EMAIL:         Thomas.Dahl@compaq.com
NAME:          Tom Dahl
TOPIC:         Contrast
COPYRIGHT:     I SUBMIT TO THE STANDARD RAYTRACING COMPETITION COPYRIGHT.
TITLE:         Illumination
COUNTRY:       USA
WEBPAGE:       http://www.gis.net/~crawdahl/ray_tracing.html
RENDERER USED: Self-written ray tracer
TOOLS USED:    Self-written object modeling code. Paper and pencil.
               Irfan View to convert from BMP to JPG.
RENDER TIME:   1d 17h 12m 36s
HARDWARE USED: Compaq AlphaServer ES40 running OpenVMS V7.3,
               Alpha EV6 667MHz CPU

IMAGE DESCRIPTION:

Color and colorlessness; light and shadow. As an amateur photographer,
these are some primary aspects of contrast for me. The prisms in this
scene combine with the controlled lights to reveal a world of such
contrasts.

DESCRIPTION OF HOW THIS IMAGE WAS CREATED:

The image was modeled and rendered with tools I've written from scratch
over the past 15 years or so. See my first IRTC entry, A Little
Paradise (litpdise.jpg from the July-August 2000 stills round) for a
summary of the renderer.

This scene depends heavily on the caustics (forward ray tracing)
capability in the renderer. There are seven white light sources: one in
each of the six slit-lamps, and a general one overhead. The long
rendering time is largely a result of the caustics pre-computations.
The spectra are automatically generated by the renderer, based on the
scene geometry and the properties of the refracting glass.

The white light is modeled at five discrete wavelengths. The glass has
a wavelength-dependant index of refraction. The result yields a
reasonably smooth spectrum, so long as the caustic photon distribution
is relatively dense, and the dispersed light rays aren't cast over a
long distance (which would reveal the discrete bands, like an emission
spectrum).

The ground plane, the central sculpture, and the lamp innards are white.
The overhead light is fairly dim, making everything appear dark except
where light from the high intensity slit lamps falls. The lamps shine
through slits so as to aim their light which is then refracted through
the prisms. The overhead light itself creates interesting reflections
and refractions off the prisms.

The ground plane wrinkle texture is procedurally generated in the
renderer, as is the slightly mottled brass on the lamp housings.

All of the geometry was created via a C program I wrote which defines
primitive triangles, parallelograms, disks, and sections of cones to
form all of the shapes. About half of the primitives are consumed in
the screwheads and hex nuts in the lamps. Most of the rest come from the
signature in the corner (which is part of a 3D font I hand-defined
previously).

The image was rendered with a minimum of 16 root days per pixel, for
spatial anti-aliasing and smooth shadows.

      Spheres in scene: 0
 (P)Triangles in scene: 14774
     (P)Quads in scene: 489
     (P)Rings in scene: 50
     (P)Cones in scene: 247
Fractal faces in scene: 0
   Invisibles in scene: 0
 Total visible objects: 15560
         Total extents: 501
        Total pixels computed: 640000
        Total caustic objects: 7272
           Total caustic rays: 348015894 (347876624 interceptions/misses, 99.96%)
           Total caustic hits: 441070 (20937297 summations)
         Total K-D tree cells: 130303 (abandoned 0, max depth 18)
            Total rays traced: 471081044
  Average root rays per pixel: 16.30, Max: 128
 Average total rays per pixel: 736.06
  Max intersections for 1 ray: 25
            Total depth sorts: 386574548
      Average depth sort size: 3.39
Pre-computation time (dhms) 1:06:29:27
        Elapsed time (dhms) 1:17:12:36