使用QT顯示OpenCV讀取的圖檔,關鍵是将CV::Mat對象轉換成QT的QImage對象。
目錄
- 1. 概述
- 2. 實作
- 2.1. 代碼
- 2.2. 解析
- 3. 結果
OpenCV自帶了一部分常用的GUI功能,但是更多的圖像處理功能需要其他GUI架構來輔助實作,這裡通過QT來顯示OpenCV讀取的圖檔。
在QtCreator中建立一個基于QMainWindow的應用:
其中QImageShowWidget就是用于顯示圖像的控件,它是繼承于QWidget實作的,可以将其嵌入QMainWindow的centralwidget中:
QImageShowWidget是自定義的顯示元件,可以首先在QtCreator的設計師界面拖入一個QWidget,再通過“視窗部件提升”功能提升為QImageShowWidget。
qimageshowwidget.h代碼如下:
#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 *); //繪制
void Release();
private:
uchar* winBuf; //視窗填充buf
int winWidth; //視窗像素寬
int winHeight; //視窗像素高
int winBandNum; //波段數
};
#endif // QIMAGESHOWWIDGET_H
qimageshowwidget.cpp代碼如下:
#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)
{
//從檔案中讀取成灰階圖像
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;
}
//重新實作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的類都可以重新實作界面重繪事件paintEvent(),它會在界面需要的時候(例如調用update())自動重繪。在這個事件函數中可以通過圖形繪制接口QPainter繪制:
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繪制的其實是QImage對象,也就是重點是構造QImage這個對象。這個對象是由申請的記憶體winBuf來建構的。顯示的圖像是由寬、高以及波段組成的,需要将三維空間壓縮為一維空間——簡單來講,記憶體的組成為RGBRGBRGB...,并且起點位置為左上角,由左至右,由上至下。
OpenCV讀取的圖像為Mat對象:
//從檔案中讀取成灰階圖像
Mat img = imread(imagePath);
if (img.empty())
{
fprintf(stderr, "Can not load image %s\n", imagePath);
return false;
}
Mat對象可以通過data()方法直接通路讀取的圖像記憶體。而這塊記憶體也是RGBRGBRGB...的結構組成,并且起點位置也是左上角,由左至右,由上至下。将其逐像素傳入到申請的記憶體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];
}
}
}
通過界面加載一張圖像,顯示結果如下: