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Alain wrote:
> Maxime Marrow nous apporta ses lumieres en ce 2008/03/23 10:32:
>> Consider the following POV-Ray code:
>>
>> #include "functions.inc"
>>
>> background{1}
>>
>> camera {
>> location 1.5
>> look_at 0
>> }
>>
>> isosurface{
>> function { f_noise3d(3*x, 3*y, 3*z) - 1/2 }
>>
>> max_gradient 4
>>
>> hollow
>> pigment { rgbf 1 }
>>
>> interior{
>> media{
>> intervals 100
>> absorption 1
>> }
>> }
>> }
>>
>> What is the reason for the black spots and is there a way to avoid them?
>>
>> Thank you,
>> Maxime
> Apart from the obvious isue with max_trace_level.
Thanks to you and Warp for the max_trace_level suggestion. I changed the
value to 20 and this removed almost all artefacts. Is there way to
remove the remaining artefacts?
> You may need to add "all_intersections" to your isosurface. Without
> that, you will miss most surfaces after the first one encountered.
Doesn’t this apply only to isosurfaces which are used in CSG operations?
If no, can you give an example (not involving CSG) where the omission of
all_intersections results in omission of surfaces?
> Maybe the 100 intervals are causing some artefacts.
>
> Try this for your media:
>
> media{ samples 300 absorbtion 1}
I tried it – the image is visually the same. It seems that the 100
intervals are not causing artefacts in this scene.
> This will guive you the same total number of samples as your current
> setting.
> Should be a lot faster to.
> Media defaults: method 3, samples 3, intervals 1.
These values contradict the values in the POV-Ray help (POV-Ray version
3.6.1c.icl8.win32). The default values for media in the help are: method
3, samples 1, 1, intervals 10.
> Don't change intervals.
> Keep samples larger than 2.
> Please read about media sampling method 3, whitch is the default with
> all versions greater than 3.5.
>
> In short, it's always beter to increase the samples that increasing the
> intervals. LOT faster, beter quality, reduction of possible artefacts.
Thanks for this advice,
Maxime
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