C++/OpenCV：Mat初始化赋值误区

#include <opencv2/opencv.hpp>
#include <iostream>

using namespace cv;
using namespace std;

int main() {
    int pic_height = 2;
    int pic_width = 2;

    {
        Mat alpha_map = Mat::ones(pic_height, pic_width, CV_32FC4);
        cout << "alpha_map = " << endl << alpha_map << endl;
        //alpha_map =
        //    [1, 0, 0, 0, 1, 0, 0, 0;
        //     1, 0, 0, 0, 1, 0, 0, 0]
    }
    {
        Mat alpha_map = Mat::ones(pic_height, pic_width, CV_32FC4);
        alpha_map.setTo(1);
        cout << "alpha_map = " << endl << alpha_map << endl;
        //alpha_map =
        //    [1, 1, 1, 1, 1, 1, 1, 1;
        //     1, 1, 1, 1, 1, 1, 1, 1]
    }
    {
        Mat alpha_map(pic_height, pic_width, CV_32FC4, Scalar(1.0, 1.0, 1.0, 1.0));
        cout << "alpha_map = " << endl << alpha_map << endl;
        //alpha_map =
        //    [1, 1, 1, 1, 1, 1, 1, 1;
        //     1, 1, 1, 1, 1, 1, 1, 1]
    }
    return 0;
}

一直以为下面这样会将每个通道均初始化为1，导致一个bug调了半天根本没有怀疑过这里。

连deepseek和chatgpt也这样说，实际上只会对一个通道初始化。

Mat alpha_map = Mat::ones(pic_height, pic_width, CV_32FC4);