PHP snippet to convert RGB to HSL and HSL to RGB.

rgbToHSL.php

<?php
function rgbToHsl($r, $g, $b) 
{
	$r /= 255;
	$g /= 255;
	$b /= 255;

    $max = max($r, $g, $b);
	$min = min($r, $g, $b);

	$l = ($max + $min) / 2;
	$d = $max - $min;

    if ($d == 0) {
        $h = $s = 0; // achromatic
    }
    else {
        $s = $d / (1 - abs(2 * $l - 1));

		switch ($max) {
	        case $r:
	            $h = 60 * fmod((($g - $b) / $d), 6); 
                if ($b > $g) {
                    $h += 360;
                }
                break;
            case $g: 
                $h = 60 * (($b - $r) / $d + 2); 
                break;
            case $b: 
                $h = 60 * (($r - $g ) / $d + 4); 
                break;
        }
	}

	return [round($h, 2), round($s, 2), round($l, 2)];
}

function hslToRgb($h, $s, $l)
{
    $c = (1 - abs(2 * $l - 1)) * $s;
	$x = $c * (1 - abs(fmod(($h / 60), 2) - 1));
	$m = $l - ($c / 2);

	if ($h < 60) {
		$r = $c;
		$g = $x;
		$b = 0;
	}
    else if ($h < 120) {
		$r = $x;
		$g = $c;
		$b = 0;			
	}
    else if ($h < 180) {
		$r = 0;
		$g = $c;
		$b = $x;					
	}
    else if ($h < 240) {
		$r = 0;
		$g = $x;
		$b = $c;
	}
    else if ($h < 300) {
		$r = $x;
		$g = 0;
		$b = $c;
	}
    else {
		$r = $c;
		$g = 0;
		$b = $x;
	}

	$r = ($r + $m) * 255;
	$g = ($g + $m) * 255;
	$b = ($b + $m) * 255;

    return [floor($r), floor($g), floor($b)];
}
?>