OpenCV入门——图像视频的加载与展示一些API

OpenCV创建显示窗口

多看源码参考文档

import cv2
cv2.namedWindow('new', cv2.WINDOW_NORMAL)
cv2.imshow('new', 0)key = cv2.waitKey(0)
if(key == 'q'):exit()cv2.destroyAllWindows()

import cv2
cv2.namedWindow('new', cv2.WINDOW_NORMAL)
cv2.resizeWindow('new', 1920, 1080)
cv2.imshow('new', 0)key = cv2.waitKey(0)
if(key == 'q'):exit()cv2.destroyAllWindows()

OpenCV加载显示图片

import cv2
cv2.namedWindow('img', cv2.WINDOW_NORMAL)
# cv2.resizeWindow('img', 1920, 1080)
img = cv2.imread('E://pic//mylove.jpg')
cv2.imshow('img', img)key = cv2.waitKey(0)
if(key &0xff == ord('q')):cv2.destroyAllWindows()

可以看官方文档

其中提到，cv2.waitKey()返回值是int类型，而ASCII码是8位(char)，所以我们需要用key &0xff取它的低八位来实现，而ord函数是Python中的另一个内建函数，用于将字符转换为对应的ASCII码。

OpenCV保存文件

import cv2
cv2.namedWindow('img', cv2.WINDOW_NORMAL)
# cv2.resizeWindow('img', 1920, 1080)
img = cv2.imread('E://pic//mylove.jpg')while True:cv2.imshow('img', img)key = cv2.waitKey(0)if(key & 0xff == ord('q')):breakelif(key & 0xff == ord('s')):cv2.imwrite("E://pic//picc//mylove.png", img)breakelse:print(key - 32)cv2.destroyAllWindows()

利用OpenCV从摄像头采集视频

# -*- coding: utf-8 -*-
import cv2# 创建窗口
cv2.namedWindow('video', cv2.WINDOW_NORMAL)
cv2.resizeWindow('video', 640, 480)# 获取视频设备
cap = cv2.VideoCapture(0)while True:# 从摄像头读取视频帧ret, frame = cap.read()# 将视频帧在窗口中显示cv2.imshow('video', frame)# 等待键盘事件，如果为q，退出key = cv2.waitKey(1)if(key & 0xff == ord('q')):break# 释放VideoCapture
cap.release()
cv2.destroyAllWindows()

从多媒体文件中读取视频帧

和之前从摄像头采集视频最大的区别是，要根据视频的fps来修改cv2.waitKey()里的值，如果你是22fps的视频，相当于1s走22帧，即1000ms走22帧，即一帧需要1000 / 22ms，而这个就是cv2.waitKey()里应该填的值

# -*- coding: utf-8 -*-
import cv2# 创建窗口
cv2.namedWindow('video', cv2.WINDOW_NORMAL)
cv2.resizeWindow('video', 640, 480)# 获取视频设备/从视频文件中读取视频帧
# cap = cv2.VideoCapture(0)
cap = cv2.VideoCapture("E://DownloadPack//Video//particles.mp4")while True:# 从摄像头读取视频帧ret, frame = cap.read()# 将视频帧在窗口中显示cv2.imshow('video', frame)# 等待键盘事件，如果为q，退出key = cv2.waitKey(40)if(key & 0xff == ord('q')):break# 释放VideoCapture
cap.release()
cv2.destroyAllWindows()

将视频数据录制成多媒体文件

# -*- coding: utf-8 -*-
import cv2# 创建VideoWriter为写多媒体文件
fourcc = cv2.VideoWriter_fourcc('m', 'p', '4', 'v')
vw = cv2.VideoWriter('.//out.mp4', fourcc, 24, (1280, 720))# 创建窗口
cv2.namedWindow('video', cv2.WINDOW_NORMAL)
cv2.resizeWindow('video', 640, 480)# 获取视频设备/从视频文件中读取视频帧
cap = cv2.VideoCapture(0)
# cap = cv2.VideoCapture("E://DownloadPack//Video//particles.mp4")while True:# 从摄像头读取视频帧ret, frame = cap.read()# 将视频帧在窗口中显示cv2.imshow('video', frame)# 写数据到多媒体文件vw.write(frame)# 等待键盘事件，如果为q，退出key = cv2.waitKey(40)if(key & 0xff == ord('q')):break# 释放VideoCapture
cap.release()# 释放VideoWriter
vw.release()cv2.destroyAllWindows()

# -*- coding: utf-8 -*-
import cv2# 创建VideoWriter为写多媒体文件
fourcc = cv2.VideoWriter_fourcc('m', 'p', '4', 'v')
vw = cv2.VideoWriter('.//out.mp4', fourcc, 24, (1280, 720))# 创建窗口
cv2.namedWindow('video', cv2.WINDOW_NORMAL)
cv2.resizeWindow('video', 640, 480)# 获取视频设备/从视频文件中读取视频帧
cap = cv2.VideoCapture(0)
# cap = cv2.VideoCapture("E://DownloadPack//Video//particles.mp4")# 判断摄像头是否为打开状态
while cap.isOpened():# 从摄像头读取视频帧ret, frame = cap.read()if ret == True:# 将视频帧在窗口中显示cv2.imshow('video', frame)# 重新将窗口设置为指定大小cv2.resizeWindow('video', 640, 480)# 写数据到多媒体文件vw.write(frame)# 等待键盘事件，如果为q，退出key = cv2.waitKey(40)if(key & 0xff == ord('q')):breakelse:break;# 释放VideoCapture
cap.release()# 释放VideoWriter
vw.release()cv2.destroyAllWindows()

OpenCV控制鼠标

# -*- coding: utf-8 -*-
import cv2
import numpy as np# 鼠标回调函数
def mouse_callback(event, x, y, flags, userdata):print(event, x, y, flags, userdata)# 创建窗口
cv2.namedWindow('mouse', cv2.WINDOW_NORMAL)
cv2.resizeWindow('mouse', 640, 360)# 设置鼠标回调
cv2.setMouseCallback('mouse', mouse_callback, "666")# 显示窗口和背景
img = np.zeros((360, 640, 3), np.uint8)
while True:cv2.imshow('mouse', img)key = cv2.waitKey(0)if key & 0xff == ord('q'):breakcv2.destroyAllWindows()

关于np.uint8

OpenCV中的TrackBar控件

TrackBar的使用

OpenCV颜色空间默认BGR格式

# -*- coding: utf-8 -*-
import cv2
import numpy as npdef callback():pass# 创建窗口
cv2.namedWindow('trackbar', cv2.WINDOW_NORMAL)# 创建trackbar
cv2.createTrackbar('R', 'trackbar', 31, 255, callback)
cv2.createTrackbar('G', 'trackbar', 24, 255, callback)
cv2.createTrackbar('B', 'trackbar', 0, 255, callback)# 创建一个背景图片
img = np.zeros((480, 640, 3), np.uint8)while True:# 获取当前trackbar的值r = cv2.getTrackbarPos('R', 'trackbar')g = cv2.getTrackbarPos('G', 'trackbar')b = cv2.getTrackbarPos('B', 'trackbar')# 改变背景图片颜色img[:] = [b, g, r]cv2.imshow('trackbar', img)key = cv2.waitKey(10)if key & 0xff == ord('q'):breakcv2.destroyAllWindows()

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