How to make the opencv-contrib module work?

Question

I followed this guide to install opencv (version 3.4.4) and the contrib modules because I want to work with the SIFT algorithm. https://www.pyimagesearch.com/2018/05/28/ubuntu-18-04-how-to-install-opencv/ When I noticed, it was not working as expected after the installation, I deleted the build folder and tried again, but this did not work as well. I imported like this:

import cv2 as cv 

I tried to use SIFT (in python 3.6) in the following ways:

sift = cv.SIFT_create()
sift = cv.xfeatures2d.SIFT_create()
sift = cv.SIFT()
sift = cv.xfeatures2d.SIFT()

As this usually results in errors like this: Attribute Error: module cv2 has no attribute 'SIFT_create' (same thing happens for the other 3 options), I figure that I am either using it in an incorrect way or the installation process itself did not work properly.

After this, I found the pip install opencv-contrib-python and used it. With no results at all.

I would really appreciate some hints on how I can make opencv with contrib modules work.

Answer 1

You may have to say cv2.xfeatures2d_SIFT or similar. the modules of OpenCV don't necessarily map to python submodules.

Since the patent on SIFT expired in 2019, OpenCV moved it back into features2d (main repo) from xfeatures2d (opencv_contrib repo). Please use the most recent 3.4.x release, or 4.x.