I'm having a problem understanding the light fading computation in POV. I'm
not sure it is a bug or just I who don't do it right. Here goes.

I was starting to setup a scene and wanted to test the lighting setup but
the render didn't show what I was expecting. Light seemed to fade way too
slowly. So I wrote a simple anim designed to test the inverse square law and
checked the values I picked from the frames with the values computed by the
light fading formula found in section 6.5.7.9 of the help file. And the set
of values are way different.

Could someone explain what I am doing wrong or if my setup is right, explain
the differences in light intensity from the samples frames and the formula?
Really, I'm at lost.

Here is the simple scene (set final_frame = 30 in povray.ini) :

global_settings {
  assumed_gamma 1.0
}
#declare Finish=finish{diffuse 1.0 ambient 0.0}
#declare White=texture{pigment{rgb<1,1,1>} finish{Finish}}
#declare WhiteLight=<1,1,1>;
light_source{
  <0, 0, 0>
  color WhiteLight
  fade_power 2.0
  fade_distance 5.0
}
camera{
  location  <0, 0, 0>
  direction <0, 0, -1>
  up        <0, 1, 0>
  right     <-1, 0, 0>
  angle 4
  translate  <0, 0, 1-frame_number>
}
box{
  <-10, -10, 0>, <10, 10, -1>
  texture {White}
  translate  <0, 0, -4-frame_number>
 }

And here are the values. First column are the intensity values sampled from
each frame of the anim and second column is computed from the formula.

254   256
232   210
213   173
196   144
181   121
168   102
156    88
146    76
137    66
129    58
122    51
116    46
110    41
105    37
100    33
96     30
92     27
88     25
85     23
82     21
79     20
76     18
74     17
71     16
69     15
67     14
65     13
63     12
62     11
60     11

Thanks

White Zebra

Post a reply to this message

Drop assumed_gamma or use assumed_gamma 2.2 or whatever your
display_gamma is in povray.ini. This way you get linear samples.


_____________
Kari Kivisalo

Post a reply to this message