A11Y’S HIDDEN DIMENSION
Vladimir Khokhlov shares Little Voice’s approach for delivering accessible type across multiple devices
Vladimir Khokhlov discusses delivering accessible type across multiple devices
Typography has to be accessible and consistent, regardless of what platform or device it is viewed on. Office printers, smart-home displays and smart watches are viewed within different contexts and from different distances. Furthermore, the physical size of the rendered font depends on the font metrics. This means Roboto will be different in size to Avenir, even when both are set to the same point size. To complicate matters, the same font will differ in size depending on the rendering engine.
Little Voice believes accessibility needs to go beyond guidelines and consider how the user ends up seeing something. This said, we struggled to determine what font size was best for readability. So, we drew on scientific research published in 2011 by G Legge and C Bigelow ( https://netm.ag/2zk29yc).
The Legge-Bigelow study, Does Print Size Matter for Reading? A Review of Findings from Vision Science and Typography found restrictions to the range of font sizes that offer optimal readability. It argued that to be accurate in measuring font size, you have to consider the angular size in degrees (projected image size at the eye retina) and how it is contingent on the physical size of type and viewing distance. An approximate conversion is as follows: angular size in degrees = 57.3 × physical size ∕/ viewing distance.
We combined the research with the context and distance users interact with devices. A user is three metres away from a TV, 65cm away from a monitor, 45cm away from a laptop, 30cm away from a mobile phone and 18cm away from a watch. This led us to a distinct approach to defining a font size in the UI.
We identify a range in the viewing distance by the user and calculate the physical dimensions of the font based on viewing distance and the angular size for optimal reading speed. The physical size can be calculated as: physical size = viewing distance × angular size / 57.3. Once we have the desired physical size range, we measure the rendered font used on the particular device to find the corresponding point sizes to be used in the UI software code.
The science and the method enables Little Voice to choose the right font size and avoid the pitfall of designing for accessibility in two dimensions.