bzz - Online in the Cloud

PROGRAM:

NAME

bzz - DjVu general purpose compression utility.

SYNOPSIS

Encoding:
bzz -e[blocksize] inputfile outputfile

Decoding:
bzz -d inputfile outputfile

DESCRIPTION

The first form of the command line (option -e) compresses the data from file inputfile and
writes the compressed data into outputfile. The second form of the command line (option
-d) decompressed file inputfile and writes the output to outputfile.

OPTIONS

-d Decoding mode.

-e[blocksize]
Encoding mode. The optional argument blocksize specifies the size of the input
file blocks processed by the Burrows-Wheeler transform expressed in kilobytes. The
default block sizes is 2048 KB. The maximal block size is 4096 KB. Specifying a
larger block size usually produces higher compression ratios and increases the
memory requirements of both the encoder and decoder. It is useless to specify a
block size that is larger than the input file.

ALGORITHMS

The Burrows-Wheeler transform is performed using a combination of the Karp-Miller-
Rosenberg and the Bentley-Sedgewick algorithms. This is comparable to (Sadakane, DCC 98)
with a slightly more flexible ranking scheme. Symbols are then ordered according to a
running estimate of their occurrence frequencies. The symbol ranks are then coded using a
simple fixed tree and the ZP binary adaptive coder (Bottou, DCC 98).

The Burrows-Wheeler transform is also used in the well known compressor bzip2. The
originality of bzz is the use of the ZP adaptive coder. The adaptation noise can cost up
to 5 percent in file size, but this penalty is usually offset by the benefits of
adaptation.

PERFORMANCE

The following table shows comparative results (in bits per character) on the Canterbury
Corpus ( http://corpus.canterbury.ac.nz ). The very good bzz performance on the
spreadsheet file excl puts the weighted average ahead of much more sophisticated
compressors such as fsmx.

┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
├─────────────────────────────────────────────────────────────────────────────────────────────────────────────┤
│ fsmx 2.10 0.79 1.89 1.48 2.52 1.84 2.21 2.24 2.29 2.91 2.35 1.63 2.06 │
│ bzz 2.25 0.76 2.13 0.78 2.67 2.00 2.40 2.52 2.60 3.19 2.52 1.44 2.16 │
└─────────────────────────────────────────────────────────────────────────────────────────────────────────────┘

Note that DjVu contributors have several entries in this table. Program compress was
written some time ago by Joe Orost. Program ppmd is an improvement of the PPM-C method
invented by Paul Howard.

CREDITS

Program bzz was written by Léon Bottou <[email protected]> and was then improved
by Andrei Erofeev <[email protected]>, Bill Riemers <[email protected]> and
many others.

Use bzz online using onworks.net services