Automatic Keystone Correction for Camera-Assisted Presentation Interfaces

Abstract

Projection systems have become the ubiquitous infrastructure for presentation technology. However, unless the projector is precisely aligned to the presentation screen, the resulting image su.ers from perspective (keystone) distortions requiring manual optical or digital correction. This tedious process must be repeated whenever the projector or screen is moved and is increasingly relevant given the emerging trend towards highly-portable LCD projection systems. This paper presents a presentation interface that pre-warps the image to be projected in such a way that the distortions 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 automatically determine the pre-warping parameters. This vision-based system is augmented with a natural interface that enables the user to interactively re.ne the suggested recti.cation. Arbitrary distortions due to projector placement are negated, allowing the projector (and camera) to be placed anywhere in the presentation room - for instance, at the side rather than the center of the room. Our solution works with existing projector hardware, and could easily be incorporated into the next generation of LCD projector systems.

Rahul Sukthankar is now with Carnegie Mellon University and Compaq Cambridge Research Lab. Robert Stockton and Matthew Mullin are now with WhizBang! Labs.

In related work, “keystoning” refers speci.cally to a symmetric, trapezoidal distortion caused by projector pitch misalignment. Here, the term refers to the broader class of distortions caused by any misalignments in projector position or orientation.