cv::Mat image;

[10, 103, 196]

cv::Mat image = cv::Mat::zeros(2,3,CV_32SC3)

[0, 0, 0, 0, 0, 0, 0, 0, 0;
  0, 0, 0, 0, 0, 0, 0, 0, 0]

image = image + Scalar(3,0,0);  // the result will be same as image=image+3;

[3, 0, 0, 3, 0, 0, 3, 0, 0;
 3, 0, 0, 3, 0, 0, 3, 0, 0]

image = image +Scalar(3,2,-3);

[3, 2, -3, 3, 2, -3, 3, 2, -3;
 3, 2, -3, 3, 2, -3, 3, 2, -3]

cv::Mat image = cv::Mat::zeros(2,3,CV_32SC3);
subtract(image,Scalar(2,3,1),image);

[-2, -3, -1, -2, -3, -1, -2, -3, -1;
 -2, -3, -1, -2, -3, -1, -2, -3, -1]