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 = QImagecvMat(image);

    cvtColor(mat, mat ,CV_BGR2GRAY);

    image = cvmatqimage(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 = ; i < width; i++)

    {

        for(int j= ; 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 QImagecvMat(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_8UC, (void*)image.constBits(), image.bytesPerLine());

        break;

    case QImage::Format_RGB888:

        mat = cv::Mat(image.height(), image.width(), CV_8UC, (void*)image.constBits(), image.bytesPerLine());

        cv::cvtColor(mat, mat, CV_BGR2RGB);

        break;

    case QImage::Format_Indexed8:

        mat = cv::Mat(image.height(), image.width(), CV_8UC, (void*)image.constBits(), image.bytesPerLine());

        break;

    default:

        qDebug() << "What's the format?";

        break;

    }

    return mat;

}

/* 2. Mat --> Qimage */

QImage cvMatQImage(const cv::Mat& mat)

{

    // 8-bits unsigned, NO. OF CHANNELS = 1

    if(mat.type() == CV_8UC)

    {

        QImage image(mat.cols, mat.rows, QImage::Format_Indexed8);

        // Set the color table (used to translate colour indexes to qRgb values)

        image.setColorCount();

        for(int i = ; i < ; i++)

        {

            image.setColor(i, qRgb(i, i, i));

        }

        // Copy input Mat

        uchar *pSrc = mat.data;

        for(int row = ; 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_8UC)

    {

        // 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_8UC)

    {

        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();

    }

}