使用QT显示OpenCV读取的图片

1. 概述

OpenCV自带了一部分常用的GUI功能,但是更多的图像处理功能需要其他GUI框架来辅助实现,这里通过QT来显示OpenCV读取的图片。

2. 实现

在QtCreator中新建一个基于QMainWindow的应用:

QMainWindow应用

其中QImageShowWidget就是用于显示图像的控件,它是继承于QWidget实现的,可以将其嵌入QMainWindow的centralwidget中:

QT显示图像

QImageShowWidget是自定义的显示组件,可以首先在QtCreator的设计师界面拖入一个QWidget,再通过“窗口部件提升”功能提升为QImageShowWidget。

2.1. 代码

qimageshowwidget.h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;
    }
}

2.2. 解析

所有基于QWidget的类都可以重新实现界面重绘事件paintEvent(),它会在界面需要的时候(例如调用update())自动重绘。在这个事件函数中可以通过图形绘制接口QPainter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));

可以看到QPainter绘制的其实是QImage对象,也就是重点是构造QImage这个对象。这个对象是由申请的内存winBuf来构建的。显示的图像是由宽、高以及波段组成的,需要将三维空间压缩为一维空间——简单来讲,内存的组成为RGBRGBRGB...,并且起点位置为左上角,由左至右,由上至下。

OpenCV读取的图像为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内存。而这块内存也是RGBRGBRGB...的结构组成,并且起点位置也是左上角,由左至右,由上至下。将其逐像素传入到申请的内存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];
        }
    }
}

3. 结果

通过界面加载一张图像,显示结果如下:

QT显示图像

posted @ 2020-02-23 18:42  charlee44  阅读(2086)  评论(0编辑  收藏