We propose a new affine-covariant feature, the Stable Affine Frame (SAF). SAFs lie on the boundary of extremal regions, i.e. on isophotes. But instead of requiring the whole isophote to be stable with respect to intensity perturbation as in maximally stable extremal regions (MSERs), stability is required only locally, for the primitives constituting the three-point frames. The primitives are extracted by an affine invariant process that exploits properties of bitangents and algebraic moments.

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... us, instead of using closed stable isophotes, i.e. MSERs, and detecting affine frames on them, stable affine frames are attempted, on all, even unstable, extremal regions. We show experimentally on standard datasets that SAFs have repeatability comparable to the best affine covariant detectors tested in the state-of-the-art report [11] and consistently produce a significantly higher number of features per image. Moreover, the features cover images more evenly than MSERs, which facilitates robustness to occlusion. Without significant computational effort, it is possible to modify the detector to construct stable homography covariant frames.