Cornell Box
Encyclopedia
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. 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.
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 basic environment consists of:
Objects are often placed inside the box. The first objects placed inside the environment were two white boxes. Another common version first used to test photon mapping
includes two spheres: one with a perfect mirror
surface and one made of glass
.
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.
Today, the Cornell Box is often used to show off renderers in a similar way as the Stanford Bunny
, the Utah teapot
, and Lenna
: computer scientists often use the scene just for its visual properties without comparing it to test data from a physical model.
Rendering (computer graphics)
Rendering is the process of generating an image from a model , by means of computer programs. A scene file contains objects in a strictly defined language or data structure; it would contain geometry, viewpoint, texture, lighting, and shading information as a description of the virtual scene...
software by comparing the rendered scene with an actual photograph
Photograph
A photograph is an image created by light falling on a light-sensitive surface, usually photographic film or an electronic imager such as a CCD or a CMOS chip. Most photographs are created using a camera, which uses a lens to focus the scene's visible wavelengths of light into a reproduction of...
of the same scene. It was created by Cindy M. Goral, Kenneth E. Torrance, Donald P. Greenberg
Donald P. Greenberg
Donald Peter Greenberg is the Jacob Gould Schurman Professor of Computer Graphics at Cornell University.Greenberg earned his undergraduate and Ph.D. degrees from Cornell University, where he played on the tennis and soccer teams and was a member of Tau Delta Phi and the Quill and Dagger society...
, and Bennett Battaile at the Cornell University
Cornell University
Cornell University is an Ivy League university located in Ithaca, New York, United States. It is a private land-grant university, receiving annual funding from the State of New York for certain educational missions...
Program of Computer Graphics for their paper Modeling the Interaction of Light Between Diffuse Surfaces published and presented at SIGGRAPH
SIGGRAPH
SIGGRAPH is the name of the annual conference on computer graphics convened by the ACM SIGGRAPH organization. The first SIGGRAPH conference was in 1974. The conference is attended by tens of thousands of computer professionals...
'84.
A physical model of the box is created and photographed with a CCD camera
Charge-coupled device
A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...
. The exact settings are then measured from the scene: emission spectrum
Emission spectrum
The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted by the element's atoms or the compound's molecules when they are returned to a lower energy state....
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 basic environment consists of:
- One light source in the center of a white ceiling
- A greenGreenGreen is a color, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 520–570 nanometres. In the subtractive color system, it is not a primary color, but is created out of a mixture of yellow and blue, or yellow and cyan; it is considered...
right wall - A redRedRed is any of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 630–740 nm. Longer wavelengths than this are called infrared , and cannot be seen by the naked eye...
left wall - A whiteWhiteWhite is a color, the perception of which is evoked by light that stimulates all three types of color sensitive cone cells in the human eye in nearly equal amounts and with high brightness compared to the surroundings. A white visual stimulation will be void of hue and grayness.White light can be...
back wall - A white floor
Objects are often placed inside the box. The first objects placed inside the environment were two white boxes. Another common version first used to test photon mapping
Photon mapping
In computer graphics, photon mapping is a two-pass global illumination algorithm developed by Henrik Wann Jensen that solves the rendering equation. Rays from the light source and rays from the camera are traced independently until some termination criterion is met, then they are connected in a...
includes two spheres: one with a perfect mirror
Mirror
A mirror is an object that reflects light or sound in a way that preserves much of its original quality prior to its contact with the mirror. Some mirrors also filter out some wavelengths, while preserving other wavelengths in the reflection...
surface and one made of glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
.
The physical properties of the box are designed to show diffuse interreflection
Diffuse reflection
Diffuse reflection is the reflection of light from a surface such that an incident ray is reflected at many angles rather than at just one angle as in the case of specular reflection...
. 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.
Today, the Cornell Box is often used to show off renderers in a similar way as the Stanford Bunny
Stanford Bunny
The Stanford Bunny is a computer graphics 3D test model developed by Greg Turk and Marc Levoy in 1994 at Stanford University.The Bunny consists of data describing 69,451 triangles determined by 3D scanning a ceramic figurine of a rabbit. The data can be used to test various graphics algorithms;...
, the Utah teapot
Utah teapot
The Utah teapot or Newell teapot is a 3D computer model which has become a standard reference object in the computer graphics community. It is a mathematical model of an ordinary teapot of fairly simple shape, which appears solid, cylindrical and partially convex...
, and Lenna
Lenna
Lenna or Lena is the name given to a 512 x 512 pixel standard test image originally cropped from the centerfold of November 1972 issue of Playboy magazine. It is a picture of Lena Söderberg, a Swedish model, shot by photographer Dwight Hooker...
: computer scientists often use the scene just for its visual properties without comparing it to test data from a physical model.
See also
- 3D modeling3D modelingIn 3D computer graphics, 3D modeling is the process of developing a mathematical representation of any three-dimensional surface of object via specialized software. The product is called a 3D model...
- Utah teapotUtah teapotThe Utah teapot or Newell teapot is a 3D computer model which has become a standard reference object in the computer graphics community. It is a mathematical model of an ordinary teapot of fairly simple shape, which appears solid, cylindrical and partially convex...
- Stanford BunnyStanford BunnyThe Stanford Bunny is a computer graphics 3D test model developed by Greg Turk and Marc Levoy in 1994 at Stanford University.The Bunny consists of data describing 69,451 triangles determined by 3D scanning a ceramic figurine of a rabbit. The data can be used to test various graphics algorithms;...
- Suzanne (3D model)
- List of common 3D test models