Carnegie Mellon University
Smarter Presentations: Exploiting Homography in Camera-Projector Systems

Rahul Sukthankar, Robert Stockton, and Matthew Mullin
Proceedings of the International Conference on Computer Vision, 2001.

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Standard presentation systems consisting of a laptop connected to a projector suffer from two problems: (1) the projected image appears distorted (keystoned) unless the projector is precisely aligned to the projection screen; (2) the speaker is forced to interact with the computer rather than the audience. This paper shows how the addition of an uncalibrated camera, aimed at the screen, solves both problems. Although the locations, orientations and optical parameters of the camera and projector are unknown, the projector-camera system calibrates itself by exploiting the homography between the projected slide and the camera image. Significant improvements are possible over passively calibrating systems since the projector actively manipulates the environment by placing feature points into the scene. For instance, using a low-resolution (160x120) camera, we can achieve an accuracy of $\pm$3 pixels in a 1024x768 presentation slide. The camera-projector system infers models for the projector-to-camera and projector-to-screen mappings in order to provide two major benefits. First, images sent to the projector are pre-warped in such a way that the distortions induced by the arbitrary projector-screen geometry are precisely negated. This enables projectors to be mounted anywhere in the environment -- for instance, at the side of the room, where the speaker is less likely to cast shadows on the screen, and where the projector does not occlude the audience's view. Second, the system detects the position of the user's laser pointer dot in the camera image at 20Hz, allowing the laser pointer to emulate the pointing actions of a mouse. This enables the user to activate virtual buttons in the presentation (such as ``next slide'') and draw on the projected image. The camera-assisted presentation system requires no special hardware (aside from the cheap camera) and runs on a standard laptop as a Java application. It is now used by the authors for all of their conference presentations.

projector camera system, computer vision, multi-view geometry

Associated Center(s) / Consortia: Vision and Autonomous Systems Center

Text Reference
Rahul Sukthankar, Robert Stockton, and Matthew Mullin, "Smarter Presentations: Exploiting Homography in Camera-Projector Systems," Proceedings of the International Conference on Computer Vision, 2001.

BibTeX Reference
   author = "Rahul Sukthankar and Robert Stockton and Matthew Mullin",
   title = "Smarter Presentations: Exploiting Homography in Camera-Projector Systems",
   booktitle = "Proceedings of the International Conference on Computer Vision",
   year = "2001",