如何找到线和轮廓之间的交点答案

【问题标题】：How to find intersection points between lines and contours如何找到线和轮廓之间的交点
【发布时间】：2021-06-16 18:04:20
【问题描述】：

考虑下图，轮廓以绿色显示，直线以红色显示

我们如何找到直线切割轮廓的交点

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

# Read image img

# Binarize
img_gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
_,thresh = cv2.threshold(img_gray, 127, 255, cv2.THRESH_BINARY)

# Find Contours
_, contours, _ = cv2.findContours(thresh, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

# Draw Contours
blank_mask = np.zeros((thresh.shape[0],thresh.shape[1],3), np.uint8)
cv2.drawContours(blank_mask, contours, -1, (0, 255, 0), 1) 

# Define lines coordinates
line1 = [x1, y1, x2, y2]
line2 = [x1, y1, x2, y2]
line3 = [x1, y1, x2, y2]

# Draw Lines over Contours
cv2.line(blank_mask, (line1[0], line1[1]), (line1[2], line1[3]), (255, 0, 0), thickness=1)
cv2.line(blank_mask, (line2[0], line2[1]), (line2[2], line2[3]), (255, 0, 0), thickness=1)
cv2.line(blank_mask, (line3[0], line3[1]), (line3[2], line3[3]), (255, 0, 0), thickness=1)

# Show Image
fig = plt.figure()
ax  = fig.add_subplot(111)
ax.imshow(blank_mask)

Sample Image

【问题讨论】：

标签： python opencv opencv-contour

【解决方案1】：

您可以逐个像素检查它们重叠的位置。在绘制线条之前，您必须保留轮廓所在像素的副本，因为这会用线条的颜色覆盖重叠的像素。在此处添加几行代码

# Draw Contours
blank_mask = np.zeros((thresh.shape[0],thresh.shape[1],3), np.uint8)
cv2.drawContours(blank_mask, contours, -1, (0, 255, 0), 1)
contours_idx = blank_mask[...,1] == 255

# Define lines coordinates
line1 = [x1, y1, x2, y2]
line2 = [x1, y1, x2, y2]
line3 = [x1, y1, x2, y2]

# Draw Lines over Contours
cv2.line(blank_mask, (line1[0], line1[1]), (line1[2], line1[3]), (255, 0, 0), thickness=1)
cv2.line(blank_mask, (line2[0], line2[1]), (line2[2], line2[3]), (255, 0, 0), thickness=1)
cv2.line(blank_mask, (line3[0], line3[1]), (line3[2], line3[3]), (255, 0, 0), thickness=1)
lines_idx = blank_mask[...,0] == 255

然后

overlap = np.where(contours_idx * lines_idx)

这会给你类似于以下的东西（我不得不猜测你的线坐标和图像调整大小的形状，所以我可能有点偏离）

(array([ 90, 110, 110, 140, 140], dtype=int64), array([ 80,  40, 141,  27, 156], dtype=int64))

如果你想要它们在像素坐标的元组中

list(zip(*overlap))

编辑：对于轮廓/线条的颜色在多个平面上的更通用的解决方案，您可以在每次绘制后检查每个像素的全色。例如

# Change these
contours_idx = blank_mask[...,1] == 255
lines_idx = blank_mask[...,0] == 255

# To this
contours_idx = np.all(blank_mask == (0, 255, 0), axis=-1)
lines_idx = np.all(blank_mask == (255, 0, 0), axis=-1)

【讨论】：