在opencv中，Fast特征提取器的函数原型：
static Ptr<FastFeatureDetector> cv::FastFeatureDetector::create ( int threshold = 10, bool nonmaxSuppression = true, FastFeatureDetector::DetectorType type = FastFeatureDetector::TYPE_9_16 ) threshold指的是中心像素与周围像素强度的差的阈值nonmaxSuppression是为了去除特征点聚集的情况DetectorType提供了三种不同的邻域类型 提取函数原型： virtual void cv::Feature2D::detect ( InputArray image, std::vector< KeyPoint > & keypoints, InputArray mask = noArray() )