一个图片缩略图方法

/*
 *   缩略图
 * @param background 原图
 * @param width 缩略图的宽度
 * @param height 缩略图的高度
 * @param newfile 新图片的名称
 * @param object $geo_info  翻转角度   由函数geo_info 获得 主要针对苹果手机上传图片问题
 */
function thumb($background, $width, $height, $newfile, $geo_info='') {
    if( isWap() && isset($geo_info['orientation'])){  //手机上传并且图片翻转
        $orientation = $geo_info['orientation'];

        if($orientation == 1){
            $degrees = 0;
        }else if($orientation == 3){
            $degrees = 180;
        }else if($orientation == 6){
            $degrees = 270;
        }else if($orientation == 8){
            $degrees = 90;
        }
    }
    //按比例获取缩略图的宽高
    $temp = getimagesize($background);
    $s_type = $temp['mime'];
    $s_w = $temp[0];
    $s_h = $temp[1];

    //90度的奇数倍时要宽高互换
    if($orientation == 6 || $orientation==8){
        $tmp_th = $s_w;
        $s_w = $s_h;
        $s_h = $tmp_th;
    }


    if ($width && ($s_w < $s_h)) {
        $width = ($height / $s_h) * $s_w;
    } else {
        $height = ($width / $s_w) * $s_h;
    }

    $new = imagecreatetruecolor($width, $height);
    switch($s_type){
        case 'image/png' :
            $img = imagecreatefrompng($background);
            break;
        case 'image/gif':
            $img = imagecreatefromgif($background);
            break;
        case 'image/jpg':
            $img = imagecreatefromjpeg($background);
            break;
        case 'image/jpeg':
            $img = imagecreatefromjpeg($background);
            break;
        default :
            return false;
    }
    if($degrees>0)$img = imagerotate($img, $degrees, 0xffffff);   //翻转图片

    $otsc = imagecolortransparent($img);
    if($otsc >=0 && $otsc < imagecolorstotal($img)){
        $tran=imagecolorsforindex($img, $otsc);
        $newt=imagecolorallocate($new, $tran["red"], $tran["green"], $tran["blue"]);
        imagefill($new, 0, 0, $newt);
        imagecolortransparent($new, $newt);
    }
    imagecopyresized($new, $img, 0, 0, 0, 0, $width, $height, $s_w, $s_h);
    switch($s_type){
        case 'image/png' :
            imagepng($new, $newfile);
            break;
        case 'image/gif':
            imagegif($new, $newfile);
            break;
        case 'image/jpg':
            imagejpeg($new, $newfile);
            break;
        case 'image/jpeg':
            imagejpeg($new, $newfile);
            break;
        default :
            return false;
    }
    imagedestroy($new);
    imagedestroy($img);
    return true;
}