python - 有没有办法使用 cv2.approxPolyDP 来近似开放曲线？

Question

我想用线段链来近似平滑线。

OpenCV 3.4中的cv2.approxPolyDP在闭合曲线的情况下取得了不错的效果。

原点闭合曲线: 近似闭合曲线:

但是在开曲线的情况下，cv2.approxPolyDP没有达到预期的效果。

原点开放曲线: 近似开曲线:

我想要的结果应该是一串线段而不是闭合的多边形，像这样(这张图是用Photoshop而不是Python程序创建的):

有没有办法使用 cv2.approxPolyDP 来近似开曲线？

我的Python程序如下:

import cv2

img = cv2.imread('1.jpg')

gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

cv2.imshow("gray", gray)
cv2.waitKey(0)

_, binary = cv2.threshold(gray, 10, 255, cv2.THRESH_BINARY)

# cv2.imshow("binary", binary)
# cv2.waitKey(0)

_, contours, _ = cv2.findContours(binary, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

for contour in contours:
    epsilon = 0.009 * cv2.arcLength(contour, True)
    approx = cv2.approxPolyDP(contour, epsilon, closed=True)
    cv2.drawContours(img, [approx], -1, (0, 255, 255), 1)

cv2.imshow("approx", img)
cv2.waitKey(0)

cv2.destroyAllWindows()

我程序中使用的原图如下。

Close curve photo Open curve photo

Answer 1

这里是如何使用 cv2.approxPolyDP 在 Python/OpenCV 中做到这一点

输入(截屏标题栏)

import numpy as np
import cv2

# read input
img = cv2.imread('curve.png')
hh, ww = img.shape[:2]

# convert to grayscale
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

# threshold
thresh = cv2.threshold(gray, 100, 255, cv2.THRESH_BINARY)[1]

# get points
points = np.column_stack(np.where(thresh.transpose() != 0))

# list points
for pt in points:
    ptx = pt[0]
    pty = pt[1]
    print(ptx,pty)

# approximate polygon
poly = cv2.approxPolyDP(points, 0.02 * ww, False)

# list polygon points
for p in poly:
    px = p[0]
    py = p[0]
    print(px,py)

# draw polygon on copy of input
result = img.copy()
cv2.polylines(result, [poly], False, (0,0,255), 1)

# save results
cv2.imwrite('curve_polygon.png', result)

cv2.imshow("thresh", thresh)
cv2.imshow("result", result)
cv2.waitKey(0)