1、原理

将两张图片重新绘制在一张空白图上（按上下位置拼接）

2、代码

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QPixmap>
#include <QPainter>
#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

    QPixmap stitchPixmap(QPixmap srcPix1, QPixmap srcPix2); //按上下位置拼接图像

private:
    Ui::MainWindow *ui;

    /*
     * 存储上面的图片
     */
    QPixmap m_upPixmap;

    /*
     * 存储下面的图片
     */
    QPixmap m_downPixmap;
};

#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);

    //load image
    m_upPixmap.load("1.jpeg");
    m_downPixmap.load("1.jpeg");

    //set mainwindow's size
    this->setFixedSize(m_upPixmap.width(), m_upPixmap.height() * 2);

    //stitch image
    QPixmap stitchPix = stitchPixmap(m_upPixmap, m_downPixmap);

    //show image
    ui->label->setPixmap(stitchPix);
}

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

//拼接
QPixmap MainWindow::stitchPixmap(QPixmap srcPix1, QPixmap srcPix2)
{
    QPixmap stitchPix(srcPix1.width(), srcPix1.height() + srcPix2.height());
    QPainter p(&stitchPix);

    //绘制两幅小图到QPixmap上
    p.drawPixmap(0, 0, srcPix1.width(), srcPix1.height(), srcPix1);
    p.drawPixmap(0, srcPix1.height(), srcPix2.width(), srcPix2.height(), srcPix2);

    return stitchPix;
}

3、结果