Problems of Implementation
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Because designers of WYSIWYG applications typically have to account for a variety of different output devices, each of which has different capabilities, there are a number of problems that must be solved in each implementation. These can be seen as tradeoffs between multiple design goals, and hence applications that use different solutions may be suitable for different purposes.
Typically, the design goals of a WYSIWYG application may include the following:
- Provide high-quality printed output on a particular printer
- Provide high-quality printed output on a variety of printers
- Provide high-quality on-screen output
- Allow the user to visualize what the document will look like when printed
It is not usually possible to achieve all of these goals at once.
The major problem to be overcome is that of varying output resolution. As of 2007, monitors typically have a resolution of between 92 and 125 pixels per inch. Printers generally have resolutions between 240 and 1440 pixels per inch; in some printers the horizontal resolution is different from the vertical. This becomes a problem when trying to lay out text; because older output technologies require the spacing between characters to be a whole number of pixels, rounding errors will cause the same text to require different amounts of space in different resolutions.
Solutions to this include the following:
- Always laying out the text using a resolution higher than the user is likely to use in practice. This can result in poor quality output for lower resolution devices (although techniques such as spatial anti-aliasing may help mitigate this), but provides a fixed layout, allowing easy user visualisation. This is the method used by Adobe Acrobat.
- Laying out the text at the resolution of the printer on which the document will be printed. This can result in low quality on-screen output, and the layout may sometimes change if the document is printed on a different printer (although this problem occurs less frequently with higher resolution printers, as rounding errors are smaller). This is the method used by Microsoft Word.
- Laying out the text at the resolution of a specific printer (in most cases the default one) on which the document will be printed using the same font information and kerning. The character positions and number of characters in a line are exactly similar to the printed document.
- Laying out the text at the resolution for the output device to which it will be sent. This often results in changes in layout between the on-screen display and printed output, so is rarely used. It is common in web page designing tools that claim to be WYSIWYG, however.
Other problems that have been faced in the past include differences in the fonts used by the printer and the on-screen display (largely solved by the use of downloadable font technologies like TrueType) and differences in color profiles between devices (mostly solved by printer drivers with good color model conversion software).
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