php 图片不预览下载

$file = 'uploads/qr_code/qr_code_1.png';

$fileTmp = pathinfo($file);

$fileExt = $fileTmp['extension'];

$saveFileName = (time().uniqid().'.'.$fileExt);

$fp=fopen($file,"r");

$file_size=filesize($file);

//下载文件需要用到的头

Header("Content-type: application/octet-stream");

Header("Accept-Ranges: bytes");

Header("Accept-Length:".$file_size);

Header("Content-Disposition: attachment; filename=".$saveFileName);

$buffer=1024;

$file_count=0;

//向浏览器返回数据

while(!feof($fp) && $file_count<$file_size){

$file_con=fread($fp,$buffer);

$file_count+=$buffer;

echo $file_con;

}

fclose($fp);

exit;