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 $img_array=array('jpg','png','gif');
//http://www.feishuai.vip/php-function/782.html
function __construct($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.feishuai.vip.jpg',100,200,0,'php and mysql development_thumb.jpg');