[Qt5] Develop openCV3 by QML on Qt-creator

static void _gray(QString sourceFile, QString destFile)
{  
    QImage image(sourceFile);
    if(image.isNull())
    {
        qDebug() << "load " << sourceFile << " failed! ";
        return;
    }
    qDebug() << "depth - " << image.depth();

#if 1
    /* test */
    qDebug() << "Let‘s openCV." << endl;
    cv::Mat mat = QImage2cvMat(image);

    cvtColor(mat, mat ,CV_BGR2GRAY);
    image = cvmat2qimage(mat);

    qDebug() << "openCV done." << endl;

#else
　　/*
　　/* 就没必要使用/关心 QT自身的图像处理接口。
　　 */

    int width = image.width();
    int height = image.height();
    QRgb color;
    int gray;
    for(int i = 0; i < width; i++)
    {
        for(int j= 0; j < height; j++)
        {
            color = image.pixel(i, j);
            gray = qGray(color);
            image.setPixel(i, j, qRgba(gray, gray, gray, qAlpha(color)));
        }
    }
#endif

    image.save(destFile);
}

/* 1. Qimage --> Mat */
cv::Mat QImage2cvMat(QImage image)
{
    cv::Mat mat;
    qDebug() << image.format();
    switch(image.format())
    {
    case QImage::Format_ARGB32:
    case QImage::Format_RGB32:
    case QImage::Format_ARGB32_Premultiplied:
        mat = cv::Mat(image.height(), image.width(), CV_8UC4, (void*)image.constBits(), image.bytesPerLine());
        break;

    case QImage::Format_RGB888:
        mat = cv::Mat(image.height(), image.width(), CV_8UC3, (void*)image.constBits(), image.bytesPerLine());
        cv::cvtColor(mat, mat, CV_BGR2RGB);
        break;

    case QImage::Format_Indexed8:
        mat = cv::Mat(image.height(), image.width(), CV_8UC1, (void*)image.constBits(), image.bytesPerLine());
        break;

    default:
        qDebug() << "What‘s the format?";
        break;
    }
    return mat;
}

/* 2. Mat --> Qimage */
QImage cvMat2QImage(const cv::Mat& mat)
{
    // 8-bits unsigned, NO. OF CHANNELS = 1
    if(mat.type() == CV_8UC1)
    {
        QImage image(mat.cols, mat.rows, QImage::Format_Indexed8);
        // Set the color table (used to translate colour indexes to qRgb values)
        image.setColorCount(256);
        for(int i = 0; i < 256; i++)
        {
            image.setColor(i, qRgb(i, i, i));
        }
        // Copy input Mat
        uchar *pSrc = mat.data;
        for(int row = 0; row < mat.rows; row ++)
        {
            uchar *pDest = image.scanLine(row);
            memcpy(pDest, pSrc, mat.cols);
            pSrc += mat.step;
        }
        return image;
    }
    // 8-bits unsigned, NO. OF CHANNELS = 3
    else if(mat.type() == CV_8UC3)
    {
        // Copy input Mat
        const uchar *pSrc = (const uchar*)mat.data;
        // Create QImage with same dimensions as input Mat
        QImage image(pSrc, mat.cols, mat.rows, mat.step, QImage::Format_RGB888);
        return image.rgbSwapped();
    }
    else if(mat.type() == CV_8UC4)
    {
        qDebug() << "CV_8UC4";
        // Copy input Mat
        const uchar *pSrc = (const uchar*)mat.data;
        // Create QImage with same dimensions as input Mat
        QImage image(pSrc, mat.cols, mat.rows, mat.step, QImage::Format_ARGB32);
        return image.copy();
    }
    else
    {
        qDebug() << "ERROR: Mat could not be converted to QImage.";
        return QImage();
    }
}