AdvanceCOMP

AdvanceCOMP is a set of cross-platform command line data (re-)compression tools. The utilities allow modifying an already-compressed file, with the intent of reducing the file-size by optimising the compressed representation. The AdvanceCOMP suite is freely available under the terms of the GPLv3 license.

AdvanceCOMP works with files using the LZ/Huffman-based compression algorithm known as DEFLATE, the most widely used compression encoding systems in use. A large number of file-formats include DEFLATE as part of their specification, most notably PNG, gzip and ZIP.

DEFLATE specifies a stream-encoding such that any compliant decoder is able to parse any valid stream; the algorithm and program used for the compression stage are not mandated.

For generation of compressed sections of DEFLATE data, an encoder available in the zlib/gzip reference implementation has typically been utilised. The zlib/gzip compressor offers the user a sliding scale between CPU usage and the likely amount of reduction in size achieved on a range of -0 (no compression) to -9 (maximum gzip compression).

The 7-Zip and Zopfli DEFLATE encoders, used in the AdvanceCOMP suite, effectively extend the sliding scale further. A much more detailed search of compression possibilities is performed, at the expense of significant further processor time spent searching. Effectively, the 10-point scale used in gzip is extended to include extra settings above -9, the previous maximum search level. There will be no difference in decompression speed, regardless of the level of compressed size achieved or time taken to encode the data.