c++ - type of openCV output SIFT descriptors -


what or should type of output descriptors mat in opencv c++ ?

c++: void sift::operator()(inputarray img, inputarray mask, vector& keypoints, outputarray descriptors, bool useprovidedkeypoints=false) parameters: 

    img – input 8-bit grayscale image     mask – optional input mask marks regions should detect features.     keypoints – input/output vector of keypoints     descriptors – output matrix of descriptors. pass cv::noarray() if not need them.     useprovidedkeypoints – boolean flag. if true, keypoint detector not run. instead, provided vector of keypoints used , algorithm computes descriptors.

what mean "descriptors – output matrix of descriptors."

thanks.

as rule of thumb: whenever see outputarray, don't have worry size or type.

just supply uninitialized mat, function fill it.

in case , output nxm float mat n(rows) number of keypoints, , m(cols) 128, length of sift feature.


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