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Cornell Box Lecture S.Wilson Lecture Notes for Presentation titled: Cornell Box Lecture S.Wilson This lecture contains videos with audio, hookup A/V components prior to presentation. 1. Open slide. Which image is a photograph and which is a 3D render? Can you tell? 2. Realism is the goal: Hint: The image on the right is the photograph, the image on the left is a 3D recreation. 3. The Cornell University Program of Computer Graphics: The Cornell box is a test aimed at determining the accuracy of rendering software by comparing the rendered scene with an actual photograph of the same scene, and has become a commonly used 3D test model. It was created by Cindy M. Goral, Kenneth E. Torrance, Donald P. Greenberg, and Bennett Battaile at the Cornell University Program of Computer Graphics for their paper “Modeling the Interaction of Light Between Diffuse Surfaces” published and presented at SIGGRAPH'84. 4. Radiosity / Diffuse Interreflection: A physical model of the box is created and photographed with a CCD camera. The exact settings are then measured from the scene: emission spectrum of the light source, reflectance spectra of all the surfaces, exact position and size of all objects, walls, light source and camera. The same scene is then reproduced in the renderer, and the output file is compared with the photograph. The physical properties of the box are designed to show diffuse interreflection. For example, some light should reflect off the red and green walls and bounce onto the white walls, so parts of the white walls should appear slightly red or green. 5. Reference Image: The Cornell Box is based on a physical model that is photographed and measured for light readings. This information is programmed into the 3D simulations for accurate rendering. Our work final should represent the original as best as we can. 6. Reference Image: Certain details are the hallmark of a good Cornell Box: a. Radiosity: The red wall is reflected on the box next to it, the red “spills” onto the wall at the back. Similar with the green wall. b. Soft shadows, as realistic as possible.. shadows from a single light source. c. Ceiling light, for casting rays. d. Even lighting, not too dark or bright. e. Contoured objects in scene for evaluating reflections/material properties Our own work should contain all of these elements. 7. Test Render Video with Moving Light: This test render shows radiosity, and the moving light source shows true ray casting of shadows and highlights. 8. Comparison - Old vs New: On the left is the original Cornell Box presented in 1984, on the right is an example from 2009. While great advances in computational power have increased (Moores Law) render times have somewhat remained constant (Blinns Law). Because we demand more realism and higher quality, render times increase with our computing speed. 9. The Utah Teapot: This computer rendering of a standard white Melitta teapot as a 3D model has become the standard reference object for testing new applications. It is possibly the most famous data set in the world of computer graphics. The mathematical model was designed in 1975 by Martin Newell at the University of Utah. Newell made the mathematical data that described the teapot’s geometry publicly available. Soon other researchers began to use the same data for their computer graphics experiments, so they did not have to laboriously enter geometric data for some other object. 10. Teapotahedron - A Platonic Solid: Due to advances in technology, the act of rendering the teapot is no longer the challenge it was in 1975. Yet the teapot continues to be used as a reference object. Utah is considered to be the design equivalent to the “Hello, World” code as a way to create an easy 3D scene. The image above left is from1987. This is titled as “The Six Platonic Solids” and the joke emerged that the “Teapotahedron” is the elusive sixth platonic solid. FYI: In three-dimensional space, a Platonic solid is a regular, convex polyhedron. It is constructed by congruent (identical in shape and size) regular (all angles equal and all sides equal) polygonal faces with the same number of faces meeting at each vertex. Only five solids meet those criteria. 11. Video: How a Teapot Revolutionized Computer TRT: 2:41 12. Bonus Trivia: Jim Blinn 13. Final Slide: Today, the Cornell box is often used to demonstrate and evaluate renderers and can be capability pieces for animators to showcase their skills. In this lesson we will create and render our box with Raytracing. What will you place in your scene to demonstrate your quality rendering skills? Notice the teapots in this scene? In a future project we will use an advanced rendering system to demonstrate Radiosity! .
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