PHP实现图片压缩

/** * 生成图片 * @param string $im 源图片路径 * @param string $dest 目标图片路径 * @param int $maxwidth 生成图片宽 * @param int $maxheight 生成图片高 */function resizeImage($im, $dest, $maxwidth, $maxheight) { $img = getimagesize($im); switch ($img[2]) {  case 1:   $im = @imagecreatefromgif($im);   break;  case 2:   $im = @imagecreatefromjpeg($im);   break;  case 3:   $im = @imagecreatefrompng($im);   break; }  $pic_width = imagesx($im); $pic_height = imagesy($im); $resizewidth_tag = false; $resizeheight_tag = false; if (($maxwidth && $pic_width > $maxwidth) || ($maxheight && $pic_height > $maxheight)) {  if ($maxwidth && $pic_width > $maxwidth) {   $widthratio = $maxwidth / $pic_width;   $resizewidth_tag = true;  }   if ($maxheight && $pic_height > $maxheight) {   $heightratio = $maxheight / $pic_height;   $resizeheight_tag = true;  }   if ($resizewidth_tag && $resizeheight_tag) {   if ($widthratio < $heightratio)    $ratio = $widthratio;   else    $ratio = $heightratio;  }    if ($resizewidth_tag && !$resizeheight_tag)   $ratio = $widthratio;  if ($resizeheight_tag && !$resizewidth_tag)   $ratio = $heightratio;  $newwidth = $pic_width * $ratio;  $newheight = $pic_height * $ratio;   if (function_exists("imagecopyresampled")) {   $newim = imagecreatetruecolor($newwidth, $newheight);   imagecopyresampled($newim, $im, 0, 0, 0, 0, $newwidth, $newheight, $pic_width, $pic_height);  } else {   $newim = imagecreate($newwidth, $newheight);   imagecopyresized($newim, $im, 0, 0, 0, 0, $newwidth, $newheight, $pic_width, $pic_height);  }   imagejpeg($newim, $dest);  imagedestroy($newim); } else {  imagejpeg($im, $dest); }} /** * 图片压缩处理 * @param string $sFile 源图片路径 * @param int $iWidth 自定义图片宽度 * @param int $iHeight 自定义图片高度 * @return string  压缩后的图片路径 */function getThumb($sFile,$iWidth,$iHeight){ //图片公共路径 $public_path = ''; //判断该图片是否存在 if(!file_exists($public_path.$sFile)) return $sFile; //判断图片格式(图片文件后缀) $extend = explode("." , $sFile); $attach_fileext = strtolower($extend[count($extend) - 1]); if (!in_array($attach_fileext, array('jpg','png','jpeg'))){  return ''; } //压缩图片文件名称 $sFileNameS = str_replace(".".$attach_fileext, "_".$iWidth.'_'.$iHeight.'.'.$attach_fileext, $sFile); //判断是否已压缩图片，若是则返回压缩图片路径 if(file_exists($public_path.$sFileNameS)){  return $sFileNameS; }  //生成压缩图片，并存储到原图同路径下 resizeImage($public_path.$sFile, $public_path.$sFileNameS, $iWidth, $iHeight); if(!file_exists($public_path.$sFileNameS)){  return $sFile; } return $sFileNameS;}

//原图 img/img.jpg//生成压缩图 img/img_300_300.jpggetThumb('img/img.jpg',300,300);