tmcw/wcag-contrast

wcag color contrast

This module produces WCAG contrast ratio measurement and scoring. It's an accessibility standard, intended to make sure websites have high enough contrast to be readable by everyone, including people with low vision and age-related vision problems. This module is a low-level utility, useful for its implementation of the underlying math: to test a page, you'll want to use something like Google Chrome’s Lighthouse tools, or the axe extension for Chrome and Firefox.

I (personally, speaking as Tom) have doubts about the universality, accuracy, and application of this particular standard. High contrast is a good value, but I argue that the standard is over-strict and doesn't precisely match human perception.

API

luminance

Get the contrast ratio between two relative luminance values

Parameters

• a number luminance value
• b number luminance value

Examples

luminance(1, 1); // = 1

Returns number contrast ratio

rgb

Get a score for the contrast between two colors as rgb triplets

Parameters

• a array
• b array

Examples

rgb([0, 0, 0], [255, 255, 255]); // = 21

Returns number contrast ratio

hex

Get a score for the contrast between two colors as hex strings

Parameters

• a string hex value
• b string hex value

Examples

hex('#000', '#fff'); // = 21

Returns number contrast ratio

score

Get a textual score from a numeric contrast value

Parameters

• contrast number

Examples

score(10); // = 'AAA'

Returns string score