c++ - 如何修改/分配矩阵元素值？

Question

这段代码给我错误。该程序“停止工作”。我可以知道出了什么问题吗？我做对了吗？

short* pixelX = grad_x.ptr<short>(0);
short* pixelY = grad_y.ptr<short>(0);
cv::Mat grad = cv::Mat::zeros(original_Mat.size(), CV_64F);

cv::Mat grad_x = cv::Mat::zeros(original_Mat.size(), CV_64F); 
cv::Mat grad_y = cv::Mat::zeros(original_Mat.size(), CV_64F);
int a=0,b=0;

for(int i = 0; i < grad_x.rows * grad_x.cols; i++) 
{
    double directionRAD = atan2(pixelY[i], pixelX[i]);
    int directionDEG = (int)(180 + directionRAD / CV_PI * 180);
    grad.at<double>(a,b)=directionDEG;// this is the one giving me error
    if(a%=319)
    {
        a=0;
        b++;
    }
    else
    a++;
}

Answer 1

这是您访问/修改矩阵元素的方式。您可以在此基础程序的基础上进一步构建，以用您想要的值填充矩阵:

cv::Mat grad = cv::Mat::zeros(4, 5, CV_64F);

int a = 0, b = 0;

for (int i = 0; i < grad.rows * grad.cols; i++)
{
grad.at<double>(b, a) = i;    // this is the one giving me error
if (a == grad.cols - 1)
    {
    a = 0;
    b++;
    }
else
    a++;
}
cout << grad << endl;

这给出:

[0, 1, 2, 3, 4;
5, 6, 7, 8, 9;
10, 11, 12, 13, 14;
15, 16, 17, 18, 19]