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While electronic document have many advantages, the computer display devices on which these documents are often viewed are significantly inferior to print. Most screens (whether based on cathode-ray tube (CRT) or liquid crystal screen (LCD) technology) offer at best 90 dpi. It is possible to use a technique called anti-aliasing to shade the pixels at the edges of characters and lines but this provides a small improvement only. The contrast ratios between black text on screen and a white background are also deficient compared to paper. In late 1998 Microsoft announced a new display technology called ClearType to work with font rendering on computer screens and improve readability. This is claimed by Dick Brass, Microsoft's vice president of technology development, to "make inexpensive screens look as good as the finest displays, and the finest displays look as good as paper" [Trott, 1998]. Whether this is in fact the case will not be known until it ships (probably some time in 1999), but such an announcement does indicate that software manufacturers recognize that the resolution difference between the screen and paper is significant.
The literature on the relative readability of print versus screen is somewhat confused. One study by Wilkinson and Robinshaw reported significantly higher reading fatigue associated with computer screens relative to paper [Wilkinson and Robinshaw, 1987]. Their results showed a degradation in performance over a fifty minute task. [Valauskas, 1994] also argues for the superiority of print for extended reading. Another study by Gould et. al. [Gould and et. al., 1987] suggests that the quality of the monitors used can remove the fatiguing effects. An article reviewing these studies concludes that
users do not find reading from monitors intrinsically fatiguing, but that performance levels may be more difficult to sustain over time when reading from average quality screens [Dillon, 1988]
This study also points out that reading is a complex grouping of activities.
the type of task performed in many of these studies represents ... a subset of what is labelled 'reading'. Browsing, light reading and formal studying are probably more frequent interactions with written material [Dillon, 1988, p. 460].
Almost all electronic document technologies have no practical annotation facility whatsoever. The original version of Mosaic (the first WWW browser available for the Macintosh and Windows) had the ability to create either text or recorded voice annotations for Web pages. These annotations were stored locally and displayed in the margin the next time the remote Web page was accessed. The intention was ultimately to provide group annotation features as well. Unfortunately, this feature did not survive the transition of the developers of Mosaic to Netscape and sank without a trace. It is possible to annotate Adobe PDF files, but one needs the full Acrobat Exchange product to do so (rather than the free Acrobat Reader). This means that very few readers of PDF can make use of this facility. Most readers of on-line documents (like the author) therefore have to print out documents in order to annotate them.
Electronic documents need a power source. This is only infrequently an issue for desktop machines but limits portable use. Notebook computer batteries are improving all the time, but 3 hours of usage is still the upper limit for most systems.
Electronic documents also have a number of what might be called system weaknesses. One of the most commonly-cited is the ease with which it can be copied, and therefore the ease with which plagiarism can be carried out. Interestingly, the ACM has been using fast searching and indexing algorithms together with large document stores accessible over the Internet as a mechanism to identify such plagiarism [Denning, 1995]. Another weakness is difficulties in ensuring digital document integrity [Lynch, 1994a]. Thirdly, licensing provisions and copyright mechanisms for multimedia information or for documents that embed multimedia objects are problematic [Lyman, 1995].
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