1. A system for single step x-ray imaging, comprising: a clinical x-ray source; a first coded aperture mask disposed between the x-ray source and an object to be imaged; a photon counting spectral detector disposed to detect x-rays passing through the object; a second coded aperture mask disposed between the object to be imaged and the photon counting spectral detector; and an image processing system configured to generate a differential phase contrast image of the object based on output of the photon counting spectral detector; wherein the image processor is configured to model the intensity of the x-rays at the photon counting spectral detector as: I ⁡ ( R , E ) = I ⁡ ( 0 , E ) - R k ⁢ I ⁡ ( 0 , E ) ⁢ ϕ ′ ⁡ ( x ) .