Opencv scalar passes in three parameters, which can only be displayed in black, white and gray. Solve the problem

The error code is ：

cv::Mat img2(h, w, CV_8UC1, cv::Scalar(0, 255, 0));

scalar The three parameters passed in are BGR, The above function I want to generate is a green picture , However, what is actually produced is white .
The problem lies in the third parameter , Parameter is CV_8UC1 It means that the black-and-white gray pattern is generated . You need to change the parameter to CV_8UC3, This time can produce the correct results .

cv::Mat img2(h, w, CV_8UC3, cv::Scalar(0, 255, 0));