Method for Processing of Periodic Images at Reduced Levels of Electron Irradiation

Abstract

Meaningful high resolution microscope of specimens that are sensitive to radiation damage is limited in resolution by considerations of statistics and contrast in the image. The product of contrast, C, and resolution, d, must satisfy the inequality where S/n is the minimum acceptable ratio of real contrast to statistical fluctuations in intensity, f is the fraction of electrons incident upon the specimen that actually contribute to image formation, and D min is the minimum dose or exposure that causes structural disorder at the resolution, d. While the value of S/N must be approximately 5 for visual perception of structure, a very much smaller value can be made acceptable by spatial superposition or “averaging” of similar images. In most circumstances this is practical only for objects with a determinable spatial redundancy. We report here on the construction of an experimental system for (1) recording statistically noisy images, (2) determining the image redundancy, and (3) executing the desired spatial averaging.