1. An electronic device comprising:a dielectric cover layer defining a finger sensing surface;
at least one optical image sensor below the dielectric cover layer;
at least one optical element associated with the at least one optical image sensor;
a plurality of light sources below the dielectric cover layer and selectively operable in subsets of light sources; and
a controller configured to sequentially operate the subsets of light sources in a first pass in a first direction, and in a second pass in a second direction transverse to the first direction while acquiring biometric image data from the at least one optical image sensor.