使用Python和OpenCV,我正在检测二进制掩模的轮廓:
import numpy as np
import cv2
import matplotlib.pyplot as plt
mask = np.zeros(20000, dtype=np.uint8).reshape(100, 200)
mask[5:-5,5:-5] = 255
mask[10:70,40:80] = 0
plt.subplot(121)
plt.imshow(mask, cmap='Greys_r', interpolation='none')
_, contours, hierarchy = cv2.findContours(mask.copy(),
cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE,
offset=(0, 0))
导致预期行为:
plt.subplot(122)
cv2.drawContours(mask, contours, -1, (127, 127, 127), 2)
plt.imshow(mask, cmap='Greys_r', interpolation='none')
plt.show()
然而,我似乎无法理解完全激活掩模的结果:
mask = np.ones(20000, dtype=np.uint8).reshape(100, 200)
mask *=255
_, contours, hierarchy = cv2.findContours(mask.copy(),
cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE,
offset=(0, 0))
print contours[0]
这会产生:
(1 1), (1 98), (198 98), (198 1)
而不是 (0 0), (0 99), (199, 99), (199, 0)
为什么opencv的findcontours函数表现得像这样,带有偏移量1?