remove black background when resize image in php

 /* image resize in php when form submit */

if(isset($_POST['submit']))
{

  function resize($width, $height){
 

  include('conn.php');
 
  $root=$_POST['root'];
   $category=$_POST['category'];
   $sub_category=$_POST['sub-category'];
  $product_name=$_POST['product_title'];
 
  $product_specification=mysqli_real_escape_string($con,$_POST['product_description']);
 
  list($w, $h) = getimagesize($_FILES['image']['tmp_name']);
  $ratio = max($width/$w, $height/$h);
  $h = ceil($height / $ratio);
  $x = ($w - $width / $ratio) / 2;
  $w = ceil($width / $ratio);
  $path= '../product_images/'.$width.'x'.$height.'_'.$_FILES['image']['name'];
 
  $product_title= $_POST['product_title'];
  $product_description= $_POST['product_description'];
 
 $actual_link = "http://$_SERVER[HTTP_HOST]$_SERVER[REQUEST_URI]";
 $actual_link = dirname($actual_link);
  $full_img_url = $actual_link.'/'.$path;
 

  $sql="insert into `products` (id, root, category, sub_category, product_name, specification, image_path) values('', '".$root."', '".$category."', '".$sub_category."','".$product_name."','".$product_specification."','".$full_img_url."')";

   $result = mysqli_query($con,$sql);
 
  /* read binary data from image file */
  $imgString = file_get_contents($_FILES['image']['tmp_name']);
  /* create image from string */
  $image = imagecreatefromstring($imgString);
 

 
   $tmp = imagecreatetruecolor($width, $height);
  
/*  Below three lines for remove black background when resize img php */
imagecolortransparent($tmp, imagecolorallocatealpha($tmp, 0, 0, 0, 127));
imagealphablending($tmp, false);
imagesavealpha($tmp, true);
  
  
  
  
  imagecopyresampled($tmp, $image,
    0, 0,
    $x, 0,
    $width, $height,
    $w, $h); 
  /* Save image */
  switch ($_FILES['image']['type']) {
    case 'image/jpeg':
      imagejpeg($tmp, $path, 100);
      break;
    case 'image/png':
     
    imagepng($tmp, $path, 0);



       break;
    case 'image/gif':
      imagegif($tmp, $path);
      break;
    default:
      exit;
      break;
  }
  return $path;
  /* cleanup memory */
  imagedestroy($image);
  imagedestroy($tmp);
}


// settings
$max_file_size = 1000*600;
$valid_exts = array('jpeg', 'jpg', 'png', 'gif');
// thumbnail sizes
$sizes = array(600 => 400);

if ($_SERVER['REQUEST_METHOD'] == 'POST' AND isset($_FILES['image'])) {
  if( $_FILES['image']['size'] < $max_file_size ){
    // get file extension
    $ext = strtolower(pathinfo($_FILES['image']['name'], PATHINFO_EXTENSION));
    if (in_array($ext, $valid_exts)) {
      /* resize image */
      foreach ($sizes as $w => $h) {
        $files[] = resize($w, $h);
         if($files)
   {
      $message="Project Added successfully";
   }
   else
   {
      $message="Project Not Added";
   }
       
      }

    } else {
      $msg = 'Unsupported file';
    }
  } else{
    $msg = 'Please upload image smaller than 200KB';
  }
}

}