Space , colour and typography on visual display terminals

Some guidelines are given to meet the observed need for rules about layout, the use of colour and typography on display sereens so as to create texts with optimallegibility. Examples of videotex pages are used to illustrate right and wrong layouts, applications of colour and of letter type. The guidelines can be generalized to other types of display sttch as those used in personal computers and, to a more limited extent, totheuse of grapbics instead oftext. Finally, figures are given on the general public's subjective appreciation of some alternative display layouts. 1. Introduetion Th is paper may be considered as a companion to that on perceptuallimits in VDTs which was recently publisbed in this joumal (Van Nes 1984). Whereas the former paper focused on the influence of luminous contrast and character contiguration on legibility, the present one will deal with the ways space, colour and typography can be used to maximize text legibility. Being easy to read, texts with a high legibility enable the reader to devote his attention to onderstanding whatever information the text conveys. The paper has been prompted by the relative scarcity of guidelines in this area: apart from Tinker's classic treatise (1964) on printed text, and the articles by Reynolds (1979) and Long (1984) on text displayed by cathode-ray tubes, not too much appears to have been publisbed on this topic, although there is an evident need for practical guidance, either explicitly expressed, or implicitly demonstrated by the errors which are frequently manifest when text displays are viewed carefully. Such electronic text displays may be edited fora large public, as in videotex, or fora limited number of users, as in personal computing. In both cases, however, the editors often seem to Jack the professional knowledge of layout and colour use which is cominonplace in the printing industry. As a predecessor ofthis paper, an advice was written in 1981 for the Dutch teletext information service which has been broadcast by television since April 1980. With that background, the display examples given here concern texts in the Dutch language. In the meantime, the legibility of teletext in The Netherlands has fortunately improved considerably. The teletext origin of the examples shows up intheir format: 24lines with 40 spaces each ofusually bright text on a dark background. Seven colours can be used for text and background, viz. red, green, blue, yellow, magenta, cyan and 'white'. Yellow, magenta, cyan and 'white' in this case are the result ofthe combinedemission from, respectively, the red and green, the red and blue, the green and blue and the red, green and blue phosphors. For this reason, among others, the luminances and brightnesses of these seven colours are unequal. In the sequel, some basic properties of the visual reading process will bedescribed first. Then, theseparate effects of the use of space, colour and typography on legibility wiJl be treated, foliowed by some illustrations of the combined effect of these image parameters. Finally, some practical guidelines are formulated which mostly apply to multicolour text displays in general and, toa certain extent, mayalso be generalized to the use of graphics.