Maintaining Text Legibility Regarding Font Size Based on User Distance in Mobile Devices: Application Development and User Evaluation

The text’s legibility can dramatically influence any device’s usability, and a wealth of research has examined the ideal font characteristics for various displays regarding legibility and readability. However, mobile devices have an additional factor that influences viewing conditions; their greatest strength, i.e., portability, is their biggest weakness in this regard. Furthermore, the freedom to use the device in diverse situations and positions (sitting, standing, in transit, or while waiting in line) can influence various facets related to legibility, such as the user’s holding position, operating style, and the environment’s light directed to the phone. The application developed aims to maintain user-preferred text font size -in all typical distances that users operate their phones- by automatically adjusting the font size according to the distance between the user and the device by using the device’s camera to calculate the distance in real-time. A two-part experiment (n = 34) revealed that the application scored an excellent usability score while the visual landmarks used showed a promising start at addressing an issue related to our approach.