title: Camera Parameters - iPhone 7
body: <p>Good evening folks of Stackoverflow,</p>
  
  <p>I've been trying to find accurate data for calculating the focal parameter of <a href="http://docs.opencv.org/trunk/d4/d0a/structcv_1_1detail_1_1CameraParams.html#a9af414e5bbf7063c105ce8c9a2ec36ba" rel="nofollow noreferrer">CameraParams</a> for quite some time but actively failed.</p>
  
  <p>Here's what I got so far:</p>
  
  <pre><code>iPhone 7
  Sensor width: 3.99mm
  Focal length: 7.21mm
  Random image: 400x400
  </code></pre>
  
  <p><strong>Calculation:</strong></p>
  
  <p><code>focal(in pixel) = image width(in pixel)*focal(in mm)/sensor width(mm)</code></p>
  
  <p><code>focal = 400 * 7.21 / 3.99</code></p>
  
  <p>But that results to look very inaccurate. Is there something I'm missing?</p>