I stumbled upon this 'artifact' when I tried to use a bozo pattern:



#include "colors.inc"
camera {
	location <0,1000,0>
    direction <0,0,1>
    look_at  <0, 0, 0>
}
light_source { <0,30000,0> color White }
plane { y, 0 pigment { bozo scale .01}}


gives different color patterns in four quadrants.
Any idea?

-- 
+------------------------------------------------------+
| Rob Wieringa                                         |
| Philips  Research  Laboratories   Eindhoven          |
| __X__: remove this from email address                |
| email: wie### [at] natlabresearchphilipscom          |
+------------------------------------------------------+

Post a reply to this message

ir. R.M.A. Wieringa wrote:

> I stumbled upon this 'artifact' when I tried to use a bozo pattern:
> gives different color patterns in four quadrants.
> Any idea?
> | Rob Wieringa                                         |

I can't even begin to speculate why it renders with four different
patterns as you describe. What really got my attention was the fact
that even with no specific color declaration it defaulted to for colors.
Red, Green, Blue, and White. I did notice after scaling it up to 100
it behaved in it's normal manner.

Post a reply to this message

It seems you're viewing the bozo pattern from so far away, and scaled so
small, that perhaps these effects are caused by aliasing? I'd guess that
the texture is viewed so small that POV simply can't display it properly,
and in fact I can't really see why you'd want the texture to be so small
anyway...

The fact that it was displayed as usual after it was scaled 100 times
larger might appear to support this.

Hope that helps,

Matt

ir. R.M.A. Wieringa <wie### [at] natlabresearchphilipscom> wrote in article
<35C040E3.91C03D61@natlab.research.philips.com>...
> I stumbled upon this 'artifact' when I tried to use a bozo pattern:
> 
> 
> 
> #include "colors.inc"
> camera {
> 	location <0,1000,0>
>     direction <0,0,1>
>     look_at  <0, 0, 0>
> }
> light_source { <0,30000,0> color White }
> plane { y, 0 pigment { bozo scale .01}}
> 
> 
> gives different color patterns in four quadrants.
> Any idea?
> 
> -- 
> +------------------------------------------------------+
> | Rob Wieringa                                         |
> | Philips  Research  Laboratories   Eindhoven          |
> | __X__: remove this from email address                |
> | email: wie### [at] natlabresearchphilipscom          |
> +------------------------------------------------------+
>

Post a reply to this message

Aliasing comes from decimation of fields with large
scale correlations.  If bozo is truly random, it would
be impossible to get aliasing effects at any magnification.
However, pseudorandom number generators have finite domain over
which they behave in a pseudorandom fashion, and it appears
the extensive magnification used here has revealed the
limits of the one used here.

Dan


Matthew Bennett wrote:
> 
> It seems you're viewing the bozo pattern from so far away, and scaled so
> small, that perhaps these effects are caused by aliasing?
> > camera {
> >       location <0,1000,0>
> >     direction <0,0,1>
> >     look_at  <0, 0, 0>
> > }
> > light_source { <0,30000,0> color White }
> > plane { y, 0 pigment { bozo scale .01}}

-- 
http://www.flash.net/~djconnel/

Post a reply to this message

I noticed that ALL patterns have a default colormap.
Older pigment patterns, written before 3.02 (where any pattern apply to 
normal, pigment, and tex_map (and media now)), have their own default
coloured map : try wood, agate, marble,...
Newer ones have a grayscale map as default.

Cheers,
Fabien.

Post a reply to this message

All colormaps have that default if none is specified.  Just like checker
uses two default colors if the colors aren't specified in the correct
manner.  I didn't get the chance to render that scene, but I think this may
be what you are talking about.  I think it was introduced in one of the
latter versions of 3.01 (or there abouts).  Hope that helps (i.e.  just add
a color_map to fix the problem).

--
Lance Birch
http://come.to/the.zone
Remove the smiley to e-mail.

Post a reply to this message