语法格式：
retval,dst=cv2.threshold(src,thresh,maxval,type)retval，thresh：阈值
maxval：最大值
type：类型
cv2.THRESH_BINARY：二进制阈值化
cv2.THRESH_BINARY_INV：反二进制阈值化
cv2.THRESH_TRUNC：截断阈值化
cv2.THRESH_TOZERO：阈值化为0
cv2.THRESH_TOZERO_INV：反阈值化为0
程序示例：
import cv2
img=cv2.imread("lena.bmp",cv2.IMREAD_UNCHANGED)
retval,result=cv2.threshold(img,128,255,cv2.THRESH_BINARY)
cv2.imshow("lena",img)
cv2.imshow("result",result)
cv2.waitKey()
cv2.destroyAllWindows()结果：
