A new teletext character set with enhanced legibility Citation for published version (APA): Nes, van, F. L. (1986). A new teletext character set with enhanced legibility. Proceedings of the SID, 27(3), 239- 242. Document status and date: Published: 01/01/1986 Document Version: Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. 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If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, please follow below link for the End User Agreement: www.tue.nl/taverne Take down policy If you believe that this document breaches copyright please contact us at: [email protected] providing details and we will investigate your claim. Download date: 30. Sep. 2021 ' L. jl~. '2 , .. A New Teletext Charncter Set with Enhanced Legibility FLORIS L. vAN NES Abstract-Teletext is difficult to read, partly because of the letter be read by somebody with an average visual acuity, i.e., fonts employed. Present fonts are contained in a matrix of 6 (horizon· 1.0 (equivalent to 20/20), subtends 5 min of are. To avoid tal) x 10 (vertical) elements. Research on matrix characters of opti­ mum legibillty started in 1969 at the lnstitute for Perception Research. letters with a simHar contiguration being confused during Criteria resulting from this research have now been used to design al­ reading a text, it should be made up of letters that are phanumeric characters in a matrix of 12 x 10 elements for use in considerably higher, for example 12 min of are to quote Teletext. Several verslons of each character were designed and their a tigure from a human-factors handhook [2]. legibility tested in recognltion experiments. The legibility of the best For a large-screen TV display with Teletext letters of new version for each letter was compared with and shown generally to be greater than that of the presently used version. the regular size, this value corresponds to a viewing dis­ tanee of 1.6 m, i.e., less than half of that which is typical for viewing TV. Therefore, it is worth optimizing ebar­ l. INTRODUCTION aeter discriminability. OT-MATRIX characters are used for text display on We designed alphanumeric characters and punctuation Dconventional TV receivers in an increasing number marks on a matrix of 12 x 10 elements (horizontal x of consumer-electronics app1ications, such as Teletext, vertical, including gaps between letters and rows). Such videotex, electronk games, and personal computing. The a matrix allows more refined as well as more acceptable resolution of a TV display is rather limited because of configurations, compared to the 6 x 10 matrix now mostly bandwidth limitations of the TV channel and the video in use. The latter format presents minimal possibilities for amplifier, etc. Therefore, the dot matrix of which the designing upper- and lower-case letters. The resulting characters are composed is relatively coarse, implying that character configurations were judged by viewers as being they can only be schematic approximations of the elabo­ too square with too thin diagonal strokes. To counteract rate detailed fonts used in print. In order to ensure good such etfects, "character rounding" was introduced by legibility of such schematic letters and digits, they should adding half dots at the appropriate positions, close to the be designed with three criteria in mind [ 1]: acceptability, diagonal strokes [3]. The rounding rules are based on an identifiability, and discriminability. A character has high interlaced scan pattem; however, the use of two inter­ acceptability when its shape closely corresponds to a con­ laeed fields in one TV frame creates an annoying "line cept that observers have of this shape; it is highly iden­ flicker" effect when watching Teletext. Most present-day tifiable when its parts stand out clearly against the ebar­ European TV sets therefore do not interlace in the Tele­ aeter background; it has high discriminability when the text mode thus, unfortunately, obliterating character chances of it being confused with a similar character are rounding. In view of this outcome and, on the other hand, low. Such confusion may occur under difficult observa­ developments in the Oerman "Bildschermtext" (view­ tion conditions, such as low contrast between character data) service, a 12 x 10 matrix format has been recently and background or reading from a distance. A luminous adopted as the new videotex matrix standard by the Euro­ contrast that is too low occurs, for instance, when red or pean Conference of Posts and Telecommunications blue letters are used on a black background, or yellow Administrations (CEPT}. letters on a white background. With respect to viewing 11. DESIGN AND TESTS OF LOWER-CASE LETTERS distance, applications such as Teletext are commonly viewed from the same distance as normal TV programs. The first phase of this project consisled of designing Aowever, this di stance is too large for the si ze of Teletext four configurations for each lower-case character using the characters, which means that, especially for viewers with results of previous experiments on the acceptability as well a reduced visual acuity, Teletext is inherently difficult to as discriminability of another comparable character set as read. The following may illustrate this point: the height guidelines [I]. The new characters we re designed on a of the row of capitalletters on a Snellen chart, which can terminal screen by assembling matrix "dots" in a grapb­ ical representation of the character matrix that was mag­ nified approximately 15 times compared to the normal Manuscript received October 7, 1985; revised March 4, 1986. size. The resulting contiguration could subsequently be The author is with the lnstitute of Perception Research, IPO, Eindho­ ven, The Netherlands. observed on a TV screen at normal display size. In this IEEE Log Number 8608715. way, a stimulus set of 4 x 26 = 104 characters was ob- 0018-9383/86/0800-1222$0 I .00 © 1986 IEEE Proc~~din2s of the SID. Vol. 27/3. 1986 239 Rec:ogJIIzed .. : WORST VERSlONS • .. c d I I h I I k I M n o p Q r • u ' • ? • 4 1 1 •1 10 7 2 3 1 1 2 .. 1 12 2 1 3 1 5 4 c 1 18 3 1 1 3 1 3 •3 d 1 1 21 1 1 3 1 2 1 • 1 .2313 1121 2 ~ I • • 14 1 21 (a) (b) (c) (d) 3 7 1 3 1 10 1 1 3 3 f • 20 2 12 •I 19 5 1 10 12 Fig. I. Four configurations for the letter a that were used in the first two ! 1 2 •••• ~ J 33 ·-1 experiments. 16 • 2 10 1 11 1 4 2 1 2 .. I 2 5 13 8 2 9 5 12 m 1 3 1 • "i . 7 23 1 4 tained. Fig. l(a) to (d) shows the four different versions 0 7 2 1 5 13 1 1 1 i.. • 2 • 17 • of the letter a. 15. .• 1 1 ~ : 2031 1 2 2 1 • 8 3 1 1 1 1 1 1 • 1 These 104 eh araeters we re presented in random order I • 3 12 11 1 i • 18 1 ,. to two groups of 12 subjects each in two experiments. In iii . 1 1 241 • . • 14 14 the tirst experiment the characters were presented foveally . 7 1 1 3 5 5 2 2 '!_ 1 1 1 2 1 5 1 2 __ _1_~ for 2 s, on a 25-in color TV set (maximum horizontal • 5 1 2 • 2 5 3 screen dimension 53 cm, frame rate 50 Hz) at an abser­ vation distance of 8 m. At this distance the character box •• e 1 z:s 10 1 a te ze 11 ,. ze 11 •• '' 12 11 et a 13 :s• za a z • 10 11 of 12 x 10 dot-matrix elements, as shown in Fig. 1, sub­ Fig. 2, Confusion matrix for the worst versions of the investigated lower­ tended a viewing angle of 4.5 min of are horizontally and case letter configurations in a discriminability experiment with periph­ 6.5 min of are vertically. In the second experiment, the eral stimulus presentation. characters were presented peripherally for 0.1 s to the left or right (in random order) of a tixation cross that was gen­ erated in the center of the screen from the same TV set. Recoped as : BEST VERStONS •ttcdetghiJII.I 0 • • r o I u •• • r a '? In this experiment an observation distance of 4 m was • 1823 1 1 1 1 2 8 1 1 1 2 2 2 4 used, and the stimuli were presented at an eccentricity of : : 23 d 2 1 27 1 3 5 1 3 4 1 1 • 2 1 2 2 1 • plus or minus 2 degrees; the character box then subtend­ 1 15 1 1112 1 5 1 1 2 7 2 3 1 ing a viewing angle of 9 min of are horizontally and 13 125 25 3 1 8 min of are vertically.