Thanks for replying ! And pointing out the problems ,I’ll fix those problems. I didn’t think much about this approach . I cloned this codes from this repository , code it wrong . I did sift descriptor matching before this , but the result is bad (I only use 2 images for test), only 1 of 6 pairs is the correct match . But I think I got your point. Your proposal and explanation are very helpful ! Also I looked the doc you provide , The convert function is a static function , like this cv2.KeyPoint.convert().