[Qt + OpenCV] Displaying Images and Convert to Grayscale

If you are interested to just display the image, see displaying image in Qt with OpenCV.
1. Create a new Qt GUI Application project.
2. Add a new Label and 3 Push Buttons (Open Image, To Grayscale, and Reset buttons) in the form.
3. Do the rest with writing the program:



This is the header displaywin.h:

#ifndef DISPLAYWIN_H

#define DISPLAYWIN_H

#include <QMainWindow>

#include <opencv/cv.h>

#include <opencv/highgui.h>

namespace Ui {

class DisplayWin;

}

class DisplayWin : public QMainWindow

{

    Q_OBJECT

public:

    explicit DisplayWin(QWidget *parent = 0);

    ~DisplayWin();

private slots:

    void openImage();

    void toGrayscaleImg();

    void on_btnOpen_clicked();

    void on_btnReset_clicked();

    void on_btnToGray_clicked();

private:

    Ui::DisplayWin *ui;

    QString fileName;

    IplImage *iplImg;

    char* charFileName;

    QImage qimgNew;

    QImage qimgGray;

};

#endif // DISPLAYWIN_H

displaywin.cpp:

#include "displaywin.h"
#include "ui_displaywin.h"
#include <opencv2/opencv.hpp>
#include <QFileDialog>


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

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

void DisplayWin::openImage()
{
    fileName = QFileDialog::getOpenFileName(this,tr("Open Image"),QDir::currentPath(),tr("Image Files [ *.jpg , *.jpeg , *.bmp , *.png , *.gif]"));
    charFileName = fileName.toLocal8Bit().data();
    iplImg = cvLoadImage(charFileName);
    qimgNew = QImage((const unsigned char*)iplImg->imageData,iplImg->width,iplImg->height,QImage::Format_RGB888).rgbSwapped();
    ui->lblImage->setPixmap(QPixmap::fromImage(qimgNew));
}
void DisplayWin::toGrayscaleImg()
{
    ui->lblImage->clear();
    IplImage *imgGray = cvLoadImage(charFileName, CV_LOAD_IMAGE_GRAYSCALE);
    qimgGray = QImage((const unsigned char*)imgGray->imageData,imgGray->width,imgGray->height,QImage::Format_Indexed8);
    qimgGray.setPixel(0,0,qRgb(0,0,0));
    ui->lblImage->setPixmap(QPixmap::fromImage(qimgGray));
}
void DisplayWin::on_btnOpen_clicked()
{
    openImage();
}
void DisplayWin::on_btnReset_clicked()
{
    ui->lblImage->clear();
}

void DisplayWin::on_btnToGray_clicked()
{
    toGrayscaleImg();
}

main.cpp:
#include "displaywin.h"
#include <QApplication>

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

You can download the project here