Legibility Index for Examining Common Viewing Situations: A New Definition Using Solid Angle
نویسنده
چکیده
The legibility levels of text and graphics can be assessed using the Legibility Index, conventionally defined as the distance at which material can be read with perfect accuracy (the legibility distance) divided by the character height. The ratio equals the inverse tangent of the visual angle subtended by the character. The definition assumes that the viewing material is perpendicular to the observer, which is not always true. Although text and graphics are, in reality, often viewed not perpendicular to the display, they are rarely studied. To examine the legibility of characters viewed not perpendicular to the display, this paper has redefined the Legibility Index as the inverse square root of the solid angle subtended by the target, based on a hypothesis that the three-dimensional solid angle, rather than the twodimensional visual angle, both subtended by the character, captures how people recognize text and graphics that usually have two significant dimensions (width and height). This hypothesis proves consistent with how retinal images of text and graphics activate cones in the fovea of a viewer’s eyes, and has also been verified in a laboratory using legibility data collected from 20 human subjects. Using these data, the calculated steady redefined Legibility Index closely matches the fact that the 20 subjects have similar recognition performance (critical legibility level with 100 percent accuracy) of text (same target) under the same lighting conditions (Lb!120 cd/m , C%!97.9, zero ambient light) at different viewing angles (perpendicular or not perpendicular to the displays), while the calculated ratio of legibility distance to character height rapidly decreases with increased viewing angles. Keywords—Legibility Index, viewing angle, text and graphics, nonperpendicular viewing, solid angle, visual angle, equation. 1. (Corresponding author) Research Associate, Department of Building Services Engineering, Hong Kong Polytechnic University, Kowloon, Hong Kong, [email protected] 2. Research Professor, University of Michigan Transportation Research Institute, 2901 Baxter Rd., Ann Arbor, MI 48109, [email protected] L E U K O S V O L 5 N O 4 A P R I L 2 0 0 9 P A G E S 2 7 9 – 2 9 5 ©2009 The Illuminating Engineering Society of North America doi: 10.1582/LEUKOS.2008.05.04.002
منابع مشابه
I STUDIES IN DISPLAY SYMBOL LEGIBILITY PART VIE : Legibility
This report describes the findings of a study in symbol legibility which investigated the reading time and errors for common five-letter words when they are projected by a solid stroke and when they are shown by a broken stroke. The latter was produced on a 945-line TV monitor at 10, 7, and 5 active lines per symbol height. This study is similar to an earlier report on the readability of common...
متن کاملEsd - Tr - 65 - 385 Tm - 4239 Studies in Display Symbol Legibility
This report describes the findings of a study in symbol legibility which investigated the reading time and errors for common five-letter words when they are projected by a solid stroke and when they are shown by a broken stroke. The latter was produced on a 945-line TV monitor at 10, 7, and 5 active lines per symbol height. This study is similar to an earlier report on the readability of common...
متن کاملConsidering a New Sample Unit Definition for Pavement Condition Index
One of the main components of pavement management system (PMS) is pavement evaluation. Several indices have been defined for the evaluation of existing pavement. The Pavement Condition Index (PCI) is a common index used for pavement evaluation. In order to calculate PCI, a significant volume of condition data -based on distress surveying- is required. The objective of this research is to reduce...
متن کاملGoniocolorimetry: from measurement to representation in the CIELAB color space
The classical definitions of color are well adapted to diffusing objects, whose color is almost independent of the viewing angle, and to very glossy object observed in the specular direction in respect to the light source. For glossy or iridescent objects, the color is difficult to characterize due to its dependence on the viewing direction. In order to cope with such objects and to represent t...
متن کاملA study of operators’ computing efficiency with special focus on the readability under different viewing angles of a desktop
The main objective of this work is to determine the reading performance of operators’ under different viewing angles of a desktop computer. The effects of text/background color, viewing distance and character size on the speed of reading were investigated. The text and/or the background color combination were varied, with constant luminance contrast. Performance was recorded in terms of words p...
متن کامل