AN IMAGE-PROCESSING APPROACH TO CRYSTAL-STRUCTURE DETERMINATION

An approach to crystal structure determination based on a single high- resolution electron microscope image and the corresponding electron di ffraction pattern is introduced. The procedure contains two parts -- i mage deconvolution and image resolution enhancement. The first part is to transform the image taken at an arbitrary defocused condition into the structural image by image deconvolution. The resolution of the de convoluted image is limited by the resolution of the electron microsco pe so that only part of the atoms can be seen. The second part is to e nhance the resolution of the deconvoluted image to about 1 Angstrom so that all non-overlapped atoms can be resolved. The principle of the m ethod is briefly described and the application to a conventional cryst al structure and an incommensurate modulated structure is demonstrated . Since the principle is based on the weak phase object approximation, the validity of the latter is discussed by means of an approximate im age contrast theory -- pseudo weak phase abject approximation -- befor e the principle of the method is introduced.