private void extractFileHeader(DataInputStream is)
        throws IOException, AWTException
    {
        is.read(bfType);
        if ( bfType[0] != 'B' || bfType[1] != 'M' )
            throw new AWTException("Not BMP format");
        bfSize = pullVal(is, 4);
        is.skipBytes(4);
        bfOffset = pullVal(is, 4);
    }