How to open usb camera using openCV and paint it into a custom widget?

gabrielschubert

Hello, I'm quite new on qt. I'm trying to create a tab on my ui that can give the option to count how many usb cameras are connected to computer and list then using OPENCV. After that, I want to select one of then and start streaming a video into a custom widget, using paintEvent. My main difficulties are: how to start and stop a streaming one the buttons are presses. Below i'm posting my code.

mainwindow.h

//includes...
namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

public slots:
    void on_CheckCamerasButton_clicked();
    void on_StartStreamingButton_clicked();

private:
    Ui::MainWindow *ui;
    cameraimage camera;
};
#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_StartStreamingButton_clicked(){
    camera.startStreaming();
}

void MainWindow::on_CheckCamerasButton_clicked(){
    camera.stopStreaming();
}

camerawindow.h

//includes...
class cameraimage : public QWidget
{
    Q_OBJECT
public:
    explicit cameraimage(QWidget *parent = nullptr);

private:
    QPoint mPoint;
    QTimer *timer;
    cv::VideoCapture captureVideo;

public slots:
    void paintEvent(QPaintEvent * event);
    void startStreaming();
    void stopStreaming();
};
#endif // CAMERAIMAGE_H

cameraimage.cpp

#include "cameraimage.h"

cameraimage::cameraimage(QWidget *parent) : QWidget(parent)
{
    setMouseTracking(true); 

    captureVideo.open(0);
    if (captureVideo.isOpened() == false){
           qDebug() << "Camera can't open";
            return;
      }
      timer = new QTimer(this);
      connect(timer, SIGNAL(timeout()), this, SLOT(update()));

void cameraimage::startStreaming(){
        qDebug() << "Starting Streaming";
        timer->start(1);
}

void cameraimage::stopStreaming(){
        captureVideo.release();
        qDebug() << "Stop Streaming";
        timer->stop();
}

void cameraimage::paintEvent(QPaintEvent *){
    cv::Mat tmpImage;
    cv::Mat image;
    captureVideo.read(tmpImage);

    if (tmpImage.empty() == true){
        qDebug() << "EMPTY!";
        return;
    }

    cv::cvtColor(tmpImage, image, CV_BGR2RGB);
    QImage img((const unsigned char*)(image.data), image.cols, image.rows, QImage::Format_RGB888);

    QPixmap pixmap = QPixmap::fromImage(img);
    QPainter painter(this);

    float comprimento = 1.0*width()/pixmap.width();
    float altura = 1.0*height()/pixmap.height();
    float ratio = 0.;

    if (comprimento<=altura)
        ratio = comprimento;
    else
        ratio = altura;

    QSize size = ratio*pixmap.size();
    size.setHeight(size.height()-10);

    QPoint p;
    p.setX(0 + (width()-size.width())/2);
    p.setY(5);

    painter.drawPixmap(QRect(p, size), pixmap.scaled(size, Qt::KeepAspectRatio));
    painter.setPen(QPen(Qt::red, 20, Qt::SolidLine));

}

The start and top buttons are on mainwindow, when i click, image do not appear.

Can someone help me?

Thank you for your attention.

Regards :D

joeQ

@gabrielschubert
Hi, friend,welcome.

Can you show some debug info below code?

void cameraimage::paintEvent(QPaintEvent *){
    cv::Mat tmpImage;
    cv::Mat image;
    captureVideo.read(tmpImage);

    if (tmpImage.empty() == true){
        qDebug() << "EMPTY!";
        return;
    }

    cv::cvtColor(tmpImage, image, CV_BGR2RGB);
    QImage img((const unsigned char*)(image.data), image.cols, image.rows, QImage::Format_RGB888);

#if 1
    qDebug() << "img Size: "<< img.size();
#endif

    QPixmap pixmap = QPixmap::fromImage(img);
    QPainter painter(this);

    float comprimento = 1.0*width()/pixmap.width();
    float altura = 1.0*height()/pixmap.height();
    float ratio = 0.;

    if (comprimento<=altura)
        ratio = comprimento;
    else
        ratio = altura;

    QSize size = ratio*pixmap.size();
    size.setHeight(size.height()-10);

    QPoint p;
    p.setX(0 + (width()-size.width())/2);
    p.setY(5);
#if 1
    qDebug() << "p: " << p;
    qDebug() << "size:" << size;
#endif
    painter.drawPixmap(QRect(p, size), pixmap.scaled(size, Qt::KeepAspectRatio));
    painter.setPen(QPen(Qt::red, 20, Qt::SolidLine));

gabrielschubert

Hello @joeQ , thank you for your answer.

When you say debug info you're saying the app output? If yes, here it is:

Starting Streaming
Starting Streaming
VIDEOIO ERROR: V4L2: Pixel format of incoming image is unsupported by OpenCV
Unable to stop the stream: Device or resource busy
Camera can't open
EMPTY!
EMPTY!

When I pass the mouse on the cameraimage widget, it keeps printing "EMPTY!", cause of the "mouseTracking(true)".

If it is not debug info, could you tell me how can I get this?

Thank you again :)

joeQ

@gabrielschubert

Camera can't open

Your camera didn't open, how to get the pixmap ?

gabrielschubert

@joeQ, now camera is opened. I made a mistake and was opening camera twice. But still not starting steaming when I click on start streaming button, that is on mainwindow. Below the code and output.

#include "cameraimage.h"

cameraimage::cameraimage(QWidget *parent) : QWidget(parent)
{
    setMouseTracking(true);
}

void cameraimage::startStreaming(){
    qDebug() << "Starting Streaming";
    captureVideo.open(-1);
    if (captureVideo.isOpened() == false){
        qDebug() << "Camera can't open";
        return;
    }
    timer = new QTimer(this);
    connect(timer, SIGNAL(timeout()), this, SLOT(update()));

    timer->start(1);
}

void cameraimage::stopStreaming(){
    captureVideo.release();
    timer->stop();
}

void cameraimage::paintEvent(QPaintEvent *){
        cv::Mat tmpImage;
        cv::Mat image;
        captureVideo.read(tmpImage);

        if (tmpImage.empty() == true){
            qDebug() << "EMPTY!";
            return;
        }

        cv::cvtColor(tmpImage, image, CV_BGR2RGB);
        QImage img((const unsigned char*)(image.data), image.cols, image.rows, QImage::Format_RGB888);

    #if 1
        qDebug() << "img Size: "<< img.size();
    #endif

        QPixmap pixmap = QPixmap::fromImage(img);
        QPainter painter(this);

        float comprimento = 1.0*width()/pixmap.width();
        float altura = 1.0*height()/pixmap.height();
        float ratio = 0.;

        if (comprimento<=altura)
            ratio = comprimento;
        else
            ratio = altura;

        QSize size = ratio*pixmap.size();
        size.setHeight(size.height()-10);

        QPoint p;
        p.setX(0 + (width()-size.width())/2);
        p.setY(5);
    #if 1
        qDebug() << "p: " << p;
        qDebug() << "size:" << size;
    #endif
        painter.drawPixmap(QRect(p, size), pixmap.scaled(size, Qt::KeepAspectRatio));
}

output after button clicked:

Starting Streaming...
EMPTY!
EMPTY!
EMPTY!
...

gabrielschubert

Problem solved, changed line

camera.startStreaming()

on mainwindow.cpp to

ui->cameraWidget->startString()

Now it's running.

Thank you. :)