Finding cropped similar images

Question

The 2 images have same color,pattern,etc. One image is cropped from the other one. The algorithms I've found mostly use location to compare difference between images, so it produces false result for cropped image. How to know those 2 images are similar?

Thanks

Answer 1

You really need to provide more information, but maybe you can use a cross-correlation algorithm? You basically slide the cropped images across every point in the image to match against, and find the similarity. If there is a point where they match above a certain threshold, you can assume that the smaller image is a subset of the larger in that location.

You can speed up the process a lot by using an FFT algorithm instead of actually sliding it along.

Wikipedia calls this "phase correlation"

MATLAB example: Registering an Image Using Normalized Cross-Correlation

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