“foreground and background colour combinations provide sufficient contrast when viewed by someone having colour deficits, or when viewed on a black and white screen.” Assessing conformance with Checkpoint 2.2 of the Web Content Accessibility Guidelines 1.0Ĭheckpoint 2.2 of the WCAG 1.0 requires that The Colour Contrast Analyser ( CCA) is useful to help determine, in particular, the legibility of text on a web page and the legibility of image based representations of text. (maximum (Red value 1, Red value 2) – minimum (Red value 1, Red value 2)) + (maximum (Green value 1, Green value 2) – minimum (Green value 1, Green value 2)) + (maximum (Blue value 1, Blue value 2) – minimum (Blue value 1, Blue value 2))The difference between the background colour and the foreground colour should be greater than 500. Colour Difference FormulaĬolour difference is determined by the following formula: ![]() This brightness value gives a perceived brightness for a colour. Note: This algorithm is taken from a formula for converting RGB values to YIQ values. ((Red value X 299) + (Green value X 587) + (Blue value X 114)) / 1000The difference between the background brightness, and the foreground brightness should be greater than 125. Colour Brightness FormulaĬolour brightness is determined by the following formula: Note: Hewlett Packard (HP) provide an online colour contrast verification tool that uses the W3C algorithms, but sets the Colour Difference range at > 400, which results in a greater range of foreground & background colour combinations being deemed acceptable. “ Two colours are considered to provide good colour visibility if the brightness difference and the colour difference between the two colours are greater than a set range.” The range suggested by the W3C is > 125 for colour brightness and > 500 for colour difference. ![]() Determining “colour visibility” is based on algorithms suggested by the World Wide Web Consortium (W3C): It is a tool for checking foreground & background colour combinations to determine if they provide good colour visibility. Support further development: Make a using PayPal. ![]() Colour Contrast Analyser 1.0 On this page:
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