QImage::save() doesn't get the raw bytes of the image, it converts the image to a file format. If you really want the raw bytes, do something like QByteArray ba((const char *)preview.constBits(), preview.byteCount());

@SGaist Thank you for your suggestion. I would like to know anyone particularly used Qt for Electronic paper Display. If yes, then I would like to get the difference if any. I believe the users can give suggestion. Meanwhile, I will post the same in interest mailing list also.