High resolution micrographs are often of poor quality, due to a variety of distortions and especially due to a very low signal-to- noise ratio. For micrographs of quasi-periodic arrays or sets of images of ostensibly identical free-standing particles, visual quality can be improved significantly by using correlation- averaging techniques. We have improved algorithms that we have previously developed for the translational and rotational alignment of different views of ostensibly identical specimens and for the compensation of spatial deformations in quasi-periodic crystalline structures. We have developed a technique for the quantitative assessment of spatial resolution that is equally applicable to periodic and non- periodic structures. This approach is based on the estimation of a spectral signal-to-noise ratio. These methods have been applied successfully to structure determination and quantitative assessment of T7 Virus. They are currently being used for the analysis of micrographs of skeletal muscle filaments in both relaxed and rigor state.
