How to find Coordinates Pixel Value

I have an image and

1)I get rows and derivative image with using sobel

2)Than I found gradient value

3)I found neighbor coordinates

4)I want to find neighbor coordinates pixel value but I cant do it I use intensity but I cant get a result Here is my code

int main() { 
   int scale = 1, delta = 0, ddepth = CV_16S,col=0; 
   Mat img =  imread("a.jpg"),newimg; 
   vector<Mat> line; 
   vector<Mat>line2;
   vector<Point> xmin,xmax,ymin,ymax;//Komşu noktalar için vektörler 

   for (int i = 0; i < img.rows; i++) 
   { 
   line.push_back(img.row(i)); 
   GaussianBlur(line[i],line[i], Size(5, 5), 0, 0, BORDER_DEFAULT); 

                /// Convert it to gray 
                cvtColor(line[i], line[i], CV_BGR2GRAY); 

                /// Generate grad_x and grad_y 
                Mat grad_x, grad_y; 
                Mat abs_grad_x, abs_grad_y; 

                /// Gradient X 
                //Scharr( src_gray, grad_x, ddepth, 1, 0, scale, delta, BORDER_DEFAULT ); 
                Sobel(line[i], grad_x, ddepth, 1, 0, 3, scale, delta, BORDER_DEFAULT); 
                double minx, maxx; 
                Point minloc,maxloc; 
                  minMaxLoc(grad_x, &minx, &maxx, &minloc, &maxloc); 
              //  cout <<i<<". Satir: "<<"Min Loc: "<<minloc<<"->Deger: "<<minx <<" Max Loc: "<<maxloc<<"->Deger: "<<maxx<<endl; 
                  if(minloc.x==0&&minloc.y==0) 
                { 
                    xmin.push_back(Point(0,0)); 
                    xmax.push_back(Point(0,0)); 
                } 
                else 
                { 
                xmin.push_back(Point(minloc.x-1,minloc.y)); 
                xmax.push_back(Point(maxloc.x+1,maxloc.y)); 
                } 
                cout<<"Xsol komsu: "<<xmin[i]<<"-"<<"Xsag komsu: "<<xmax[i]<<endl; 
             //   Scalar intensity = img.at<uchar>(xmin[i], xmax[i]);
             Scalar intensity = img.at<uchar>(Point(xmin[i], xmax[i]));
                cout<<intensity<<endl;
              //  img.at<uchar>(&minloc,&maxloc);

                convertScaleAbs(grad_x, abs_grad_x); 

                Sobel(line[i], grad_y, ddepth, 0, 1, 3, scale, delta, BORDER_DEFAULT); 
                convertScaleAbs(grad_y, abs_grad_y); 





   }