Accessibility 9: Alt Text
When you think about alternative text, it is sometimes better not to think about text at all. Think, instead, about listening. Imagine someone (or remember someone!) who blethers on, and on, and on. What did you listen to; what did you hear? Think, also, about speaking. When you talk to someone, what is it important to get across; what has to stand out?
Alt text needs to sum up what needs to stand out. I might have a terrific image of a graph, with good white space and clear contrasts, excellent labels complementing an efficient colour key, none of which a non-visual user can see. The labels give text that conveys the information with colour, the colour key is a big bonus for those who can perceive colour, the white space lets all sorts of other users ‘manage’ the graph they are trying to read — but all of it presupposes vision.
It is of some but little use to non-visual users to be told that a graph is describing something, or that it shows something. Instead of describing the visual effects, get to the point. A graph of the mistakes made by BBC live AI subtitling could be given alt text that said just that: ‘a graph of the mistakes made by BBC live AI subtitling’. Having read that alt text, I know nothing. On the other hand, the alternative text could be: ‘graph shows that BBC live subtitling peaks on Fridays’. (Just an example: I do not know if it does.) Writing alternative text means focus on what you are trying to say, not how a picture might have said it.
Alt text can be moody, too. The unseen picture may be there to communicate an atmosphere or emotion, which alt text needs to recreate in only a few words: ‘picture of two people’ just doesn’t cut it. ‘Friends embracing’ might. Alt text for Easy Read can work like this. It communicates the big picture of a situation, not the detail of an argument.
Either way, alt text is not every detail. It has to be short.