how to convert back QImage to cv::Mat

Question

I have graped an image from videoCapture object then i converted it to QImage to send it to server. After i receive it from the server side i want to do some image processing on the received image which is QImage. So before i performing any processing i have to convert it back to cv::Mat image.

I have function converting cv::Mat to QImage

    // Copy input Mat
    const uchar *qImageBuffer = (const uchar*)mat.data;
    // Create QImage with same dimensions as input Mat
    QImage img(qImageBuffer, mat.cols, mat.rows, mat.step, QImage::Format_RGB888);
    //en
    img.bits();
    return img.rgbSwapped();

have function converting QImage to cv::Mat

Mat QImageToMat(const QImage& src){

cv::Mat tmp(src.height(),src.width(),CV_8UC3,(uchar*)src.bits(),src.bytesPerLine());

cv::Mat result = tmp ; // deep copy just in case (my lack of knowledge with open cv)

for (int i=0;i<src.height();i++) {
    memcpy(result.ptr(i),src.scanLine(i),src.bytesPerLine());
}
cvtColor(result, result,CV_RGB2BGR);


return result;

}

I have been searching for about 2 days how to convert QImage to cv::Mat but with no luck non of the code snippet works for me. I don't know why, the image after conversion looks bad. you can see the image to left.

Does someone have any idea, about what could be cause the problem? Thanks in advance.

LEFT:image after converted from QImage to Mat RIGHT: the origranl Image which is in QImage format