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:

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