PHP Re-size Image

<?php
function resize_image($img, $thumb_width, $newfilename) {
 	$max_width=$thumb_width;
    //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;
    }   
    /*** calculate the aspect ratio ***/
    $aspect_ratio = (float) $height_orig / $width_orig;
    /*** calulate the thumbnail width based on the height ***/
	$thumb_width = $max_width;
    $thumb_height = round($thumb_width * $aspect_ratio);
	//while($thumb_height>$max_width) {
//        $thumb_width-=10;
//        $thumb_height = round($thumb_width * $aspect_ratio);
//    }   
    $newImg = imagecreatetruecolor($thumb_width, $thumb_height);   
    /* Check if this image is PNG or GIF, then set if Transparent*/ 
    if(($image_type == 1) || ($image_type==3)) {
        imagealphablending($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 $newfilenamea
    switch ($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;
}
?>