Printing a value of Mat object

Question

I tried to get the N*N matrix. to do that i used following code but printing a one value all the time. any idea to take the correct value of matrix.

I checked the destination mat using imread function which is not null. countervalue. But in the printf comes \377 value which int count=0;

 Size s=destination.size();

    int count=0;
    for(int i=0 ;i<s.height; i++)
    {
        for (int j=0; j<s.width; j++) {
            unsigned char* byte = destination.ptr<unsigned char>(i,j);
            count++;
            printf("valeue %s ",byte);
            printf("\n");

        }
    }

output

valeue \377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377 .......

Answer 1

ptr accepts as argument the row number. You can thus get the pointer to the starting element of each row by calling pointer on each i (outside inner loop).

Then you need %d (or %u) in your printf (or you can use cout). Check the code below:

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

int main() 
{
    int N = 10;

    // Init matrix
    Mat destination(N, N, CV_8UC1);
    randu(destination, Scalar(0), Scalar(255));

    Size s = destination.size();
    int count = 0;
    for (int i = 0; i<s.height; i++)
    {
        unsigned char* pByte = destination.ptr<unsigned char>(i);
        for (int j = 0; j<s.width; j++) {
            count++;
            printf("value %d ", pByte[j]);
            printf("\n");

            //cout << "value " << int(pByte[j]) << endl;
        }
    }

    return(0);
}

You can see in my other answer other methods to get the value at specific position in a Mat.

Answer 2

For printing the Mat values, you just need to iterate over Mat.

Here is some piece of code:

Mat in = imread("image.bmp",CV_LOAD_IMAGE_GRAYSCALE);
if(in.empty())
{
  puts("Cannot open image!");
  return -1;
}
//Print the values
for(int i=0;i<in.rows;i++)
{
    for(int j=0;j<in.cols;j++)
    {
        cout<<in.at<uchar>(i,j)<<" ";
    }
    cout<<endl;
}

Here basically I am loading the image, checking whether it is empty or not, and then printing the values.

As my image is grayscale image, I have used in.at<uchar>(i,j) where uchar means unsigned char.