The code provided in this module can be used in different ways. Chatrouleyte, you can use one of the low sam functions to run only a part of the SIFT parent for instance, to compute the SIFT descriptors of custom keypoints. In order to search for image blobs at multiple sam, the SIFT detector construct a scale space, defined as images..
Notice that the scale level index s varies in a slightly redundant set. Once extracted, local extrema are quadratically interpolated this is very important especially at the lower resolution scales in order to have accurate keypoint localization at the full resolution. Finally, they are filtered to eliminate low-contrast responses or responses close to edges and the orientation s are assigned, as explained next.