Perceptually-Tuned Grayscale Characters

A perceptually-tuned character grayscaling method has been developed for displaying anti-aliased characters on low resolution devices such as LCD displays. The so-obtained variable intensity character images combine high-contrast and detail rendition, without exhibiting the jaggies commonly found in bilevel characters.

In order to automatically generate improved quality grayscale characters similar to the characters which would be designed manually by skilled typographic designers, we created a software package which applies modifications to the outline of the characters according to information specifying character structure elements such as bars, curved stems and serifs [Hersch93]. These modifications ensure that the left edge of vertical bars have a sharp contrast and that similar bars and curved stems have similar intensity profiles [Hersch95a]. Furthermore, we preserve the structure of characters by enlarging character parts which would be too thin to be correctly displayed. Grayscale characters are specially suited for LCD displays.

To judge the effect of perceptually-tuned grayscale, please download the grayscale image files and display them preferably on a LCD display. Don't visualize the character in a Web browser, since, due to resampling effects, the quality will strongly decrease.

Perceptually-tuned grayscale characters produced from outline characters. See Hersch et al., Perceptually-Tuned Generation of Grayscale Fonts, IEEE CG&A, 1995)

Bilevel characters from outlines produced with EPFL's automatic grid-fitting methods, see Hersch, Betrisey, Model-based Matching and Hinting of Fonts, ACM SIGGRAPH'91 Proceedings, Computer Graphics, Vol 25, No 4, pp. 71-80.

Recent publications on the subject.