Systems, methods, and computer program products are disclosed to localize and/or image a dense array of particles. In some embodiments, a plurality of particles may be imaged using an imaging device. A plurality of point spread function dictionary coefficients of the image may be estimated using a point spread function dictionary; where the point spread function dictionary can include a plurality of spread function responses corresponding to different particle positions. From the point spread function dictionary coefficients the number of particles in the image can be determined. Moreover location of each particle in the image can be determined from the point spread function dictionary coefficients.