A calibration image including dots and scale points is projected at first and second display surfaces. A location of a scale point may be modified. A location for a registration point is determined and the registration point is added to the calibration image. The projected calibration image is captured. A location of the captured registration point and locations captured scale points are identified. Captured dots that are projected onto the first display surface and their locations are identified. Each of the captured dots identified as being projected onto the first display surface are mapped to a corresponding dot of the calibration image. Dots of the calibration image that are not projected onto the first display surface are identified, locations of each of the identified dots are determined, and a synthetic dot is added to the captured image for each identified dot. The captured image may be provided as input to a process for determining one or more inverse offsets.