二值化的cv2.threshold函数

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像素高于阈值时，给像素赋予新值，否则，赋予另外一种颜色。函数是cv2.threshold()
cv2.threshold(src,thresh,maxval,type[,dst])->retval,dst
作用：用于获取二元值的灰度图像
thresh:阈值，maxval:在二元阈值THRESH_BINARY和逆二元阈值THRESH_BINARY_INV中使用的最大值
返回值retval其实就是阈值

type:使用的阈值类型

例子：

#python 3.5.3  蔡军生    #http://edu.csdn.net/course/detail/2592    #import cv2import matplotlib.pyplot as pltimg = cv2.imread('test1.jpg',0) #直接读为灰度图像#二值化ret,thresh1 = cv2.threshold(img,1,255,cv2.THRESH_BINARY)ret,thresh2 = cv2.threshold(img,127,255,cv2.THRESH_BINARY_INV)ret,thresh3 = cv2.threshold(img,127,255,cv2.THRESH_TRUNC)ret,thresh4 = cv2.threshold(img,127,255,cv2.THRESH_TOZERO)ret,thresh5 = cv2.threshold(img,127,255,cv2.THRESH_TOZERO_INV)titles = ['img','BINARY','BINARY_INV','TRUNC','TOZERO','TOZERO_INV']images = [img,thresh1,thresh2,thresh3,thresh4,thresh5]for i in range(6):    plt.subplot(2,3,i+1),plt.imshow(images[i],'gray')    plt.title(titles[i])    plt.xticks([]),plt.yticks([])plt.show()