Numerical Hydrodynamics Data From Digital Image Arrays

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Abstract
The acquisition of analog video data, its conversion to digital data, and subsequent storage, transmission and reconversion to visual form is a well-practiced art. The specific application discussed herein is to record, measure and calculate the size distribution of a large number (several thousand) of air bubbles in a water flow. Previously, experimenters had acquired these data from 8 x 10 photographs, employing mechanical measurement techniques. In this technique data were taken from individual frames of high speed 16 mm motion pictures of the two-phase flow. Each frame was scanned and stored digitally as light intensity levels in a 256 x 256 array. The data array was processed using an on-line PDP-11 minicomputer. Using an input discrimination level, the PDP-11 examined each pixel sequentially until one was found which was part of a bubble. The program then followed the contour of the bubble, measuring perimeter, maximum X and Y excursion and integrating to determine area. At the completion of the contour program, control dropped into a routine which calculated desired bubble statistics. Control then reverted to the routine examining pixels. The techniques described herein were developed to solve a specific problem. These specific methods, if generalized, could be used to extract numerical data from digitized video data in a wide variety of fields.© (1979) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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