1. A method for determining correspondence between locations on a display surface having an arbitrary shape and pixels in an output image of a projector, comprising: projecting a set of known calibration patterns onto the display surface; sensing directly an intensity of light at each of a plurality of locations on the display surface for each calibration pattern, there being one discrete optical sensor associated with each location; and correlating the intensities at the locations to determine correspondences between the plurality of locations and pixels in an output image of the projector.