The Mach Phenomenon*(as perceived on photographic film) is herein investigated as a function of edge acutance, contrast and illumination level for the purpose of determining its probable effect in the area of visual image evaluation. The results indicate that dark Mach band widths increase as acutance decreases and dark band width is independent of contrast and illumination level while light band widths remain constant, over the ranges investigated. Using these findings as a basis, a dark band width predictor equation was found, taking the form; dark band width (in microns) =K/acutance, when average edge gradient is the measure of acutance. The probable effects (which increase in importance as acutance decreases) of the Mach bands on visual image evaluation is then discussed.

* a visual sensation of density bands near edges

Library of Congress Subject Headings

Visual discrimination; Mach bands; Images, Photographic

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Physical copy available from RIT's Wallace Library at TR222 .N54


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