如何在openCV中将裁剪图像的数据数组转换为Qt中的RGB直方图

Question

I have an interface that is formed of two QGraphicsView: One QGraphicsView is used to show images from a right camera and the second QGraphicsView is used to show images from a left camera. Both QGraphicsViews are also used to upload images (eg from file) so that it is possible to perform image processing operations. Once the image is uploaded on, for example, the left QGraphicsView I am able to draw a box on a particular feature of the image and extract it. As soon as I right click the mouse button I open a menu. One of the functions that I am struggling with is that I am trying to transform the cropped image derived from the drawn box into an RGB histogram. I am using openCV to transform the image into a series of array, and pass these array to 3 QLabels to show R, G, B histograms. However I am not able to draw the RGB histograms and can't catch the mistake. I am attaching a snapshot of the UI for information:

The code is also attached below:

clipscene.h

#ifndef CLIPSCENE_H
#define CLIPSCENE_H
#include <QDialog>
#include <QGraphicsScene>
#include <QGraphicsPixmapItem>
#include "opencv2/imgproc.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui.hpp"
#include "opencv2/highgui/highgui.hpp"

namespace Ui {
class clipScene;
}

class clipScene : public QDialog
{
    Q_OBJECT
public:
    explicit clipScene(QWidget *parent = 0);
    ~clipScene();
    void setImage(QImage img);
    void setBoundingBox(QRect rect);
private slots:
    void on_closeBtn_clicked();
    void on_acceptBtn_clicked();
    void showEvent(QShowEvent *);
private:
    Ui::clipScene *ui;
    QImage simg, simgR, simgG, simgB;
    QRect srect;
    QGraphicsScene *scene;
};
#endif // CLIPSCENE_H 

And clipscene.cpp

#include "clipscene.h"
#include "ui_clipscene.h"

using namespace cv;
clipScene::clipScene(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::clipScene)
{
    ui->setupUi(this);

    scene = new QGraphicsScene();
    ui->graphicsViewClipped->setScene(scene);
    ui->redImg->setText("<b>Calculate Graph</b>");
    ui->greenImg->setText("<b>Calculate Graph</b>");
    ui->blueImg->setText("<b>Calculate Graph</b>");
}
clipScene::~clipScene()
{
    delete ui;
}
void clipScene::setImage(QImage img)
{
    simg = img;
    QGraphicsPixmapItem* item = new QGraphicsPixmapItem(QPixmap::fromImage(simg));
    scene->addItem(item);
    ui->graphicsViewClipped->show();
    cv::Mat input = cv::Mat(simg.height(), simg.width(), QImage::Format_ARGB32, simg.bits(), simg.bytesPerLine());
    cv::Mat channel[3];
    // Establish the number of bins
    int hbins = 30, sbins = 32;
    int histSize[] = {hbins, sbins};    
    // Set the ranges ( for B,G,R) )
    float hranges[] = { 0, 180 };
    // saturation varies from 0 (black-gray-white) to 255 (pure spectrum color)
    float sranges[] = { 0, 256 };
    const float* histRange[] = { hranges, sranges };
    bool uniform = true; bool accumulate = false;

    split(input, channel);
    int channels[] = {0, 1}; // Now for one channel (R)
    MatND hist;

    cv::calcHist(&input, 1, channels, Mat(), hist, 1, histSize, histRange, uniform, accumulate);
    // The actual splitting.
    double maxVal=0;
    minMaxLoc(hist, 0, &maxVal, 0, 0);

    int scale = 10;
    Mat histImg = Mat::zeros(sbins*scale, hbins*10, CV_8UC3);

    for( int h = 0; h < hbins; h++ )
        for( int s = 0; s < sbins; s++ )
        {
            float binVal = hist.at<float>(h, s);
            int intensity = cvRound(binVal*255/maxVal);

            // The arrays of data in openCV should be used here to draw 
            // the histogram

        }
    ui->redImg->setScaledContents(true);
    ui->redImg->setPixmap(QPixmap::fromImage(QImage(channel[0].data, channel[0].cols, channel[0].rows, channel[0].step, QImage::Format_ARGB32) \
            .scaled(200,200,Qt::KeepAspectRatio,Qt::SmoothTransformation)));
}

I found this and I was also reading additional material from openCV documentation but still the problem persists. Any idea on how to solve this problem?

Answer 1

Using this example of OpenCV, also to show the graph use QChartView as shown below:

#include <QApplication>

#include <QtCharts>
QT_CHARTS_USE_NAMESPACE

#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui/highgui.hpp"

static cv::Mat QImageToMat(const QImage & image){
    cv::Mat out;
    switch(image.format()) {
    case QImage::Format_Invalid:
    {
        cv::Mat empty;
        empty.copyTo(out);
        break;
    }
    case QImage::Format_RGB32:
    {
        cv::Mat view(image.height(),image.width(),CV_8UC4,(void *)image.constBits(),image.bytesPerLine());
        view.copyTo(out);
        break;
    }
    case QImage::Format_RGB888:
    {
        cv::Mat view(image.height(),image.width(),CV_8UC3,(void *)image.constBits(),image.bytesPerLine());
        cv::cvtColor(view, out, cv::COLOR_RGB2BGR);
        break;
    }
    default:
    {
        QImage conv = image.convertToFormat(QImage::Format_ARGB32);
        cv::Mat view(conv.height(),conv.width(),CV_8UC4,(void *)conv.constBits(),conv.bytesPerLine());
        view.copyTo(out);
        break;
    }
    }
    return out;
}

static std::vector<cv::Mat> calculate_histogram(const QImage & image){
    cv::Mat src = QImageToMat(image);

    std::vector<cv::Mat> bgr_planes;
    cv::split(src, bgr_planes );
    /// Establish the number of bins
    int histSize = 256;

    /// Set the ranges ( for B,G,R) )
    float range[] = { 0, 256 } ;
    const float* histRange = { range };

    bool uniform = true; bool accumulate = false;

    std::vector<cv::Mat> hist;
    for(std::size_t i = 0; i < bgr_planes.size(); ++i){
        hist.push_back(cv::Mat());
        cv::calcHist( &bgr_planes[i], 1, 0, cv::Mat(), hist[i], 1, &histSize, &histRange, uniform, accumulate );
    }

    return hist;
}

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QImage image(":/lena.png");

    QChartView *view = new QChartView;
    QChart *chart = new QChart;
    view->setChart(chart);

    const QStringList titles{"Blue", "Green", "Red"};
    std::vector<cv::Mat> hist_planes = calculate_histogram(image);

    for(std::size_t i = 0; i< 3; ++i){
        const cv::Mat mat = hist_planes[i];
        QLineSeries *series = new QLineSeries;
        series->setColor(QColor(titles[i]));
        series->setName(titles[i]);
        for(int j=0; j < mat.rows; ++j){
            *series << QPoint(j, mat.at<float>(j));
        }
        chart->addSeries(series);
    }

    chart->createDefaultAxes();
    chart->axisX()->setGridLineVisible(false);
    chart->axisY()->setGridLineVisible(false);

    QLabel *label = new QLabel;
    label->setPixmap(QPixmap::fromImage(image));

    QWidget w;
    QHBoxLayout *lay = new QHBoxLayout(&w);
    lay->addWidget(label);
    lay->addWidget(view);

    w.show();

    return a.exec();
}

In the following link you can find the complete example.