accessing the pixel of an image going wrong in Mat

Question

I am implementing a simple demosaicing algorithm. I think I am accessing a pixel in the right way, but the output is showing that I am accessing it in the wrong way. I was supposed to get this as an output

but instead, I am getting this

It is zooming in on the left top corner. My code is pasted below

pixel demosiac_interpol(float win[3][3], int r, int c)
{
    pixel new_pix; 
    if (r % 2 == 0 && c % 2 == 0)
    {
        new_pix.r = (win[1][0] + win[1][2]) / 2;
        new_pix.g = win[1][1] * 2;
        new_pix.b = (win[0][1] + win[2][1]) / 2;
    }
    else if (r % 2 == 0 && c % 2 == 1)
    {
        new_pix.r = win[1][1];
        new_pix.g = (win[1][0] + win[2][1] + win[0][1] + win[1][2]) / 2;
        new_pix.b = (win[2][0] + win[0][2] + win[2][2] + win[0][0]) / 4;
        
    }
    else if (r % 2 == 1 && c % 2 == 0)//blue
    {
        new_pix.r = (win[0][2] + win[2][0] + win[2][2] + win[0][0]) / 4;
        new_pix.g = (win[1][0] + win[1][2] + win[2][1] + win[2][1]) / 2;
        new_pix.b = win[1][1];
    }
    else
    {
        new_pix.r = (win[0][1] + win[2][1]) / 2;
        new_pix.g = win[1][1] * 2;
        new_pix.b = (win[1][0] + win[1][2]) / 2;
    }
    return new_pix;

}
int main(int argc, char** argv)
{
Mat input = imread("C:/Users/20181217/image_data/raw_rc_3.png");//262x518;rowsxcols
    cout << endl << input.rows << "," << input.cols;
    //cout << (int)input.at<uchar>(200, 200) << endl;
    //imwrite("C:/Users/20181217/image_data/raw_rc_3.png", input);
    input.convertTo(input, CV_32FC1);
    input = input / 256.0;
    cout << (int)input.at<float>(200, 200) << endl;
    Mat final_img(input.rows - 2, input.cols - 2, CV_8UC3);//260x516; size
    cout <<endl<< final_img.rows << "," << final_img.cols;
    const int height = 262;
    const int width = 518;

    float window[3][3];
    float line_buf[2][width];
    float pixel_in;
    pixel out_pix;
    
    for (int row = 0; row < height; row++)
    {
        //cout <<endl<< row<<endl;
        for (int col = 0; col < width; col++)
        {
            //cout << col << ",";
            //if(row>1 && col> 512)
            //cout << "1,";
            pixel_in = input.at<float>(row, col);
            if (row == 200 && col == 200)
                cout <<endl<< "at " << row << "and" << col << ", value is:" << pixel_in<<endl;
            if (row == 261 && col == 517)
            {
                cout << "printing at 261,517";
                cout << endl << pixel_in;
            }
            
            for (int i = 0; i < 3; i++)
            {
                window[i][0] = window[i][1];
                window[i][1] = window[i][2];
            }
            
            window[0][2] = line_buf[0][col];
            window[1][2] = line_buf[0][col] = line_buf[1][col];
            window[2][2] = line_buf[1][col] = pixel_in;
            if (row == 200 && col == 200)
                display_win(window);
            if (row > 1 && col > 1 && row < height  && col < width)
            {
                
                out_pix = demosiac_interpol(window, row - 2, col - 2);
                

                    final_img.at<Vec3b>(row - 2, col - 2)[0] = uchar(fmax(fmin((out_pix.r *255.0), 255.0), 0.0));
                    final_img.at<Vec3b>(row - 2, col - 2)[1] = uchar(fmax(fmin((out_pix.g *255.0), 255.0), 0.0));
                    final_img.at<Vec3b>(row - 2, col - 2)[2] = uchar(fmax(fmin((out_pix.b *255.0), 255.0), 0.0));
                
            }

        }//cout << endl<< row ;
    }

I am assuming that while accessing the pixel the row and col is getting interchanged at pixel_in = input.at<float>(row, col);. This assumption is based on the images of ideal and output.

Why is it zooming the top left corner?

Answer 1

The problem was with the usage of imread(),

even though, the image was single channel one, imread by default read it as an RGB image. when I used the flag -1, which suggests the data should be read as specified by the image, it worked perfectly.

imread("path_to_image",-1);

thanks to @Micka for suggesting the solution.

cheers