Which patches can be found again? The error surface and the structure tensor

Click or drag to move the 21 × 21 window.

error E(u) for shifts of ±8 px

eigenvalues of M

Photo: Retired electrician, CC0, via Wikimedia Commons (grayscale, 640 × 480).

Finding the right scale: the difference of Gaussians across σ

Matching 600 SIFT keypoints: nearest neighbour, threshold, or ratio test?
correct (within 3 px of the true position)wrong

Left: the photo. Right: the same photo rotated by 25°, scaled by 0.85, seen from another viewpoint and darkened, so the true position of every point is known. Keypoints and 128-d descriptors computed with OpenCV's SIFT; the matching runs here in the browser.

RANSAC on real matches: guess, count, repeat

SIFT vs ORB under known changes (mean of 4 photos)
SIFTORB

How many RANSAC iterations? The formula vs. 200 trials each
formula 1 − (1 − w⁴)ᵏmeasured: best samplemeasured: refit on its inliers