Hi Guys, I'm implementing SURF algorithm and I'm referring to the Chris Evan's OpenSURF (Sorry, The link doesn't seem to work).
In OpenSURF and in almost all the other SURF implementations I see that when Dxx and Dyy are computed a multiplying factor 3 is used(look at the code below). No where in the SURF paper or OpenSURF paper is it mentioned why they do it. I have no problem in doing the same but I'm curious to know why this multiplication is being carried out. If it is important for the Dxx and Dyy computations then why is it not mentioned anywhere? Am I missing it?
Can anyone having experience with this give me some explanation?
Regards
Vikram
Dxx and Dyy along with Dxy are used to calculate the Determinant
Dxx = BoxIntegral(img, r - l + 1, c - b, 2*l - 1, w)
- BoxIntegral(img, r - l + 1, c - l / 2, 2*l - 1, l)*3; // Why 3 here?
Dyy = BoxIntegral(img, r - b, c - l + 1, w, 2*l - 1)
- BoxIntegral(img, r - l / 2, c - l + 1, l, 2*l - 1)*3; // Why 3 here?