使用Opencv-python库读取图像、本地视频和摄像头实时数据

Python中使用OpenCV读取图像、本地视频和摄像头数据很简单，
首先需要安装Python，然后安装Opencv-python库

pip install opencv-python

然后在PyCharm或者VScode等IDE中输入对应的Python代码

一、使用opencv-python读取图像

比如说我们要显示上面这幅数字图像处理中的lena.jpg这幅图像，读取的python代码如下所示：

import cv2

# Load an image using imread
img = cv2.imread("images/lena.jpg")
# img = cv2.imread("Resources/test.png")
# Display image
cv2.imshow("Lena image", img)
cv2.waitKey(0)
cv2.destroyAllWindows()

在Python中运行结果如下：
显示图像

使用opencv-python读取本地视频

Opencv-python在线文档中有关于的Python示例代码：https://docs.opencv.org/4.9.0/dd/d43/tutorial_py_video_display.html

import numpy as np
import cv2 as cv
cap = cv.VideoCapture('vtest.avi')
while cap.isOpened():
    ret, frame = cap.read()
    # if frame is read correctly ret is True
    if not ret:
        print("Can't receive frame (stream end?). Exiting ...")
        break
    gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
    cv.imshow('frame', gray)
    if cv.waitKey(1) == ord('q'):
        break
cap.release()
cv.destroyAllWindows()

视频资源可以到https://github.com/murtazahassan/Learn-OpenCV-in-3-hours/blob/master/Resources/test_video.mp4下载
相关的显示本地视频的Python代码如下：

import cv2

frameWidth = 640
frameHeight = 480
cap = cv2.VideoCapture("Resources/test_video.mp4")
while True:
    success, img = cap.read()
    img = cv2.resize(img, (frameWidth, frameHeight))
    cv2.imshow("Result", img)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break
cap.release()
cv2.destroyAllWindows()

相应的运行结果如下图所示：
读取本地视频并显示

三、使用opencv-python读取摄像头数据并实时显示

使用opencv-python读取摄像头数据是非简单，opencv-python文档tutorial_py_video_display里面有对应的示例代码，如下：

import numpy as np
import cv2 as cv
cap = cv.VideoCapture(0)
if not cap.isOpened():
    print("Cannot open camera")
    exit()
while True:
    # Capture frame-by-frame
    ret, frame = cap.read()
    # if frame is read correctly ret is True
    if not ret:
        print("Can't receive frame (stream end?). Exiting ...")
        break
    # Our operations on the frame come here
    gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
    # Display the resulting frame
    cv.imshow('frame', gray)
    # 等待1毫秒，如果用户按下q键则退出循环
    if cv.waitKey(1) == ord('q'):
        break
# When everything done, release the capture
cap.release()
cv.destroyAllWindows()

我本地读取摄像头数据并显示的python代码如下：

import cv2

frameWidth = 640
frameHeight = 480
cap = cv2.VideoCapture(0)
# cap.set(3, frameWidth)
cap.set(cv2.CAP_PROP_FRAME_WIDTH, frameWidth)
# cap.set(4, frameHeight)
cap.set(cv2.CAP_PROP_FRAME_HEIGHT, frameHeight)
# cap.set(10, 50)
cap.set(cv2.CAP_PROP_BRIGHTNESS, 50)

while True:
    success, img = cap.read()
    cv2.imshow("Result", img)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

cap.release()
cv2.destroyAllWindows()