OpenCV旅程第一站

#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>

using namespace cv;

int main(int argc, char *argv[])
{
    Mat img = imread("01.jpg", CV_LOAD_IMAGE_COLOR);
    if(img.empty())
       return -1;
    namedWindow( "01", CV_WINDOW_AUTOSIZE );
    imshow("01", img);
    waitKey(0);
    return 0;
}
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将一张名字为01的图片放到与cpp文件同一个文件夹下。编译运行成功，说明你的OpenCV配置正确了。

打开第一个视频

#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>

using namespace cv;

int main(int argc, char *argv[])
{
    cv::namedWindow("box", cv::WINDOW_AUTOSIZE);
    cv::VideoCapture cap;
    cap.open("box.mp4");
    cv::Mat frame;
    for(;;) {
        cap >> frame;
        if(frame.empty()) break;
        cv::imshow("box", frame);
        if(cv::waitKey(33) > 0) break;
    }
    return 0;
}
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在系统里随意搜了一个mp4文件，拷贝到cpp文件夹下，编译运行，按下任意键退出。

带有进度条的视频播放

根据LearningOpenCV3书上第一章里的例子综合而来，必要的解释已经添加在注释中。

#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>
#include <fstream>

using namespace cv;
using namespace std;

int g_slider_position = -1; // 为了在开始时激活回调函数，显示第一帧
int g_run = 1, g_dontset = 0;
int lowThreshold = 50; // 边缘检测的下门限
int maxLowThreshold = 100; // 下门限的最低值
int upLowRatio = 3; // 上门限与下门限之比

VideoCapture g_cap;

string windowName = "boxWindow";
string videoName = "box.mp4";
string trackbarName = "position";
string procWindow = "procWin";
string thresholdTrackbar = "threshold";
string pyrWindow = "pyrWindow";

cv::Mat frame;
cv::Mat procFrame;
cv::Mat pyrFrame;

void onTrackbarSlide(int pos, void*) {
    g_cap.set(CAP_PROP_POS_FRAMES, pos);

    g_cap >> frame; // 该句执行完后g_cap.get(CAP_PROP_POS_FRAMES)会+1，除非frame为空
    if(!frame.empty()) {
        imshow(windowName, frame);
        cvtColor(frame, procFrame, COLOR_BGR2GRAY); // 转灰度图
        GaussianBlur(procFrame, procFrame, Size(5,5), 3, 3); // 高斯模糊

        pyrDown(procFrame, pyrFrame); // 金字塔下采样
        imshow(pyrWindow, pyrFrame);

        Canny(procFrame, procFrame, lowThreshold, lowThreshold * upLowRatio); // 边缘检测
        imshow(procWindow, procFrame);
    } else {
        g_cap.set(CAP_PROP_POS_FRAMES, 0); // 重头开始
    }

    // 在连续播放模式下通过鼠标移动了进度条时可以中断连续播放
    if (!g_dontset) {
        g_run = 0; // 不允许自动前进一步
        cout << " run mode paused! " << endl;
    }
    g_dontset = 0;
}

int main(int argc, char *argv[])
{
    namedWindow(windowName, cv::WINDOW_AUTOSIZE);
    namedWindow(procWindow, cv::WINDOW_AUTOSIZE);
    namedWindow(pyrWindow, cv::WINDOW_AUTOSIZE);

    if (!g_cap.open(videoName)) return -1;
    int frames = g_cap.get(CAP_PROP_FRAME_COUNT);
    int width = g_cap.get(CAP_PROP_FRAME_WIDTH);
    int height = g_cap.get(CAP_PROP_FRAME_HEIGHT);
    cout << "video has " << frames << " frames of dimensions(" <<
        width << ", " << height << ")." << endl;

    createTrackbar(trackbarName, windowName, &g_slider_position, frames-1, onTrackbarSlide); // 进度条的范围是0~frames-1
    createTrackbar(thresholdTrackbar, procWindow, &lowThreshold, 100); // 不需要回调函数，效果会在进入下一帧时显示

    for(;;) {
        if (g_run != 0) {
            // 第一次执行时current_pos为0，所以在setTrackbarPos时会执行回调函数
            int current_pos = g_cap.get(CAP_PROP_POS_FRAMES);
            cout << "Current pos = " << current_pos << endl;

            g_dontset = 1;

            // 该语句执行时，若current_pos与trackbar当前的游标位置不同，则会执行回调函数
            setTrackbarPos(trackbarName, windowName, current_pos);
            g_run -= 1;
            cout << "g_dontset = " << g_dontset << endl;
        }

        char c = (char) waitKey(1);
        if (c == 's') {
            g_run = 1;
            cout << "Single mode, run = " << g_run << endl;
        } else if (c == 'r') {
            g_run = -1;
            cout << "Run mode, run = " << g_run << endl;
        } else if (c == 27) {
            break;
        }
    }
    g_cap.release();
    destroyAllWindows();
    return 0;
}
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效果如图。

打开摄像头并录制视频

代码如下。

#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>
#include <fstream>

using namespace cv;
using namespace std;

VideoCapture g_cap;

string windowName = "Window";
string polarWinName = "polarWindow";
string outFile = "output.avi";

cv::Mat frame;
cv::Mat polarFrame;

int main(int argc, char *argv[])
{
    cv::namedWindow(windowName, cv::WINDOW_AUTOSIZE);
    cv::namedWindow(polarWinName, cv::WINDOW_AUTOSIZE);

    g_cap.open(0);
    if (!g_cap.isOpened()) {
        cerr << "Can not open camera!" << endl;
    }
    double fps = g_cap.get(CAP_PROP_FPS);
    // 我这里摄像头视频流的fps读出来是0，只好做个保护
    fps = fps >= 1 ? fps : 30;
    int width = g_cap.get(CAP_PROP_FRAME_WIDTH);
    int height = g_cap.get(CAP_PROP_FRAME_HEIGHT);
    cout << "video is of dimensions(" <<
        width << ", " << height << ") and fps = " << fps << endl;
    Size vidSize(width, height);

    VideoWriter writer;
    writer.open(outFile, CV_FOURCC('M', 'J', 'P', 'G'), fps, vidSize);

    for(;;) {

        g_cap >> frame;
        if(frame.empty()) break;
        imshow(windowName, frame);
        // 转成极坐标图像
        logPolar(frame, polarFrame, Point2f(frame.cols/2, frame.rows/2), 40, WARP_FILL_OUTLIERS);
        imshow(polarWinName, polarFrame);

        writer.write(frame); // 保存录制视频

        char c = (char) waitKey(33);
        if (c == 27) {
            break;
        }
    }
    g_cap.release();
    writer.release();
    destroyAllWindows();
    return 0;
}
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