python - OpenCV 中的 Flann KNN Matcher 只返回一个点而不是一对

Question

当我运行 Flann KNN 匹配器时，有时 KNN 匹配器只返回一个点，因为依赖于两个点的匹配器之后的代码会失败:

flann = cv2.FlannBasedMatcher(index_params, search_params)

matches = flann.knnMatch(descriptors1, descriptors2, k=2)

# Retrieve good matches
good_matches = []

# ratio test as per Lowe's paper
for i, (m, n) in enumerate(matches):
    if m.distance < 0.7*n.distance:
        good_matches.append((m, n))

抛出这个错误:

Traceback (most recent call last):
  File "main.py", line 161, in <module>
    main(vid, video_file)
 ...
  File "main.py", line 73, in consume_for_homography_error
    matches = flann_matcher(descriptors1, descriptors2)
  File "main.py", line 48, in flann_matcher
    for i, (m, n) in enumerate(matches):
ValueError: need more than 1 value to unpack

这里似乎有什么问题？

Answer 1

问题是匹配项似乎填充为固定长度的列表列表，在本例中 len(matches) == 500 即使找到的匹配项数量少于该数量。

尝试添加这个:

matches = [match for match in matches if len(match) == 2]
(or even better)
good_matches = [match[0] for match in matches if len(match) == 2 and match[0].distance 
                                                        < .7*match[1].distance]


before the for loop to delete these (empty lists?).