python-opencv图片二值化

简单阈值

像素值高于阈值时，我们给这个像素附一个新值，否则我们给他赋予另外一种颜色，这个函数是cv2.threshhold()。这个函数有两个返回值，第一个为retval，第二个就是处理后的图像这个函数的第一个参数就是原图像，原图像应该是灰度图。第二个参数就是用来对像素值进行分类的阈值。第三个参数就是当像素值高于（有时是小于）阈值时应该被赋予的新的像素值。第四个参数是阈值方法，这些方法包括：

●cv2.THRESH_BINARY

●cv2.THRESH_BINARY_INV

●cv2.THRESH_TRUNC

●cv2.THRESH_TOZERO

●cv2.THRESH_TOZERO_INV

import cv2
import numpy as np
from matplotlib import pyplot as plt

img=cv2.imread('obama.bmp')
GrayImage=cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
ret,thresh1=cv2.threshold(GrayImage,80,255,cv2.THRESH_BINARY)
ret,thresh2=cv2.threshold(GrayImage,80,255,cv2.THRESH_BINARY_INV)
ret,thresh3=cv2.threshold(GrayImage,80,255,cv2.THRESH_TRUNC)
ret,thresh4=cv2.threshold(GrayImage,80,255,cv2.THRESH_TOZERO)
ret,thresh5=cv2.threshold(GrayImage,80,255,cv2.THRESH_TOZERO_INV)
titles = ['Gray Image','BINARY','BINARY_INV','TRUNC','TOZERO','TOZERO_INV']
images = [GrayImage, thresh1, thresh2, thresh3, thresh4, thresh5]
for i in xrange(6):
plt.subplot(2,3,i+1),plt.imshow(images[i],'gray')
plt.title(titles[i])
plt.xticks([]),plt.yticks([])
plt.show()

样本图：