If the z coordinate is positive then the PSF image from a negative index
(below the z-centre) is used. If the z-coordinate is negative then the
PSF image from a positive index (above the z-centre) is used. I.e. the
input stack is assumed to be imaged axially with increasing z-stage
position moving the stage closer to the objective.
Changed default desnityRadius to 1000 nm
Changed random generator to one with a longer sequence.