EMAIL: bobzien@acpub.duke.edu
NAME: William Bobzien
TOPIC: Physics & Math
COPYRIGHT: I SUBMIT TO THE STANDARD RAYTRACING COMPETITION COPYRIGHT.
TITLE: "Full Spectrum"
COUNTRY: USA
RENDERER USED: POV-Ray 3.01 for Windows
TOOLS USED: Paint Shop Pro 4.12 (JPEG conversion and signature)
RENDER TIME: 9 minutes 17 seconds
HARDWARE USED: P166, 16 Mb RAM

IMAGE DESCRIPTION:
The classic high-school optics demonstration: a beam of white light is
narrowed by a card with a slit in it and then strikes a prism; because
the shape and refractive qualities of the prism bend the wavelengths by
different amounts, the light is split into its component colors, which
show up as a spectrum on another card.

DESCRIPTION OF HOW THIS IMAGE WAS CREATED:
All objects in this scene are either primitives or CSG objects.

Ironically for a ray-traced image (and one about the properties of
light, no less), there are no lights in this scene! As I recall from my
(ever more distant) high-school days, this type of demonstration works
best in a darkened room. Of course, no classroom can be made easily
light-tight, so some dim illumination creeps in from under doors,
between the slats in the window blinds, etc. At first, I had a dim
spotlight shining down on the demonstration, but I couldn't keep it from
looking like, well, a light shining down, so I eliminated it and just
started playing with ambients. That only worked so well, with all areas
of each object equally bright (i.e. flat-looking objects), so I finally
got around to trying out texture_maps, to vary the ambient level across
the objects. The worst problem with dropping the light was that I lost
the pebbled surface on the body of the "light source" that I had created
with a normal perturbation. With the light it looked just like the rough
surface I remembered from similar equipment in school, but I was only
able to imitate the look with ambient tricks, not duplicate it. I also
lost the nice phong highlight on the "lens." It was a case of increasing
realism in one area by decreasing it in another.

Initially, I had a spotlight shining from the light source to the "slit
card," which worked great, right up to the part where it plowed through
the "prism" like it wasn't there and kept going. So I dropped that light
too. I used halos at first for the "beam" and the horizontal "spectrum,"
but they didn't work any better than using gradients, at least not when
one considers the increase in rendering time. Also, it was hard matching
the horizontal spectrum halos to the gradient I was already using, out
of necessity, for the vertical component of the spectrum. So I
eventually went to gradients for everything that was supposed to be a
"light."

I had a lot of fun creating this image, and learned a lot as well about
texture and pigment patterns. For example, I had never used the 
"onion" pattern before this image. I deliberately avoided using "canned"
textures from textures.inc etc. I did mostly use pre-defined pigments
from colors.inc.