Le_Forgeron <jgr### [at] freefr> wrote:

>
> ...checking the documentation:
> The crand keyword can be added to a finish to cause a minor random
> darkening in the diffuse reflection of direct illumination.

I actually didn't know about this 'direct illumination' caveat until several
weeks ago; I had not read the documentation carefully enough. (I thought crand
would always show up over the entire scene, regardless of lights or no lights.)

Sven, try running this simple scene (with antialiasing or without it.) It shows
that crand appears only on directly-lighted surfaces. Crand will not show up in
un-lighted shadows OR on surfaces that are only 'illuminated' by emission or
ambient. And it does not appear on objects that are pure black in color (rgb
0.0)-- probably because 'black crand on black' looks like pure black anyway, as
Le Forgeron says.

--------------
#version 3.7;
global_settings {assumed_gamma 1.0}

camera {
  perspective
  location  <.5, .5, -15>
  look_at   <.5, .5,  0>
  right     x*image_width/image_height
  angle 20
}

light_source {
  0*x
  color rgb 1.0
  translate <20, 40, -20>
}

plane{z,1.5
    pigment{rgb .1} // If this is pure BLACK, no crand shows up,
// regardless of any lighting.
    finish{ambient 0 emission .05 diffuse .95 crand 1.0}
    }

sphere{0,1 translate 1*y
  pigment{rgb .5} finish{ambient 0 emission .1 diffuse .9 crand 1.0}
  }

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