Image averaging by optical filtering

The theory of an optical method of image averaging suitable for use with electron micrographs containing regular arrays of like units is discussed, and the modification of a commercially available optical diffractometer for this purpose is described. By inserting suitable masks in the diffraction plane of the diffractometer, the superposition of any required number of individual units may be accomplished in the final image. In this way an “average image” is obtained with a consequent reduction in image “noise.” A variety of different types of averaging can be realized by appropriate design of the mask. Electron micrographs of a transverse section of α-keratin and a paracrystal of tropcmyosin are used as examples to illustrate the uses of the method.