How to convert QImage to opencv Mat

Question

I have searched on the internet but I cannot find a method of converting a QImage(or QPixmap) to a OpenCV Mat. How would I do this?.

Answer 1

My attempt in OpenCV 3.1+ style code:

void qimage_to_mat(const QImage& image, cv::OutputArray 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());
            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;
        }
    }
}

void mat_to_qimage(cv::InputArray image, QImage& out)
{
    switch(image.type())
    {
        case CV_8UC4:
        {
            cv::Mat view(image.getMat());
            QImage view2(view.data, view.cols, view.rows, view.step[0], QImage::Format_ARGB32);
            out = view2.copy();
            break;
        }
        case CV_8UC3:
        {
            cv::Mat mat;
            cvtColor(image, mat, cv::COLOR_BGR2BGRA); //COLOR_BGR2RGB doesn't behave so use RGBA
            QImage view(mat.data, mat.cols, mat.rows, mat.step[0], QImage::Format_ARGB32);
            out = view.copy();
            break;
        }
        case CV_8UC1:
        {
            cv::Mat mat;
            cvtColor(image, mat, cv::COLOR_GRAY2BGRA);
            QImage view(mat.data, mat.cols, mat.rows, mat.step[0], QImage::Format_ARGB32);
            out = view.copy();
            break;
        }
        default:
        {
            throw invalid_argument("Image format not supported");
            break;
        }
    }
}