OpenCV Scalar multiplication gives weird result

Question

In OpenCV, multiplying two scalars returns unexpected result, for example:

cv::Scalar s1(2, 3, 4);
cv::Scalar s2(2, 3, 4);
cv::Scalar s3 = s1 * s2; 

where I expect s3 should be [4,9,16,0] ,however the result is [-21, 12, 16, 0] , I would like to know the logic behind it. Thanks!

Answer 1

From the commonet above ，I would like to summary that the source code of operator* is defined here and the logic behind it is quaternion product .