Automatic Keystone Correction for Camera-assisted Presentation Interfaces

Projection systems have become the ubiquitious infrastructure for presentation technology. How-ever, unless the projector is precisely aligned to the presentation screen, the resulting image suffersfrom perspective (keystone) distortions requiring manual optical or digital correction. This tediousprocess must be repeated whenever the projector or screen is moved and is increasingly relevantgiven the emerging trend towards highly-portable LCD projection systems. This paper presentsa presentation interface that pre-warps the image to be projected in such a way that the distor-tions induced by the projector-screen geometry precisely negate the warping. An uncalibrated,low-resolution digital camera is used to infer the projector-screen geometry and to automaticallydetermine the pre-warping parameters. This vision-based system is augmented with a natural in-terface that enables the user to interactively refine the suggested rectification. Arbitrary distortionsdue to projector placement are negated allowing the projector (and camera) to be placed anywherein the presentation room — for instance, at the side rather than the center of the room. Our solutionworks with existing projector hardware but it could easily be incorporated into the next generationof LCD projector systems. This interface has been integrated into a complete camera-assistedpresentation tool since December 1999, and has received very favorable feedback.