modified renderer.cpp

if (last_image_.rows == msg->height && last_image_.cols == msg->width)
{
  cv::cvtColor(last_image_, cv_image.image, CV_BGR2GRAY);
  used_last_image_ = true;
}
else
{
  cv_image.image = cv::Mat(msg->height, msg->width, CV_8U);
  cv_image.image = cv::Scalar(128);
}