Expert Compression Settings
Note: If you purchased DropStuff as part of StuffIt Deluxe, the settings you make below will also be applied to StuffIt Deluxe and Magic Menu.
hen you choose ÒCustomÓ in the ÒCompression LevelÓ preference DropStuff offers an "Expert" mode dialog that allows you to configure exactly how the compression algorithm goes about the job of compressing your files. You can use format options to change the compression settings, and you can also use this dialog StuffIt X Compression Method
Compression method allows you to select different compressors for use when adding files to a StuffIt X archive with compression.
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Method 0 (No Compression): Files will be added to the archive without being compressed.
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Method 1 (Fastest Compression): Method 1 provides compression that is optimized for speed of compression and decompression. It works by replacing a series of bytes with a reference to a previous occurrence of the same series of bytes. Method 1 is used when the compression level is set to "Faster" in Menu Preferences, DropStuff, or StuffIt Deluxe.
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Method 2 (Best Binary Compression): Method 2 is optimized for the compression of binary files (such as applications) and also for fast decompression. Method 2 works in the same way as Method 1, except that it has a more exact way of representing the offsets and lengths, which makes it compress a little more, but at the cost of slower compression and decompression. Typically Method 2 will provide you with the best results when youÕre compressing applications.
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Method 3 (Best Size/Speed Trade Off): Method 3 provides the best trade off between compression/decompression speed and archive file size and works well on a variety of different file types. This compression method does a reversible sort on the data, which places like data closer together which makes it more compressible.
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Method 4 (Best text Compression): Method 4 provides compression that is primarily optimized for text. This compression method works by ÒpredictingÓ what the next byte will be based on previous data. For example, if it is predicting the byte following ÒtÓ and ÒhÓ, it will give high probabilities to ÒeÓ, and ÒaÓ.
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Method 5 (Choose Method by File Type): This compression method uses a combination of Method 3 and method 4 to achieve better results. If the file being compressed is a mostly text file, it uses method 4, otherwise it uses method 3.
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Method 6 (Choose Method by Analysis): This method breaks the file being compressed into bite size pieces and compresses each piece with methods 2 through 4. Whichever method produces the smallest output is used for that chunk of data. This makes it very slow but it generally produces the smallest possible files.
Setting the Compression Level and Extent
Levels generally set Òhow hardÓ each method tries to compress.
In the matching algorithms (method 1 & 2), levels 1-9 generally correspond to Gzip's compression levels. The higher the number the harder it tries to find a match (more compression, but slower). Levels above 9 use a different, more exhaustive search for previous matches, which gets extra compression, but at the expense of speed. In the ÒpredictionÓ algorithm, the level corresponds to how many previous bytes to use when making the prediction.
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Note: Not all the compression methods used by StuffIt X support setting compression levels. You cannot specify compression levels for methods 3 or 5.
Extents has a direct relationship to how much memory is used. In methods 1 & 2, the extent sets how far back to look for a match. In method 4, extent sets how much memory to use for storing the prediction information. Text Encoding
StuffIt X archives can also be converted to ASCII text format. Three text encoding methods are available, Base64 (-L 1), Base 88 (-L 2) and Base 222 (-L 3). The levels of available text encoding determine how much of the full ACSII character set will be used to encode the data.The more characters used, the less size overhead will be imposed as a result of translating the binary data of the archive into text characters. When sending archives via E-mail, it is best to use Base64. This uses the fewest characters, but as a result is the most compatible. Base 222 is a good choice if files are being posted to a news group. Encryption Settings
StuffIt X archives can be created with encryption. There are 4 compression methods supported:
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1=RC4 - Supports up to 512bit key lengths.
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2=DES - Supports to 64bit key lengths
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3=BlowFish - Supports up to 448bit key lengths
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4=AES - Supports up to 256bit key lengths
Error Correction or Redundancy
StuffIt X archives can be created with Error Correction. Adding error correction code to an archive will increase its size, but its availability allows the engine to reconstruct data damaged as the result of bad media or transfer errors during the decode phase. You can vary the amount of error correction code applied to an archive during the encode phase. The more error correction you add, the larger the archive will become. But more error correction also adds the ability to repair larger disasters. It is, of course, possible to have large enough damage that even error correction will not be able to save the entire contents of the archive. The range of values supported are as follows:
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1/128 of a block (1% Overhead)
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1/64 of a block (3% Overhead)
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1/32 of a block (6% Overhead)
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1/16 of a block (14% Overhead)
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1/8 of a block (33% Overhead)
Optimizers
Optimizers are special compression methods designed to handle specific file types. StuffIt Deluxe includes optimizers designed to compress Wave sound files, Tiff graphics, and text files. Block Mode
The Block Mode setting determines whether StuffIt will group files together in order to compress them more efficiently. Expert Compression Settings for StuffIt (.sit) archives
When creating StuffIt (.sit) archives you can choose between the following compression methods: ÒFastestÓ, ÒBestÓ and ÒChoose Method by AnalysisÓ. The latter choice breaks the file being compressed into bite size pieces and compresses each piece using whichever method produces the smallest output for that chunk of data. This makes it very slow but it generally produces the smallest possible files. You can also choose to use "No compression" when creating archives.
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