# The Stanford Bunny

The Stanford Bunny is one of the most commonly used test models in computer graphics. It is a collection of 69,451 triangles, and it was assembled from range images of a clay bunny that is roughly 7.5 inches high. Below is a synthetic rendering of the model, courtesy of Peter Lindstrom. This Web page describes where the model came from, tells why it was created in the first place, discusses the relative merits of using it as a test model in graphics research, and shows some example images.

## Range Scanning

The Bunny was created using a technique that I developed together with Marc Levoy to create polygonal models from several range scans. Our original paper on this technique is:
"Zippered Polygon Meshes from Range Images"
Greg Turk and Marc Levoy
Siggraph 94, pp. 311-318
on-line version of paper available here
Before we talk about the bunny itself, it is worth understanding what range scans are. A range scan is a grid of distance values that tell how far the points on a physical object is from the device that creates the scans (usually known as a range scanner). One way to think of a range scan is as a 2D image of pixels, but in which each pixel contains a distance value instead of a color. In fact, one common way to examine a range image is to draw it as a black-and-white image, with shorter distances shown as bright pixels and farther distances being darker. It is usually necessary to piece together several range scans in order to capture the full geometry of an object.

The particular range scanner that we used for our project was built by a company called Cyberware. The technique that the Cyberware scanner uses to make a range image is to move an object through a sheet of bright red laser light. The sheet of laser light is created by sending a laser beam through a cylindrical lens. Below is a schematic diagram of a scanner. A video camera (not shown in diagram) observes the object as it passes through the sheet of light, and this camera is tuned to the particular wavelength of light from the laser. The camera sees a ribbon of light that wiggles as the object (such as a vase or a bunny) moves through the sheet of laser light. One such image from the camera is drawn at the right in the figure below. The range scanner examines one row of pixels in such an image, and the position of the brightest part of the ribbon gives a measure of distance (or depth) of the object from the source of laser light. One such depth value is placed at grid position in a range image. A single image from the camera yields a column of range image distance values, and putting together all such columns (as the object moves throught the light) gives a complete range image.

It is important to note that in order for an object to be visible to the camera of the range scanner, its surface must reflect the red laser light. A black object cannot be scanned, and even a bright blue or green object may not scan well if it reflects little in the red wavelengths. In addition, objects that are very shiny (specular) will sometimes cause parts of an object to be indirectly illuminated through reflection, and this results in false depth readings. For this reason, I was on the lookout for objects to scan that reflected red light well and that were diffuse (non-shiny). In addition, I knew the limitations of our current algorithm in terms of the geometric complexity of the models that we could work with. I wanted to find objects that were fairly smooth and that did not have a whole lot of intricate folds and holes.

## Bunny Origin

I was a postdoc at Stanford University with Marc Levoy in 1993 and 1994. One day, close to the Easter holiday, I was out shopping on University Avenue near the Stanford campus. I entered a shop that sold various decorative items for the home and garden. On one of the shelves of the store was a large collection of clay bunny rabbits, all identical. I had range scanning on my mind, and these bunnies looked to be about the right shape and size for our scanning project. Even better, these bunnies were made of terra cotta (red clay), so they were red and diffuse. I bought one of these bunnies. Had I known how popular the digital model would become, I would have bought many! I brought this clay bunny back to the Stanford Graphics Lab and scanned it from several directions. Using the methods that Marc and I developed, I aligned a collection of ten such range scans to one another and merged them into a single polygonal mesh. The resulting model has come to be known as the Stanford Bunny. The original bunny still lives at Stanford.

Below is a color image of the original bunny, courtesy of Marc Levoy.

## Research Bunny

As mentioned above, the Stanford Bunny has been used extensively as a test model for various research projects in computer graphics. Topics of some of the research articles that use the bunny include polygonal simplification, compression, surface smoothing, non-photorealistic rendering, and texture mapping. But is it really a good idea to use the bunny for graphics research? I actually consider the bunny to be too good as a test model. It is fairly smooth, it has manifold connectivity, and it isn't too complex (69,451 triangles is small by today's standards). The bunny is so smooth that there is a lot of redundant information in the original collection of triangles, so simplification and compression algorithms give wonderful results. I bought the original bunny in part because it was not complex geometrically. About the only bad thing about the model is that there are five holes in it. Three of these holes (one under the chin and two on the base) result from not having scans to cover these locations, and two holes in the base are really there in the original clay model -- the bunny is hollow.

My opinion is that the bunny makes a nice object to start with, but one should also use more difficult models to really challenge one's algorithms. Here are some places to look for larger models:

It was Marc Levoy's idea to make the original bunny model publically available, and the first of the Web sites above is the original distribution site. Recently, Marc and his students spent a year in Italy scanning the statues of Michelangelo, and some of the models from this project are at their site, listed above. At least part of the motivation for this recent project of Marc's is to make available to the graphics community more challenging models than the bunny.

## Bunny Images

Even though I have suggested that researchers shouldn't use the bunny too much, I cannot resist including some of my favorite bunny pictures from various research papers. Below are some of the more entertaining images of the bunny, along with pointers to the papers in which they appear.

"Simplification Envelopes"
Jonathan Cohen, Amitabh Varshney, Dinesh Manocha, Greg Turk, Hans Weber,
Pankaj Agarwal, Frederick Brooks, William Wright
Siggraph 1996, pp. 119-128

"Art-Based Rendering of Fur, Grass and Trees"
Michael A. Kowalski, Lee Markosian, J.D. Northrup, Lubomir Bourdev,
Ronen Barzel, Loring S. Holden and John F. Hughes
Siggraph 1999, pp. 433-438

Image appears in
"Animating Fracture"
James F. O'Brien and Jessica K. Hodgins
Communications of the ACM
Vol. 43, No. 7, July 2000
Algorithm published in
"Graphical Modeling and Animation of Brittle Fracture"
James F. O'Brien and Jessica K. Hodgins
Siggraph 1999, pp. 137-146

"Lapped Textures"
Emil Praun, Adam Finkelstein, and Hugues Hoppe
Siggraph 2000, pp. 465-470
(This image also appears on the proceedings cover.)

"Real-Time Fur over Arbitrary Surfaces"
Jed Lengyel, Emil Praun, Adam Finkelstein, and Hugues Hoppe
ACM Symposium on Interactive 3D Graphics
Research Triangle Park, North Carolina, 2001
pp. 227-232

"Melting and Flowing"
Mark Carlson, Peter Mucha, Brooks Van Horn III, and Greg Turk
ACM Symposium on Computer Animation
San Antonoi, Texas, July 21-22

Lego bunny (pattern and photo). Design by Andrew P. Van Pernis of Clemson University.

This page was written by Greg Turk , August 2000.