Get the color palette for an image using PHP

Posted on Wednesday January 04, 2012 by Eric Potvin

Have you every wonder what kind of colors you should get to match your logo for your website? Here's a very simple script that generates a color palette for an image using the PHP GD library. This will help you find out which colors you can use to improve quality of your site.

Requirement:

  • GD Library for PHP

The script:

function detectColors($image, $num, $level = 5) {
  $level = (int)$level;
  $palette = array();
  $size = getimagesize($image);
  if(!$size) {
    return FALSE;
  }
  switch($size['mime']) {
    case 'image/jpeg':
      $img = imagecreatefromjpeg($image);
      break;
    case 'image/png':
      $img = imagecreatefrompng($image);
      break;
    case 'image/gif':
      $img = imagecreatefromgif($image);
      break;
    default:
      return FALSE;
  }
  if(!$img) {
    return FALSE;
  }
  for($i = 0; $i < $size[0]; $i += $level) {
    for($j = 0; $j < $size[1]; $j += $level) {
      $thisColor = imagecolorat($img, $i, $j);
      $rgb = imagecolorsforindex($img, $thisColor);
      $color = sprintf('%02X%02X%02X', (round(round(($rgb['red'] / 0x33)) * 0x33)), round(round(($rgb['green'] / 0x33)) * 0x33), round(round(($rgb['blue'] / 0x33)) * 0x33));
      $palette[$color] = isset($palette[$color]) ? ++$palette[$color] : 1;
    }
  }
  arsort($palette);
  return array_slice(array_keys($palette), 0, $num);
}

$img = 'icon.png';
$palette = detectColors($img, 6, 1);
echo '<img src="' . $img . '" />';
echo '<table>';
foreach($palette as $color) {
  echo '<tr><td style="background:#' . $color . '; width:36px;"></td><td>#' . $color . '</td></tr>';
}
echo '</table>';

Example:

Ubuntu Logo

Will output:

#FFFFFF
#000000
#CCCCCC
#FFCC99
#FF6600
#FF9900