Signal to noise enhancement in dark field electron micrographs of vasopressin: filtering of arrays of images in reciprocal space

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Abstract
A technique for filtering arrays of images of dispersed molecules is presented which takes advantage of the crystallographic properties of regular arrays and the rapidity of optical treatment. A filter in reciprocal space consisting of perforations in a square or rectangular lattice, as determined by the image arrangement, reduces noise and averages the images simultaneously by transmitting only regularly recurring image structure. The filter is universal for all image contents and introduces no additional biases. The signal to noise improvement approaches √N for N independent images of the same molecule in the same configuration. The procedure, which is simple, rapid and inexpensive, is demonstrated with the aid of dark field electron micrographs of the protein vasopressin and combined with iodination of that molecule to elucidate its structure.