[Method for direct determination of the rotational symmetry of thick muscle filaments by digital image processing]

We present a method based on digital image processing techniques that permits to determine directly the rotational symmetry of muscle thick filaments. Electron micrographs of transverse sections of relaxed muscle rapidly frozen against a copper block cooled with liquid helium were digitized, aligned to give maximal cross correlation and averaged. The final averaged image permits to determine directly the number of projections on the backbone surface.