PHP Image Resizer

gistfile1.php

function resize($incoming, $max_width, $max_height, $crop = true){
    $original_name = explode('.', $incoming);
    $original_ext = strtolower(array_pop($original_name));
    $original_name = implode('.', $original_name);
    if(!file_exists($incoming)) $error = 'Original file doesn\'t exist.';
    else{
        if(!$original_info = getimagesize($incoming)) $error = 'Original file isn\'t a valid image.';
        else{
            $original_width = $original_info[0];
            $original_height = $original_info[1];
            switch($original_ext){
                case 'jpg' :
                case 'jpeg';
                    $original = imagecreatefromjpeg($incoming);
                    break;
                case 'png';
                    $original = imagecreatefrompng($incoming);
                    break;
                case 'gif';
                    $original = imagecreatefromgif($incoming);
                    break;
            }
            if(!$original) $error = 'Invalid format.';
            else{
                $original = imagecreatefromjpeg($incoming);
                $x = 0;
                $y = 0;
                if($max_width == 0) $max_width = ($max_height / $original_height) * $original_width;
                if($max_height == 0) $max_height = ($max_width / $original_width) * $original_height;
                $new_width = $max_width;
                $new_height = ($max_width / $original_width) * $original_height;
                if($crop){
                    if($new_height < $max_height){
                        $new_height = $max_height;
                        $new_width = ($max_height / $original_height) * $original_width;
                    }
                    $x = ($max_width / 2) - ($new_width / 2);
                    $y = ($max_height / 2) - ($new_height / 2);
                    $temp = imagecreatetruecolor($max_width, $max_height);
                }
                else{
                    if($new_height > $max_height){
                        $new_height = $max_height;
                        $new_width = ($max_height / $original_height) * $original_width;
                    }
                    $temp = imagecreatetruecolor($new_width, $new_height);
                }
                imagecopyresampled($temp, $original, $x, $y, 0, 0, $new_width, $new_height, $original_width, $original_height);
                switch($original_ext){
                    case 'jpg' :
                    case 'jpeg';
                        imagejpeg($temp, $original_name . '_small.' . $original_ext, 100);
                        break;
                    case 'png';
                        imagepng($temp, $original_name . '_small.' . $original_ext);
                        break;
                    case 'gif';
                        imagegif($temp, $original_name . '_small.' . $original_ext);
                        break;
                }
                imagedestroy($original);
                imagedestroy($temp);
                return $original_name . '_small.' . $original_ext;
            }
        }
    }
    die($error);
}