title: Corner detection in Image processing Opencv Python
body: <p>I have an image of the box. I am trying to detect corners and mark those corner from circles. I am using the following code for this:</p>
  <pre><code>import cv2
  import numpy as np
  
  img_file = 'Image.jpg'
  img = cv2.imread(img_file, cv2.IMREAD_COLOR)
  
  imgDim = img.shape
  dimA = imgDim[0]
  dimB = imgDim[1]
  
  # RGB to Gray scale conversion
  img_gray = cv2.cvtColor(img,cv2.COLOR_RGB2GRAY)
  # Noise removal with iterative bilateral filter(removes noise while preserving edges)
  noise_removal = cv2.bilateralFilter(img_gray,9,75,75)
  # Thresholding the image
  ret,thresh_image = cv2.threshold(noise_removal,220,255,cv2.THRESH_OTSU)
  th = cv2.adaptiveThreshold(noise_removal, 255, cv2.ADAPTIVE_THRESH_GAUSSIAN_C, cv2.THRESH_BINARY, 11, 2)
  
  # Applying Canny Edge detection
  canny_image = cv2.Canny(th,250,255)
  canny_image = cv2.convertScaleAbs(canny_image)
  
  # dilation to strengthen the edges
  kernel = np.ones((3,3), np.uint8)
  # Creating the kernel for dilation
  dilated_image = cv2.dilate(canny_image,kernel,iterations=1)
  np.set_printoptions(threshold=np.nan)
  
  _, contours, h = cv2.findContours(dilated_image, 1, 2)
  contours= sorted(contours, key = cv2.contourArea, reverse = True)[:1]
  
  
  corners    = cv2.goodFeaturesToTrack(thresh_image,6,0.06,25)
  corners    = np.float32(corners)
  
  for item in corners:
      x,y    = item[0]
      cv2.circle(img,(x,y),10,255,-1)
  cv2.namedWindow(&quot;Corners&quot;, cv2.WINDOW_NORMAL)
  cv2.imshow(&quot;Corners&quot;,img)
  cv2.waitKey()
  </code></pre>
  <p>This code will return my image with pointing edges with circles but you can see that two edges (edges at the back of the box) are detected incorrectly. I know there is some problem in determining the corners because here we are just plotting the corners. Can anyone guide me where I am doing it wrong ? Thanks <a href="https://i.stack.imgur.com/iQV2y.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/iQV2y.jpg" alt="enter image description here" /></a></p>
  <p><a href="https://i.stack.imgur.com/iVb2f.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/iVb2f.jpg" alt="enter image description here" /></a></p>