Monitoring and correction of geometric distortion in projected displays

Abstract

Off-axis placement of light projectors induces significant planar parallax on the display surface. Although commodity solutions exist for removing this distortion, they involve iterative, menu-driven user interaction or physical alignment of the projector, and in either case interrupt the use of the display. User interaction is infeasible in a number of scenarios including mechanically aligned multi-projector displays that are subject to mechanical drift and situations in which projectors are often reconfigured.

We present a general technique for continuous rectification of arbitrary off-axis distortions that does not require user interaction. A camera automatically detects when the projector's orientation has changed, without requiring explicit fiducials or targets in the world. The method runs in concert with interactive display applications and has minimal impact on framerate. An initial rectifying transform is recovered automatically by projecting target points and observing them in the camera. The display is then warped and passively monitored for calibration error and motion of the projector. The technique distinguishes between distortions due to miscalibration and intentional framebuffer changes. A consistency score is measured by generating a predicted view based on the current framebuffer contents and correlating this prediction with the camera's captured image. Poor correlation scores indicate that the projector has moved and re-calibration and geometric correction is required. Initial experiments show that the calibration consistency measures are sufficiently robust to distinguish small motion of the projector from continuously changing imagery.