Creating bigger image out of small image Mat [opencv, background subtraction]

Question

I have an image i1. I am supposed to create another Mat m1 of size (image.rows*3, image.cols*3). In m1, I'm supposed to fill the pixel value in the following way. (Please do see the image):

Here is my code-

#include <highgui.h>  
#include "opencv2/opencv.hpp"  
#include <fstream>  
using namespace cv;
static Mat NeurMap1, NeurMap2, NeurMap3, frame, hsv_Frame;
std::ofstream myfile;
void InitializeNeurMap(cv::Mat Channel[3])
{  
            int i=0,j=0,m_i=0,m_j=0, t1=0, t2=0;

    for(i=0; i < frame.rows; i++)
    {
        for(j=0;j < frame.cols;j++)
        {
            t1= i*n+1; t2 = j*n+1;
            for(m_i=t1-1; m_i <= t1+1;m_i++)
            {
                for(m_j=t2-1; m_j <= t2+1; m_j++)
                {
                    NeurMap1.at<uchar>(m_i,  m_j)= frame.at<uchar>(i,j); 
                }
            }
        }
    }
    std::cout<<m_j;
    myfile<<frame;

}
int main()
{

    myfile.open("NeurMaptext.txt");
    String filename="BootStrap/b%05d.bmp";// sequence of frames are read
    VideoCapture cap(filename);
    if(!cap.isOpened())  // check if we succeeded
        return -1;
    namedWindow("edges",1);
    //namedWindow("frames",1);
    Mat Channel[3];
    cap>>frame;
    NeurMap1 = Mat::zeros(frame.rows*n, frame.cols*n, frame.type());
    InitializeNeurMap(Channel);
    imshow("edges",NeurMap1);waitKey(33);
    for(;;)
    {
        cap>>frame;
        if(frame.empty())
            break;
    }   

    system("pause");
    return 0;
}

The input image is RGB[160*120]. Why am I not getting the columns in the output image given in the link above?.

Answer 1

You can simply call resize() by passing the INTER_NEAREST parameter, i.e. using the nearest-neighbor interpolation.

#include <opencv2/opencv.hpp>
#include <iostream>
using namespace cv;
using namespace std;

int main()
{
    unsigned char data[] = { 1, 2, 3, 4, 5, 6 };
    Mat img(2, 3, CV_8UC1, data);
    cout << img << endl;

    Mat res(6, 9, CV_8UC1);
    resize(img, res, res.size(), 0, 0, INTER_NEAREST);
    cout << res << endl;

    return 0;
}

You will get:

Answer 2

In you are getting three only one-third of image filled because, probably you are passing 3 channel(colour) image to the function and treat it as a single channel image. So change the above code to,

void InitializeNeurMap(cv::Mat Channel[3])
{
 for(int i=0; i < frame.rows; i++){
  for(int j=0;j < frame.cols;j++){

   for(int k=0;k<n;k++){
    for(int l=0;l<n;l++){
     NeurMap1.at<Vec3b>(i*n+k,j*n+l)[0] = frame.at<Vec3b>(i,j)[0]; //Access Blue channel
     NeurMap1.at<Vec3b>(i*n+k,j*n+l)[1] = frame.at<Vec3b>(i,j)[1];//Access green channel
     NeurMap1.at<Vec3b>(i*n+k,j*n+l)[2] = frame.at<Vec3b>(i,j)[2]; //Access red channel
    }
   }
  }
 }
 myfile<<frame;
}

See the reult