Exact_Pacthes

After detecting a feature point by using Hessian detector, then we get a initial x0,y0 and sigma0. The range of x0 is [0, width-1], the range of y0 is [0, height-1], sigma0=power(2, i/L), i is the index of level, and L is the number of levels in a octave . Then we further fintune the location of x0 and y0 and optimize the value of sigma0, and get the final x1,y1 and sigma1. Now, we assume the feature point located in the 0th octave and 2th level. According to the x1, y1, and sigma1, we crop a 64*64 patch from the DoG in the 0th octave and 2th level. Here, a affine transform matrix is constructed as LAF=[sigma1,0,x1;0,sigma1,y1] to crop the patch. Note, the range of sigma1 should be [1, 2].
About the sigma1, can I understand it is a radius? namely, centered at point (x1,y1) in the DoG, then the area within the radius are croped and then resampled to 64*64 patch?

[yunyundong]

I got it, thank you very much for your patient explanation.

[ducha-aiki]

@yunyundong Yes, exactly.