text: # 0901.py
  import cv2
  import numpy as np
  
  src = cv2.imread('./data/chessBoard.jpg')
  gray = cv2.cvtColor(src, cv2.COLOR_BGR2GRAY)
  
  #1
  fastF = cv2.FastFeatureDetector.create(threshold = 30)
  kp = fastF.detect(gray)
  dst = cv2.drawKeypoints(gray, kp, None, color = (0, 0, 255))
  print('len(kp)=', len(kp))
  cv2.imshow('dst', dst)
  
  
  #2
  fastF.setNonmaxSuppression(False)
  kp2 = fastF.detect(gray)
  dst2 = cv2.drawKeypoints(src, kp2, None, color = (0, 0, 255))
  print('len(kp2)=', len(kp2))
  cv2.imshow('dst2', dst2)
  
  #3
  dst3 = src.copy()
  points = cv2.KeyPoint_convert(kp)
  for cx, cy in points:
      cv2.circle(dst3, (cx, cy), 3, color = (255, 0, 0), thickness= 1)
  cv2.imshow('dst3', dst3)
  cv2.waitKey()
  cv2.destroyAllWindows()