Recent, striking examples of x-ray image sharpening are based on Fresnel edge diffraction. A simple model shows that image sharpening can be achieved under less stringent conditions as could be thought. The extreme spatial coherence of third-generation synchrotron sources appears helpful but not strictly necessary, and high time coherence is not an essential requirement. These conclusions, consistent with the results of other authors, strongly enhance the potential impact in medical x-ray applications, materials science and other fields. (C) 1999 American Institute of Physics. [S0021-8979(99)01107-X].