.
I tested with dimmer lights and a bit less reflective surface and it
works as it should: it gets darker every time it reflects.

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Warp wrote:

>   Speaking of which, does it handle total internal reflection properly?

Yeah, I think it does. But I don't have proper objects to test it
properly so I'm not 100% sure yet. I tried to place camera inside a
glass sphere and I did saw internal reflection (basically you see a
circular "window" and the outside is dark).

>   (OTOH, that would also be something which should be specified with a
> physically accurate BRDF instead of being hard-coded into the renderer...)

I have no idea how to represent an arbitary BRDF or BSDF. But you get
quite far even with traditional refraction/specular/diffuse models.

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"Zeger Knaepen" <zeg### [at] povplacecom> wrote:
> > Yes, the inside of a RL glass surface reflects about the same as
> > the outside, sometimes a bit more reflective, since grime can
> > build up on the outside, but not on the inside.
>
> Are you sure?  A watersurface seems a lot more reflective from underneath
> the water than from above the water. Could be an optical illusion though.
>
> <snip>

http://en.wikipedia.org/wiki/Total_internal_reflection

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> > Are you sure?  A watersurface seems a lot more reflective from underneath
> > the water than from above the water. Could be an optical illusion though.
> >
> > <snip>
>
> http://en.wikipedia.org/wiki/Total_internal_reflection

We were not talking about total internal reflections, but normal specular
reflections. I have the impression that they happen about equally to both
directions.

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Severi Salminen wrote:
> Warp wrote:
> 
>>   Speaking of which, does it handle total internal reflection properly?
> 
> Yeah, I think it does. But I don't have proper objects to test it
> properly so I'm not 100% sure yet.

  Try with the example at wikipedia:
http://en.wikipedia.org/wiki/Image:Total_internal_reflection.jpg

>>   (OTOH, that would also be something which should be specified with a
>> physically accurate BRDF instead of being hard-coded into the renderer...)
> 
> I have no idea how to represent an arbitary BRDF or BSDF. But you get
> quite far even with traditional refraction/specular/diffuse models.

  The problem with the "traditional" lighting models is that they are
not physically accurate and thus do not produce completely realistic
results.

  The whole reason why the "traditional" lighting models were developed
was precisely to avoid having to send millions of rays from each
intersection point. They try to approximate (often poorly) what would
happen if you would send the millions of rays and have a physically
accurate BRDF, but they are only approximations.

  If you are bruteforce-rendering anyways, using these limited lighting
models kind of becomes moot. They were created precisely for
non-bruteforce rendering because bruteforce rendering was unfeasible.
Now that you are bruteforce-rendering, there's no need to use them. You
can use realistic BRDFs.

  In principle a BRDF is quite simple: It's a function which takes an
incoming direction vector and an outcoming direction vector as (const)
parameters, and returns a factor for each color component between 0.0
and 1.0. That's it. Its usage is equally simple: When you have
calculated a ray which intersects a surface and want to reflect that ray
to some direction, you shoot that reflected ray and then multiply the
color returned by that ray with the factor returned by the BRDF of that
surface. This will be the color returned by the original incoming ray.

  Of course implementing the BRDF to be physically accurate is not that
simple.

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