I am trying to go a little further then 'dumb user' and understand the 
exact (mathematical) way colors interact with fog and media. Which led 
me to questions about filter and transmit.

* fog works like transmit : it adds its color, which is a function of 
the distance between the camera and the object seen through the fog, to 
a fraction of this object color. The color vectors are added, something 
like this : fog_local_color(fog_settings, 
distance)+fog_local_transmit(fog_settings, distance)*object_local_color

* absorption media works in a way similar to filter : it "absorbs 
frequencies". I believe the mechanics are rather different : the filter 
works by multiplying color vectors (is this correct ?) while media color 
is substracted (?).

* emission media works the other way : the local media color is added to 
the seen-trough-media object (?)

* scattering media is another beast altogether ;-)


Is there a place I can find the formulas used for filter, transmit, fog 
and medias (other than source-code) ? (I mean the code for color 
interaction between seen-trough and seen, not the code used to determine 
local density or anything like that... just the way the colors affect 
one another to produce final color.)

I do not know a way to produce a media that reproduce the behaviour of 
fog... is this possible ? (to benefit from localisation in an interior 
and density capabilities of media)


TIA


Povingly,

Philippe

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