    int ExvImage::writeHeader(BasicIo& outIo) const
    {
        // Exv header
        byte tmpBuf[7];
        tmpBuf[0] = 0xff;
        tmpBuf[1] = 0x01;
        std::memcpy(tmpBuf + 2, exiv2Id_, 5);
        if (outIo.write(tmpBuf, 7) != 7) return 4;
        if (outIo.error()) return 4;
        return 0;
    }
Unknown