Perception of letter glyph parameters for InfoTypography

The advent of variable font technologies---where typographic parameters such as weight, x-height and slant are easily adjusted across a range---enables encoding ordinal, interval or ratio data into text that is still readable. This is potentially valuable to represent additional information in text labels in visualizations (e.g., font weight can indicate city size in a geographical visualization) or in text itself (e.g., the intended reading speed of a sentence can be encoded with the font width). However, we do not know how different parameters, which are complex variations of shape, are perceived by the human visual system. Without this information it is difficult to select appropriate parameters and mapping functions that maximize perception of differences within the parameter range. We provide an empirical characterization of seven typographical parameters of Latin fonts in terms of absolute perception and just noticeable differences (JNDs) to help visualization designers to choose typographic parameters for visualizations that contain text, as well as support typographers and type designers when selecting which levels of these parameters to implement to achieve differentiability between normal text, emphasized text and different headings.