Question

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

#include <QtGui>

//make QImage point to the contents of cv::Mat
inline QImage const mat_to_qimage_ref(cv::Mat &mat)
{
  return QImage((unsigned char*)(mat.data), mat.cols, mat.rows, mat.step1(), QImage::Format_RGB32);
}

int main(int argc, char *argv[])
{
  QApplication a(argc, argv);
  QImage img("lena2.jpg");
  cv::Mat mat(img.height(), img.width(), CV_8UC4, img.bits(), img.bytesPerLine());
  QImage img = mat_to_qimage_ref(mat); //#1
  //QImage img2((unsigned char*)(mat.data), mat.cols, mat.rows, mat.step, QImage::Format_RGB32); #2

  QLabel label;
  label.setPixmap(QPixmap::fromImage(img)); //crash at here
  label.show();

  return a.exec();
}

(#2) is ok, but #1 will occur undefined behavior?(my case is crash)

Besides, if you use it as the codes below, It is okay

 cv::Mat img = cv::imread("lena2.jpg");
 QLabel label;
 label.setPixmap(QPixmap::fromImage(mat_to_qimage_ref(img)));
 label.show();

Don’t know what is happening, something related to cycle dependency?

Answer 1

your function should be like this:

    QImage mat_to_qimage_ref(const cv::Mat3b &src) {
        QImage dest(src.cols, src.rows, QImage::Format_ARGB32);
        for (int y = 0; y < src.rows; ++y) {
                const cv::Vec3b *srcrow = src[y];
                QRgb *destrow = (QRgb*)dest.scanLine(y);
                for (int x = 0; x < src.cols; ++x) {
                        destrow[x] = qRgba(srcrow[x][2], srcrow[x][1], srcrow[x][0], 255);
                }
        }
        return dest;
    }