title: OpenCV: subtract same BGR values from all pixels
body: <p>I have some BGR image:</p>
  
  <pre><code>cv::Mat image;
  </code></pre>
  
  <p>I want to subtract from all the pixels in the image the vector:</p>
  
  <pre><code>[10, 103, 196]
  </code></pre>
  
  <p>Meaning that the blue channel for all the pixels will be reduced by 10, the green by 103 and the red by 196.</p>
  
  <p>Is there a standard way to do that, or should I run for loops over all the channels and all the pixels?</p>