1、新建 Qt Application；

2、点击.ui,插入两个按钮 Push Buttons到Form中去，修改其属性，一个名字为OpenImage，一个为Process，右键按钮选择connect signal为其添加响应函数，选择clicked（）。对应的cpp文件多出了on_OpenImage_clicked函数

3、qtshowimage.h

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

class qtshowimage : public QMainWindow
{
Q_OBJECT

public:
qtshowimage(QWidget *parent = 0, Qt::WindowFlags flags = 0);
~qtshowimage();

private:
Ui::qtshowimageClass ui;
cv::Mat image;//cv图片

private slots:
void on_OpenImage_clicked();
void on_Process_clicked();
};

#endif // QTSHOWIMAGE_H

4、qtshowimage.cpp

#include "qtshowimage.h"
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include "opencv2/imgproc/imgproc.hpp"
#include <QString>
#include <QLabel>

using namespace std;
using namespace cv;

qtshowimage::qtshowimage(QWidget *parent , Qt::WindowFlags flags)
: QMainWindow(parent, flags)
{
ui.setupUi(this);
}

qtshowimage::~qtshowimage()
{

}

void qtshowimage::on_OpenImage_clicked()
{
QString fileName = QFileDialog::getOpenFileName(this, tr("Open Image"), ".", tr("Image Files (*.png *.jpg *.jpeg *.bmp)"));
image = cv::imread(fileName.toLatin1().data());
cv::namedWindow("Original Image");
cv::imshow("Original Image", image);
}

void qtshowimage::on_Process_clicked()
{
cv::cvtColor(image, image, CV_BGR2RGBA);
QImage img = QImage((const unsigned char*)(image.data), image.cols, image.rows, QImage::Format_RGB32);
QLabel *label = new QLabel(this);
label->move(200, 50);
label->setPixmap(QPixmap::fromImage(img));
label->resize(label->pixmap()->size());
label->show();
/*
cv::flip(image, image, 1);
cv::namedWindow("Output Image");
cv::imshow("Output Image", image);
*/
}

5、点击Openimage 加载图像

6、点击Process 处理后图像

7、还可参考：https://blog.csdn.net/yang_xian521/article/details/6968012