PHP jpeg image created from file is low quality

This script is used to randomly select a background whenever you access the site. I do this by setting background-image in my stylesheet to this php file

It works fine, but the image is compressed heavily. Is there a way to keep the quality?

<?php

  $img = array('dx1.jpg', 'dx2.jpg', 'dx3.jpg' ); // Adds the names of all images into an array

  $i = rand(0, count($img)-1); // Generates a random number (max being the last element's index from the array)

  $chosenimg = "$img[$i]"; // Sets the variable $chosenimg to equal to whatever the random image name was (from the above array)

  $image = imagecreatefromjpeg($chosenimg);

  imagealphablending($image, false);
  imagesavealpha($image, true);

  header('Content-Type: image/jpeg');


  imagejpeg($image);
  imagedestroy($image);

?>