title: detecting lines of a rectangle image using hough transform
body: <p>i wanna detect this rectangles lines using hough transform, 
  <a href="https://i.stack.imgur.com/V3Z51.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/V3Z51.jpg" alt="enter image description here"></a></p>
  
  <p>here is the opencv code :</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>import cv2
  import numpy as np
  
  img = cv2.imread('C:/Users/hp/rectangles.jpg')
  gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
  edges = cv2.Canny(gray,50,150,apertureSize = 3)
  
  lines = cv2.HoughLines(edges,1,np.pi/180,200)
  for rho,theta in lines[0]:
      a = np.cos(theta)
      b = np.sin(theta)
      x0 = a*rho
      y0 = b*rho
      x1 = int(x0 + 1000*(-b))
      y1 = int(y0 + 1000*(a))
      x2 = int(x0 - 1000*(-b))
      y2 = int(y0 - 1000*(a))
  
      cv2.line(img,(x1,y1),(x2,y2),(0,0,255),2)
  
  cv2.imwrite('houghlines3.jpg',img)</code></pre>
  </div>
  </div>
  </p>
  
  <p>but it only detects one line, how can i detect all lines ?</p>
  
  <p>after testing this code and choosing these parameters :</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>    import cv2
      import numpy as np
  
  
          img = cv2.imread('dave.jpg')
          gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
          edges = cv2.Canny(gray,50,150,apertureSize = 3)
          minLineLength = 100
          maxLineGap = 10
          lines = cv2.HoughLinesP(edges,1,np.pi/180,100,minLineLength,maxLineGap)
          for x1,y1,x2,y2 in lines[0]:
              cv2.line(img,(x1,y1),(x2,y2),(0,255,0),2)
  
          cv2.imwrite('houghlines5.jpg',img)</code></pre>
  </div>
  </div>
  </p>
  
  <p>i got this result :</p>
  
  <p><a href="https://i.stack.imgur.com/sb6Sc.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/sb6Sc.jpg" alt="enter image description here"></a></p>
  
  <p>i changed parameters but that one line isnt detected, how should i change parameters to make that line detected?</p>