Am 22.11.2020 um 16:22 schrieb Kenneth:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>> In Norbert Kern's Bluebell Wood discussion, there was mention of the use
>> of basckside illumination by Alain and myself. Here is an example of its
>> use, a 2019 update of a 2012 scene from the Iskander/Gancaloon universe.
>> Backside illumination was applied to the curtains.
>>
>> --
>> Thomas
> 
> I have not yet used backside illumination, so I'm curious as to what I should
> see in your scene. I assume that the curtain objects themselves are
> semi-transparent(?), and that the effect is seen as the small triangular light
> patches on the left-side curtain?
> 
> So many tricks to learn, so little time ;-)
> 
> 
> 
As all I know, backside illumination and semi transparency is not the 
same. Semi transparency can be achieved by using an alpha-channel within 
a png-based texture. Backside illumination is a special calculation of 
diffuse reflections.

I used
      finish { diffuse albedo 0.55,0.4 }
in this image:
      http://news.povray.org/5f2ae26d%40news.povray.org
at all of the balloons.

As I understand it, it means that 55 % of the light from front 
lightsources is diffuse reflected and that 40 % of light from sources at 
the backside of an object can pass through.

Best regards
Michael

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