opencv color conversions code example

Example 1: bgr2gray opencv

img = cv2.imread(path)
img_gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

Example 2: opencv rgb to gray custom

cv::transform(white_balance_image, i_test_base, cv::Matx13f(0.114, 0.587, 0.299));