"Tom Melly" <tom### [at] tomandlucouk> wrote in message
news:3d3fbdf0@news.povray.org...
>
> The Original version 11m 38s (collect on for glass objects, spacing 0.02)
> Bad-Artifact version 0m 26s (collect off for glass objects, spacing 0.02)
> Non-Artifact version 1m 40s (collect off for glass objects, spacing 0.01)

Wish I had some insight into this to add but I use photons only a fraction
for renderings so it isn't something I'm not extremely familiar with. At
least not for all sorts of situations that can be encountered.

Just wanted to say that I'm making a oil lamp using photons now and noticed
a couple peculiarities. There are crystals hanging from the glass shade,
which I added to the main "chimney" and base. While checking on things, I
removed everything except those crystal pieces and tried collect off to see
how they'd appear alone. The photons stopped showing on the wall and the
render was much slower. I changed back to collect on and it sped up (perhaps
twice as fast) and the photons reappeared on the wall behind them. I wasn't
expecting that to happen.

I was under the impression that collect off only removed photons from the
object itself. Maybe there was some other explanation for what happened, or
even how it works. I was thinking collect off had become a boolean for
turning photons on/off instead of using target to do so.

So anyway that is unlike what your test found. I'm using a spacing of 0.04
but it had been set to 0.06, and 0.1 is still good enough for test renders.
I just realized something else, this depends on dispersion being used too.
Without it I am not seeing the photons occur whether or not collect is on or
off. However, the speed change is still evident. If you are curious, please
try the following scene, it renders in just over 2 minutes on this 800MHz P3
CPU for a 160x120 res. image.

global_settings {
        max_trace_level 9
        photons {
                spacing 0.1
                }
}

camera {
  location  <0, 3, -12>
  look_at   <0, 2,  0>
  right     x*image_width/image_height
}

light_source {
        <15,10,-15>,1
}

box {
        <-36,-12,-36>,<36,24,12>
        pigment {
                rgb 1
        }
}

#declare Crystal_M=
material {
        texture {
                pigment {
                        rgbf 0.999
                }
                finish {
                        ambient 0 diffuse 0.09 specular 0.9 roughness 0.002
                        reflection {0.1,0.5 fresnel}
                }
        }
                interior {
                        ior 1.5 fade_distance 3 fade_power 1111 fade_color
<0.2,0.5,0.7>
                        dispersion 1.05 dispersion_samples 9
 // remove dispersion and photons will also be removed?
                }
}

#local I=9;

#declare Crystal=
intersection {
#while (I>0)
        plane {
                x,1 rotate 15*z rotate 40*I*y
        }
        plane {
                x,1 rotate -30*z rotate 40*I*y
        }
#local I=I-1;
#end
 scale 0.15
}

#local I=6;

#while (I>0)
object {
        Crystal
        material {Crystal_M}
        translate 2.75*x rotate 30*I*y
        translate y
photons {
        target
        reflection on
        refraction on
        collect off // on is faster shows photons, off slower no photons
        }
}
#local I=I-1;
#end

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