     if (argc < 2)
     {
         log_info(stderr, "nvExtractReads [options] input output\n");
-        log_info(stderr, "  extract a set of reads to a plain ASCII or packed file with one read per line (.txt)\n\n");
+        log_info(stderr, "  extract a set of reads to a plain ASCII_FORMAT or packed file with one read per line (.txt)\n\n");
         log_info(stderr, "options:\n");
         log_info(stderr, "  --verbosity\n");
         log_info(stderr, "  -F | --skip-forward          skip forward strand\n");
         log_info(stderr, "  -R | --skip-reverse          skip forward strand\n");
-        log_info(stderr, "  -a | --ascii                 ASCII output\n");
+        log_info(stderr, "  -a | --ascii                 ASCII_FORMAT output\n");
         log_info(stderr, "  -p2 | --packed-2             2-bits packed output\n");
         log_info(stderr, "  -p4 | --packed-4             4-bits packed output\n");
         log_info(stderr, "  -i  | --idx string           save an index file\n");


    switch (format)
    {
    case ASCII:
        success = to_ascii( reads_name, output_file, output_index, qencoding, io::SequenceEncoding(encoding_flags) );
        break;
    case PACKED2:
        success = to_packed<2u>( reads_name, output_file, output_index, qencoding, io::SequenceEncoding(encoding_flags) );
        break;
    case PACKED4:
        success = to_packed<4u>( reads_name, output_file, output_index, qencoding, io::SequenceEncoding(encoding_flags) );
        break;
    }

        else if (strcmp( argv[i], "-a" ) == 0 ||
                 strcmp( argv[i], "--ascii" ) == 0)  // ascii format
        {
            format = ASCII_FORMAT;
        }
        else if (strcmp( argv[i], "-p2" ) == 0 ||
                 strcmp( argv[i], "--packed-2" ) == 0)  // 2-bits packed
        {
            format = PACKED2_FORMAT;
        }
        else if (strcmp( argv[i], "-p4" ) == 0 ||
                 strcmp( argv[i], "--packed-4" ) == 0)  // 4-bits packed
        {
            format = PACKED4_FORMAT;
        }
        else if (strcmp( argv[i], "-i" ) == 0 ||
                 strcmp( argv[i], "--idx" ) == 0)       // index file
