A 250 × 250 Active Pixel Sensor (APS) with on-chip spatiotemporal difference computation capabilities is presented. The spatiotemporal difference imager, fabricated in TSMC 0.35μ process, contains in-pixel storage elements for previous and current frames and difference computational units outside the imaging array. A novel scan out technique allows for parallel computation of spatial and temporal 1-D derivatives on read out. The final motion estimation, i.e. the ratio of the temporal and spatial derivates, is computed off chip, but it can be easily implemented in hardware. Experimental data is presented to validate the accuracy of the magnitude and angle of the computed target velocities. The chip consumes 20mW at 50 fps from 3.3V power supply.