// detects keypoints using fast multi-scale Hessian detector
void operator()(const Mat& img, const Mat& mask,
vector<KeyPoint>& keypoints) const;
- // detects keypoints and computes the SURF descriptors for them
+ // detects keypoints and computes the SURF descriptors for them;
+ // output vector "descriptors" stores elements of descriptors and has size
+ // equal descriptorSize()*keypoints.size() as each descriptor is
+ // descriptorSize() elements of this vector.
void operator()(const Mat& img, const Mat& mask,
vector<KeyPoint>& keypoints,
vector<float>& descriptors,