A processing system for an input device includes a sensor module, a filter module, and a determination module. The sensor module is configured to drive a plurality of transmitter electrodes with transmitter signals; receive, with a plurality of receiver electrodes, resulting signals comprising effects corresponding to the transmitter signals; and produce a first sensor image based on the resulting signals. The filter module is configured to produce a transformed sensor image by applying a spatial filter to the first sensor image. The determination module is configured to positional information and/or the validity of a baseline for the input device based on the transformed sensor image.