Quantifying performance of overlapped displays

We consider two physical systems where overlapped displays are employed: (1) Wobulation -a single projector that rapidly shifts the entire display in time by a subpixel amount; (2) Several projector displays overlaid in space with a complex array of space-varying subpixel offsets. In this work we focus on quantifying the resolution increase of these approaches over that of a single projector. Because of the nature of overlapping projections with different degrees of prospective distortion, overlaid pixels have space-varying offsets in both dimensions. Our simulator employs the perspective transformation or homography associated with the particular projector geometry for each subframe. The resulting simulated displays are stunningly accurate. We use "grill" patterns to assess the resolution performance that vary in period, phase, and orientation. A new Fourier-based test procedure is introduced that generates repeatable results that eliminate problems due to phase and spatial variation. We report on results for 2 and 4 position wobulation, and for 1, 2, 4, and 10 overlaid projectors using the frequency-domain based contrast modulation metric. The effects of subpixel phase are illustrated for various grill periods. The results clearly show that resolution performance is indeed improved for overlapped displays.