Dan Connelly wrote:
> 
> H.A. van der Meiden wrote:
> >
> > Whilst expirimenting with the media feature, I've noticed something odd.
> >
> > A media with absorption 1.0 blocks all passing light, given that the way
> > of the light through the object is 1 unit long.
> 
> Actually, this isn't true.  There is an exponential fall-off of light
> as it passes through the object : in a given distance, a given fraction
> of the light is absorbed.  But over any finite distance, a finite
> fraction of the light survives, subject to ADC bailout and color
> quantization.

You're right ! 
After some trial it seems that the absorption parameter is an
exponentional falloff rate. 
If r=1 then, at 1 unit distance, exp(-1)=37% of the light remains.
If r=2 then exp(-2)=14% of the light remains.
Basically an absorbtion rate '-log(fraction)/distance' determines that
'fraction' of the light remains after 'distance' units. 
Supposedly the emission parameter works in a similar way, determining
some exponentional increase of light. 

Unfortunatly high values for both absorption and emission (>2.0) result
in noisy images, although high sample rates seem reduce this effect.
Does anyone know why ?
(by the way : I'm using the pov31b6 msdos version)

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