使用QT显示OpenCV读取的图片

OpenCV带有一些常用的GUI功能，但是更多的图像处理功能需要其他GUI框架来协助实现. 在这里，QT用于显示OpenCV读取的图片.

在QtCreator中基于QMainWindow创建一个新应用程序:

QImageShowWidget是用于显示图像的控件qt读取图片并显示，它继承自QWidget，并且可以嵌入QMainWindow的中央窗口中:

QImageShowWidget是一个自定义显示组件，您可以先将其拖入QtCreator设计器界面中的QWidget，然后通过“窗口小部件升级”功能将其升级为QImageShowWidget.

qimageshowwidget.h的代码如下:

#ifndef QIMAGESHOWWIDGET_H
#define QIMAGESHOWWIDGET_H
#include <QWidget>
class QImageShowWidget : public QWidget
{
    Q_OBJECT
public:
    explicit QImageShowWidget(QWidget *parent = nullptr);
    ~QImageShowWidget();
    bool LoadImage(const char* imagePath);
signals:
public slots:
protected:
    void paintEvent(QPaintEvent *);     //绘制
    void Release();
private:
    uchar* winBuf;      //窗口填充buf
    int winWidth;      //窗口像素宽
    int winHeight;      //窗口像素高
    int winBandNum;      //波段数
};
#endif // QIMAGESHOWWIDGET_H

qimageshowwidget.cpp的代码如下:

#include "qimageshowwidget.h"
#include <opencv2\opencv.hpp>
#include <QPainter>
#include <QDebug>
#include <iostream>
using namespace cv;
using namespace std;
QImageShowWidget::QImageShowWidget(QWidget *parent) : QWidget(parent)
{
    //填充背景色
    setAutoFillBackground(true);
    setBackgroundRole(QPalette::Base);
    winBuf = nullptr;
    winWidth = rect().width();
    winHeight = rect().height();
    winBandNum = 3;
}
QImageShowWidget::~QImageShowWidget()
{
    if(winBuf)
    {
        delete[] winBuf;
        winBuf = nullptr;
    }
}
bool QImageShowWidget::LoadImage(const char* imagePath)
{
    //从文件中读取成灰度图像
    Mat img = imread(imagePath);
    if (img.empty())
    {
        fprintf(stderr, "Can not load image %s\n", imagePath);
        return false;
    }
    Release();
    winWidth = rect().width();
    winHeight = rect().height();
    size_t winBufNum = (size_t) winWidth * winHeight * winBandNum;
    winBuf = new uchar[winBufNum];
    memset(winBuf, 255, winBufNum*sizeof(uchar));
    for (int ri = 0; ri < img.rows; ++ri)
    {
        for (int ci = 0; ci < img.cols; ++ci)
        {
            for(int bi = 0; bi < winBandNum; bi++)
            {
                size_t m = (size_t) winWidth * winBandNum * ri + winBandNum * ci + bi;
                size_t n = (size_t) img.cols * winBandNum * ri + winBandNum * ci + bi;
                winBuf[m] = img.data[n];
            }
        }
    }
    update();
    return true;
}
//重新实现paintEvent
void QImageShowWidget::paintEvent(QPaintEvent *)
{
    if(!winBuf)
    {
        return;
    }
    QImage::Format imgFomat = QImage::Format_RGB888;
    QPainter painter(this);
    QImage qImg(winBuf, winWidth, winHeight, winWidth*winBandNum, imgFomat);
    painter.drawPixmap(0, 0, QPixmap::fromImage(qImg));
}
void QImageShowWidget::Release()
{
    if(winBuf)
    {
        delete[] winBuf;
        winBuf = nullptr;
    }
}

所有基于QWidget的类都可以重新实现接口重绘事件paintEvent（），它将在接口需要它时自动重绘（例如调用update（））. 在此事件功能中，您可以通过图形绘制界面QPainter进行绘制:

QImage::Format imgFomat = QImage::Format_RGB888;
QPainter painter(this);
QImage qImg(winBuf, winWidth, winHeight, winWidth*winBandNum, imgFomat);
painter.drawPixmap(0, 0, QPixmap::fromImage(qImg));

您可以看到QPainter实际上是在绘制QImage对象，也就是说，关键是构造QImage对象. 该对象由应用程序内存winBuf构造. 显示的图像由宽度，高度和波段组成，三维空间需要简单地压缩为一维空间，存储组成为RGBRGBRGB ...，起始点为左上角落qt读取图片并显示，从左到右，从上到下.

OpenCV读取的图像是Mat对象:

//从文件中读取成灰度图像
Mat img = imread(imagePath);
if (img.empty())
{
    fprintf(stderr, "Can not load image %s\n", imagePath);
    return false;
}

Mat对象可以通过data（）方法直接访问读取的图像存储器. 此内存也由RGBRGBRGB ...组成，起点也是左上角，从左到右，从上到下. 逐像素将其传递到应用的内存winBuf:

winWidth = rect().width();
winHeight = rect().height();
size_t winBufNum = (size_t) winWidth * winHeight * winBandNum;
winBuf = new uchar[winBufNum];
memset(winBuf, 255, winBufNum*sizeof(uchar));
for (int ri = 0; ri < img.rows; ++ri)
{
    for (int ci = 0; ci < img.cols; ++ci)
    {
        for(int bi = 0; bi < winBandNum; bi++)
        {
            size_t m = (size_t) winWidth * winBandNum * ri + winBandNum * ci + bi;
            size_t n = (size_t) img.cols * winBandNum * ri + winBandNum * ci + bi;
            winBuf[m] = img.data[n];
        }
    }
}

通过界面加载图片，显示结果如下:

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