php图片压缩成指定大小的方法

1、按照指定的尺寸压缩图片

/**
* 按照指定的尺寸压缩图片
* @param $source_path  原图路径
* @param $target_path  保存路径
* @param $imgWidth目标宽度
* @param $imgHeight    目标高度
* @return bool|string
*/
    function resize_image($source_path,$target_path,$imgWidth,$imgHeight)
    {
   $source_info = getimagesize($source_path);
   $source_mime = $source_info['mime'];
   switch ($source_mime)
   {
  case 'image/gif':
 $source_image = imagecreatefromgif($source_path);
 break;

  case 'image/jpeg':
 $source_image = imagecreatefromjpeg($source_path);
 break;

  case 'image/png':
 $source_image = imagecreatefrompng($source_path);
 break;

  default:
 return false;
 break;
   }
   $target_image= imagecreatetruecolor($imgWidth, $imgHeight); //创建一个彩色的底图
   imagecopyresampled($target_image, $source_image, 0, 0, 0, 0, $imgWidth, $imgHeight, $source_info[0], $source_info[1]);
   //保存图片到本地
   $dir = ''.$target_path. '/'. date("Ymd") . '/';
   if (!is_dir($dir)) {
  mkdir($dir, 0777);
   }

   $fileName = $dir.date("YmdHis").uniqid().'.jpg';
   if(!imagejpeg($target_image,'./'.$fileName)){
  $fileName = '';
   }
   imagedestroy($target_image);
   return $fileName;
    }

2、按照比例裁剪图片

/**
* 图像裁剪
* @param $title string 原图路径
* @param $content string 需要裁剪的宽
* @param $encode string 需要裁剪的高
* @param $target_path string 需要保存的路径
*/
    function image_cropper($source_path, $target_width, $target_height, $target_path)
    {
   $source_info= getimagesize($source_path);
   $source_width= $source_info[0];
   $source_height= $source_info[1];
   $source_mime= $source_info['mime'];
   $source_ratio= $source_height / $source_width;
   $target_ratio= $target_height / $target_width;


   if ($source_ratio > $target_ratio) // 源图过高
   {
  $cropped_width = $source_width;
  $cropped_height = $source_width * $target_ratio;
  $source_x = 0;
  $source_y = ($source_height - $cropped_height) / 2;

   }elseif ($source_ratio < $target_ratio){  // 源图过宽

  $cropped_width = $source_height / $target_ratio;
  $cropped_height = $source_height;
  $source_x = ($source_width - $cropped_width) / 2;
  $source_y = 0;
   }else{ // 源图适中

  $cropped_width = $source_width;
  $cropped_height = $source_height;
  $source_x = 0;
  $source_y = 0;
   }

   switch ($source_mime)
   {
  case 'image/gif':
 $source_image = imagecreatefromgif($source_path);
 break;

  case 'image/jpeg':
 $source_image = imagecreatefromjpeg($source_path);
 break;

  case 'image/png':
 $source_image = imagecreatefrompng($source_path);
 break;

  default:
 return false;
 break;
   }

   $target_image = imagecreatetruecolor($target_width, $target_height);
   $cropped_image = imagecreatetruecolor($cropped_width, $cropped_height);

   // 裁剪
   imagecopy($cropped_image, $source_image, 0, 0, $source_x, $source_y, $cropped_width, $cropped_height);
   // 缩放
   imagecopyresampled($target_image, $cropped_image, 0, 0, 0, 0, $target_width, $target_height, $cropped_width, $cropped_height);

   //保存图片到本地(两者选一)
   $dir = ''.$target_path. '/'. date("Ymd") . '/';
   if (!is_dir($dir)) {
  mkdir($dir, 0777);
   }

   $fileName = $dir.date("YmdHis").uniqid().'.jpg';
   if(!imagejpeg($target_image,'./'.$fileName)){
  $fileName = '';
   }
   imagedestroy($target_image);
   return $fileName;
    }

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