PHP resize

<?php
function resize_img($img, $max_size, $newfilename) {

  //Check if GD extension is loaded
  if (!extension_loaded('gd') && !extension_loaded('gd2')) {
    trigger_error('GD is not loaded', E_USER_WARNING);
    return false;
  }

  //Get Image size info
  list($width_orig, $height_orig, $image_type) = getimagesize($img);

  switch ($image_type) {
    case 1: $im = imagecreatefromgif($img); break;
    case 2: $im = imagecreatefromjpeg($img);  break;
    case 3: $im = imagecreatefrompng($img); break;
    default:  trigger_error('Unsupported filetype!', E_USER_WARNING);  break;
  }

  if ($width_orig > $height_orig) {
    $thumb_width = $max_size;
    $aspect_ratio = (float) $height_orig / $width_orig;
    $thumb_height = round($thumb_width * $aspect_ratio);
  }
  else {
    $thumb_height = $max_size;
    $aspect_ratio = (float) $width_orig / $height_orig;
    $thumb_width = round($thumb_height * $aspect_ratio);
  }

  $newImg = imagecreatetruecolor($thumb_width, $thumb_height);

  // Check if this image is PNG or GIF, then set if Transparent
  if(($image_type == 1) OR ($image_type==3)) {
    imagealphablending($newImg, false);
    imagesavealpha($newImg,true);
    $transparent = imagecolorallocatealpha($newImg, 255, 255, 255, 127);
    imagefilledrectangle($newImg, 0, 0, $thumb_width, $thumb_height, $transparent);
  }
  imagecopyresampled($newImg, $im, 0, 0, 0, 0, $thumb_width, $thumb_height, $width_orig, $height_orig);

  //Generate the file, and rename it to $newfilename
  switch ($image_type) {
    case 1: imagegif($newImg, $newfilename); break;
    case 2: imagejpeg($newImg, $newfilename); break;
    case 3: imagepng($newImg, $newfilename); break;
    default: trigger_error('Failed resize image!', E_USER_WARNING); break;
  }

  return $newfilename;
}
?>

<?php
  $source = './images/orig/wallpaper.jpg'; // súbor, z ktorého chceš zmenšeninu vytvoriť
  $target = './images/800x600/wallpaper.jpg'; cesta a názov súboru, kde to chceš uložiť nový zmenšený súbor

  resize_img($source, '800', $target);
?>