title: Convert vec3b into mat
body: <p>I have color image in <code>im</code>, i want to get the pixel value of 3 channels image using vec3b using the following code</p>
  
  <pre><code>    for (int i = 0; i &lt; im.rows; i++)
  {
      for (int j = 0; j &lt; im.cols; j++)
      {
          for (int k = 0; k &lt; nChannels; k++)
          {
              zay[k] = im.at&lt;Vec3b&gt;(i, j)[k]; //get the pixel value and assign to new vec3b variable zay
  
  
          }
  
      }
  
  }
  </code></pre>
  
  <p>After that, i want to multiply the following mat 3x3 filter with that vec3b in zay</p>
  
  <pre><code>    Filter= (Mat_&lt;double&gt;(3, 3) &lt;&lt; 0, 0, 0,
                                  0, 1, 0,
                                  0, 0, 0);
  </code></pre>
  
  <p>How to convert vec3b into mat matrix so i can multiplied with mat Filter?? And vec3b is an array 3x1?
  Thanks</p>