OpenCV学习笔记（一）

由于毕业设计涉及到对视频的帧处理，所以需要学习一个python的库来实现对视频的处理

一、安装

pip3 install opencv-python

二、读取图片

import cv2
img=cv2.imread("/Users/zixiluo/Documents/test.png")#读取图片
cv2.imshow("image",img)#打开一个名为“image”的窗口并展示图片
cv2.waitKey(0)#不加这句窗口会一闪就关闭
cv2.destroyAllWindows()#使用后释放窗口是好习惯

　　

三、读取视频

import cv2
cap=cv2.VideoCapture("/Users/zixiluo/Documents/test.avi")
while(1):
    # get a frame
    ret, frame = cap.read()
    # show a frame
    cv2.imshow("capture", frame)
    if cv2.waitKey(100) & 0xFF == ord('q'):
        break
cap.release()
cv2.destroyAllWindows()

　　

四、获取视频属性

print ("W:{}".format(cap.get(3)))#输出视频的宽度
print ("H:{}".format(cap.get(4)))#输出视频的高度
print ("frames:{}".format(cap.get(7)))#输出视频的总帧数

运行结果：

W:1920.0

H:1080.0

frames:912.0

get方法参数按顺序对应下表（从0开始编号

propId –

Property identifier. It can be one of the following:

• CV_CAP_PROP_POS_MSEC Current position of the video file in milliseconds or video capture timestamp.
• CV_CAP_PROP_POS_FRAMES 0-based index of the frame to be decoded/captured next.
• CV_CAP_PROP_POS_AVI_RATIO Relative position of the video file: 0 - start of the film, 1 - end of the film.
• CV_CAP_PROP_FRAME_WIDTH Width of the frames in the video stream.
• CV_CAP_PROP_FRAME_HEIGHT Height of the frames in the video stream.
• CV_CAP_PROP_FPS Frame rate.
• CV_CAP_PROP_FOURCC 4-character code of codec.
• CV_CAP_PROP_FRAME_COUNT Number of frames in the video file.
• CV_CAP_PROP_FORMAT Format of the Mat objects returned by retrieve() .
• CV_CAP_PROP_MODE Backend-specific value indicating the current capture mode.
• CV_CAP_PROP_BRIGHTNESS Brightness of the image (only for cameras).
• CV_CAP_PROP_CONTRAST Contrast of the image (only for cameras).
• CV_CAP_PROP_SATURATION Saturation of the image (only for cameras).
• CV_CAP_PROP_HUE Hue of the image (only for cameras).
• CV_CAP_PROP_GAIN Gain of the image (only for cameras).
• CV_CAP_PROP_EXPOSURE Exposure (only for cameras).
• CV_CAP_PROP_CONVERT_RGB Boolean flags indicating whether images should be converted to RGB.
• CV_CAP_PROP_WHITE_BALANCE_U The U value of the whitebalance setting (note: only supported by DC1394 v 2.x backend currently)
• CV_CAP_PROP_WHITE_BALANCE_V The V value of the whitebalance setting (note: only supported by DC1394 v 2.x backend currently)
• CV_CAP_PROP_RECTIFICATION Rectification flag for stereo cameras (note: only supported by DC1394 v 2.x backend currently)
• CV_CAP_PROP_ISO_SPEED The ISO speed of the camera (note: only supported by DC1394 v 2.x backend currently)
• CV_CAP_PROP_BUFFERSIZE Amount of frames stored in internal buffer memory (note: only supported by DC1394 v 2.x backend currently)

五、抽帧显示

import cv2
cap=cv2.VideoCapture("/Users/zixiluo/Documents/test.avi")
print ("W:{}".format(cap.get(3)))
print ("H:{}".format(cap.get(4)))
count=cap.get(7)
while(count>0):
    ret, frame = cap.read()
    if count%5==0:
        print(count)
        gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
        cv2.imshow("capture", gray)
        if cv2.waitKey(1) & 0xFF == ord('q'):
            break
    count+=-1
cap.release()
cv2.destroyAllWindows()

此程序实现每读取五帧显示一帧