FONT LEGIBILITY - EFFECTS OF PIXEL DENSITY AND SMOOTHING

Title FONT LEGIBILITY - EFFECTS OF PIXEL DENSITY AND SMOOTHING
Author, Co-Author Aaron Zimmerman, James Sheedy, Manoj Venkiteshwar, John R. Hayes
Topic
Year
2003
Day
Program Number
Poster 34
Room
Affiliation
The Ohio State University, College of Optometry
Abstract PURPOSE: Greater pixel density on computer displays improves character resolution, however the density level of no further returns is not known. This study examines the effects of pixel density and text smoothing upon legibility.

METHODS: Twenty-five subjects (18-35 years) with best corrected visual acuity of 20/20 or better were used. Visual acuity was measured using capital letters, lower case letters, and lower case words presented in Verdana font on an LCD display with 10 pixel densities (6, 8, 9, 12, 14, 16, 20, 31, 39, and 49 vertical pixels) and two font smoothing modes (aliased and Clear Type). Visual acuity was measured using stepped viewing distances to create acuity line steps. Steps in pixel density were created by changes in font size and display magnification, visual angles were equalized with different viewing distances for each size. The mean visual acuity of the subject group for each condition represents the relative legibility for the condition. All main effects and two-way interactions were tested for statistical significance with repeated measures ANOVA. Post hoc comparisons were conducted using a Helmert transformation in which each individual pixel height within stimulus category was compared to the mean of subsequent higher pixel heights within that single stimulus category.

RESULTS: There was a significant main effect of pixel density (p<0.0001) but not for smoothing. Significant (p<0.01) legibility improvements occur with added pixel density up to 9 pixels vertical height, pixel densities greater than 9 do not improve legibility. Font smoothing decreased legibility only for 6 pixel capital letters (p<0.05) and lower case letters (p=0.0016), but not for words.

CONCLUSIONS: The pixel density had a significant effect on legibility up to a vertical height of 9 pixels - equivalent to 10 point font at 100% magnification.

ADDITIONAL COMMENTS: ACKNOWLEDGMENT: The study was supported by a grant from Microsoft Inc., USA.
Affiliation of Co-Authors The Ohio State University, College of Optometry, The Ohio State University, College of Optometry, The Ohio State University, College of Optometry
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