contrast_ratio

The WCAG contrast ratio between two colors, from 1.0 (identical) to 21.0 (black on white).

It is (L1 + 0.05) / (L2 + 0.05) where L1 is the relative luminance of the lighter color and L2 of the darker one, so the order of the arguments does not matter. WCAG 2.x asks for at least 4.5 for normal text and 3.0 for large text (level AA), 7.0 and 4.5 for AAA.

Import

use helpers4::color::contrast_ratio;

Cargo feature color (enabled by default). To compile only this module:

cargo add helpers4 --no-default-features --features color

or in Cargo.toml:

[dependencies]
helpers4 = { version = "0.0.6", default-features = false, features = ["color"] }

Signature

pub fn contrast_ratio(a: Rgb, b: Rgb) -> f64

Parameters

Parameter	Type	Description
a	Rgb	One color, for instance the text.
b	Rgb	The other color, for instance its background.

Returns

f64 — The ratio, 1.0..=21.0.

Examples

use helpers4::color::{contrast_ratio, Rgb};

let ratio = contrast_ratio(Rgb::new(0, 0, 0), Rgb::new(255, 255, 255));
assert!((ratio - 21.0).abs() < 1e-9);
assert!(contrast_ratio(Rgb::parse("#767676")?, Rgb::new(255, 255, 255)) >= 4.5);

Source

src/color/contrast_ratio.rs