Image restoration for biological objects using external TEM control and electronic image recording

Abstract

Image restoration of low-contrast biological specimens resulting in an extended transfer range in the Fourier domain can be obtained from a small number of images of the same object area, recorded at defocus values ranging from small to rather strong underfocus (or under- and overfocus). External TEM control and electronic image recording greatly facilitate the application of this method. A carbon-film specimen, and proteasome particles embedded in vitreous ice, have been used as test objects. It was found that defocusing alters the magnification of the images. Correction for the magnification changes and for sign reversals of the phase contrast transfer function significantly improves the cross-correlation peak and thus the alignment of the images. After these corrections the correlation peak was recognizable even in cross-correlation functions between close-to-focus and stronger-defocused images of the ece-series. In the phase part of the restored image of the frozen-hydrated sample, details become visible which cannot be recognized in any of the original images. Some problems and further developments are discussed.