An analysis of scale-space sampling in SIFT

The most popular image matching algorithm SIFT, introduced by D. Lowe a decade ago, has proven to be sufficiently scale invariant to be used in numerous applications. In practice, however, scale invariance may be weakened by various sources of error. The density of the sampling of the Gaussian scale-space and the level of blur in the input image are two of these sources. This article presents an empirical analysis of their impact on the extracted keypoints stability. We prove that SIFT is really scale and translation invariant only if the scale-space is significantly oversampled. We also demonstrate that the threshold on the difference of Gaussians value is inefficient for eliminating aliasing perturbations.