title: Opencv Python resize with one constant
body: <p>I want to resize my image with given one edge's new length by using <code>cv2.resize()</code> method.</p>
  
  <p>For example my image has dimension 300x400, and I want to increase my height from 400 to 500 but I should write only one edge's new size(just 500), the other edge should automatically be increased. What is sequence?</p>