Am 02.03.2011 12:59, schrieb Bill Pragnell:
> Stephen<mcavoys_at@aoldotcom>  wrote:
>> I did a test without aa and there are more artefacts in the non-aa
>> rendering.
>
> I see what you mean. The artifacts were definitely lessened by aa, but they were
> lessened much more by increasing the sampling :)

I'd expect AA - instead of increasing samples - to give a benefit 
nonetheless, as it avoids increasing the number of samples shot in areas 
where everything is smooth as a baby's behind.

(I personally favor focal blur over AA though, as I think the 
confidence/variance approach is superior the AA's mechanism.)

> Well, I was basically just tweaking until it looked good. I don't really
> understand what the subsurface:mm_per_unit ratio means, although the
> scattering:absorption ratio of the subsurface values seems more intuitive (not
> dissimilar to media).

The "mm_per_unit" ratio specifies - not surprisingly - how many mm are 
in a POV-Ray unit.

This is required because the subsurface coefficients are specified in 
[average scattering/absorption events] "per mm", rather than "per 
POV-Ray unit", in order to faciliate creating re-usable material 
libraries. Otherwise what would like marble in one scene might look like 
soap in another, depending on the scene's dimensions.

If you feel like multiplying "mm_per_unit" by some value just to make 
your material look right, instead divide the coefficients by that value.

> I think the mm_per_unit value kind of makes sense - most everyday experience
> with translucent stone objects is small statues/knick-knacks. For larger items
> (metres and larger), I would expect the translucency to be much more subtle, or
> even invisible, due to the greater path lengths.

Yup, that's exactly the point of it.

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