Ensure that text and graphics are readable by users with limited vision or reading disorders
Rationale
Text and graphics need to be clear enough, large enough and laid out in a way that makes them easily read and understood by people with a wide range of vision impairments, including colour vision deficiencies, or people with reading disorders such as dyslexia.
When colour contrast between foreground and background is low or text sizes are too small, then all users will experience difficulties. People with vision impairments may have even more difficulty reading text that is not in large, clear,static type and contrasted well against the background.
The colour of the full guide (blue on blue) can make it hard to read.
Guidelines survey respondent.
People with colour vision deficiency can have problems with particular combinations of colours. Similar problems may occur within graphics, such as icons. In addition to the text and graphics itself, poor layout or the existence of moving content that distracts the eye can make reading difficult. Some of these problems also affect people with reading disorders, even if their vision is perfect.
The great variability in colour vision capabilities across the user population means it is not possible to specify a single size and colour scheme that will suit everyone. It is very useful if individual users can be given the option to change the text presentation style (e.g. Size, colour and background colour) to suit their needs and preferences. In a 2004 survey of people with disabilities by Fain, the ability to adjust text size and colour in the programme guide were given average usefulness ratings of 3.4 and 3.2 out of a possible 4 by participants with low vision. Deaf participants gave ratings of 3.8 and 3.6 for the ability to adjust the size and colour of subtitles. Participants who were hard of hearing gave still significant ratings of 3.2 and 3 out of four.
Directions and techniques
Ensure that text and graphics appear within the area of the screen that can be clearly seen (high priority)
All informational text and graphics should appear within the title safe area that is the visible area where the text will not be cut regardless of the over scan (margin of the video image that is normally not visible) of the television used.
Use a clear typeface and lettering for easy on-screen reading (high priority)
To maximise readability, use a screenfont a typeface that has been specifically designed for viewing on television displays at typical viewing distances. Ideally, the same font should be used throughout the interface.
The text size should be sufficient to be readable across a wide range of visual acuity. The recommendation of DIGITALEUROPE in the Industry Self-Commitment to Improve the Accessibility of Digital TV Receiving Equipment Sold in the European Union is to use 24 line minimum for body text and 18 minimum for upper-case text on a 576 line display.
Italic, underlined, oblique, condensed, all upper case or fancy fonts can cause problems for some people and should be avoided in favour of plain, mixed case lettering.
Blinking or moving text or graphics should be avoided as it can be difficult to track and can distract the eye, making it difficult to read other static text.
Carefully choose colours and colour combinations (high priority)
Ensure that there is sufficient contrast between text and its background for the text to be easily distinguished and read. Dark colours on a light, non-patterned background or light colours on a dark background can both be used. Combinations of red and green should be avoided since they can be difficult to differentiate for people with the most common form of colour vision deficiency. Saturated or bright colours such as pure white or absolute black should also be avoided. The European Industry Self-Commitment recommends that colours be limited to an absolute maximum of 85% saturation to avoid text appearing to distort or flicker.
Figure 4. Low contrast between text and background colours may cause difficulties for some viewers.
Graphics should be treated in a similar way to text, with similar requirements for contrasts between adjacent, overlaid or background colours.
Information should not be presented using colour alone. Ensure a second, redundant indicator is provided. For example, in a list of recorded programmes, if those that have been watched are coloured red and those that have not been watched are coloured green, people with colour blindness will have difficulty perceiving the difference. An additional clear ‘unwatched’ symbol placed next to the green items could be used to provide the same information to those who cannot perceive the colour differences. Colour may be used to indicate meaning, as long as it is not the only indication.
Give users choice
Users should be given the option of altering the text presentation style. This can be achieved by providing a simple menu containing a few well-chosen pre-set styles, such as:
- Standard presentation
- Large text
- High Contrast 1 (larger very light text on a dark
background) - High Contrast 2 (larger dark text on a very light
background)
The option to adjust each parameter individually text size, typeface, text colour, background colour, etc. Can also be provided. As this will increases complexity, requiring a significant level of set-up work by the user, it should only be used in conjunction with the simple menu of pre-set styles, as an alternative, but not as a replacement.
If size changes are allowed, care should be taken to ensure that the largest text size does not result in the text extending beyond the visible area of the display.
Adopt a layout that makes reading easy
Use left-aligned text in preference to centred, right-aligned or justified text.
Use short paragraphs in preference to long ones.
Avoid using multiple columns of text as these can lead to content comprehension problems or disorientation for some users. If multiple columns are appropriate, to indicate logical relationships for example, ensure there is a sufficient margin between columns and an adequate column width when the selected font size is large.
Text should have adequate line and paragraph spacing. Recommended line spacing is at least half the height of the text. Recommended paragraph spacing is one and a half times the line spacing.
Avoid the need for scrolling, which is difficult for some people, causing them to lose track of where they are or resulting in important options disappearing off screen. If it is important to put more text on one screen than can fit without scrolling, an embedded scrolling text box can be used to ensure that other information or functions remain on screen while scrolling.
How you could test for this
To find out whether text and graphics are easily read, it is necessary to run tests with a wide range of users, including people with vision impairments, including colour vision deficiencies, and people with reading disorders such as dyslexia.
It can also be useful to collect feedback from customers who have been using the on-screen interface for a period of time. Asking them about what changes might make it easier for them to use is likely to reveal any needs for improved clarity of text or graphics. These questions could be addressed within general long term user trials encompassing the whole process of setting up, learning and using the equipment.