First, a survey on optical scaling is carried out, both from the traditional point of view and from that of today’s digital typography. Then the special case of large characters, such as braces or integral signs, is considered. It is shown that such variable sized symbols should be computed at print time in order to approach the quality of metal typesetting. Finally, an implementation of such dynamic fonts, still in progress in the Grif editor, is described.

This thesis investigates the possibility to improve the quality of text composition. Two typographic extensions were examined: margin kerning and composing with font expansion. Margin kerning is the adjustments of the characters at the margins of a typeset text. A simplified employment of margin kerning is hanging punctuation. Margin kerning is needed for optical alignment of the margins of a typeset text, because mechanical justification of the margins makes them look rather ragged. Some characters can make a line appear shorter to the human eye than others. Shifting such characters by an appropriate amount into the margins would greatly improve the appearance of a typeset text. Composing with font expansion is the method to use a wider or narrower variant of a font to make interword spacing more even. A font in a loose line can be substituted by a wider variant so the interword spaces are stretched by a smaller amount. Similarly, a font in a tight line can be replaced by a narrower variant to reduce the amount that the interword spaces are shrunk by. There is certainly a potential danger of font distortion when using such manipulations, thus they must be used with extreme care. The potentiality to adjust a line width by font expansion can be taken into consideration while a paragraph is being broken into lines, in order to choose better breakpoints. These typographic extensions were implemented in pdfT E X, a derivation of T E X. Heavy experiments have been done to examine the influence of the extensions on the quality of typesetting. The extensions turned out to noticeably improve the appearance of a typeset text. A number of `real-world' documents have been typeset using these typographic extensions, including this thesis. Contents 1

Typesetting of mathematical formulae has conflicting requirements: on the one hand, optical scaling is a need for large symbols; in the other hand, large symbols are made of composite items that are neither easily nor nicely put together.

picture A specific language, called P language, is used to describe presentation rules for each type of element defined in the DTD. Interpretation of these presentation rules is based on the concept of abstract pictures [27]. When Grif has a document to print or to display in a DYNAMIC OPTICAL SCALING AND VARIABLE-SIZED CHARACTERS 245 Formula String "m = " Sum Lower_exp String "k = min(1,i)" Symbol " " Upper_exp String "n" Operand String "sin" Superscript "2" String "x" Subscript "k" Figure 13. Abstract picture corresponding to formula (1) window, it first builds an abstract picture which is a high-level description of that document image. This description is device-independent and allows the editor to update the image dynamically in a simple way. In a second step, it translates this abstract picture into the real image which is displayed on the screen or printed on paper sheets. The abstract picture is the interaction support between the application and the user...