@mdhnpm/color-contrast-ratio-calculator

color-contrast-ratio-calculator

Node module to calculate the contrast of two colors for accessibity based on Web Contenet Accessibility Guideline (WCAG).

Example

colorContrastRatioCalculator takes two argument.

• foregroundColor: a hexadecimal string (with or without #) or an array of RBG.
• backgroundColor: a hexadecimal string (with or without #) or an array of RBG.

import { colorContrastRatioCalculator } from '@mdhnpm/color-contrast-ratio-calculator';

colorContrastRatioCalculator('11AA55', 'AA8811'); // return 1.11

colorContrastRatioCalculator('#E9FAF5', '#FFFFFF'); // return 1.08

colorContrastRatioCalculator([0, 0, 0], [255, 255, 255]); // return 21

Color Contrast

As part of web accessibility requirements, we need to have the color contrast between background and foreground content (usually text) should be great enough to ensure legibility (see here)

WCAG 2.0 level AA requires a contrast ratio of at least 4.5:1 for normal text and 3:1 for large text. WCAG 2.1 requires a contrast ratio of at least 3:1 for graphics and user interface components (such as form input borders). WCAG Level AAA requires a contrast ratio of at least 7:1 for normal text and 4.5:1 for large text.

Large text is defined as 14 point (typically 18.66px) and bold or larger, or 18 point (typically 24px) or larger.

Contrast ratio is calculated as (L1 + 0.05) / (L2 + 0.05) where

• L1 is the relative luminance of the lighter of the colors, and
• L2 is the relative luminance of the darker of the colors.

See Contrast Ration here

According to WCAG, the relative luminance of a color for the sRGB colorspace is defined as L = 0.2126 * R + 0.7152 * G + 0.0722 * B where R, G and B are defined as:

• if RsRGB <= 0.03928 then R = RsRGB/12.92 else R = ((RsRGB+0.055)/1.055) ^ 2.4
• if GsRGB <= 0.03928 then G = GsRGB/12.92 else G = ((GsRGB+0.055)/1.055) ^ 2.4
• if BsRGB <= 0.03928 then B = BsRGB/12.92 else B = ((BsRGB+0.055)/1.055) ^ 2.4

and RsRGB, GsRGB, and BsRGB are defined as:

• RsRGB = R8bit/255
• GsRGB = G8bit/255
• BsRGB = B8bit/255

See here for the details.