rgb2hsl · PHP Function to Convert Colors from RGB to HSL

function rgb2hsl ($r, $g, $b) {

    $r_ratio = $r / 255;
    $g_ratio = $g / 255;
    $b_ratio = $b / 255;

    $min = min($r_ratio, $b_ratio, $g_ratio);
    $max = max($r_ratio, $b_ratio, $g_ratio);

    $l_ratio = ($min + $max) / 2;

    $range = $max - $min;
    if ($range === 0) return ['h' => 0, 's' => 0, 'l' => 0];

    $h_ratio = (function () use ($r_ratio, $g_ratio, $b_ratio, $max, $range) {
        if ($max === $r_ratio) return ($g_ratio - $b_ratio) / $range;
        if ($max === $g_ratio) return 2 + ($b_ratio - $r_ratio) / $range;
        return 4 + ($r_ratio - $g_ratio) / $range;
    })();

    $s_range = min($l_ratio, 1 - $l_ratio);

    return [
        'h' => fmod(($h_ratio + 6), 6) * 60,
        's' => ($max - $min) / (2 * $s_range) * 100,
        'l' => $l_ratio * 100,
    ];

}