OpenCV的等高线画法

用于圈出图片上颜色深浅不同的区域

处理步骤：gray + threshold + open + distanceTransform + medianBlur + find_contours

from skimage import io,color
import numpy as np
import cv2
from matplotlib import pyplot as plt
from IPython.display import display
from ipywidgets import interact,interactive,fixed
plt.style.use('classic')

1.读取图片，并二值化

img = io.imread('img.JPG')
img2 = io.imread('img2.JPG')

gray = cv2.cvtColor(img2,cv2.COLOR_BGR2GRAY)
# ret 值多凭感觉
thresh = np.ones_like(gray)
ret = 168
thresh[gray < ret] = 255
thresh[gray > ret] = 0

fig = plt.figure(figsize=(16, 6))
plt.subplot(131),plt.imshow(img)
plt.subplot(132),plt.imshow(gray,'gray')
plt.subplot(133),plt.imshow(thresh,'gray')
plt.show()

2.降噪，扩张并获得距离参数

# noise removal
kernel = np.ones((3,3),np.uint8)
opening = cv2.morphologyEx(thresh,cv2.MORPH_OPEN,kernel, iterations = 2)

# sure background area
sure_bg = cv2.dilate(opening,kernel,iterations=3)

# Finding sure foreground area
dist_transform = cv2.distanceTransform(opening,cv2.DIST_L2,5)

# distanceTransform
fig = plt.figure(figsize=(16, 6))
plt.subplot(131),plt.imshow(opening,'gray')
plt.subplot(132),plt.imshow(sure_bg,'gray')
plt.subplot(133),plt.imshow(dist_transform,'gray')

plt.show()

3.滑动调节等高线高度，绘制等高线

def distance(dist_transform,thresh=0.1):
    ret, sure_fg = cv2.threshold(dist_transform,thresh*dist_transform.max(),255,0)
    sure_fg = np.uint8(sure_fg)
    median_img = cv2.medianBlur(sure_fg,17)
    fig = plt.figure(figsize=(20,18))
    plt.subplot(121),plt.imshow(median_img,'gray'),plt.xticks([]),plt.yticks([])

    im2, contours, hierarchy = cv2.findContours(median_img, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
    img_ground = img2.copy()
    cv2.drawContours(img_ground,contours,-1,(0,255,225),5)

    plt.subplot(122),plt.imshow(img_ground),plt.xticks([]),plt.yticks([])
    plt.show()

    return median_img,img_ground

lims = (0.0,1.0,0.05)
w = interactive(distance,dist_transform = fixed(dist_transform),thresh = lims)
display(w)

可以拖动进度条调整阈值，以改变等高线位置