I using the opencv3.
I tried
A = cv2.imread(str,0).
img = cv2.imread(str,1).
B = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY).
now A is not equal B. I think, there are difference method.
I found B 's method in http://docs.opencv.org/master/de/d25/imgproc_color_conversions.html#gsc.tab=0
but can't found A 's method.
how to trance to gray in A ? where the fomula ?