Some images are frequently associated with text to give information: this is the case of “unread messages” when a badge shows the number of messages to read and which describes a “message”. However, this raises an issue for users of screen readers that vocalize abbreviations literally: to correct these vocalizations, simply place a text alternative on the text that will contain the expanded text. Space on mobile is reduced, we often use abbreviations for text. On mobile, where all components can have a text alternative, it is possible to enrich the native vocalization of an element, including a simple text. Thanks to the text alternatives, a visually impaired user can use an application without loss of information.Īs for images, it is important to add a text alternative when information is not available for the VoiceOver users: this is the case of components that provide information by colour, shape, position, sound… The Accessibility Inspector tool provides a specific Color Contrast Calculator feature that reaches the same purpose since Xcode 11. The Colour Contrast Analyser application (version 2.3) can quickly measure colour contrast levels (free for Windows and Mac). In this case, the Differentiate Without Colour accessibility option will allow this display only at the user's demand. These two elements propose to the greatest number a very comfortable reading that the contrast unfortunately can't assure on its own (see the end of this section to discover the proper tool for automatic calculations).Ĭhoosing the appropriate colours finally amounts to checking each and every constraint previously exposed for:Īdding different forms to differentiate the information provided only by colours may unnecessarily overlay the graphic interface if the user doesn't need them. In order to deliver an optimal user experience in accessibility, it's mandatory to take into account the following two additional colorimetric characteristics: However, to substantially improve the legibility, it's still better and highly recommended to write dark text on a light background (text with a positive contrast). With Dynamic Type whose purpose is to adapt the font size according to the user settings, the contrast isn't necessary fixed and must be adapted to the text size.Ībide by the contrast ratio is crucial but a too high contrast accentuates eye strain and may cause a visual sensation of blurring on the text.įor light sensitive persons, a pure black text on a pure white background may significantly make the halo effect appear that will force to squint to read. The normal font type will require a higher contrast than the previous case.

The bold font type will allow a weaker contrast for the lowest font sizes. Some colours are associated with concepts or feelings but we must never forget the part of the population that does not correctly distinguish colours. Colours have a very important role in the transmission of information.

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