Convert RGB color values to HSL and vice versa in PHP. Adapted from the Javascript over here: https://github.com/mjijackson/mjijackson.github.com/blob/master/2008/02/rgb-to-hsl-and-rgb-to-hsv-color-model-conversion-algorithms-in-javascript.txt

rgb2hsl.php

<?php

//adapted from https://github.com/mjijackson/mjijackson.github.com/blob/master/2008/02/rgb-to-hsl-and-rgb-to-hsv-color-model-conversion-algorithms-in-javascript.txt

/**
 * @param array $rgb integer values (r,g,b) in range 0-255
 *
 * @return array HSL
 */
function rgb2hsl($rgb){
	$r = $rgb[0]/255;
	$g = $rgb[1]/255;
	$b = $rgb[2]/255;

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

	$h = $s = 0;
	$l = ($max+$min)/2;

	if($d > 0){
		$s = $l > 0.5 ? $d/(2-$max-$min) : $d/($max+$min);
		switch($max){
			case $r: $h = ($g-$b)/$d+($g < $b ? 6 : 0); break;
			case $g: $h = ($b-$r)/$d+2; break;
			case $b: $h = ($r-$g)/$d+4; break;
		}
		$h /= 6;
	}

	return array($h, $s, $l);
}

/**
 * @param array $hsl float values (h,s,l) in range 0.0-1.0
 *
 * @return array RGB
 */
function hsl2rgb($hsl){
	$h = $hsl[0];
	$s = $hsl[1];
	$l = $hsl[2];

	$r = $g = $b = $l;
	if($s <> 0){
		$q = $l < 0.5 ? $l*(1+$s) : $l+$s-$l*$s;
		$p = 2*$l-$q;
		$r = hue2rgb($p, $q, $h+1/3);
		$g = hue2rgb($p, $q, $h);
		$b = hue2rgb($p, $q, $h-1/3);
	}

	return array($r*255, $g*255, $b*255);
}

function hue2rgb($p, $q, $t){
	if($t < 0) $t += 1;
	if($t > 1) $t -= 1;
	if($t < 1/6) return $p+($q-$p)*6*$t;
	if($t < 1/2) return $q;
	if($t < 2/3) return $p+($q-$p)*(2/3-$t)*6;
	return $p;
}


?>