Text on TV screens
There can be problems when text is rendered on low resolution TV screens, and this is particularly important for subtitles, where a viewer may be expected to read these over long periods. There is a well-defined ‘safe area' on a TV screen, well away from the screen boundaries where text is less distorted and graphics do not distort as they can do at the edges. Captions placed at the very edge of some ‘safe areas’ can sometimes be clipped when viewed on a poorly set-up domestic 4:3 receiver / Set Top Box combination, so the safe area is best regarded as the maximum allowable width for captions.
Interlaced TV screens are designed to display moving images, so fine stationary lines can be problematic because they tend to ‘twitter’, as the horizontal elements of a line are rendered differently on each of the two interlaced scans. This can make small patterns or text in graphics difficult to decipher even for fully sighted people. Even though a TV screen may be larger than a computer monitor, the 'safe area', the lower resolution and longer viewing distance mean that the image size on the retina is much smaller than when looking at a computer. This has implications for the interface design and legibility of any typefaces used.
The diagram above shows how one particular ‘safe area’ is defined – designers should take the broadcaster’s advice on which safe area definition to use for their particular application.
The size and position of visual information on the screen may determine whether a blind or partially sighted person can perceive it or not. Text should be displayed sparingly in small paragraphs so it can be read more easily. Light text on a dark background is easier to read on a TV screen. High contrast is always an important factor. A large - 24 point minimum - sans serif typeface should be used. Increased line spacing will increase readability, but this requires more screens to display the same amount of information so clear navigation becomes increasingly important. Multiple columns can be difficult to negotiate.
For digital television services much thought has been given to the display of text and graphics, and a detailed specification can be found in the DTG publication ‘UK Digital TV Receiver Recommendations’.
Examples of these recommendations include:
- Use a typeface designed for use on television displays and typical TV viewing distances, and optimised to reduce confusion between letter shapes. When choosing a font, consider its readability. Favour a sans serif font over a serif one. Tiresias Screenfont is generally recommended.
- Mixed case is ideal, but when choosing one case only, then favour lower case text over upper case.
- Avoid italic, underlined, oblique, condensed or fancy fonts.
- Avoid flashing and scrolling text.
- Text size should be a minimum of 24 lines high on a capital ‘V’.
- Readability is improved with extra spacing between letters (but take care to increase spacing between words in proportion), words and lines.
- Provide generous inter-line spacing to minimise problems of visual tracking.
Useful guidelines on the provision of text on TV screens and numerous links can be found on the Ofcom website.
Checklist for text on TV screens
Last updated: 20.11.2009 © Copyright reserved Website design: Digital Accessibility Team