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The Effect of Font Weight and Rendering System on Glance-Based Text Legibility

Introduction​

This paper explores how font weight (the thickness of text characters) and rendering systems impact text legibility in glance-based contexts, especially relevant to in-vehicle displays. Lightweight fonts have gained popularity in interface design, but their legibility under time-constrained conditions (e.g., quick glances while driving) has not been thoroughly studied. This study compares four font weights under suboptimal and optimal rendering conditions to determine which combinations best support quick and accurate reading.

Target​

The findings are crucial for designers of automotive user interfaces, digital display systems, and safety-critical environments where brief information retrieval is essential.

Key Insights​

  • Font Weight and Legibility:
    • Suboptimal Rendering: Under less refined rendering systems, lighter fonts are significantly harder to read, as they often appear faint or unclear.
    • Optimal Rendering: With high-quality rendering, lighter fonts become more legible, even outperforming heavier fonts due to clearer stroke definition and reduced visual clutter.
  • Rendering Impact on Typeface Perception:
    • Poor rendering exacerbates issues with lighter fonts, leading to increased reading times and potential safety risks in glance-based tasks.
    • Optimal rendering, specifically with Continuous Stroke Modulation (CSM), supports better character clarity across font weights. CSM is a feature that allows for the contours of the typeface to be optimised for the monitor being used.
  • Critical Thresholds in Time-Pressured Reading:
    • Differences in font weight become more pronounced in time-sensitive contexts. Lightweight fonts may require longer glances to read accurately, posing challenges for drivers who rely on quick glances.

Supporting Data​

  • Empirical Findings:
    • In suboptimal rendering, the lightest weight font led to longer reading times and higher error rates, while regular, medium, and bold fonts performed similarly.
    • With optimal rendering, a linear improvement was seen with lighter fonts, indicating that under ideal conditions, lighter fonts can offer better legibility without causing strain.

Other Insights​

  • Crowding Effect: The study notes a possible "crowding" effect, where characters appear less distinct in denser visual layouts. Optimal rendering mitigates this, especially for lighter fonts, which benefit from higher inter-character spacing.
  • Implications for Interface Design: Suboptimal rendering limitations suggest a need for adaptive font choices based on display quality, ensuring legibility is not compromised by aesthetic preferences.

Practical Applications​

  • Use Optimal Rendering for Safety-Critical Interfaces: In automotive interfaces, employ optimal rendering systems that support lighter fonts effectively, reducing driver distraction.
  • Avoid Lightweight Fonts in Low-Quality Displays: For displays with limited rendering capabilities, use regular or bold fonts to maintain readability.
  • Customize Font Choices Based on Context: Tailor font weight choices to match the quality of the display and the intended reading conditions, balancing aesthetics with functional legibility.

Reference​

Dobres, J., Reimer, B., & Chahine, N. 2016. The Effect of Font Weight and Rendering System on Glance-Based Text Legibility. Proceedings of the 8th International Conference on Automotive User Interfaces and Interactive Vehicular Applications, ACM.