title: Accessing elements of OpenCV CV_8UC1 cv::Mat
body: <p>I have a cv::Mat of type CV_8UC1 (8-bit single channel image) and I would like to access elements using the <code>at&lt;&gt;</code> operator as follows: <code>image.at&lt;char&gt;(row, column)</code>. However, when casting to <code>int</code>: <code>(int) image.at&lt;char&gt;(row, column)</code>, some values become negative, e.g., 255 becomes -1. </p>
  
  <p>This might be a stupid question, but I can't tell why this happens and what would be a better way to convert the entries to <code>int</code>. </p>
  
  <p>Thanks in advance!</p>