we present theoretical analyses and computer simulations for incoherent imaging through a thin slab waveguide of length land slit opening 2a. Such an optical channel has a spatially varying point spread function, which introduces severe distortion. we show that phase diversity imaging, where the diversity is introduced by a simple spatial shift of the object, can significantly reduce the distortion. The spatial shift diversity is new to the literature. The results are shown with and without noise at 8-bit pixel quantization and are compared with the diffraction-limited image caused by imaging through the slit aperture alone.