…or probably many millions by now! When you watch subtitles on digital TV in the UK, you are seeing letters and numbers displayed in a font that was specially developed for the job back in 1998.

Known as “Tiresias” (named after the blind prophet of Thebes in Greek mythology) the typeface was designed by a team led by Dr John Gill, then Chief Scientist of the Royal National Institute for the Blind. It may seem a paradox that the RNIB were involved in subtitling, but the goal was to create a font that was as legible as possible, particularly for those with visual impairment.

In the analogue days, when Hard Of Hearing (HOH) subtitling was carried by teletext, there was very little choice in how characters on the screen were presented. Teletext characters were defined in a coarse 5 x 7 dot matrix, due to the limitations of the memory technology of the time, and these had to be displayed as double-height to make them readable. The characters were mono-spaced; that is, each character occupied the same width regardless of its shape. Digital TV, however, transmits subtitles as images, giving the opportunity to create a much more legible character set with fewer restrictions that would also be suitable for the emerging widescreen display formats.

The new typeface had to remain compatible with the teletext version so that subtitles prepared for the analogue world could be used on digital TV, especially during the long period of digital changeover, when both systems were in use.

Dr Gill, an accessibility expert, worked with a team including Janet Silver, from Moorfields Eye Hospital, together with representatives from the RNIB, RNID (now Action on Hearing Loss), BBC, ITV, the ITC (predecessor of Ofcom) and other industry experts to design Tiresias. Test videos were created to allow groups of hearing-impaired people to try out the font and improvements and adjustments to the final font were made as a result of their feedback.

The key factors that influenced the final design included character shape, relative thickness of the characters and inter-character spacing. Special consideration was given to characters that could be confused — for example, the numbers 6, 8 and 9 can often be difficult to distinguish for some with sight impairment. Also, letters such as the lower case “l” were designed to ensure they were different from the number “1”.

Tiresias has been adopted by broadcasters in Ireland, Denmark, Finland and New Zealand for their respective digital TV systems. In addition to its use in subtitling, the Tiresias typeface has variants for use for information labelling, labels on keyboards and keypads, publication labelling and high-visibility signage.

So when you next watch subtitles, it’s worth reflecting on the amount of research, development and testing that has gone into Tiresias to make it as readable as it can be – it’s definitely more than just a pretty (type)face!

John Hedger, Technology Consultant, Access Services.