python cv2 feature matching give different results

77 views
Skip to first unread message

Zhang Xun

unread,
Aug 21, 2018, 10:30:18 PM8/21/18
to OpenCV with Python Blueprints
Hi,I am new to opencv. When I match SIFT feature using FLANN,I found same input descriptor give different match pairs in same process.

I found the matches in line 11 is different although my input descriptor(des1,des2) is same,I guess the reason is kd-tree cache,but I can't solve it.Any one could help me?

I want the matches result is always same. My cv2 version is 3.4.0, Thanks in advance.


import cv2
 def match(des_q, des_t):
    FLANN_INDEX_KDTREE = 1
    ratio = 0.7  
    index_params = dict(algorithm=FLANN_INDEX_KDTREE, trees=5)
    search_params = dict(checks=50)
    flann1 = cv2.FlannBasedMatcher(index_params, search_params)
    two_nn = flann1.knnMatch(des_q, des_t, k=2)
    matches = [(first.queryIdx, first.trainIdx) for first, second in two_nn
                   if first.distance < ratio * second.distance]
    print(matches)

def img_sim(img1, img2):
    img1 = cv2.cvtColor(img1, cv2.IMREAD_GRAYSCALE)
    img2 = cv2.cvtColor(img2, cv2.IMREAD_GRAYSCALE)
    sift = cv2.xfeatures2d.SIFT_create()
    eps = 1e-7
    # find the keypoints and descriptors with SIFT
    kp1, des1 = sift.detectAndCompute(img1, None)
    des1 /= (des1.sum(axis=1, keepdims=True) + eps)
    des1 = np.sqrt(des1)
    kp2, des2 = sift.detectAndCompute(img2, None)
    des2 /= (des2.sum(axis=1, keepdims=True) + eps)
    des2 = np.sqrt(des2)
    match(des1, des2)
    match(des1, des2)

img1 = cv2.cvtColor(cv2.imread(img1), cv2.COLOR_BGR2RGB)
img2 = cv2.cvtColor(cv2.imread(img2), cv2.COLOR_BGR2RGB)
img_sim(img1, img2)

Michael Beyeler

unread,
Dec 11, 2018, 12:42:47 PM12/11/18
to OpenCV with Python Blueprints
Hi,

You're not the only one having this problem. FLANN uses some probabilistic method to find the matches. That's why you get different results each time.

Unfortunately, I don't think you can seed the random generator in Python... Or even in C++... Bad design.

Cheers,
Michael
Reply all
Reply to author
Forward
0 new messages