Data Compression


Criteria

Survey Formats

Basics

Compression Methods

Data Formats

Files

BZIP2

GZIP

ZIP

Specification

Characteristics

Compression

File Structure

Security Features

Platforms

Applications

Audio Data

Image Data

Video Data


Glossary

Index


Download


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ZIP Compression Methods


The internal header attributes on file and directory lever allow the following compression methods:


uncompressed
Original data will be embedded directly.

Shrunk
Modified LZW (Lempel-Ziv-Welch) compression method with partial clearing and dynamical addressing of the table entries.

Reduced (1 to 4)
A dictionary based algorithm used for addressing byte sequences from former contents. Finally a variable length coding is applied according to the probability distribution of the codes. This method is scalable in four steps.

Imploded
A dictionary based algorithm accessing a 4 or 8 KByte large dictionary. Sequence lengths, addresses and uncompressed symbols (optional) use Shannon Fano codes.

Tokenizing (reserviert)
Tokenizing is only part of the parameter list. The implementation is not specified and it is not used by PKWARE.

Deflate
A dictionary based algorithm accessing an up to 32 KByte large dictionary. Additionally a Huffman coding will be used for redundancy reduction.

Deflate [Deflate]


Deflate64™
Equivalent to Deflate, but using an up to 64 KByte large dictionary.

Deflate64™ [Deflate64™]


BZIP2
BZIP2 is only part of the parameter list and not part of the "Appliction Note". PKWARE refers to the internet for further information.

BZIP2 [BZIP2]


It is not neccessary for a compatible ZIP application to support any of these compression methods for encoding. It is only required that a decoder is able to process them.


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