php生成图片缩略图的类方法

分享一个php生成缩略图片的方法，支持jpg,gif,png格式，支持按原图片的比例进行缩放，可以选择在图片缩放的过程中是否需要对图片进行裁切，加入了图片质量控制，可以实现缩略图片质量最高化。完整类的代码如下：

//php生成缩略图片的类
class ResizeImage{
    public $type;//图片类型
    public $width;//实际宽度
    public $height;//实际高度
    public $resize_width;//改变后的宽度
    public $resize_height;//改变后的高度
    public $cut;//是否裁图
    public $srcimg;//源图象  
    public $dstimg;//目标图象地址
    public $im;//临时创建的图象
    public $quality;//图片质量
    public $img_array=array('jpg','png','gif');
    //http://www.maopiaopiao.com/php-function/782.html
    function __construct($img,$wid,$hei,$c,$dstpath,$quality=100){
        $this->srcimg=$img;
        $this->resize_width=$wid;
        $this->resize_height=$hei;
        $this->cut=$c;
        $this->quality=$quality;
        //$this->type=strtolower(substr(strrchr($this->srcimg,'.'),1));//图片的类型
        $this->type=$this->checkFileType($this->srcimg);//更为严格的检测图片类型
        if(!in_array($this->type,$this->img_array)){
            return '';
        }
        $this->initi_img();//初始化图象
        $this -> dst_img($dstpath);//目标图象地址
        $this->width=imagesx($this->im);
        $this->height=imagesy($this->im);
        $this->newimg();//生成图象
        ImageDestroy($this->im);
    }
    function newimg(){
        $resize_ratio=($this->resize_width)/($this->resize_height);//改变后的图象的比例
        $ratio=($this->width)/($this->height);//实际图象的比例
        if(($this->cut)=='1'){//裁图
            if(function_exists('imagepng')&&(str_replace('.','',PHP_VERSION)>=512)){//针对php版本大于5.12参数变化后的处理情况
                $quality=9;
            }
            if($ratio>=$resize_ratio){//高度优先
                $newimg=imagecreatetruecolor($this->resize_width,$this->resize_height);
                imagecopyresampled($newimg,$this->im,0,0,0,0,$this->resize_width,$this->resize_height,(($this->height)*$resize_ratio),$this->height);
                imagejpeg($newimg,$this->dstimg,$this->quality);
            }
            if($ratio<$resize_ratio){//宽度优先
                $newimg=imagecreatetruecolor($this->resize_width,$this->resize_height);
                imagecopyresampled($newimg,$this->im,0,0,0,0,$this->resize_width,$this->resize_height,$this->width,(($this->width)/$resize_ratio));
                imagejpeg($newimg,$this->dstimg,$this->quality);
            }
        }else{//不裁图
            if($ratio>=$resize_ratio){
                $newimg=imagecreatetruecolor($this->resize_width,($this->resize_width)/$ratio);
                imagecopyresampled($newimg,$this->im,0,0,0,0,$this->resize_width,($this->resize_width)/$ratio,$this->width,$this->height);
                imagejpeg($newimg,$this->dstimg,$this->quality);
            }
            if($ratio<$resize_ratio){
                $newimg=imagecreatetruecolor(($this->resize_height)*$ratio,$this->resize_height);
                imagecopyresampled($newimg,$this->im,0,0,0,0,($this->resize_height)*$ratio,$this->resize_height,$this->width,$this->height);
                imagejpeg($newimg,$this->dstimg,$this->quality);
            }
        }
    }
    function initi_img(){//初始化图象
        if($this->type=='jpg'){
            $this->im=imagecreatefromjpeg($this->srcimg);
        }
        if($this->type=='gif'){
            $this->im=imagecreatefromgif($this->srcimg);
        }
        if($this->type=='png'){
            $this->im=imagecreatefrompng($this->srcimg);
        }
    }
    function dst_img($dstpath){//图象目标地址
        $full_length=strlen($this->srcimg);
        $type_length=strlen($this->type);
        $name_length=$full_length-$type_length;
        $name=substr($this->srcimg,0,$name_length-1);
        $this->dstimg=$dstpath;
        //echo $this->dstimg;
    }
    //读取文件前几个字节 判断文件类型
    function checkFileType($filename){
        $file=fopen($filename,'rb');
        $bin=fread($file,2); //只读2字节
        fclose($file);
        $strInfo =@unpack("c2chars",$bin);
        $typeCode=intval($strInfo['chars1'].$strInfo['chars2']);
        $fileType='';
        switch($typeCode){
            case 7790:
                $fileType='exe';
            break;
            case 7784:
                $fileType='midi';
            break;
            case 8297:
                $fileType='rar';
            break;
            case 255216:
                $fileType='jpg';
            break;
            case 7173:
                $fileType='gif';
            break;
            case 6677:
                $fileType='bmp';
            break;
            case 13780:
                $fileType='png';
            break;
            default:
                $fileType='unknown'.$typeCode;
            break;
        }
        if($strInfo['chars1']=='-1'&&$strInfo['chars2']=='-40'){
            return 'jpg';
        }
        if($strInfo['chars1']=='-119'&&$strInfo['chars2']=='80'){
            return 'png';
        }
        return $fileType;
    }
}

该类的使用方法也很简单，如下就是根据原图片生成一个宽不超过100，高不超过200的缩略图片：

$resizeimage=new resizeimage('www.maopiaopiao.com.jpg',100,200,0,'php and mysql development_thumb.jpg');