How to filter a shape from a binary image

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I think squares.cpp(or squares.py) in samples folder can help you.

you can change some parts of the code and detect any simple objects (like square,circle,triangle...)

You could try matching a shape you know against the global image (link to opencv documentation on matchShapes). It works solidly and fast and will work with scaling but not with rotations or perspective transformations.

This q&a can give you pointers to more sophisticated comparisons.

Think it works, need some finetunning!

My suggestion is to use BRISK and FREAK. I use this for Objectdetection an it works fine. In the OpenCV FREAK Example the use the Surfdetector but this doesn´t give me good Matches. But you should try it with the binary images. Hope this helps.

std::vector<keypoint> keypointsA, keypointsB;

Mat descriptorsA, descriptorsB;

std::vector<dmatch> matches;

BRISK detector(30,9,1.0F);

FREAK extractor;

BFMatcher matcher(NORM_HAMMING,false);

detector.detect( imgA, keypointsA );

extractor.compute( imgA, keypointsA, descriptorsA );

detector.detect( imgB, keypointsB );

extractor.compute( imgB, keypointsB, descriptorsB );

matcher.knnMatch(descriptorsA, descriptorsB, matches, 2);

drawMatches(imgAs, keypointsA, imgB, keypointsB, good_matches, imgMatch);