15. An imaging system comprising: a plurality of optical elements configured to image a plurality of objects, wherein the optical elements generate a point spread function, and wherein the point spread function changes as a function of the axial location of the plurality of objects; an imager configured to image the plurality of objects located onto an image plane; a memory including a point spread function dictionary that includes a plurality of point spread function responses that each correspond with a different position of an object; and a processor configured to estimate a plurality of point spread function dictionary coefficients of an image of the plurality of objects using the point spread function dictionary and determine the number and/or position of objects in the image using the point spread function dictionary coefficients.
19. The system according to claim 15 , wherein the point spread function dictionary comprises a plurality of point spread function responses that correspond with a three-dimensional spatial position of the objects.