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The digital computer is undeniably an asset in the examination of many classes of geologic problems. Unfortunately, it is ill suited for handling pictorial information which constitutes a large percentage of geologic data. For certain kinds of problems, the inherent physical properties of optical lenses can be used to perform analyses that are impractical using a digital approach. For example, in a current study of pore structure in reservoir rocks, the pore pattern of an area 24 × 24 millimeters on a thin section was digitized, yielding more than one million data points. Spectral analysis was used to determine the relative contributions of spatial frequencies to the total porosity, but even with the Fast Fourier Transform, a two-dimensional spectral analysis of a single thin section is very expensive even on a large computer. In contrast, a proper optical lens system will produce a Fourier transform and map the power spectrum on film in a few seconds. A digital approach is more expensive by three or four orders of magnitude. Optical-processing methods are especially well suited for study of radar imagery air photographs and gross fabric patterns, as well as microscopic textures in rocks.

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