On Sun, 03 Jan 2010 21:18:18 -0300
Nicolas Alvarez <nic### [at] gmailcom> wrote:

> > I've now noticed that in a 800x600 image, the problem is on line 299,
> > and, in a 1200x900, the problem is on line 449 - exactly the
> > (vertical) center of the image.
> 
> Interesting. Try moving or rotating your camera by a very small amount.

Here are more tests. I eliminated other elements as much as possible. I
removed the fireworks background, and put in a simple 'Darkgreen' one.

Surprisingly, the artifact spills out of the lathe into the background!

http://jcoppens.com/misc/glass_g1.png and
http://jcoppens.com/misc/glass_rt1.png

In both cases, the camera is looking down ever so slightly:

camera {
   perspective
   location <0, 0.273, -18.5>
   sky <0, 1, 0>
   direction <0, 0, 1>
   right <1.3333, 0, 0>
   up <0, 1, 1e-2>
   look_at <0, 0, -2>
   angle 34   
   translate <15.75, 15.75, 0>
}

Eliminating the 0.273 in location (making the line-of-sight horizontal),
the artifact almost disappears:

http://jcoppens.com/misc/glass_rt0.png

As requested, a slightly rotated camera version (0.1 degrees):

http://jcoppens.com/misc/glass_g2.png

... interesting: the artifact disappears slowly at its first height, and
seems to be appearing a little below.

John

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