作业&练习

• 检测各种多边形
• 编写代码检测定位药丸
• 实操课：
• 相机标定
• 车道线检测
• 实时模板匹配
  • 找到目标并进行透视变换（恢复期望形状）
  • 查找指定物体（圈出目标区域）
• 车道线检测（视频）

参考资源

处理封闭路径的备选函数：

• 计算面积：cv2.contourArea(contour)
• 计算周长：cv2.arcLength(curve, True)
• 多边形逼近：cv2.approxPolyDP(curve, epsilon, True)
• 判断是否是凸多边形：cv2.isContourConvex(contour)
• 绘制封闭路径：cv2.cv.drawContours( img, contours, -1, (0, 255, 0), 3 )
• 参数3为-1时：绘制所有contours轮廓
• 参数3为>-1的n时：绘制contours[n]轮廓

• 判断多边形边数：len(approxCurve)

• 可直接通过len函数获取逼近后的多边形边数

• 判断连续三个点连线构成的夹角：

def angle_cos(p0, p1, p2):
    d1, d2 = (p0-p1).astype('float'), (p2-p1).astype('float')
    return abs( np.dot(d1, d2) / np.sqrt( np.dot(d1, d1)*np.dot(d2, d2) ) )

• 读取视频&导出视频

• 读取

  import cv2
  import numpy as np
  
  # Create a VideoCapture object and read from input file
  # If the input is the camera, pass 0 instead of the video file name
  cap = cv2.VideoCapture('chaplin.mp4')
  
  # Check if camera opened successfully
  if (cap.isOpened()== False): 
    print("Error opening video stream or file")
  
  # Read until video is completed
  while(cap.isOpened()):
    # Capture frame-by-frame
    ret, frame = cap.read()
    if ret == True:
  
      # Display the resulting frame
      cv2.imshow('Frame',frame)
  
      # Press Q on keyboard to  exit
      if cv2.waitKey(25) & 0xFF == ord('q'):
        break
  
    # Break the loop
    else: 
      break
  
  # When everything done, release the video capture object
  cap.release()
  
  # Closes all the frames
  cv2.destroyAllWindows()
  

• 写出

  import cv2
  import numpy as np
  
  # Create a VideoCapture object
  cap = cv2.VideoCapture(0)
  
  # Check if camera opened successfully
  if (cap.isOpened() == False): 
    print("Unable to read camera feed")
  
  # Default resolutions of the frame are obtained.The default resolutions are system dependent.
  # We convert the resolutions from float to integer.
  frame_width = int(cap.get(3))
  frame_height = int(cap.get(4))
  
  # Define the codec and create VideoWriter object.The output is stored in 'outpy.avi' file.
  out = cv2.VideoWriter('outpy.avi',cv2.VideoWriter_fourcc('M','J','P','G'), 10, (frame_width,frame_height))
  
  while(True):
    ret, frame = cap.read()
  
    if ret == True: 
  
      # Write the frame into the file 'output.avi'
      out.write(frame)
  
      # Display the resulting frame    
      cv2.imshow('frame',frame)
  
      # Press Q on keyboard to stop recording
      if cv2.waitKey(1) & 0xFF == ord('q'):
        break
  
    # Break the loop
    else:
      break  
  
  # When everything done, release the video capture and video write objects
  cap.release()
  out.release()
  
  # Closes all the frames
  cv2.destroyAllWindows()