一、出现的问题

这几天做了手机上传照片并裁出缩略图的接口的测试，发现不管怎么，生成的缩略图都是一片漆黑。:-(

然后就把这个缩略图类单拿出来进行测试，发现只要是手机拍出来的照片都不能进行缩略图的处理。。。。

二、问题分析以及解决方案

经过群里的请教，发现问题可能是出现在文件的类型的判断上，因为png图片自带一个透明的图层，导致不能直接转换成jpg的文件，而手机排出的照片扩展名是jpg.

所以，得出的结论是手机拍出的是jpg扩展名的png图片。

由于扩展名是可以随意修改的，不是很能保证文件的信息的准确性，所以我们采用了 getimagesize 函数进行文件类型的获取。

//获取真实的图片类型 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;      }

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三、生成缩略图类

下面把修改后的生成缩略图的类贴出来，供大家指正~

/** * php生成缩略图类 * 修改者 点点细雨  * 文章出处 ： http://blog.csdn.net/diandianxiyu_geek * 2014-07-23 解决了图片类型不能正常识别的问题 */class thumb {    public $sur_file; //读取的原图片    public $des_file; //生成目标图片    public $tem_file; //临时图片    public $tag;  //缩略标签  0,默认,按固定的高宽生成  1,按比列或固定最大长度生成  -1,按某个宽度或某个高度缩小    public $resize_width;  //$tag为0时,目标文件宽    public $resize_height;  //$tag为0时,目标文件高    public $sca_max; //$tag为1时,1时为最大长度(高或宽之中的最大值)    public $type;  //图片类型    public $width;  //原图片宽    public $height;  //原图片高    public $size;     //原图大小    //构造函数    public function __construct($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; //获取图片类型        $this->init_img(); //初始化图片        $this->des_file = $despic; //目标图片地址        $this->width = $width;        $this->height = $height;        $this->size = filesize($surpic);        $this->new_img();        imagedestroy($this->tem_file);    }    //图片初始化函数    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        }    }    //图片生成函数    private function new_img() {        $ratio = ($this->width) / ($this->height); //原图比例        $resize_ratio = ($this->resize_width) / ($this->resize_height); //缩略后比例        $newimg = imagecreatetruecolor($this->resize_width, $this->resize_height); //生成新图片        imagealphablending($newimg, false); //这里很重要,意思是不合并颜色,直接用$img图像颜色替换,包括透明色;        imagesavealpha($newimg, true);        if ($this->tag == 0) { //按固定高宽截取缩略图            $newimg = imagecreatetruecolor($this->resize_width, $this->resize_height); //生成新图片            if ($ratio >= $resize_ratio) {//即等比例下,缩略图的高比原图长,因此高不变                imagecopyresampled($newimg, $this->tem_file, 0, 0, 0, 0, $this->resize_width, $this->resize_height, (($this->height) * $resize_ratio), $this->height);            } elseif ($ratio tem_file, 0, 0, 0, 0, $this->resize_width, $this->resize_height, $this->width, (($this->width) / $resize_ratio));            }        } elseif ($this->tag == 1) { //按固定比例或最大长度缩小            if ($this->sca_max width) * ($this->sca_max)), (($this->height) * ($this->sca_max))); //生成新图片                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) { //按某个最大长度缩小                if ($ratio >= 1) { //宽比高长                    $newimg = imagecreatetruecolor($this->sca_max, ($this->sca_max / $ratio)); //生成新图片                    imagecopyresampled($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), $this->sca_max); //生成新图片                    imagecopyresampled($newimg, $this->tem_file, 0, 0, 0, 0, ($this->sca_max * $ratio), $this->sca_max, $this->width, $this->height);                }            }        } elseif ($this->tag == -1) { //按某个宽度或某个高度缩小            if ($resize_ratio >= 1) {//新高小于新宽,则图片按新宽度缩小                $newimg = imagecreatetruecolor($this->resize_width, ($this->resize_width / $ratio)); //生成新图片                imagecopyresampled($newimg, $this->tem_file, 0, 0, 0, 0, $this->resize_width, ($this->resize_width / $ratio), $this->width, $this->height);            } elseif ($resize_ratio resize_height * $ratio), $this->resize_height); //生成新图片                imagecopyresampled($newimg, $this->tem_file, 0, 0, 0, 0, ($this->resize_height * $ratio), $this->resize_height, $this->width, $this->height);            }        }        //输出新图片        if ($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}

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