Issue No.08 - August (2006 vol.39)
Published by the IEEE Computer Society
DOI Bookmark: http://doi.ieeecomputersociety.org/10.1109/MC.2006.251
Computational Cameras: Redefining the Image
Shree K. Nayar
Computational cameras use unconventional optics and software to produce new forms of visual information. This concept can be taken one step further by using controllable optics to realize programmable imaging systems that can change their functionalities based on the needs of the user or the application. Finally, using a programmable illumination source as a camera flash offers many benefits.
Ultimately, the success of these concepts will depend on technological advances made in imaging optics, image detectors, and digital projectors. If progress in these fields continues at the remarkable pace we have seen in the past decade, we can expect the camera to evolve into a more versatile device that could further impact the ways in which we communicate with each other and express ourselves.
The Moment Camera
Michael F. Cohen and Richard Szeliski
When coupled with computation and a user interface, digital cameras can bring back the ability to capture moments as opposed to just instantaneous snapshots. Such computational cameras or computational photography systems can provide a wealth of opportunities for both professional and casual photographers.
The hypothetical moment camera contains new light-capture modalities that can leverage several recent research developments in computer graphics, computer vision, and the subfield at their intersection, image-based rendering. Future cameras might have even more advanced capabilities. For example, cameras that notice when someone is smiling are already being developed. Future cameras could suggest better ways to frame a scene and indicate that we should back up or point the camera just a bit higher.
Light Fields and Computational Imaging
From borehole tomography in geophysical exploration to confocal microscopy in the biological sciences, the use of computers during image formation has revolutionized our ability to observe and analyze the natural and manmade worlds. Many of these imaging methods operate at visible wavelengths, and many of those relate to the flow of light through space.
Arun Gershun defined the light field concept, which gives the amount of light traveling in every direction through every point in space. Gershun recognized that the amount of light arriving at points in space varies smoothly from place to place and could therefore be characterized using calculus and analytic geometry.
With the advent of computers, color displays, and inexpensive digital sensors, we can now record, manipulate, and display Gershun's light field. Researchers have used these fields to fly around scenes without creating 3D models of them, relight these scenes without knowing their surface properties, refocus photographs after they've been captured, create nonperspective panoramas, and build 3D models of scenes from multiple images of them.
Virtual Cinematography: Relighting through Computation
Modern photographic techniques have made it possible to capture considerably more information about the light in a scene. Color photography records another dimension of information: the amount of incident light for a range of wavelengths. We can thus describe a color image as a 3D function. Motion pictures record how the incident light changes with time, adding another dimension to our function. Most of the photographic imagery we view today records and reproduces light across all these dimensions, providing an even more compelling virtual experience of scenes from other times and places.
There is something new and exciting in the ability to record relightable imagery of people, objects, and environments. Instead of having just photographs, we have a more immediate representation that we can relight and reinterpret in a new creative vision, taking a step closer to having preserved the subject itself. While these new techniques can never rival the original impact of photography, the quality of seeing a person's face virtually reflecting the light of a cathedral she has never been to must certainly contain a small and distant echo of the magic in the first photograph.
Collaborative Spam Filtering Using E-Mail Networks
Joseph S. Kong, Behnam A. Rezaei, Nima Sarshar, Vwani P. Roychowdhury, and P. Oscar Boykin
The tremendous convenience that e-mail affords comes at a high price: Although the network's underlying connectivity is hidden, making it almost impossible to build a comprehensive directory of every individual's contact lists, e-mail addresses themselves can be easily obtained from publicly available documents.
One promising approach to beat spammers harnesses the same e-mail network and service infrastructure that they exploit. The authors have developed a system that lets users query all of their e-mail clients to determine if another user in the system has already labeled a suspect message as spam. Because the network is latent, the system is message-based and distributed, enabling users to query for information without flooding the network.