這幾天做了手機上傳照片並裁出縮圖的介面的測試，發現不管怎麼，生成的縮圖都是一片漆黑。:-(

然後就把這個縮圖類單拿出來進行測試，發現只要是手機拍出來的照片都不能進行縮圖的處理。。。。

經過群裡的請教，發現問題可能是出現在檔案的型別的判斷上，因為png圖片自帶一個透明的圖層，導致不能直接轉換成jpg的檔案，而手機排出的照片副檔名是jpg.

所以，得出的結論是手機拍出的是jpg副檔名的png圖片。

由於副檔名是可以隨意修改的，不是很能保證檔案的資訊的準確性，所以我們採用了
getimagesize 函式進行檔案型別的獲取。

//獲取真實的圖片型別
 list($width, $height, $type, $attr) = getimagesize($this->sur_file);
    switch($type) {  
        case 1 :  
            $img_type = `gif`;  
            break;  
        case 2 :  
            $img_type = `jpeg`;  
            break;  
        case 3 :  
            $img_type = `png`;  
            break;  
        case 15 :  
            $img_type = `wbmp`;  
            break;  
        default :  
            return false;  
    }  

三、生成縮圖類

下面把修改後的生成縮圖的類貼出來，供大家指正~

/**
 * php生成縮圖類
 * 修改者 點點細雨 
 * 文章出處 ： http://blog.csdn.net/diandianxiyu_geek
 * 2014-07-23 解決了圖片型別不能正常識別的問題
 */
class thumb {

    public $sur_file; //讀取的原圖片
    public $des_file; //生成目標圖片
    public $tem_file; //臨時圖片
    public $tag;  //縮略標籤  0,預設,按固定的高寬生成  1,按比列或固定最大長度生成  -1,按某個寬度或某個高度縮小
    public $resize_width;  //$tag為0時,目標檔案寬
    public $resize_height;  //$tag為0時,目標檔案高
    public $sca_max; //$tag為1時,<0$sca_max<1時為縮小比例;$sca_max>1時為最大長度(高或寬之中的最大值)
    public $type;  //圖片型別
    public $width;  //原圖片寬
    public $height;  //原圖片高
    public $size;     //原圖大小

    //建構函式

    public function __construct($surpic, $reswid, $reshei, $despic, $mark, $scamax) {
        $this->sur_file = $surpic;
        $this->resize_width = $reswid;
        $this->resize_height = $reshei;
        $this->tag = $mark;
        $this->sca_max = $scamax;
        list($width, $height, $type, $attr) = getimagesize($this->sur_file);
        switch ($type) {
            case 1 :
                $img_type = `gif`;
                break;
            case 2 :
                $img_type = `jpeg`;
                break;
            case 3 :
                $img_type = `png`;
                break;
            case 15 :
                $img_type = `wbmp`;
                break;
            default :
                return false;
        }
        $this->type = $img_type; //獲取圖片型別
        $this->init_img(); //初始化圖片
        $this->des_file = $despic; //目標圖片地址
        $this->width = $width;
        $this->height = $height;
        $this->size = filesize($surpic);
        $this->new_img();
        imagedestroy($this->tem_file);
    }

    //圖片初始化函式
    private function init_img() {
        if ($this->type == `jpeg`) {
            $this->tem_file = imagecreatefromjpeg($this->sur_file);
        } elseif ($this->type == `jpg`) {
            $this->tem_file = imagecreatefromjpeg($this->sur_file);
        } elseif ($this->type == `gif`) {
            $this->tem_file = imagecreatefromgif($this->sur_file);
        } elseif ($this->type == `png`) {
            $this->tem_file = imagecreatefrompng($this->sur_file);
        } elseif ($this->type == `bmp`) {
            $this->tem_file = imagecreatefrombmp($this->sur_file); //bmp.php中包含
        }
    }

    //圖片生成函式
    private function new_img() {
        $ratio = ($this->width) / ($this->height); //原圖比例
        $resize_ratio = ($this->resize_width) / ($this->resize_height); //縮略後比例
        $newimg = imagecreatetruecolor($this->resize_width, $this->resize_height); //生成新圖片
        imagealphablending($newimg, false); //這裡很重要,意思是不合並顏色,直接用$img影像顏色替換,包括透明色;
        imagesavealpha($newimg, true);
        if ($this->tag == 0) { //按固定高寬擷取縮圖
            $newimg = imagecreatetruecolor($this->resize_width, $this->resize_height); //生成新圖片
            if ($ratio >= $resize_ratio) {//即等比例下,縮圖的高比原圖長,因此高不變
                imagecopyresampled($newimg, $this->tem_file, 0, 0, 0, 0, $this->resize_width, $this->resize_height, (($this->height) * $resize_ratio), $this->height);
            } elseif ($ratio < $resize_ratio) {//即等比例下,縮圖的寬比原圖長,因此寬不變
                imagecopyresampled($newimg, $this->tem_file, 0, 0, 0, 0, $this->resize_width, $this->resize_height, $this->width, (($this->width) / $resize_ratio));
            }
        } elseif ($this->tag == 1) { //按固定比例或最大長度縮小
            if ($this->sca_max < 1) { //按比例縮小
                $newimg = imagecreatetruecolor((($this->width) * ($this->sca_max)), (($this->height) * ($this->sca_max))); //生成新圖片
                imagecopyresampled($newimg, $this->tem_file, 0, 0, 0, 0, (($this->width) * ($this->sca_max)), (($this->height) * ($this->sca_max)), $this->width, $this->height);
            } elseif ($this->sca_max > 1) { //按某個最大長度縮小
                if ($ratio >= 1) { //寬比高長
                    $newimg = imagecreatetruecolor($this->sca_max, ($this->sca_max / $ratio)); //生成新圖片
                    imagecopyresampled($newimg, $this->tem_file, 0, 0, 0, 0, $this->sca_max, ($this->sca_max / $ratio), $this->width, $this->height);
                } else {
                    $newimg = imagecreatetruecolor(($this->sca_max * $ratio), $this->sca_max); //生成新圖片
                    imagecopyresampled($newimg, $this->tem_file, 0, 0, 0, 0, ($this->sca_max * $ratio), $this->sca_max, $this->width, $this->height);
                }
            }
        } elseif ($this->tag == -1) { //按某個寬度或某個高度縮小
            if ($resize_ratio >= 1) {//新高小於新寬,則圖片按新寬度縮小
                $newimg = imagecreatetruecolor($this->resize_width, ($this->resize_width / $ratio)); //生成新圖片
                imagecopyresampled($newimg, $this->tem_file, 0, 0, 0, 0, $this->resize_width, ($this->resize_width / $ratio), $this->width, $this->height);
            } elseif ($resize_ratio < 1) {//新寬小於新高,則圖片按新高度縮小
                $newimg = imagecreatetruecolor(($this->resize_height * $ratio), $this->resize_height); //生成新圖片
                imagecopyresampled($newimg, $this->tem_file, 0, 0, 0, 0, ($this->resize_height * $ratio), $this->resize_height, $this->width, $this->height);
            }
        }

        //輸出新圖片
        if ($this->type == `jpeg` || $this->type == `jpg`) {
            imagejpeg($newimg, $this->des_file);
        } elseif ($this->type == `gif`) {
            imagegif($newimg, $this->des_file);
        } elseif ($this->type == `png`) {
            imagepng($newimg, $this->des_file);
        } elseif ($this->type == `bmp`) {
            imagebmp($newimg, $this->des_file); //bmp.php中包含
        }
    }

#function new_img() end
}