【OpenCV入门学习--python】在图像中找到轮廓

例子源于OpenCV官网–在你的图像中找到轮廓
（https://docs.opencv.org/4.x/df/d0d/tutorial_find_contours.html）
使用OpenCV函数cv::findContours在二值图像中查找轮廓。
使用OpenCV函数cv:: drawcontour绘制轮廓或填充轮廓。

from __future__ import print_function
import cv2 as cv
import numpy as np
import argparse
import random as rng
rng.seed(12345)
def thresh_callback(val):
    threshold = val
    # Detect edges using Canny。使用Canny检测边缘
    canny_output = cv.Canny(src_gray, threshold, threshold * 2)
    # Find contours，找到轮廓
    contours, hierarchy = cv.findContours(canny_output, cv.RETR_TREE, cv.CHAIN_APPROX_SIMPLE)
    # Draw contours。画出轮廓
    drawing = np.zeros((canny_output.shape[0], canny_output.shape[1], 3), dtype=np.uint8)
    for i in range(len(contours)):
        color = (rng.randint(0,256), rng.randint(0,256), rng.randint(0,256))
        cv.drawContours(drawing, contours, i, color, 2, cv.LINE_8, hierarchy, 0)
    # Show in a window显示
    cv.imshow('Contours', drawing)
# Load source image加载图像
parser = argparse.ArgumentParser(description='Code for Finding contours in your image tutorial.')
parser.add_argument('--input', help='Path to input image.', default='HappyFish.jpg')
args = parser.parse_args()
src = cv.imread(cv.samples.findFile(args.input))
if src is None:
    print('Could not open or find the image:', args.input)
    exit(0)
# Convert image to gray and blur it。转换成灰度图并且模糊它
src_gray = cv.cvtColor(src, cv.COLOR_BGR2GRAY)
src_gray = cv.blur(src_gray, (3,3))
# Create Window创建窗口
source_window = 'Source'
cv.namedWindow(source_window)
cv.imshow(source_window, src)
max_thresh = 255
thresh = 100 # initial threshold
cv.createTrackbar('Canny Thresh:', source_window, thresh, max_thresh, thresh_callback)
thresh_callback(thresh)
cv.waitKey()

原图：

检测的轮廓：