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Recompression and How to create StuffIt X Archives with DropStuff

Format Settings

StuffIt X Archives

The following options effect how DropStuff creates StuffIt X archives.
  • Compression Level: This control allows you to set the compression level used when DropStuff is creating StuffIt X archives. You can choose "Better Compression", "Faster Compression" or "No Compression"; as the names suggest the faster compression method makes archives more quickly, the Better compression method creates smaller archives and the No Compression option groups files together into an archive without compression. An additional choice, "Custom" is also available. When Custom is selected you can use the StuffIt X Expert Compression Settings dialog to configure how DropStuff will compress your files. This section offers a comprehensive explanation of the settings contained in the Expert Settings dialog.
  • Segment Size: This option is used to break the StuffIt X archive you create into smaller pieces to fit them on CD's, DVD's, or other removable media.
  • Encrypt Archives with a Passphrase: When this option is checked, the archives you create will be encrypted with a passphrase. You will be prompted to provide a passphrase before the compression begins. When you create an archive with encryption, be sure to make a careful note of your passphrase.

    Important! Smith Micro cannot recover files from encrypted archives if you have lost your passphrase. Also note that passphrases are case-sensitive.
  • Create Searchable Index Archive: When this option is checked a tiny StuffIt Index Archive that is paired with the StuffIt X archive you create will be stored locally.
    Click here to read more about StuffIt Index Archives
  • Create Backwards Compatible Archives: When this option is checked StuffIt X Archives will be created using only compression methods compatible with version 7.0 of StuffIt Expander for Macintosh.
Recompression
StuffIt includes a patented method for making files even smaller called Recompression. Like our JPEG compression, introduced in 2005, Recompression make files smaller by 'disassembling' the structure of the data type and compressing it more efficiently using the StuffIt X format's own compressors. When the item is expanded from the StuffIt X archive, the structure for that particular data type is recreated and the original content restored.

A good example to illustrate this concept is PDF recompression. Internally, a PDF may have embedded text, images, and other multimedia content. With PDF recompression, when adding a PDF file to a StuffIt X archive, the PDF is treated as a container. It is opened and its content is extracted and recompressed into the StuffIt X archive taking advantage of StuffIt's superior compression methods. Upon expansion, a PDF archive is created and the elements from the original PDF are added to it.

This recompression concept also applies to other formats like JPEG, PNG, MP3 and others, that contain compressed information as part of the structure. When preparing to compress your files, the StuffIt pre-sorts the files into types and then based on your settings passes the matching files to special Recompressors. If there isn't a matching Recompressor, or if the matching Recompressor is disabled, use a General compressor.

Bit-perfect vs. Pixel-perfect
StuffIt's Recompressors will always result in output that is a "pixel-perfect" perfect copy of the original source file. There will never be any quality reduction comparing the output to the source material. In some cases you may find that while the output file is "pixel-perfect" it may not be "bit-perfect", meaning that the output file may be slightly larger or smaller than your source file. The content itself is identical, and any ancillary data is never lost - just the bit encoding may sometimes differ.

In the example above, the recreated PDF archive and the original PDF archive will have identical contents, but the order of the contents within the internal structure of the expanded PDF may differ from the original. For most uses, the recreated PDF can be considered identical, but if check-summed, the two files may or may not match. This is commonly referred to as "pixel-perfect". In many cases, the content AND the structure will both be identical. This is commonly referred to as "bit-perfect".

Some formats, such as JPEG, have little variance in the compression used, allowing for a bit-perfect reproduction every time. For other formats, bit-perfectness depends on the data from the original file.

StuffIt X includes custom Recompressors for these file formats:

Bit-perfect

  • JPEG (.jpg, .jpeg)
  • Note: The JPEG compressor has an additional option: Include Thumbnails. When this option is enabled, a small thumbnail of the image is stored in the archive for quick previewing.
  • Bitmap (.bmp)
  • MP3 (.mp3)
  • WAV (.wav)

Pixel-perfect

  • JPEG lossless (.jls)
  • JPEG 2000 (.j2k)
    Note - recompression is only applied when a j2k file is lossless encoded
  • GIF (.gif)
  • TIFF (.tif, .tiff)
  • Note - Some are recompressed bit-perfectly, depending on how they were originally saved.
  • PSD (.psd)
  • Note - Some are recompressed bit-perfectly, depending on how they were originally saved.
  • PNG (.png)
  • PICT (.pict, .pct)
  • PxM (.pbm, .pgm, .ppm)
  • Note - Some are recompressed bit-perfectly, depending on how they were originally saved.
  • Zip (.zip, .cbz, .docx, .xlsx, .pptx, .odt, .odg, .ods, .odb)
  • PDF (.pdf)

Check each type for which you wish to enable recompression.


Zip Archives

The following options effect how DropStuff creates Zip archives.
  • Compression Level: This control allows you to set the compression level used when DropStuff is creating Zip archives. You can choose "Better Compression", "Faster Compression" or "No Compression"; as the names suggest the faster compression method makes archives quickly, the Better compression method creates smaller archives, and the No Compression option just gathers the files together into a single archive file without compressing them. An additional choice, Custom is also available. When Custom is selected you can use the Zip Expert Compression Settings dialog to determine how DropStuff will compress your files.
  • Encrypt Archives with a Passphrase: When this option is checked, the archives you create will be encrypted with a passphrase. You will be prompted to provide a passphrase before the compression begins. When you create an archive with encryption, be sure to make a careful note of your passphrase. Important! Smith Micro cannot recover files from encrypted archives if you have lost your passphrase. Also note that passphrases are case-sensitive.
  • Preserve Macintosh Content: This option determines whether or not Macintosh specific file attributes (such as a resource fork and Finder information) is preserved when adding files to Zip archives. Typically, if you are sending files to a Windows user you do not need to preserve this information, as it will not be used on a Windows-based computer. If you are sending files to a Macintosh user, we would recommend that you preserve Macintosh file information by sending your files in an archive format designed for the Macintosh, such as StuffIt X.

    Note: If you do need to send Macintosh files to other Macintosh users in Zip format, checking this option will preserve Macintosh file information in a way that is compatible with Apple's Zip implementation used in the Finder in Mac OS X 10.3 and later, but other options such as encryption may not be compatible with Apple's Zip implementation. Also note that Zip archives using Apple's method of preserving resource forks are not compatible with pre-9.x versions of StuffIt Expander for Macintosh.


Tar Archives

The following options effect how DropStuff creates Tar archives
  • Compression Method: By default, Tar archives are created without any form of compression. When you use DropStuff to create Tar archives you can specify that Tar archives be compressed after they have been created. You can choose to compress Tar archives using gzip (.gz), bzip2 (.bz2), and UNIX Compress (.Z).
  • Compression Level: This control allows you to set the compression level used when DropStuff is compressing Tar archives. You can choose either "Better Compression" or "Faster Compression". An additional choice, Custom, is also available. When Custom is selected you can use the Tar Expert Compression Settings dialog to determine how DropStuff will compress your files.
  • Preserve Macintosh Content: This option determines whether or not Macintosh-specific file attributes (such as resource forks and Finder information) is preserved when adding files to Tar archives. Typically, if you are sending files to a non-Macintosh user you do not have to preserve this information, as it cannot be used on a non-Macintosh based computer. If you are sending files to a Macintosh user, we would recommend that you preserve Macintosh file information by sending your files in an archive format designed for the Macintosh, such as StuffIt X.

    Note: Tar archives using the AppleDouble encoding method of preserving resource forks are not compatible with pre-9.x versions of StuffIt Expander for Macintosh.

See also Expert Compression Settings.