SplFileInfo类
SplFileInfo::isFile($fullpathfilename)
参数必须是全路径

一下是image类的open方法返回的结果，tp5中的image类

object(think\Image)#33 (3) {
  ["im":protected] => resource(88) of type (gd)
  ["gif":protected] => NULL
  ["info":protected] => array(4) {
    ["width"] => int(4096)
    ["height"] => int(3072)
    ["type"] => string(4) "jpeg"
    ["mime"] => string(10) "image/jpeg"
  }
}