cv2.approxPolyDP() , cv2.arcLength() 这些是如何工作的

问题描述

这些功能是如何工作的?我正在使用 Python3.7 和 OpenCv 4.2.0.提前致谢.

How do these function works? I am using Python3.7 and OpenCv 4.2.0. Thanks in Advance.

approx = cv2.approxPolyDP(cnt, 0.01*cv2.arcLength(cnt, True), True)

推荐答案

如果您正在寻找示例代码段，以下是一个:

If you are looking for a example snippet, below is one:

import cv2
import imutils

# edged is the edge detected image
cnts = cv2.findContours(edged, cv2.RETR_LIST, cv2.CHAIN_APPROX_SIMPLE)
cnts = imutils.grab_contours(cnts)
cnts = sorted(cnts, key = cv2.contourArea, reverse = True)[:5]
# loop over the contours
for c in cnts:
    # approximate the contour
    peri = cv2.arcLength(c, True)
    approx = cv2.approxPolyDP(c, 0.02 * peri, True)
    # if our approximated contour has four points, then we
    # can assume that we have found our screen
    if len(approx) == 4:
        screenCnt = approx
        break

在上面的代码片段中，它首先从边缘检测图像中找到轮廓，然后对轮廓进行排序以找到五个最大的轮廓.最后，它遍历轮廓并使用 cv2.approxPolyDP 函数来平滑和逼近四边形.cv2.approxPolyDP 适用于文档边界等轮廓中有尖锐边缘的情况.

In the above snippet, first it finds the contours from a edge detected image, then it sorts the contours to find the five largest contours. Finally it loop over the contours and used cv2.approxPolyDP function to smooth and approximate the quadrilateral. cv2.approxPolyDP works for the cases where there are sharp edges in the contours like a document boundary.