Smart Projector
We have developed a smart projector that can automatically sense its orientation with respect to a vertical or horizontal surface. The goal is a self-correcting projector to generate a rectangular image of known aspect ratio, even when aimed at an arbitrarily inclined planar surface. Furthermore, for a vertical or near-vertical display surface, the sides of the rectangle should be aligned appropriately with the world vertical. The projector is augmented with a rigidly attached camera and a tilt sensor. We exploit the homography between the projected image and the displayed image for keystone correction. By sensing the relative orientation between the screen and the projector, we can pre-warp the image so that it appears rectangular when projected. In addition to efficient pre-warping rendering methods, we have developed new techniques to calibrate the camera, projector and tilt-sensor system.
Background & Objective: A self-correcting projector that always displays a rectangular image is a desirable feature of every intelligent projector. We can eliminate the cumbersome procedure of aligning a projector with respect to a screen and make it very easy to install and use. Our approach is unique due to two features. First, we can project on blank walls i.e. without fixed markers to create two-dimensional Euclidean frame of reference. Second, we use a single self-contained device. Hence, we avoid the use of devices that are external to the projector, such as calibrated cameras mounted at known locations.
Technical Discussion: The tilt-sensors detect the out-of-vertical-plane orientation of the projector lens. Further, the camera detects the shift in the horizontal plane. The measured orientations lead to the well known 8-parameter planar homography which can be used represent the relationship between original image and the keystoned displayed image. We use an inverse of that relationship to pre-warp the image. Currently, the pre-warping is achieved in real time using 3D graphics hardware.
Technology Area: Graphics
Modification Date: July 7, 2008