contrast ratio calculator

contrast_ratio.js

// Ported from http://stackoverflow.com/a/17343790/905036
function relativeLuminance(col) {
	//Remove any leading #
	var shorthandRegex = /^#?([a-f\d])([a-f\d])([a-f\d])$/i;
	var components = {};
	col = col.replace(shorthandRegex, function(m, r, g, b) {
		return r + r + g + g + b + b;
	});

	//Convert hex to 0-1 scale
	components = {
		r: parseInt(col.substr(0, 2), 16) / 255,
		g: parseInt(col.substr(2, 2), 16) / 255,
		b: parseInt(col.substr(4, 2), 16) / 255
	};

	//Correct for sRGB
	for (var i in components) {
		var v = components[i];

		if (v <= 0.03928) {
			components[i] = v / 12.92;
		}
		else {
			components[i] = Math.pow(((v + 0.055) / 1.055), 2.4);
		}
	}

	//Calculate relative luminance using ITU-R BT. 709 coefficients
	return (components.r * 0.2126) + (components.g * 0.7152) + (components.b * 0.0722);
}

function contrastRatio(c1, c2) {
	var y1 = relativeLuminance(c1);
	var y2 = relativeLuminance(c2);

	//Arrange so y1 is lightest
	if (y1 < y2) {
		y3 = y1;
		y1 = y2;
		y2 = y3;
	}

	return (y1 + 0.05) / (y2 + 0.05);
}