1）.pro文件

#-------------------------------------------------
#
# Project created by QtCreator 2014-05-18T12:56:52
#
#-------------------------------------------------

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = myQTDemo
TEMPLATE = app


SOURCES += main.cpp        mainwindow.cpp

HEADERS  += mainwindow.h

FORMS    += mainwindow.ui
INCLUDEPATH+=d:\opencv249\include\opencv                    d:\opencv249\include\opencv2                    d:\opencv249\include

LIBS+=d:\opencv249\lib\libopencv_calib3d249.dll.a        d:\opencv249\lib\libopencv_contrib249.dll.a        d:\opencv249\lib\libopencv_core249.dll.a        d:\opencv249\lib\libopencv_features2d249.dll.a        d:\opencv249\lib\libopencv_flann249.dll.a        d:\opencv249\lib\libopencv_gpu249.dll.a        d:\opencv249\lib\libopencv_highgui249.dll.a        d:\opencv249\lib\libopencv_imgproc249.dll.a        d:\opencv249\lib\libopencv_legacy249.dll.a        d:\opencv249\lib\libopencv_ml249.dll.a        d:\opencv249\lib\libopencv_objdetect249.dll.a        d:\opencv249\lib\libopencv_video249.dll.a

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
    cv::Mat image,image2;
      QImage img;

private slots:
    void on_pushButton_clicked();

    void on_pushButton_2_clicked();

private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QString>
#include <QFileDialog>
#include <QMessageBox>
#include <opencv/cv.h>
#include <QTextCodec>
using namespace cv;
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

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

void MainWindow::on_pushButton_clicked()
{
    QString filename = QFileDialog::getOpenFileName(this,tr("Open Image"),"",tr("Image File(*.bmp *.jpg *.jpeg *.png)"));
    QTextCodec *code = QTextCodec::codecForName("gb18030");
    std::string name = code->fromUnicode(filename).data();
    image = cv::imread(name);

    if(!image.data)
    {
        QMessageBox msgBox;
        msgBox.setText(tr("image data is null"));
        msgBox.exec();
    }
    else
    {
        cv::cvtColor(image,image2,CV_BGR2RGB);
        img = QImage((const unsigned char*)(image2.data),image.cols,image.rows, image.step,  QImage::Format_RGB888);
        ui->label->clear();
        ui->label->setPixmap(QPixmap::fromImage(img));
        //ui->processPushButton->setEnabled(true);
        ui->label->resize(ui->label->pixmap()->size());
    }
}

void MainWindow::on_pushButton_2_clicked()
{
    // cv::flip(image,image,1);
    Mat gray;

    cvtColor(image,gray,CV_BGR2GRAY);
    // cvtColor(gray,gray,CV_bg)
  //  imshow("li",gray);

    // cv::cvtColor(image,image,CV_BGR2RGB);
    //      img = QImage((const unsigned char*)(image.data),image.cols,image.rows,image.cols*image.channels(),  QImage::Format_RGB888);
    img = QImage((const unsigned char*)(gray.data),gray.cols,gray.rows,gray.step,  QImage::Format_Indexed8);

    ui->label->setPixmap(QPixmap::fromImage(img));
}