Converts a hex color value to a hue-compatible CIE-space-based x, y and brightness.

PHP-Hex-To-CIE.php

<?php

$hex = 'ff00ff';
$rgb = hex2rgb($hex);
$xybri = rgbToXyBri($rgb);
echo $hex.' becomes x:'.$xybri['x'].', y: '.$xybri['y'].' and brightness: '.$xybri['bri'];

function rgbToXyBri($rgb) {
  $r = $rgb['r'];
  $g = $rgb['g'];
  $b = $rgb['b'];
  if ($r < 0 || $r > 1 || $g < 0 || $g > 1 || $b < 0 || $b > 1) {
    throw new Exception('Invalid RGB array');
  }
  
  $rt = ($r > 0.04045) ? pow(($r + 0.055) / (1.0 + 0.055), 2.4) : ($r / 12.92);
  $gt = ($g > 0.04045) ? pow(($g + 0.055) / (1.0 + 0.055), 2.4) : ($g / 12.92);
  $bt = ($b > 0.04045) ? pow(($b + 0.055) / (1.0 + 0.055), 2.4) : ($b / 12.92);

  $cie_x = $rt * 0.649926 + $gt * 0.103455 + $bt * 0.197109;
  $cie_y = $rt * 0.234327 + $gt * 0.743075 + $bt * 0.022598;
  $cie_z = $rt * 0.0000000 + $gt * 0.053077 + $bt * 1.035763;
  
  $hue_x = $cie_x / ($cie_x + $cie_y + $cie_z);
  $hue_y = $cie_y / ($cie_x + $cie_y + $cie_z);
  
  return array('x'=>$hue_x,'y'=>$hue_y,'bri'=>$cie_y);
  
}

function hex2rgb($hex) {
   $hex = str_replace("#", "", $hex);

   if(strlen($hex) == 3) {
      $r = hexdec(substr($hex,0,1).substr($hex,0,1));
      $g = hexdec(substr($hex,1,1).substr($hex,1,1));
      $b = hexdec(substr($hex,2,1).substr($hex,2,1));
   } else {
      $r = hexdec(substr($hex,0,2));
      $g = hexdec(substr($hex,2,2));
      $b = hexdec(substr($hex,4,2));
   }
   $rgb = array('r'=>($r / 255),'g'=>($g / 255),'b'=>($b / 255));
   return $rgb;
}