替换结构再判断解决办法

$s=<<
 
html;

$r= preg_replace('#.+]*>.+#s','',$s);

preg_match('#width="(\d+)"\s*height="(\d+)"#i',$r,$m);
if($m[1]>805){ 
         $h=($m[2]*805)/$m[1] ; 
         $r=preg_replace('/(width=)"(\d+)"(\s*height=)"(\d+)"/s','$1"$2"$3"'.$h.'"',$r);
}
echo $r;

------解决方案--------------------

PHP code
$s =<<< TXT

TXT;
$r= preg_replace_callback('#.+]*>.+#s', 'back', $s);

function back($r) {
  if($r[3] > 805) {
    $r[4] = round($r[4]*805/$r[3]);
    $r[3] = 805;
  }
  return <<< TXT

TXT;
}
echo $r;