POV-Ray : Newsgroups : povray.binaries.images : Backside illumination : Re: Backside illumination Server Time: 18 Jan 2021 13:28:16 GMT
  Re: Backside illumination  
From: Alain Martel
Date: 22 Nov 2020 16:56:39
Le 2020-11-22 à 11:24, MichaelJF a écrit :
> 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
> 
You understand correctly, with a little precision : The part that pass 
through does it diffusely.


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