title: OpenCV Line Detection
body: <p>I am trying to find the edges of the centered box in this image:
  <img src="https://i.stack.imgur.com/ADSTx.jpg" alt="black and white box"></p>
  
  <p>I have tried using a HoughLines using dRho=img_width/1000, dTheta=pi/180, and threshold=250
  It works great on this image, scaled to 1/3 of the size, but on the full size image it just gets lines everywhere in every direction...</p>
  
  <p>What can I do to tune this to be more accurate?</p>