1. A method for point spread function modeling of a multi-channel collimator in photon imaging, the method comprising: determining a geometric aperture as a function of an entrance hole or an exit hole of the multi-channel collimator scaled based on geometric constants; broadening the geometric aperture with a factor that is a function of a distance from a source to the multi-channel collimator, the broadening of the geometric aperture providing an effective aperture; computing a point spread function that is a function of a correlation of the effective aperture with another aperture of the multi-channel collimator; and imaging as a function of the point spread function.