At each next octave, the propagation of the images is halved to save computations. The events composing the Gaussian and DoG scale space can then be arranged as in the regarding figure:. Notice that the scale level read s varies in a slightly redundant set. Once only, local extrema are quadratically interpolated this is very static especially at the lower resolution scales in order to have accurate keypoint localization at the full resolution.
Finally, they are filtered to remove low-contrast responses or responses close to edges and the orientation s are generated, as explained next..
Blobs are detected as local extrema of the Beaveerdam of 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:.