Le 2019-09-27 à 09:11, IGM a écrit :
> Hi,
> maybe this is an ancient (and stupid?) question, but after online search I still
> don't find anything useful.
> 
> In PovRay, two semitransparent boxes with very different thickness but with same
> rgbt values have the same appearance. The absorption/transmission doesn't depend
> on box thickness. The same even using "media { absorption rgb <.,.,.> }". This
> is a sample code:
> 
> box {<-250,0,0><250,500,100>
>      texture {pigment {rgbt <.6,0,0,0.5>}}
>      interior {ior 1.5 media { absorption rgb 0.0001*<1,1,1> } }
>      hollow on
>      rotate <0,0,0> translate <-250,0,100>}
> 
> box {<-250,0,0><250,500,1000>
>      texture {pigment {rgbt <.6,0,0,0.5>}}
>      interior {ior 1.5 media { absorption rgb 0.0001*<1,1,1> } }
>      hollow on
>      rotate <0,0,0> translate <250,0,100>}
> 
> This is not physical. Is there a way to simulate the real thickness dependence
> of absorption/transmission? (Beer–Lambert law)
> 
> Thank you!
> igmar
> 
> 

What you want is to add an interior block to that object that define 
light fading through that object :

interior{fade_colour Some_Colour fade_distance Distance fade_power 1001}

For realistic results, fade_power should be 1 or 1001.
fade_distance dictate the intensity of the fading, ow how fast the 
fade_colour affect the colour of what is behind your object.

In that same interior block, you can also set an index of refraction, or 
IOR, as well as the amount of spectral dispersion. Use real world IOR 
and dispersion values.

interior{
  ior 1.33 // water. Default value is 1
  dispersion 1.01 // default to 1
  dispersion_samples 10 // optional, have a default value
}

Also, as you discovered, the interior block can also be used to fill an 
object with some media.


Alain

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