php生成图片缩略图的方法

function make_thumb($src,$dest,$desired_width)
{
 
  /* read the source image */
  $source_image = imagecreatefromjpeg($src);
  $width = imagesx($source_image);
  $height = imagesy($source_image);
  /* find the "desired height" of this thumbnail,relative to the desired width */
  $desired_height = floor($height*($desired_width/$width));
  /* create a new,"virtual" image */
  $virtual_image = imagecreatetruecolor($desired_width,$desired_height);
  /* copy source image at a resized size */
  imagecopyresized($virtual_image,$source_image,$desired_width,$desired_height,$width,$height);
  /* create the physical thumbnail image to its destination */
  imagejpeg($virtual_image,83);
}