亮度对比算法
我觉得最好的办法是Luminosity Contrast
算法:
function getContrastColor($hexColor)
{
// hexColor RGB
$R1 = hexdec(substr($hexColor, 1, 2));
$G1 = hexdec(substr($hexColor, 3, 2));
$B1 = hexdec(substr($hexColor, 5, 2));
// Black RGB
$blackColor = "#000000";
$R2BlackColor = hexdec(substr($blackColor, 1, 2));
$G2BlackColor = hexdec(substr($blackColor, 3, 2));
$B2BlackColor = hexdec(substr($blackColor, 5, 2));
// Calc contrast ratio
$L1 = 0.2126 * pow($R1 / 255, 2.2) +
0.7152 * pow($G1 / 255, 2.2) +
0.0722 * pow($B1 / 255, 2.2);
$L2 = 0.2126 * pow($R2BlackColor / 255, 2.2) +
0.7152 * pow($G2BlackColor / 255, 2.2) +
0.0722 * pow($B2BlackColor / 255, 2.2);
$contrastRatio = 0;
if ($L1 > $L2) {
$contrastRatio = (int)(($L1 + 0.05) / ($L2 + 0.05));
} else {
$contrastRatio = (int)(($L2 + 0.05) / ($L1 + 0.05));
}
// If contrast is more than 5, return black color
if ($contrastRatio > 5) {
return '#000000';
} else {
// if not, return white color.
return '#FFFFFF';
}
}
// Will return '#FFFFFF'
echo getContrastColor('#FF0000');
一些结果:
NOTE: 字体颜色由前面的函数决定。括号中的数字是对比度。
YIQ算法(不太精确)
Another 最简单且不太精确的方法 called YIQ
(因为它将 RGB 颜色空间转换为YIQ https://en.wikipedia.org/wiki/YIQ):
public function getContrastColor($hexcolor)
{
$r = hexdec(substr($hexcolor, 1, 2));
$g = hexdec(substr($hexcolor, 3, 2));
$b = hexdec(substr($hexcolor, 5, 2));
$yiq = (($r * 299) + ($g * 587) + ($b * 114)) / 1000;
return ($yiq >= 128) ? 'black' : 'white';
}