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In my case, I took 1.47 GBs of videos (different formats), images (RAW and other formats), documents (PDF, Office files, etc) and music files (MP3, M4A, etc) and passed them through each compression utility with default settings.įirst, let’s start with the setup I have and the versions. I don’t like just compressing images or just compressing documents because the differences end up being very small and it’s hard to choose a clear winner. For my tests, I decided to create a test folder with a bunch of data in various formats. Real World Compression Testįirst, let’s just look at straight compression numbers because that’s always fun. Beyond these four, there are many other options, but I found these to be the most popular and well known by most people. this article, I’ll go through four different compression tools and try to give you the advantages and disadvantages for each.

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: Check |url= value ( help) Missing or empty |title= ( help) *.delta_bit_length:1.40 = 0=>next symbol 1=>alter length start_huffman_length:5 = 0.20 starting bit length for Huffman deltas *.selector_list:1.6 = zero-terminated bit runs (0.62) of MTF'ed Huffman table (*selectors_used) selectors_used:15 = number of times that the Huffman tables are swapped (each 50 symbols) huffman_groups:3 = 2.6 number of different Huffman tables in use huffman_used_bitmaps:0.256 = bitmap, of symbols used, present/not present (multiples of 16) huffman_used_map:16 = bitmap, of ranges of 16 bytes, present/not present

origPtr:24 = starting pointer into BWT for after untransform In the worst case, it can cause an expansion of 1.25, and in the best case, a reduction to normal, 1=>randomised (deprecated) Runs of symbols are always transformed after 4 consecutive symbols, even if the run-length is set to zero, to keep the transformation reversible. Thus the sequence AAAAAAABBBBCCCD is replaced with AAAA\3BBBB\0CCCD, where \3 and \0 represent byte values 3 and 0 respectively. Sparse bit array showing which symbols are used.Īny sequence of 4 to 255 consecutive duplicate symbols is replaced by the first 4 symbols and a repeat length between 0 and 251.Delta encoding (Δ) of Huffman-code bit lengths.Unary base-1 encoding of Huffman table selection.Selection between multiple Huffman tables.Run-length encoding (RLE) of MTF result.Burrows–Wheeler transform (BWT), or block sorting.Run-length encoding (RLE) of initial data.JSTOR ( August 2021) ( Learn how and when to remove this template message)īzip2 uses several layers of compression techniques stacked on top of each other, which occur in the following order during compression and the reverse order during decompression:.Unsourced material may be challenged and removed.

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