Readability of Characters on Liquid Crystal Displays in Mobile Phones Satoshi Hasegawa1, Masako Omori2, Kazuhiro Fujikake3 and Masaru Miyao4 1. Department of Information Culture, Nagoya Bunri University, Inazawa Aichi, Japan
[email protected] 2. Faculty of Home Economics, Kobe Women’s University, Suma-ku Kobe, Japan
[email protected] 3. Graduate School of Information Science, Nagoya University, Chikusa-ku Nagoya, Japan
[email protected] 4. Information Technology Center, Nagoya University, Chikusa-ku Nagoya, Japan
[email protected]
Abstract. Subject performance in reading characters on mobile phone liquid crystal displays was researched with the use of: (1) sentences without meaning, made from randomly ordered alphanumeric characters having 3 different sizes of characters and 4 different contrasts (n=78; age=39.9±17.6), (2) Japanese characters of 5 different sizes and 2 types of font (n=98; age=44.5±18.5), and (3) Japanese characters vertically enlarged 1-4 times (n=120; age=46.9±18.6). Readability was higher with higher contrast displays, and with Gothic than with Mincho font in Japanese. Readability of Japanese characters improved when they were vertically enlarged to approximately twice the width.
Introduction The use of character information on mobile phones (MPs) has expanded to include business information, social information, disaster information [1], and other types of information in the current ubiquitous computing age. MPs are one of the most impor-
1
tant types of character terminal and an effective information delivery tool. Universal designs allow the transmission of such important information to all people including foreigners [1], elderly [2] and those with disabilities. There have been many studies on the readability of characters on cathode ray tubes (CRT) or liquid crystal displays (LCD) of computers, and recommended character sizes have been standardized in terms of video display terminal (VDT) work. However, MPs have far smaller screens than personal computers (PCs) and differ markedly from PCs in being hand-held. Reading behavior may be expected to different from that with PCs. The purpose of this study was to research the reading performance of users who read characters on LCDs in MPs, and to examine the relation of character size, display brightness and contrast to readability. Graphic characters in the Portable Network Graphics (PNG) format that had readability consistent with that of ordinary binary fonts in MPs [1] were used in this study. The use of graphic characters allows experimental display of characters of various sizes, shapes and contrasts that are beyond the normal text display functions of mobile phones.
2. Methods 2.1 Method of experiment 1 Sentences without meaning, made from randomly ordered alphanumeric characters according to ISO 9241-3 Amendment 1 [3], in which 240 characters included 15% space as in normal English sentences, were displayed on the LCDs of MPs using graphic characters. Subjects (n = 78, age = 39.9±17.1, 19-76) counted the number of times a target letter appeared by searching the strings as if they were reading the sentences carefully and as fast as possible. Searching times, viewing distances, target character count, and subjective evaluations of readability were recorded. Two different types of MPs, Type A (Kyocera WX310K: 240x320 dot 2.4 inch color LCD) and B (Kyocera W43K: 240x320 dot 2.6 inch color LCD), and three different character sizes, L (~2.5 mm height), M (~2.0 mm) and S (~1.0 mm), were examined with four
2
different contrasts consisting of W (negative), X (positive), Y (gray characters with white background) and Z (black characters with gray background), as shown in Table 1 and Fig. 1. Table 1. Luminosity and contrast of the graphic text displayed in experiment 1. Luminosity were values (cd/m2) measured (Minolta LS-110) in the display backgrounds. Back Code
Character
ground
W X Y Z
white black gray black
black white white gray
contrast ratio W
character size
Displayed on Type A luminosity
contrast
luminosity
contrast
9.1±0.5 107.5±2.5 105.1±2.2 47.0±2.0
11.9 11.9 2.5 5.2
3.2±0.0 171.4±1.2 171.0±1.8 38.2±0.8
53.8 53.8 4.4 12.2
X
L
Y
M
Fig. 1. Samples of graphic characters for experiment 1.
3
Displayed on Type B
Z
S
2.2 Method of experiment 2 Japanese sentences with two different fonts (Gothic and Mincho) and five character sizes (G1-5 and M1-5) were prepared as shown in Fig. 2. G1 and M1 have the smallest characters (8 pt, 2.8 mm) in this experiment. G2 and M2 were 1.25 times size 1 (10 pt, 3.5 mm), and size G3 and M3 were 1.5 times size 1 (12 pt, 4.2 mm). G4 and M4 were vertically enlarged 1.5 times size 1. G5 and M5 were vertically enlarged 2 times size 1. The MP used in this experiment (Sharp SH53) has an LCD of 240x320 dots (2.4 inch, color CG Silicon). Subjects (n=98; age=44.5±18.5) read aloud these sentences. The reading time, viewing distance, number of errors and subjective evaluation were recorded.
2.3 Method of experiment 3 Graphic texts with the height of size G1 (Fig. 2), and 1.25-, 1.5-, 2-, and 2.5-times the height of G1 without changes in width were evaluated by the same subjects as in experiment 2. Other Japanese subjects (n=120; age=46.9±18.6) performed with oblong characters of G1, and 2-, 3-, and 4-fold the height of G1.
(a) Gothic G1
G2
(b) Mincho M1
M2
G3
G4
G5
M3
M4
M5
Fig. 2. Graphic characters used in the experiment 2.
4
3 Results Results of experiment 1 are shown in Fig. 3(a)-(e). A two-way ANOVA with factors of MP types (Type A and Type B of character size L) and contrast (W, X, Y and Z: shown in Fig. 1 and Table 1) was conducted for each parameter. Both MP type and contrast showed significant differences (p
