opencv: 輪廓繪製 詳細拆解(圖示+源碼)

過程圖解

第一步

讀取要進行處理的原圖：

origin_pic = './pic/6.jpg'
save_folder = './generated_pics'

img = cv2.imread(origin_pic)

此時原圖如下：

第二步

將原圖轉換成單通道圖（例如本例中用cv2.cvtColor轉換成灰度圖）：

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

轉換後的單通道圖如下：

第三步

對得到的單通道圖進行閥值處理：

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

得到閥值圖片如下：

第四步

尋找輪廓並記錄在返回的 contours列表 中：

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

第五步

根據輪廓數據表，在三通道彩色圖片上繪製輪廓：

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

結果圖如下：

也可以在黑白三通道圖片上繪製輪廓：

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)

結果圖如下：

完整源碼

我自己寫的完整源碼如下：

# 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()