PHP压缩上传图片

最近手上的项目页面要显示很多图片，虽然用了jQuery的lazyload，但是效果并没理想，滑动到一个区域还要比较长的时间图片才完全显示出来。于是想着将上传上去的900KB+压缩备份一份缩略图。 
PHP压缩图片两个步骤： 
1、添加类

//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.phpernote.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);

                //上色 
                $color=imagecolorallocate($newimg,255,255,255); 
                //设置透明 
                imagecolortransparent($newimg,$color); 
                imagefill($newimg,0,0,$color); 

                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);

                //上色 
                $color=imagecolorallocate($newimg,255,255,255); 
                //设置透明 
                imagecolortransparent($newimg,$color); 
                imagefill($newimg,0,0,$color); 

                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