POV-Ray : Newsgroups : povray.binaries.images : Questions about photons : Re: Questions about photons Server Time
24 Sep 2021 05:36:27 EDT (-0400)
  Re: Questions about photons  
From: Alain Martel
Date: 5 Sep 2021 19:38:11
Message: <613554e3$1@news.povray.org>
Le 2021-09-05 à 05:04, kurtz le pirate a écrit :
> Hello,
> 
> Two questions about the test image attached here.
> 
> * Why the beam circled in black is "dimmer" than the others ?
> They are all in the same media.
> 
> 
> In the general settings, the parameters for the photons are :
> 
>    photons {
>      count 320000
>      max_trace_level 10
>      media 500, 2
>      }
> I'm not sure they are all good
> 
> Render Statistics give :
>    ---------------------------------------
>    Number of photons shot:          170798
>    Surface photons stored:             173
>    Media photons stored:             44288
>    Gather function called:         2634991
>    ---------------------------------------
> 
> * Where does the difference between the number of photons requested 
> (320000) and the number of photons shoted (170798). It's about half
> 
> 
> 
> Merci

In that scene, only the first mirror should be set as target. If there 
is a second target object in a location where no photon can reach it, 
then, the photons destined for that extra target are lost.
If you have two target, one behind the other, and even if the first 
target object is fully transparent, then, that first object will 
intercept and block all the photons shot at the second object.
Also, does the projector object restrict the beam ? That's another thing 
that may cut down the number of photons shot.

Also, if you have a second light, each light will attempt to shot it's 
half of the requested photons. Any light_source that you don't want to 
shot photons absolutely need this photon block :
photons{reflection off refraction off}

ALL light_source except the shadowless ones have this default photons 
block :
photons{reflection on refraction on}



For the dimer part, it's probably related to the media used. Looks like 
you used type 5 with a negative eccentricity, probably between -0.25 and 
-0.5. Try using an isotropic scattering media.
Try using type 1 (isotropic) or 4 (Rayleigh).


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