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Special Project: Making the Pixie

The Digital Scene I

The three dimensional scene was created using modelling and raytracing software called Bryce. This software has been available on the Macintosh for about five years, and is now available to users of Windows 95 and others. Use of the software involves building a digital representation of the scene - a model - using geometric primitives such as spheres, cubes, cylinders, cones, etc. These primitives can be stretched and rotated into any position, thus allowing the construction of complex forms. As the model is built, surface colors and textures are specified for each object - including reflectivity, transparency, indices of refraction... Thus are built sky, clouds, hills in the distance, pussy-willows, flowers, grasses, water lilies, the rippled surface of the water, and even the pebbly bottom of the lake sloping away from the observer.

 Final image composition of this digital world is done in a manner very similar to photography. The software gives the user control over the position, intensity, and color of a number of lights. Sometimes panels or flags are used to control reflections. A virtual camera can be moved and pointed in any desired direction. An effective focal length is selected to set the field of view. Finally a stereo pair of images is generated by rendering the scene from two separate camera locations.

In the case of the Pixie, however, each of the left and right renderings of the scene would also include this imported photo panel, a flat object displaying the corresponding left and right image scan of the stereo photograph of the pixie's figure. The image on these panels would not simply appear "pasted into" the rendering, but also interact with the model, such as reappearing as a reflection. (figure 2a + 2b).


Next: Photography I

What is raytracing software?

In it's earliest manifestations, computer art was just simple line art. But ever increasing computing power led eventually to a process called ray-tracing, which would at first be utilized on super-computers (in the early 1980s) to create near photo-realistic images of scenes (3-d models) resident entirely within the digital memory of the computer.

Nowadays, such software is readily available for desktop personal computers. A raytraced image is called a rendering, and consists of an array of pixels of different values, not unlike the scan of a photograph. Each rendering is the sum of billions of operations, as the computer calculates the brightness and color of each of millions of pixels in the image. The time needed to complete a rendering is a function of the final size of the image (i.e. the number of pixels needed), 3-d model complexity, surface texture complexity within the model, number of light sources, and other variables.

Most of my digital images are 2400 by 1800 pixels and take from five to twenty hours to render on a Powermac 8500/120 (and that's just for one image of two per stereo pair. For those unfamiliar with Macs, the 8500, though five years old now, is still faster than most Pentium PCs running this software). After the image file is rendered, it is taken to a service bureau on a floppy, which makes a slide using a film recorder.


Figure 2. As seen from a "remote" location: a. computer wireframe of scene, and b. rendering of same.

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