Compute WCAG 2.1 contrast ratio between two colours

Returns the contrast ratio as defined by WCAG 2.1. Values range from 1 (no contrast) to 21 (black on white). The minimum for non-text graphical elements at Level AA is 3.0:1.

Usage

pattern_contrast(colour1, colour2)

Arguments

colour1, colour2

Character colour strings (any format accepted by grDevices::col2rgb()).

Value

A numeric scalar: the contrast ratio (always >= 1).

Examples

pattern_contrast("black", "white")   # 21
#> [1] 21
pattern_contrast("black", "#4472C4") # typically around 5-6
#> [1] 4.449819
pattern_contrast("grey60", "white")  # typically around 3.5
#> [1] 2.849028