title: choosing the correct hsv boundaries and masking
body: <p>Here my code below.
  I want to detect real time shapes but as you can see there is a problem to detect that.</p>
  <pre><code>import cv2
  import numpy as np
  
  
  def nothing(x):
      pass
  
  
  cap = cv2.VideoCapture(0)
  cv2.namedWindow('Settings')
  
  cv2.createTrackbar('Lower-Hue','Settings',0,180,nothing)
  cv2.createTrackbar('Lower-Satuation','Settings',0,255,nothing)
  cv2.createTrackbar('Lower-Value','Settings',0,255,nothing)
  cv2.createTrackbar('Upper-Hue','Settings',0,180,nothing)
  cv2.createTrackbar('Upper-Saturation','Settings',0,255,nothing)
  cv2.createTrackbar('Upper-Value','Settings',0,255,nothing)
  
  font = cv2.FONT_HERSHEY_SIMPLEX
  
  while True:
      ret,frame = cap.read()
      frame = cv2.flip(frame,1)
      hsv = cv2.cvtColor(frame,cv2.COLOR_BGR2HSV)
      _, thresh = cv2.threshold(hsv, 240, 255, cv2.THRESH_BINARY)
  
      lh = cv2.getTrackbarPos('Lower-Hue','Settings')
      ls = cv2.getTrackbarPos('Lower-Saturation', 'Settings')
      lv = cv2.getTrackbarPos('Lower-Value', 'Settings')
      uh = cv2.getTrackbarPos('Upper-Hue', 'Settings')
      us = cv2.getTrackbarPos('Upper-Saturation', 'Settings')
      uv = cv2.getTrackbarPos('Upper-Value', 'Settings')
  
      lower_color = np.array([lh,ls,lv])
      upper_color = np.array([uh,us,uv])
  
      mask = cv2.inRange(hsv,lower_color,upper_color)
      kernel = np.ones((5,5),np.uint8) #maskeledikten sonra beyaz nesnelerde oluşan siyah noktaları yoketmek için yapıldı
      mask = cv2.erode(mask,kernel)
  
      contours,_ = cv2.findContours(mask,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)
  
      for cnt in contours:
          area = cv2.contourArea(cnt)  #alan hesabı yaparak belli bir değerin üzerinde alan hesabı yaptırılır
          epsilon = 0.02*cv2.arcLength(cnt,True)
          approx = cv2.approxPolyDP(cnt,epsilon,True)
  
          x = approx.ravel()[0]
          y = approx.ravel()[1]
  
          if area &gt;400:
              cv2.drawContours(frame,[approx],0,(0,0,0),5)
              if len(approx) == 3:
                  cv2.putText(frame, 'Triangle', (x, y), font, 1, (0,0,0))
              if len(approx) == 4:
                  cv2.putText(frame, 'Rectangle', (x, y), font, 1, (0,0,0))
              if len(approx) == 5:
                  cv2.putText(frame, 'Pentagon', (x, y), font, 1, (0,0,0))
              if len(approx) == 6:
                  cv2.putText(frame, 'Hexagon', (x, y), font, 1, (0,0,0))
              else:
                  cv2.putText(frame, 'Ellips', (x, y), font, 1, (0,0,0))
  
  
      cv2.imshow('frame',frame)
      cv2.imshow('mask',mask)
  
      if cv2.waitKey(3) &amp; 0xFF == ord('q'):
          break
  
  
  cap.release()
  cv2.destroyAllWindows()
  </code></pre>
  <p><img src="https://i.stack.imgur.com/ByXr8.png" alt="enter image description here" /></p>
  <p>First of all the shape is rectangle and color is white. I tried lots of hsv boundaries with trackbar. When i get the values there is a noise. How can i do better masking and How can i fix it.</p>