python计算轮廓内面积

      对于用python计算图形面积，我是先把图像背景白色255转成黑色背景，再画出轮廓后用cv2.contourArea(contour) 函数计算其轮廓面积。

from PIL import Image
import PIL.ImageOps    
import numpy as np
from skimage.io import imsave
import cv2

#背景转化为黑色
in_path  = 'D:shenduimg/bathtub/bathtub_002/airplane.jpg'
out_path = 'D:shenduimg/bathtub/bathtub_002/newairplane.jpg'

Img = cv2.imread(in_path)
Img2 = np.array(Img, copy=True)

white_px = np.asarray([255, 255, 255])
black_px = np.asarray([0  , 0  , 0  ])

(row, col, _) = Img.shape

for r in range(row):
    for c in range(col):
        px = Img[r][c]
        if all(px == white_px):
            Img2[r][c] = black_px

imsave(out_path, Img2)

#对转化后的图片进行描边
mat_img = cv2.imread(out_path)
mat_img2 = cv2.imread(out_path,cv2.CV_8UC1)
#自适应分割
dst = cv2.adaptiveThreshold(mat_img2,210,cv2.BORDER_REPLICATE,cv2.THRESH_BINARY_INV,3,10)
#提取轮廓
contours,heridency = cv2.findContours(dst,cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_SIMPLE)
#标记轮廓
cv2.drawContours(mat_img,contours,-1,(255,0,255),3)

#计算轮廓面积
area = 0
for i in contours:
    area += cv2.contourArea(i)
print(area)

原图

画出轮廓图

 遇到的坑：

1.NameError:name ‘xrange’ is not defined；这是因为在python3中range()与xrange()合并为range( )。把xrange( )函数全部换为range( )即可

2.ValueError: not enough values to unpack (expected 3, got 2)；因为cv2.findContours的opencv旧版本返回3个值，img1,contours,heridency = cv2.findContours(dst,cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_SIMPLE)，这里把img1去掉即可。