Jellby wrote:

> 
> 
>>| But I see the opposite,
>>| as if the influence of the samples was "averaged" (since most
>>samples are
>>| deep inside, the effect of the surface ones is weaker). I would have
>>| thought that the sampling algorithm (and colour calculation) would be
>>| smarter than that, but maybe that's not so easy...
>>|
>>Do you have a sample code that produces this effect?
> 
> 
> Yep, try this (povray 3.6.1, custom compile):
> 
> ---------------------------------------
> camera { location <0, 0, -10> look_at 0 }
> 
> light_source { <-20, 20, -20>, rgb 1 }
> 
> sphere {
>   0, 3
>   hollow
>   pigment { color transmit 1 }
>   interior {
>     media {
>       scattering { 5, rgb 3 }
>       method 3
>       intervals 1
>       samples 10 // try also with 200
>     }
>   }
> }
> ---------------------------------------
> 
> I've attached two images: "test1" has samples 10, "test2" has samples 200.
> 
> 
>>It takes some trial and error, but it should be possible to get the
>>same effect with a much faster render. Of course, it all depends on
>>whether you can afford to waste more time fiddling with the
>>parameters or simply letting the computer render in the background
>>while you're doing something else ;) To make accurate comparisons, 
>>you also need to make sure that the maximum number of samples is the
>>same in both cases (I'm not talking of the second parameter of the
>>"samples" keyword here, but of the number of potential samples which
>>is something in the order of min_samples * 2^aa_level). Then if you
>>set aa_threshold to 0 the results should be the same (and take
>>*forever* to render) so all you need to do is find a value that's low
>>enough to get the effect you want while not being exactly 0.
> 
> 
> In my experiments, I did not see any significant difference in the output by
> fiddling with aa. According to your explanation, "samples 10 aa_level 8
> aa_threshold 0.0001" should give similar results to "samples 160 aa_level 4
> aa_threshold 0.0001", and I don't see that with the above example. Could
> you give a more clear example?
> 
> 
>>Note that this only applies to subsurface scattering simulations: eg
>>in cases when you have a very dense nearly uniform media.
> 
> 
> Yes, my experiments are confined to uniform media. I wonder if this adaptive
> sampling and antialiasing is only valid for non-uniform media (opposite to
> your sentence above), maybe uniform media makes adaptive sampling
> unnecessary...
> 
> Or maybe I'm making some mistakes.
> 
> 
> 
> ------------------------------------------------------------------------
> 
> 
> ------------------------------------------------------------------------
> 

Interestingly, in this particular case, method 2 with intervals 1 and 
samples 100 (or possibly less) gets pretty close to method 3 with 
samples set to 200.

Abe

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