彩色图像：三个通道0-255，0-255，0-255，所以可以有2^24位空间

灰度图像：一个通道0-255,所以有256种颜色

二值图像：只有两种颜色，黑和白，1白色，0黑色

 cv.threshold( src, thresh, maxval, type[, dst] ) 

 1 enum ThresholdTypes {
 2 THRESH_BINARY = 0,
 3 THRESH_BINARY_INV = 1,
 4 THRESH_TRUNC = 2,
 5 THRESH_TOZERO = 3,
 6 THRESH_TOZERO_INV = 4,
 7 THRESH_MASK = 7,
 8 THRESH_OTSU = 8,
 9 THRESH_TRIANGLE = 16
10 };

1 　　 def threshold_demo(image):
2     gray = cv.cvtColor(image,cv.COLOR_RGB2GRAY)   #要二值化图像，要先进行灰度化处理
3     ret, binary = cv.threshold(gray,0,255,cv.THRESH_BINARY | cv.THRESH_OTSU)
4     print("threshold value: %s"%ret)　　#打印阈值，前面先进行了灰度处理0-255，我们使用该阈值进行处理，低于该阈值的图像部分全为黑，高于该阈值则为白色
5     cv.imshow("binary",binary)　　#显示二值化图像 

threshold value: 140.0　　#获取的阈值是140

ret, binary = cv.threshold(gray,0,255,cv.THRESH_BINARY | cv.THRESH_TRIANGLE)

threshold value: 67.0

ret, binary = cv.threshold(gray,127,255,cv.THRESH_BINARY_INV)

threshold value: 127.0

ret, binary = cv.threshold(gray,127,255,cv.THRESH_TRUNC)

ret, binary = cv.threshold(gray,127,255,cv.THRESH_TOZERO)