PHP image manipulation class (picture watermarking)

<?php 
/* 
$img = new Image('pic.jpg'); 
//$img->changeSize(80,50);//改变尺寸 
$img->changeSize(80);//改变尺寸 
$img->create(); 
$img->free(); 
$img = new Image('pic.jpg'); 
$img->addWatermark('logo.jpg', 50); //添加水印，第一个参数是水印的图片地址，第二个参数是透明值 
$img->create(); 
$img->free(); 
site http://bbs.it-home.org
*/ 
class Image { 
    var $imageResource = NULL; 
    var $target = NULL; 
    var $enableTypes = array(); 
    var $imageInfo = array(); 
    var $createFunc = ''; 
    var $imageType = NULL; 
     
    /* Construct for this class 
     * @param string $image 
     * @return Image 
     */ 
    function Image($image = NULL) { 
        //get enables 
        if(imagetypes() & IMG_GIF) { 
            $this->enableTypes[] = 'image/gif'; 
        } 
        if(imagetypes() & IMG_JPEG) { 
            $this->enableTypes[] = 'image/jpeg'; 
        } 
        if (imagetypes() & IMG_JPG) { 
            $this->enableTypes[] = 'image/jpg'; 
        } 
        if(imagetypes() & IMG_PNG) { 
            $this->enableTypes[] = 'image/png'; 
        } 
        //end get 
         
        if($image != NULL) { 
            $this->setImage($image); 
        } 
    } 
     
    /* set a image resource 
     * @param string $image 
     * @return boolean 
     */ 
    function setImage($image) { 
        if(file_exists($image) && is_file($image)) { 
            $this->imageInfo = getimagesize($image); 
            $img_mime = strtolower($this->imageInfo['mime']); 
            if(!in_array($img_mime, $this->enableTypes)) { 
                exit('系统不能操作这种图片类型.'); 
            } 
            switch ($img_mime) { 
                case 'image/gif': 
                    $link = imagecreatefromgif($image); 
                    $this->createFunc = 'imagegif'; 
                    $this->imageType = 'gif'; 
                    break; 
                case 'image/jpeg': 
                case 'image/jpg': 
                    $link = imagecreatefromjpeg($image); 
                    $this->createFunc = 'imagejpeg'; 
                    $this->imageType = 'jpeg'; 
                    break; 
                case 'image/png': 
                    $link = imagecreatefrompng($image); 
                    $this->createFunc = 'imagepng'; 
                    $this->imageType = 'png'; 
                    break; 
                default: 
                    $link = 'unknow'; 
                    $this->imageType = 'unknow'; 
                    break; 
            } 
            if($link !== 'unknow') { 
                $this->imageResource = $link; 
            } else { 
                exit('这种图片类型不能改变尺寸.'); 
            } 
            unset($link); 
            return true; 
        } else { 
            return false; 
        } 
    } 
     
    /*set header*/ 
    function setHeader() { 
        switch ($this->imageType) { 
            case 'gif': 
                header('content-type:image/gif'); 
                break; 
            case 'jpeg': 
                header('content-type:image/jpeg'); 
                break; 
            case 'png': 
                header('content-type:image/png'); 
                break; 
            default: 
                exit('Can not set header.'); 
                break; 
        } 
        return true; 
    } 
     
    /* change the image size 
     * @param int $width 
     * @param int $height 
     * @return boolean 
     */ 
    function changeSize($width, $height = -1) { 
        if(!is_resource($this->imageResource)) { 
            exit('不能改变图片的尺寸,可能是你没有设置图片来源.'); 
        } 
        $s_width = $this->imageInfo[0]; 
        $s_height = $this->imageInfo[1]; 
        $width = intval($width); 
        $height = intval($height); 
         
        if($width <= 0) exit('图片宽度必须大于零.'); 
        if($height <= 0) { 
            $height = ($s_height / $s_width) * $width; 
        } 
         
        $this->target = imagecreatetruecolor($width, $height); 
        if(@imagecopyresized($this->target, $this->imageResource, 0, 0, 0, 0, $width, $height, $s_width, $s_height)) 
            return true; 
        else 
            return false; 
    } 
     
    /* Add watermark 
     * @param string $image 
     * @param int $app 
     */ 
    function addWatermark($image, $app = 50) { 
        if(file_exists($image) && is_file($image)) { 
            $s_info = getimagesize($image); 
        } else { 
            exit($image . '文件不存在.'); 
        } 
        $r_width = $s_info[0]; 
        $r_height = $s_info[1]; 
        if($r_width > $this->imageInfo[0]) exit('水印图片必须小于目标图片'); 
        if($r_height > $this->imageInfo[1]) exit('水印图片必须小于目标图片'); 
         
        switch ($s_info['mime']) { 
            case 'image/gif': 
                $resource = imagecreatefromgif($image); 
                break; 
            case 'image/jpeg': 
            case 'image/jpg': 
                $resource = imagecreatefromjpeg($image); 
                break; 
            case 'image/png': 
                $resource = imagecreatefrompng($image); 
                break; 
            default: 
                exit($s_info['mime'] .'类型不能作为水印来源.'); 
                break; 
        } 
         
        $this->target = &$this->imageResource; 
        imagecopymerge($this->target, $resource, $this->imageInfo[0] - $r_width - 5, 
$this->imageInfo[1] - $r_height - 5, 0,0 ,$r_width, $r_height, $app); 
        imagedestroy($resource); 
        unset($resource); 
    } 
     
    /* create image 
     * @param string $name 
     * @return boolean 
     */ 
    function create($name = NULL) { 
        $function = $this->createFunc; 
        if($this->target != NULL && is_resource($this->target)) { 
            if($name != NULL) { 
                $function($this->target, $name); 
            } else { 
                $function($this->target); 
            } 
            return true; 
        } else if($this->imageResource != NULL && is_resource($this->imageResource)) { 
            if($name != NULL) { 
                $function($this->imageResource, $name); 
            } else { 
                $function($this->imageResource); 
            } 
            return true; 
        } else { 
            exit('不能创建图片,原因可能是没有设置图片来源.'); 
        } 
    } 
     
    /*free resource*/ 
    function free() { 
        if(is_resource($this->imageResource)) { 
            @imagedestroy($this->imageResource); 
        } 
        if(is_resource($this->target)) { 
            @imagedestroy($this->target); 
        } 
    } 
} 
?>