基于QT实现显示OpenCV读取的图片
作者:音视频开发老舅
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:
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:
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:
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