Bill Hails nous apporta ses lumieres en ce 14/06/2006 17:48:
> Hi all,
> 
> Any Ideas what's causing these artefacts?
> 
> I'm going for ersatz fluffy clouds, they'll print quite small
> so the level of detail isn't an issue.
> 
> It's a blob + media.
> 
> There's nothing special about the media:
> 
> 
> #ifndef (CloudScale)
>     #declare CloudScale = 1;
> #end
> 
> #local MCloudColour = rgb 0.95;
> 
> #local MCloudFinish = finish {
>     ambient 0.2
>     diffuse 0.6
> }
> 
> #local MCloudTexture = texture {
>     pigment {
>         #if (1)
>             colour rgbt 1
>         #else
>             colour rgb 1
>         #end
>     }
>     finish { MCloudFinish }
> }
> 
> #local MCloudInterior = interior {
>     media {
>         density { MCloudColour * 0.06 / CloudScale }
>         #if (1)
>             absorption rgb (1 - MCloudColour) * 8.0
>         #end
>         #if (1)
>             scattering { 3, MCloudColour * 0.1 }
>             // scattering { 4, MCloudColour * 1.0 }
>         #end
>         #if (1)
>             emission rgb MCloudColour * 0.07
>         #end
>     }
> }
> 
> #declare CloudMaterial = material {
>     texture { MCloudTexture }
>     interior { MCloudInterior }
> }
> 
> When I render the cloud in a scene by itself it looks fine,
> but when I put it alongside other objects in a (not too) complex
> scene these white flecks appear.
> 
> 
> 
> ------------------------------------------------------------------------
> 
It don't look like a problem with your media, but with the blob that contains it. Do a
test by 
removing the media, are the artefacts still there? If you use interior{fade_color rgb
0.5 
fade_distance 1}, do you still see the artefacts?(adjust fade_distance to the
dimentions of the blob)
Check if you have any reflection, look if you have a user deffined default
texture/finish. Check any 
personal include, or any that comes from somebody else (not from the distribution). It
came biting 
back someone else some times ago...

A few shoots in the dark:
Try adding strum in the blob deffinition it you don't use it already.
Try changing the shape of the cloud, probably just changing the random seed.
Try altering the scale of the scene.
Try moving the other elements of your scene.
Try changing the thresshold value of the blob, change the components' radius
acordingly.

It looks like your media could benefit from more samples. Increasing the samples value
don't affect 
render time that much. Don't increase the intervals value, it will realy impair your
rendering time.

-- 
Alain
-------------------------------------------------
Catholicism: If shit happens, you deserve it.

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