阈值操作

ret,dst = cv2.threshold(src,thresh,maxval,type)

src:输入图，只能输入单通道图像，一般使用灰度图
dst:输出图
thresh:阈值
maxval:当像素值超过了阈值（或者小于阈值，根据type来决定），所赋予的值
type:二值化操作的类型，包含以下5中类型：
cv2.THRESH_BINARY:超过阈值部分取maxval（最大值），否则取0
cv2.THRESH_BINARY_INV:cv2.THRESH_BINARY的反转
cv2.THRESH_TRUNC:大于阈值的部分设为阈值，否则不变
cv2.THRESH_TOZERO:大于阈值的部分不变，否则设为0
cv2.THRESH_TOZERO_INV:cv2.THRESH_TOZERO的反转

import cv2
image = cv2.imread('sample.jpg')
img_Gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
ret1,thresh1 = cv2.threshold(img_Gray, 127, 255, cv2.THRESH_BINARY)
ret2,thresh2 = cv2.threshold(img_Gray, 127, 255, cv2.THRESH_BINARY_INV)
ret3,thresh3 = cv2.threshold(img_Gray, 127, 255, cv2.THRESH_TRUNC)
ret4,thresh4 = cv2.threshold(img_Gray, 127, 255, cv2.THRESH_TOZERO)
ret5,thresh5 = cv2.threshold(img_Gray, 127, 255, cv2.THRESH_TOZERO_INV)

title = ['Original Image', 'BINARY', 'BINARY_INV', 'TRUNC', 'TOZERO', 'THRESH_TOZERO_INV']
images = [image, thresh1,thresh2, thresh3, thresh4, thresh5]

for i in range(6):
    cv2.imshow(title[i],images[i])

cv2.waitKey(0)
cv2.destroyAllWindows()