Automatic Synthesis of Contrast Controlled Grayscale Characters with Component-Based Parametrisable Fonts

A few years ago, a perceptually-tuned grayscale character generation technique was developed in order to automatically syn~ thesize grayscale characters looking like manually-tuned pixmap characters. Weight and contrast controlled grayscale characters are obtained by grid-fitting the scaled character contours. However, this technique requires that hinting information be added to the outline font description. Adding hinting information to each outline character generally requires a considerable amount of human intervention. Our component-based parametrisable font system is a newly developed font description and reproduction technology. It incorH porates for each basic character shape a software method responH siblc for the synthesis of an instance of that character. A given font is synthesized by providing appropriate font parameters to these character synthesis methods. Numerous concrete fonts can be derived by simply varying the parameters. Such variations offer high flexibility for synthesizing derived fonts (variations in condensation, weight and contrast) and enable saving a considerH able amount of storage space. This paper shows that with compoH nent-based parametrisable fonts, high quality perceptually-tuned grayscale characters can be generated without requiring hinting information. Generating perceptually-tuned grayscale characters with parametrized component-based fonts consists in automatically adapting the phase of some of the character's parameters in respect to the underlying grid and in ensuring that thin character parts are strong enough not to disappear (weight-control). 1. Component-based parametrizable fonts Most commercial font systems use outline fonts for the digital presentation of typefaces. Outline fonts are well suited for character rastcrization and printing. They however only incorporate implicit information about important font features such as the width of stems, bars and bowls, the distance between vertical stems and bowls and the parameters determining junctions between character elements and determining the shape of tenninal elements (serifs). Efforts arc made to create a more flexible character representation incorporating explicit information about features of the character, thus enabling the synthesis of coherent font variations, for example by varying weight and contrast. The main idea is to describe characters by an assembly of appropriate structure elements (components). Several attempts have been made to describe characters by structure elements. D. Knuth described his Computer Modern fonts by horizontal, vertical and diagonal strokes as well as by round parts [5]. These strokes and round parts are given by sequences of pen positions and orientations. More recently, Bauermeister et al. created the Infinifont 0-7803-5467-2/99/$10.00 ~J 1999 IEEE 348 system enabling resynthesizing an existing font from universal font generation rules and from parametric data specific to that font [6][9]. Our own efforts [II] aimed at defining character components suitable for the generation of existing and of derived typographic fonts, incorporating variations in condensation, weight and contrast. Fig. I shows a character assembled from structure elements, i.e. the two vertical sterns arc synthesized by the component named stem, the round arch is synthesized by two connecting sweep components, and the terminals are synthesized respectively by the serif and top-serif components. For the round character structure elements which are similar to a whole or a half of letter "o", we synthesize them by the loop and respectively the halfloop components (letter "o" and "b" in Fig. 2).