Function for finding a pixel's RGBa values.
function getPixelColor($image, $x, $y) {
  $color_index = imagecolorat($image->resource, $x, $y);
  $transparent_index = imagecolortransparent($image->resource);
  if ($color_index == $transparent_index) {
    return array(
      0,
      0,
      0,
      127,
    );
  }
  return array_values(imagecolorsforindex($image->resource, $color_index));
}