I want to generate SURF descriptor (a vector of length 64).
In the original paper, here it says:
The region is split up regularly into smaller 4*4 square sub-regions. For each sub-region, we compute Haar wavelet responses at 5*5 regularly spaced sample points.
With OpenCV help, I can get keypoint and its relating region (by using KeyPoint::size and angle), but my questions are:
1. how to compute Haar wavelet responses?
2. what is "at 5 x 5 regularly spaced sample points" mean?
I've read the wiki and introduction about Harr wavelet but still have no idea how to write the code.
I've known how to use the OpenCV SurfDescriptorExtractor, but I cannot use it because I need to enlarge or shrink the original region and get new descriptor.
Thanks for any hint about how to generate SURF descriptor.