在opencv中检测嵌套形状

Question

我需要在 opencv 中检测嵌套形状，但似乎即使使用层次结构我也可以做到

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edges = cv2.Canny(img,50,200)
contours,hierarchy = cv2.findContours(edges, cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)

hierarchy = hierarchy[0] # get the actual inner list of hierarchy descriptions


for comp in contours:

currentCont = comp[0]
currentHie = hierarchy[1]

x,y,w,h = cv2.boundingRect(currentContour)
  if ( currentHierarchy[1] < 0 ) 
    these are the innermost child components
    cv2.rectangle(img,(x,y),(x+w,y+h),(0,0,255),3)
    cv2.putText(img, "nes", (x, y), cv2.FONT_HERSHEY_COMPLEX, 0.5, (0, 0, 0), 2)
    cv2.drawContours(img, [currentCont], -1, (0, 255, 0), 1)
    cv2.waitKey()
    cv2.imshow("image",img)

cv2.waitKey(0)
cv2.destroyAllWindows()

Answer 1

我将向您展示如何找到嵌套的最内部轮廓。
我认为有比您的样本更复杂的结构，您必须对其进行分类。

• 我建议不要使用cv2.Canny，因为它会创建更多的层次结构。
  看看使用cv2.imshow("edges", edges) 和cv2.waitKey()。
  您可能只是反转极性以获得黑色背景上的白色三角形。

   img = 255 - img
  

• 有一个小错误（循环内）：
  您正在使用：currentHierarchy = hierarchy[1]
  而不是：currentHierarchy = component[1]

寻找嵌套轮廓：

• 从最内侧的轮廓开始。
  最内部的轮廓是没有“第一个孩子”的轮廓。
  检查是否currentHierarchy[2] < 0。

• 所有内部轮廓都将有一个父轮廓。
  原因是每个三角形都应用了两个（嵌套的）轮廓：

  • 三角形内边缘的内轮廓。
  • 三角形外边缘的外轮廓。

  我们需要得到父轮廓，并检查父轮廓是否有父轮廓。
  具有祖父母的内部三角形是嵌套三角形。

这是完整的代码示例：

import numpy as np
import cv2

img = cv2.imread('triangles.png', cv2.IMREAD_GRAYSCALE)  # Read input image as grayscale,

# edges = cv2.Canny(img, 50, 200)

# Invert polarity of img, instead of using Canny - we need the contours to be white.
img = 255 - img

contours, hierarchy = cv2.findContours(img, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

hierarchy = hierarchy[0] # get the actual inner list of hierarchy descriptions

img = cv2.cvtColor(img, cv2.COLOR_GRAY2BGR) # Convert image to BGR, for using colored text.

for component in zip(contours, hierarchy):
    currentContour = component[0]
    #currentHierarchy = hierarchy[1] # Why ?
    currentHierarchy = component[1]

    approx = cv2.approxPolyDP(currentContour, 0.01 * cv2.arcLength(currentContour, True), True)
    x = approx.ravel()[0]
    y = approx.ravel()[1] - 5

    # https://docs.opencv.org/master/d9/d8b/tutorial_py_contours_hierarchy.html
    # Hierarchy Representation in OpenCV
    # Each contour has its own information regarding what hierarchy it is, who is its child, who is its parent etc. 
    # OpenCV represents it as an array of four values : [Next, Previous, First_Child, Parent]

    #if (currentHierarchy[1] < 0) and len(approx) == 3:

    if (currentHierarchy[2] < 0) and len(approx) == 3:
        # These are the innermost child components

        parent_idx = currentHierarchy[3]  # Get the index of the parent contour
        parent_hier = hierarchy[parent_idx]  # Get the hierarchy of the parent.

        if parent_hier[3] >= 0:
            # Contour is nested only if the parent has a parent.
            cv2.putText(img, "Nested", (x, y), cv2.FONT_HERSHEY_COMPLEX, 0.5, (255, 0, 0), 2)
            cv2.drawContours(img, [currentContour], -1, (0, 255, 0), 1)
            cv2.waitKey(1000)
            cv2.imshow("image", img)

cv2.waitKey()
cv2.destroyAllWindows()

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结果：