Showing papers by "National Security Agency published in 1989"
Patent•
24 Mar 1989TL;DR: An improved asymmetric crystal topography x-ray imaging system employing aine focus horizontal line source of x-rays and a crystal monochromator used in a compression mode was presented in this article.
Abstract: An improved asymmetric crystal topography x-ray imaging system employing aine focus horizontal line source of x-rays and a crystal monochromator used in a compression mode. Relatively large horizontal and vertical dimensions of the monochromating crystal allow imaging of larger areas of imperfect crystals than previously possible, without adversely affecting image resolution. The high resolution two-dimensional images are a direct consequence of our method of controlling the probe beam divergences. An appreciably enhanced and useful intensity of monochromatic x-rays is obtained over that available with prior asymmetric crystal topography systems.
12 citations
TL;DR: A new, universal approach to reconstructing transform-coded images that views the images as a probability mass function, allowing the retained coefficients of a transform to be thought of as averages of the basis functions over the pmf.
Abstract: A new, universal approach to reconstructing transform-coded images is proposed. The method views the images as a probability mass function (pmf), allowing the retained coefficients of a transform (Karhunen-Loeve, discrete cosine, slant, etc.) to be thought of as averages of the basis functions over the pmf. This sets the stage for reconstructing the original images by using the maximum entropy principle (MEP) and the minimum relative entropy principle (MREP) with the retained coefficients as constraints in the extremizations. A formulation combining the two methods is also proposed, resulting in a reconstruction algorithm that is fast, proceeding in an iterative way using the estimate from each coefficient as a prior pmf for the next one via the MREP. The proposed approaches are illustrated with images compressed by discrete cosine transform coding, and the results are compared with standard reconstruction using the inverse discrete cosine transform.
3 citations
Patent•
01 Mar 1989TL;DR: An outer product shearing interferometer for an optical source of one-dimensional extent which provides simultaneous interference between every two points on the source was proposed in this article, where the desired outer product results from a simultaneous application of many lateral shears instead of only one at a time.
Abstract: An outer product shearing interferometer for an optical source of one-dimensional extent which provides simultaneous interference between every two points on the source. The interferometer comprises an input plane containing the source, an output plane for observing the outer product, an imaging system between the two planes, and a mask positioned in the transform plane of the imaging system and having slits arranged to effect the desired outer product. The desired outer product results from a simultaneous application of many lateral shears instead of only one at a time.
1 citations