void accessPixel(Mat& img)
{
    for (int i = 0; i < img.rows; i++)
    {
        for(int j = 0; j < img.cols; j++ )
        {
            if (img.channels() == 1)
            { 
                // gray-level image
                cout << img.at<Vec3s>(j,i)[0] << " ";

                cout << endl;
            }          
        }
    }

}

int main(int argc, char** argv)
{
    int minThreshold = 80;
    int maxThreshold = 255;
    
    Mat dst, src_gray;
    cvtColor(coverImage, src_gray, CV_RGB2GRAY);
    threshold(src_gray, dst, minThreshold, maxThreshold, CV_THRESH_BINARY);
   
    accessPixel(dst);

              // Pixel value of at row i, column j of CV_8UC1 Mat:
                unsigned char uc1 = img.at<unsigned char>(i,j);
              // To see numerical value of unsigned char, cast it to int data type
                cout << (int)uc1

//
void printCV_8UC1Pixels(const Mat & img)
{
    cout << "In printCV_8UC1Pixels: img.type() = " << img.type() << endl; // For debugging

    if (img.type() != CV_8UC1)
    {
        cerr << "This function only works with a CV_8UC1 image!" << endl;
        return;
    }

    for (int i = 0; i < img.rows; i++)
    {
        for(int j = 0; j < img.cols; j++ )
        {
            // To print numeric value, cast unsigned char to int
            cout << "Pixel at (row,col) = (" << i << "," << j
                 << "): "
                 << (int)img.at<unsigned char>(i,j) << endl;
        }
    }
}