opencv: 轮廓绘制 详细拆解(图示+源码)

过程图解

第一步

读取要进行处理的原图：

origin_pic = './pic/6.jpg' save_folder = './generated_pics' img = cv2.imread(origin_pic)

此时原图如下：

第二步

将原图转换成单通道图（例如本例中用cv2.cvtColor转换成灰度图）：

imgray = cv2.cvtColor(src=img, code=cv2.COLOR_BGR2GRAY)

转换后的单通道图如下：

第三步

对得到的单通道图进行阀值处理：

_, thresh = cv2.threshold(src=imgray, thresh=150, maxval=200, type=0)

得到阀值图片如下：

第四步

寻找轮廓并记录在返回的 contours列表 中：

image, contours, _1 = cv2.findContours(thresh, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

第五步

根据轮廓数据表，在三通道彩色图片上绘制轮廓：

contoured_colored_img = cv2.drawContours(img, contours, -1, (0, 0, 255), 2)

结果图如下：

也可以在黑白三通道图片上绘制轮廓：

thresh_expanded = np.expand_dims(thresh, axis=2) gray_img = np.concatenate([thresh_expanded, thresh_expanded, thresh_expanded], axis=2) contoured_gray_img = cv2.drawContours(gray_img, contours, -1, (0, 0, 255), 2)

结果图如下：

完整源码

我自己写的完整源码如下：

# coding=utf-8 import numpy as np import cv2 origin_pic = './pic/6.jpg' save_folder = './generated_pics' import shutil try: shutil.rmtree(save_folder) except OSError: pass import os os.makedirs(save_folder) img = cv2.imread(origin_pic) imgray = cv2.cvtColor(src=img, code=cv2.COLOR_BGR2GRAY) _, thresh = cv2.threshold(src=imgray, thresh=150, maxval=200, type=0) image, contours, _1 = cv2.findContours(thresh, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE) thresh_expanded = np.expand_dims(thresh, axis=2) gray_img = np.concatenate([thresh_expanded, thresh_expanded, thresh_expanded], axis=2) contoured_gray_img = cv2.drawContours(gray_img, contours, -1, (0, 0, 255), 2) contoured_colored_img = cv2.drawContours(img, contours, -1, (0, 0, 255), 2) cv2.imwrite(os.path.join(save_folder, 'imgray.jpg'), imgray) cv2.imshow('imgray', imgray) cv2.waitKey(2000) cv2.imwrite(os.path.join(save_folder, 'thresh.jpg'), thresh) cv2.imshow('thresh', thresh) cv2.waitKey(2000) cv2.imwrite(os.path.join(save_folder, 'image.jpg'), image) cv2.imshow('image', image) cv2.waitKey(2000) cv2.imwrite(os.path.join(save_folder, 'contoured_gray_img.jpg'), contoured_gray_img) cv2.imshow('contoured_gray_img', contoured_gray_img) cv2.waitKey(2000) cv2.imwrite(os.path.join(save_folder, 'contoured_colored_img.jpg'), contoured_colored_img) cv2.imshow('', contoured_colored_img) cv2.waitKey(2000) cv2.destroyAllWindows()