bool imagecopyresampled  ( resource $dst_image, resource $src_image, int $dst_x, int $dst_y, int $src_x, int $src_y, int $dst_w, int $dst_h, int $src_w, int $src_h)

 <?php

 suofang('./yz.jpg',200,100);

 //只能缩放 jpg的图像   自己进行类型判断

 function suofang($srcpath,$width = 100,$height = 100){

     $srcinfo = getimagesize($srcpath);

     //计算缩放后的宽高  按比例

     if($srcinfo[0] > $srcinfo[1]){ //宽 > 高  按宽的比例计算高

         $height = $srcinfo[1] * ($width/$srcinfo[0]);

     }else{

         //高 > 宽  按高的比例计算宽

         $width = $srcinfo[0] * ($height/$srcinfo[1]);

     }

     //目标资源  空白画布

     $dstim = imagecreatetruecolor($width,$height);

     //要缩放的图像  源资源

     $srcim = imagecreatefromjpeg($srcpath);

     imagecopyresampled($dstim,$srcim,0,0,0,0,$width,$height,$srcinfo[0],$srcinfo[1]);

     //保存缩放后的图像

     imagejpeg($dstim,$suopath);

     imagedestroy($dstim);

     imagedestroy($srcim);

     return $suopath;

 }