PHP 压缩图片质量

$imageFileName = './test2.jpg';
$uploadfile_resize = $imageFileName;
$pic_width_max = 1000;
$pic_height_max = 1000;
$file_type = getimagesize($imageFileName)['mime'];

if($file_type == "image/pjpeg"||$file_type == "image/jpg"|$file_type == "image/jpeg"){
    $im = imagecreatefromjpeg($imageFileName);
}else if($file_type == "image/x-png"){
    $im = imagecreatefromjpeg($imageFileName);
}else if($file_type == "image/gif"){
    $im = imagecreatefromjpeg($imageFileName);
}else {//默认jpg
    $im = imagecreatefromjpeg($imageFileName);
}
if($im) {
    ResizeImage($im, $pic_width_max, $pic_height_max, $uploadfile_resize);
    ImageDestroy($im);
}

function resizeImage($uploadfile,$maxwidth,$maxheight,$filename){
//取得当前图片大小
    $width = imagesx($uploadfile);
    $height = imagesy($uploadfile);

    //压缩比值
    $i=0.5;
    //生成缩略图的大小
    if(($width > $maxwidth) || ($height > $maxheight)){
        $newwidth = $width * $i;
        $newheight = $height * $i;
        if(function_exists("imagecopyresampled")){
            $uploaddir_resize = imagecreatetruecolor($newwidth, $newheight);
            //echo $uploaddir_resize;
            imagecopyresampled($uploaddir_resize, $uploadfile, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);
        }else{
            $uploaddir_resize = imagecreate($newwidth, $newheight);
            imagecopyresized($uploaddir_resize, $uploadfile, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);
        }

        ImageJpeg ($uploaddir_resize,$filename);
        ImageDestroy ($uploaddir_resize);
    }else{
        ImageJpeg ($uploadfile,$filename);
    }
}