// Duplicate the screenshot() trick.
    FixedVector<unsigned, NUM_DCHAR_TYPES> char_table_bk;
    char_table_bk = Options.char_table;
    init_char_table(CSET_ASCII);
    init_feature_table();

    for ( int y = min_y; y < max_y; ++y )

    for ( int y = min_y; y <= max_y; ++y )

        for ( int x = min_x; x < max_x; ++x )

        for ( int x = min_x; x <= max_x; ++x )

    // Restore char and feature tables
    Options.char_table = char_table_bk;
    init_feature_table();