一百行代码搞定Qt相机多线程

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已于 2024-12-11 21:44:39 修改

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分类专栏： Qt 文章标签： qt C++ 多线程机器视觉计算机视觉

于 2024-12-11 20:56:49 首次发布

本文链接：https://blog.youkuaiyun.com/taifyang/article/details/144305731

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单线程

首先我们在Qt designer中创建一个简单的界面，只包含一个label用来显示相机图像，和两个pushButton分别用来开启和关闭相机。
在这里插入图片描述
其对应的ui_mainwindow.h内容为：

/********************************************************************************
** Form generated from reading UI file 'mainwindow.ui'
**
** Created by: Qt User Interface Compiler version 5.14.2
**
** WARNING! All changes made in this file will be lost when recompiling UI file!
********************************************************************************/

#ifndef UI_MAINWINDOW_H
#define UI_MAINWINDOW_H

#include <QtCore/QVariant>
#include <QtWidgets/QApplication>
#include <QtWidgets/QLabel>
#include <QtWidgets/QMainWindow>
#include <QtWidgets/QMenuBar>
#include <QtWidgets/QPushButton>
#include <QtWidgets/QStatusBar>
#include <QtWidgets/QWidget>

QT_BEGIN_NAMESPACE

class Ui_MainWindow
{
public:
    QWidget *centralwidget;
    QLabel *label;
    QPushButton *pushButton_open_camera;
    QPushButton *pushButton_close_camera;
    QMenuBar *menubar;
    QStatusBar *statusbar;

    void setupUi(QMainWindow *MainWindow)
    {
        if (MainWindow->objectName().isEmpty())
            MainWindow->setObjectName(QString::fromUtf8("MainWindow"));
        MainWindow->resize(800, 600);
        centralwidget = new QWidget(MainWindow);
        centralwidget->setObjectName(QString::fromUtf8("centralwidget"));
        label = new QLabel(centralwidget);
        label->setObjectName(QString::fromUtf8("label"));
        label->setGeometry(QRect(80, 20, 640, 480));
        label->setStyleSheet(QString::fromUtf8("background:rgb(255, 255, 255)"));
        pushButton_open_camera = new QPushButton(centralwidget);
        pushButton_open_camera->setObjectName(QString::fromUtf8("pushButton_open_camera"));
        pushButton_open_camera->setGeometry(QRect(150, 520, 120, 30));
        pushButton_close_camera = new QPushButton(centralwidget);
        pushButton_close_camera->setObjectName(QString::fromUtf8("pushButton_close_camera"));
        pushButton_close_camera->setGeometry(QRect(530, 520, 120, 30));
        MainWindow->setCentralWidget(centralwidget);
        menubar = new QMenuBar(MainWindow);
        menubar->setObjectName(QString::fromUtf8("menubar"));
        menubar->setGeometry(QRect(0, 0, 800, 21));
        MainWindow->setMenuBar(menubar);
        statusbar = new QStatusBar(MainWindow);
        statusbar->setObjectName(QString::fromUtf8("statusbar"));
        MainWindow->setStatusBar(statusbar);

        retranslateUi(MainWindow);

        QMetaObject::connectSlotsByName(MainWindow);
    } // setupUi

    void retranslateUi(QMainWindow *MainWindow)
    {
        MainWindow->setWindowTitle(QCoreApplication::translate("MainWindow", "MainWindow", nullptr));
        label->setText(QString());
        pushButton_open_camera->setText(QCoreApplication::translate("MainWindow", "\346\211\223\345\274\200\347\233\270\346\234\272", nullptr));
        pushButton_close_camera->setText(QCoreApplication::translate("MainWindow", "\345\205\263\351\227\255\347\233\270\346\234\272", nullptr));
    } // retranslateUi

};

namespace Ui {
    class MainWindow: public Ui_MainWindow {};
} // namespace Ui

QT_END_NAMESPACE

#endif // UI_MAINWINDOW_H

main.cpp不用修改：

#include "mainwindow.h"

#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

接下来我们编写mainwindow的逻辑：
mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H


#include <opencv2/opencv.hpp>

#include <QMainWindow>
#include <QThread>
#include <QDebug>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT
    
public:
    MainWindow(QWidget *parent = nullptr);
    
    ~MainWindow();
    
private slots:
    void on_pushButton_open_camera_clicked();
    
    void on_pushButton_close_camera_clicked();
    
private:
    Ui::MainWindow *ui;
    
    cv::VideoCapture cap;
    
    cv::Mat frame;
};
#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::on_pushButton_open_camera_clicked()
{
    cap.open(0);
    while (cv::waitKey(1) < 0)
    {
        cap.read(frame);
        QImage image = QImage((const uchar*)frame.data, frame.cols, frame.rows, QImage::Format_RGB888).rgbSwapped();
        ui->label->setPixmap(QPixmap::fromImage(image));
        ui->label->show();
    }
}

void MainWindow::on_pushButton_close_camera_clicked()
{
    cap.release();
    ui->label->clear();
}

这样，一个单线程Qt相机采图显示界面就做完了。

一个线程采图一个线程显示

修改上面的程序，引入相机采图类Capture并继承QThread类：
mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H


#include <opencv2/opencv.hpp>

#include <QMainWindow>
#include <QThread>
#include <QDebug>

class Capture : public QThread
{
  Q_OBJECT

public:
    cv::VideoCapture cap;

    bool is_opened = false;

private:
    void run();

signals:
    void send_image(const QImage &qimage);
};

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);

    ~MainWindow();

private slots:
    void on_pushButton_open_camera_clicked();

    void on_pushButton_close_camera_clicked();

    void show_image(const QImage &qimage);

private:
    Ui::MainWindow *ui;

    Capture *capture;
};
#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    capture = new Capture;
    connect(capture, &Capture::send_image, this, &MainWindow::show_image);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::on_pushButton_open_camera_clicked()
{
    capture->cap.open(0);
    capture->start();
    capture->is_opened = true;
}

void MainWindow::on_pushButton_close_camera_clicked()
{
    capture->quit();
    capture->cap.release();
    ui->label->clear();
    capture->is_opened = false;
}

void MainWindow::show_image(const QImage &qimage)
{
    std::cout << std::this_thread::get_id() << " show image..." << std::endl;
    ui->label->setPixmap(QPixmap::fromImage(qimage));
    ui->label->show();
}

void Capture::run()
{
    cv::Mat frame;
    while (cv::waitKey(1) < 0 && is_opened)
    {
        std::cout << std::this_thread::get_id() << " grab image..." << std::endl;
        cap.read(frame);
        QImage qimage = QImage(frame.data, frame.cols, frame.rows, QImage::Format_RGB888).rgbSwapped();
        send_image(qimage);
    }
}

运行程序，相机采图正常，且打印如下：

14324 grab image...
7456 show image...
14324 grab image...
7456 show image...
14324 grab image...
7456 show image...
14324 grab image...
7456 show image...

可以看到采图和显示图像的线程id是不同的，分别在两个线程中运行。

一个线程采图一个线程运算一个线程显示

在上面的基础上继续增加图像处理类Process 并继承QThread类：
mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H


#include <opencv2/opencv.hpp>

#include <QMainWindow>
#include <QThread>
#include <QDebug>

class Capture : public QThread
{
  Q_OBJECT

public:
    cv::VideoCapture cap;

    bool is_opened = false;

private:
    void run();

signals:
    void send_image(const QImage &qimage);
};

class Process : public QThread
{
  Q_OBJECT

public:
    void receive_image(const QImage &qimage);

    bool is_opened = false;

private:
    void run();

    QImage image;

signals:
    void send_image(const QImage &qimage);
};

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);

    ~MainWindow();

private slots:
    void on_pushButton_open_camera_clicked();

    void on_pushButton_close_camera_clicked();

    void show_image(const QImage &qimage);

private:
    Ui::MainWindow *ui;

    Capture *capture;

    Process *process;
};
#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    capture = new Capture;
    process = new Process;
    connect(capture, &Capture::send_image, process, &Process::receive_image);
    connect(process, &Process::send_image, this, &MainWindow::show_image);
}

MainWindow::~MainWindow()
{
    capture->quit();
    capture->cap.release();
    process->quit();
    delete ui;
    delete capture;
    delete process;
}

void MainWindow::on_pushButton_open_camera_clicked()
{
    capture->cap.open(0);
    capture->start();
    process->start();
    capture->is_opened = true;
    process->is_opened = true;
}

void MainWindow::on_pushButton_close_camera_clicked()
{
    capture->is_opened = false;
    process->is_opened = false;
    capture->quit();
    capture->cap.release();
    process->quit();
    ui->label->clear();
}

void MainWindow::show_image(const QImage &qimage)
{
    if(!capture->is_opened) return;
    std::cout << std::this_thread::get_id() << " show image..." << std::endl;
    ui->label->setPixmap(QPixmap::fromImage(qimage));
    ui->label->show();
}

void Capture::run()
{
    cv::Mat frame;
    while (is_opened && cv::waitKey(1) < 0)
    {
        std::cout << std::this_thread::get_id() << " grab image..." << std::endl;
        cap.read(frame);
        if (frame.empty())  continue;
        QImage qimage = QImage(frame.data, frame.cols, frame.rows, QImage::Format_RGB888).rgbSwapped();
        send_image(qimage);
    }
}

void Process::run()
{
    while(is_opened && cv::waitKey(1) < 0)
    {
         std::cout << std::this_thread::get_id() << " process image..." << std::endl;
         QImage qimage_processed = image.convertToFormat(QImage::Format_Grayscale8);
         send_image(qimage_processed);
    }
}

void Process::receive_image(const QImage &qimage)
{
    image = qimage;
}

程序运行时打印如下：

5768 grab image...
13116 process image...
7832 show image...
5768 grab image...
13116 process image...
7832 show image...
5768 grab image...
13116 process image...
7832 show image...