Introduction to SIFT (Scale-Invariant Feature Transform) — OpenCV-Python Tutorials 1 documentation

Introduction to SIFT (Scale-Invariant Feature Transform) — OpenCV-Python Tutorials 1 documentation

Introduction to SIFT (Scale-Invariant Feature Transform) — OpenCV-Python Tutorials 1 documentation

In last couple of chapters, we saw some corner detectors like Harris etc. They are rotation-invariant, which means, even if the image is rotated, we can find the same corners. It is obvious because corners remain corners in rotated image also. But what about scaling? A corner may not be a corner if the image is scaled. For example, check a simple image below. A corner in a small image within a small window is flat when it is zoomed in the same window. So Harris corner is not scale invariant.

Source: opencv-python-tutroals.readthedocs.io/en/latest/py_tutorials/py_feature2d/py_sift_intro/py_sift_intro.html