Editing Scale-invariant feature transform (section)

==== Discarding low-contrast keypoints ====
To discard the keypoints with low contrast, the value of the second-order Taylor expansion <math>D(\textbf{x})</math> is computed at the offset <math>\hat{\textbf{x}}</math>. If this value is less than <math>0.03</math>, the candidate keypoint is discarded. Otherwise it is kept, with final scale-space location <math>\textbf{y} + \hat{\textbf{x}}</math>, where <math>\textbf{y}</math> is the original location of the keypoint.