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Legibility optimization of uppercase alphanumeric text for displaying messages in traffic applications

by Schnell, Thomas

Abstract (Summary)
This dissertation research investigated the legibility of uppercase, single line sets of characters/numerals or single words made up by standard highway fonts. A series of carefully controlled laboratory legibility experiments were conducted to determine the effects of letter height H, letter width-to-height ratio (W/H), stroke width-to-height ratio (SW/H), inter character spacing-to-height ratio (S/H), on the legibility of single line sets of characters/numerals or single words made up by standard highway fonts. Legibility was investigated in terms of threshold contrast for achromatic positive and negative contrast polarity and for typical highway sign color combinations. This research involved four experimental phases: 1. A pilot experiment to determine the feasible range for the independent variables (H, W/H, SW/H, background luminance, only simple, straight line letters E,F, and L used as stimuli), 2. A full factorial experiment to investigate the legibility effects of H, W/H, SW/H, S/H for positive achromatic contrast (typical street names used as stimuli), 3. A full factorial experiment to investigate the legibility effects of H, W/H, SW/H, S/H for negative achromatic contrast (typical license plate alphanumeric legends used as stimuli), 4. Two combined full factorial experiments to investigate the legibility effects of H, W/H, SW/H, S/H for chromatic stimuli for typical highway sign color combinations (positive contrast: white on green, negative contrast: black on yellow, black on orange, and blue on white). The threshold contrast data that was obtained, served as the basis for the development of a legibility optimization software package entitled OptFont. This program consists of a numerical minimization algorithm that determines the threshold contrast of a large number of combinations (specified by the user) of typographical parameters, and then ranks all typographical alternatives that satisfy the sign size constraints. OptFont is useful both for optimizing sub-optimal signs, and for confirming the superior performance of optimal or near optimal signs over other typographical alternatives. It is conceivable, that an automated legibility optimization algorithm like OpFont may become an integral part of sign- drafting packages. Continuously scaled and automatically optimized alphabets could, over time, replace the standard highway alphabets with their discrete typographical parameters. Future research is indicated.
Bibliographical Information:

Advisor:

School:Ohio University

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:legibility optimization alphanumeric text traffic applications discrete typographical parameters stroke width to height ratio letter

ISBN:

Date of Publication:01/01/1998

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