REVIEW OF LEGIBILITY RELATIONSHIPS WITHIN THE CONTEXT OF TEXTUAL INFORMATION PRESENTATION

An extended review of the relevant legibility literature was conducted to provide normalized legibility performance data for a comparison and consolidation of past legibility research. The data were normalized by expressing the legibility performance in terms of visual angle subtended by the character height. The data revealed large variations in visibility performance among the reviewed studies, despite similar or even identical experimental treatments. The normalized data were grouped into sets, relating the visual angle to the width-to-height ratio W/H, the intercharacter spacing-to-height ratio S/H, and the stroke width-to-height ratio SW/H, for both negative and positive contrast. Second-order polynomial least-squares functions were established to obtain a proposed and tentative functional relationship between the visual angle and W/H, S/H, and SW/H. As expected the data indicated that positive-contrast characters generally require smaller stroke widths than negative-contrast characters and that more widely spaced characters show an increased legibility over closely spaced characters. The present investigation provides display designers with proposed and analytical functional relationships between legibility performance (visual angle) and typographical properties.