如何在opencv python中获取视频的前一帧

我想根据视频的大小增加来检测障碍物.为此,我首先在灰色图像上应用了SIFT以获取当前帧的特征点.接下来,要将当前帧的特征点与上一帧进行比较,我想应用蛮力算法.为此,我想在上一帧中获取特征点.如何在opencv python中访问上一帧？以及当当前帧是视频的第一帧时如何避免访问前一帧？

下面是用python编写的代码,用于获取当前帧的特征点.

import cv2
import numpy as np


cap = cv2.VideoCapture('video3.mov')

  while(cap.isOpened()):

  ret, frame = cap.read()

  gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

  #detect key feature points
  sift = cv2.xfeatures2d.SIFT_create()
  kp, des = sift.detectAndCompute(gray, None)

 #draw key points detected
 img=cv2.drawKeypoints(gray,kp,gray,flags=cv2.DRAW_MATCHES_FLAGS_DRAW_RICH_KEYPOINTS)

 cv2.imshow("grayframe",img)

 if cv2.waitKey(100) & 0xFF == ord('q'):
        break

cap.release()
cv2.destroyAllWindows()

解决方法:

OpenCV中没有访问前一帧的特定功能.您可以通过在进入while循环之前调用cap.read()来解决您的问题.在读取新帧之前,使用变量prev_frame存储前一帧.最后,作为一种好的做法,您应该在执行计算之前,先验证框架是否已正确读取.您的代码可能类似于：

import cv2
import numpy as np

cap = cv2.VideoCapture('video3.mov')
ret, frame = cap.read()

while(cap.isOpened()):
    prev_frame=frame[:]
    ret, frame = cap.read()
    if ret:
        gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

        #detect key feature points
        sift = cv2.xfeatures2d.SIFT_create()
        kp, des = sift.detectAndCompute(gray, None)

        #some magic with prev_frame

        #draw key points detected
        img=cv2.drawKeypoints(gray,kp,gray, flags=cv2.DRAW_MATCHES_FLAGS_DRAW_RICH_KEYPOINTS)

        cv2.imshow("grayframe",img)
    else:
        print('Could not read frame')

    if cv2.waitKey(100) & 0xFF == ord('q'):
        break

cap.release()
cv2.destroyAllWindows()

标签：video-processing,opencv,python
来源： https://codeday.me/bug/20191110/2013990.html