resize image doesn't work in codigniter

it does not show any error, and do nothing, I can not understand whats wrong with it!

public function resize($path,$filename) {
        $config['image_library']   = 'gd2';
        $config['source_image']    = $path;
        $config['create_thumb']    = TRUE;
      $config['maintain_ratio']  = TRUE;
      $config['width']           = 75;
      $config['height']          = 50;
        $config['new_image']       = './img/uploads/users/'.$filename . '.jpg';
        $this->load->library('image_lib');
      // Set your config up
      $this->image_lib->initialize($config);
      // Do your manipulation
      $this->image_lib->clear();
        if(!$this->image_lib->resize()) {
        echo $this->image_lib->display_errors();
      }


      }