It is pointed out that the images obtained by high-resolution electron microscopes is not always reflect the crystal structure directly, and the resolution of the structure image taken under a certain defocus condition is limited by the resolution of the electron microscope. The structure image with atomic resolution can be directly obtained only with the high-voltage high-resolution electron microscopes. The advantage of introducing diffraction analysis into high-resolution electron microscopy (HREM) is clarified,and an electron crystallographic image processing technique set up by combining the diffraction crystallography with HREM is introduced in the present paper. This technique makes realizable the ab initio crystal structure determination by HREM. It is shown that the resolution of the structure image obtained with a medium-voltage electron microscope can be enhanced up to the atomic resolution.Examples of applying this technique to the study of crystal structures and defects are given.