学习Opencv（蝴蝶书/C++）代码——2.OpenCV初探

0. 图像读取与显示

示例1，来自learning OpenCV 3的配套源码
https://github.com/oreillymedia/Learning-OpenCV-3_examples/blob/master/example_02-01.cpp

//Example 2-1. A simple OpenCV program that loads an image from disk and displays it
//on the screen
#include 

void help(char** argv ) {
   
	std::cout << "\n"
	<< "A simple OpenCV program that loads and displays an image from disk\n"
	<< argv[0] <<" \n"
	<< "For example:\n"
	<< argv[0] << " ../fruits.jpg\n"
	<< std::endl;
}
	

int main( int argc, char** argv ) {
   
	
	if (argc != 2) {
   
		help(argv);
		return 0;
	}
		

  cv::Mat img = cv::imread( argv[1], -1 );

  if( img.empty() ) return -1;

  cv::namedWindow( "Example 2-1", cv::WINDOW_AUTOSIZE );
  cv::imshow( "Example 2-1", img );
  cv::waitKey( 0 );
  cv::destroyWindow( "Example 2-1" );

  return 0;
}

1. 视频文件读取与操作

1.1 示例代码

示例1：
https://github.com/opencv/opencv/blob/4.x/samples/cpp/videocapture_starter.cpp

示例2:
来自cv::VideoCapture Class Reference的Detailed Description

如果觉得上面那个写的比较复杂，不直观，可以看看简单的：

#include 
#include 
#include 
#include 

using namespace cv;
int main(int argc, char **argv)
{
   
    Mat frame;
    // 初始化一个VIDEOCAPTURE对象cap
    VideoCapture cap;
    // 使用默认的API打开默认的相机
    // cap.open(0);
    // 或者更先进的用法，选择任意一个API后端
    int deviceID = 0;        // 0 = open default camera
    int apiID = cv::CAP_ANY; // 0 = autodetect default API
    // 使用选择的API打开选择的相机
    cap.open(deviceID, apiID);
    // 判断是否正确打开视频流
    if (!cap.isOpened())
    {
   
        std::cerr << "ERROR! Unable to open camera\n";
        return -1;
    }
    // 开始读取视频
    std::cout << "Start grabbing" << std::endl
              << "Press any key to terminate" << std::endl;
    for (;;)
    {
   
        // 等待从视频读入新帧并把它存储到'frame'中
        cap.read(frame);
        // 检查是否读取成功
        if (frame.empty())
        {
   
            std::cerr << "ERROR! blank frame grabbed\n";
            break;
        }
        // 实时显示，每5ms显示一帧图像直到有任意按键
        imshow("Live", frame);
        if (waitKey(5) >= 0)
            break;
    }
    // 相机对象会在VideoCapture析构函数中自动释放
    return 0;
}

示例3:
来自learning OpenCV 3的配套源码
https://github.com/oreillymedia/Learning-OpenCV-3_examples/blob/master/example_02-03.cpp

int main(int argc, char **argv)
{
   
    cv::namedWindow("Example2");
    cv::VideoCapture cap;
    // VideoCapture可以打开和关闭很多ffmpeg支持的视频文件
    cap.open(std::string(argv[1]));
    cv::Mat frame;
    if (cap.isOpened())
    {
   
        for (;;)
        {
   
            cap >> frame;
            // Stream operator to read the next video frame
            if (frame.empty())
                break;
            cv::imshow