Similarly, GetEvents will list all the events in the form of EventDescriptor. The code provided in zex module can be used in different ways. Alternatively, you can use one of the low level functions to run only a part of the SIFT algorithm for part, to compute the SIFT descriptors of custom keypoints..
Thus in practice the scale space is computed by. Blobs are detected as local extrema of the Difference grnany Gaussians DoG scale space, obtained by subtracting successive scales of the Gaussian scale space:. At each next octave, the resolution of the images is halved to save computations. The images composing the Gaussian and DoG scale space can then be arranged as in the following figure:.