Christian Froeschlin wrote:
> But seriously, I tried it and posting that render is unnecessary.
> As was to be expected from the documentation of conserve_energy,
> the render result of
> 
> "pigment {color rgbt 1} finish {reflection 0.1 conserve_energy}"
> 
> turned out absolutely identical to my previous manual fix of
> 
> "pigment {color rgbt 0.9} finish {reflection 0.1}",
> 
> excepting, of course, the random jitter.
> 

As I understand it, it shouldn't be *exactly* identical, because the 
adjustment is done on a per-pixel basis, and the adjustment is varied 
based on the amount of light being reflected.

However, in this case, we probably couldn't tell the difference anyway :)

...Chambers

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Christian Froeschlin nous apporta ses lumieres en ce 14-02-2007 18:40:
> Ben Chambers wrote:

>> Don't forget, you are now obligated to post another render featuring 
>> this trick so we can see how it really affects things :)

>> Or else we'll send the RSCops to hunt you down and force you to do all 
>> of your future renders on a TI calculator!

> That's blackmail!

> But seriously, I tried it and posting that render is unnecessary.
> As was to be expected from the documentation of conserve_energy,
> the render result of

> "pigment {color rgbt 1} finish {reflection 0.1 conserve_energy}"

> turned out absolutely identical to my previous manual fix of

> "pigment {color rgbt 0.9} finish {reflection 0.1}",

> excepting, of course, the random jitter.

It's more usefull when you have variable reflection like reflection{0, 1} where 
you just can't do a manual balancing.

-- 
Alain
-------------------------------------------------
I find the affluence of incahol to be totally, whatever he said

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Christian Froeschlin wrote:

> Hello,
> 
> I just experimented a bit with glass, water and photons. For making
> a glass filled with water, the documentation recommends to make a
> hollow container using CSG, and filling it with a liquid object
> scaled down a bit to avoid coincident surfaces. I'm a bit unsure
> about this, as the extra transitions through a thin air slice would
> seem to cause unnecessary calculations, and yield incorrect results
> as well (e.g., I think it is possible that the expected refraction
> at a water/glass transition turns into a total internal reflection
> at a water/air transition). A problem like this was discussed some
> time ago in povray.newusers regarding "Refraction in the eye":

> So, I made three images:
> 
> 1. Uses the recommended technique
> 2. Embeds the liquid in a solid glass block (in the hope that
>     the IOR specified in the second object takes precedence)
> 3. Is a variation of 1., with the liquid scaled *up* a tiny
>     bit and the "merge"-d with the glass container to remove
>     the inner surface (but no idea how POV-Ray handles the
>     differing IORs in a merge).

If my reading of the source is correct, #2 will do *almost* the right thing. 
What should produce correct results is scaling the water slightly larger
than the hollow of the glass:

   1     2           3     4           5     6
air|glass|water+glass|water|water+glass|glass|air

What should happen is:
1: The ray exits the air, enters the glass
2: The ray exits the glass, enters the water
3: The ray has already left the glass, so this is ignored for refraction
4: The ray exits the water, enters the glass
5: The ray has already left the water, so this is ignored for refraction
6: The ray exits the glass, enters the air

The first glass-water transition will be slightly nearer the camera than it
should be, but otherwise this is correct.  The proper number of refractions
will take place, and they will all have correct IORs.


-- 
Mark Wagner

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Mark Wagner wrote:

> If my reading of the source is correct, #2 will do *almost* the right thing. 
> What should produce correct results is scaling the water slightly larger
> than the hollow of the glass:

Actually, I tried that first, but it reduced render speed so much
I thought there must be a lot of reflection or similar going on
between those two surfaces, so i tried to merge the internal
surface away (hence test #3).

I just ran a non-anti-aliased render of your suggestion which still
runs in bearable time. The result actually looks almost identical to
the classic "smaller" scaling, except for some differences with light
on the lemon and its reflection at the other side of the glass.

Note this picture uses the old "incorrect" finish without
energy conservation to allow comparison to bubbles-800.jpg
of my original post.

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Attachments:
Download 'bubbles-800-noaa-scaleplus-nomerge.jpg' (22 KB)

Preview of image 'bubbles-800-noaa-scaleplus-nomerge.jpg'

I don't know about you others, folks, to me this looks simply great! :-)

Thomas

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