feature matching + homography

Question

I have followed the tutorials on opencv in python. I am using OpenCV 3.2 and Python 3.6.1. The code was written like this:

import cv2
import numpy as np
import matplotlib.pyplot as plt

MIN_MATCH_COUNT = 10

img1 = cv2.imread('test.jpg',0)
img2 = cv2.imread('hanapin_mo.jpg',0)

sift = cv2.xfeatures2d.SIFT_create()

kp1, des1 = sift.detectAndCompute(img1,None)
kp2, des2 = sift.detectAndCompute(img2,None)

FLANN_INDEX_KDTREE = 1
index_params = dict(algorithm = FLANN_INDEX_KDTREE, trees = 5)
search_params = dict(checks = 50)

flann = cv2.FlannBasedMatcher(index_params, search_params)

matches = flann.knnMatch(des1, des2, k = 2)

good = []
for m,n in matches:
    if m.distance <0.7*n.distance:
        good.append(m)

if len(good)>MIN_MATCH_COUNT:
    src_pts = np.float32([ kp1[m.queryIdx].pt for m in good ]).reshape(-1,1,2)
    dst_pts = np.float32([ kp2[m.trainIdx].pt for m in good ]).reshape(-1,1,2)

    M, mask = cv2.findHomography(src_pts, dst_pts, cv2.RANSAC, 5.0)
    matchesMask = mask.ravel().tolist()

    h,w,d = img1.shape
    pts = np.float32([ [0,0],[0,h-1],[w-1,h-1],[w-1,0] ]).reshape(-1,1,2)
    dst = cv2.perspectiveTransform(pts,M)

    img2 = cv2.polylines(img2,[np.int32(dst)], True, 255, 3, cv2.LINE_AA)

else:
    print("Not enough matches are found - {}/{}".format(len(good), MIN_MATCH_COUNT) )
    matchesMask = None

draw_params = dict(matchColor = (0,250,0),
                   singlePointColor = None,
                   matchesMask = matchesMask,
                   flags = 2)

img3 = cv2.drawMatchesKnn(img1, kp1, img2, kp2, good, None, **draw_params)

plt.imshow(img3, 'gray'),plt.show()

As I run the module, an error occured:

Traceback (most recent call last): File "C:/Users/Albert Eli Reyes/Desktop/SIFT/SIFT.py", line 35, in h,w,d = img1.shape ValueError: not enough values to unpack (expected 3, got 2)

    h,w,d = img1.shape
    pts = np.float32([ [0,0],[0,h-1],[w-1,h-1],[w-1,0] ]).reshape(-1,1,2)
    dst = cv2.perspectiveTransform(pts,M)

    img2 = cv2.polylines(img2,[np.int32(dst)], True, 255, 3, cv2.LINE_AA)

What does it mean when it says "not enough values to unpack"? And what should I do to make it run?

Answer 1

Shape function outputs a tuple of two values only. You are trying to get three values whereas the function returns two values only

h,w = img1.shape

The above would work

Answer 2

Well, this means that img1.shape returns only two values. So if you remove the d variable initialization, the code should work as I don't see you using it in your code anyway.

h, w = img1.shape