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Lossy vs. Lossless compression
Some compression methods (typically multimedia formats such as JPEG and MP3) discard information (loss) to achieve smaller file sizes. This type of compression can’t be reversed and the resulting file will never match the original. There is a trade-off in the relationship of file size to quality degradation. Lossy compression is not used in applications where complete restoration of the original file is necessary (such as your financial records!). StuffIt uses Lossless compression.
What is recompression?
StuffIt 12 includes a new feature for making files even smaller. Like the JPEG compression we introduced in 2005, these recompressors make files smaller by 'disassembling' the structure of the data type and compressing it more efficienly 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 reassembled.
Generally this results in output that is identical to the original, but in some instances the output may not be 100% identical. The content itself, and any ancillary data is never lost - just the bit encoding changes sometimes.
A good example is Zip recompression. There are many compression attributes that can be used to create a Zip archive. When recompressing a Zip into a SITx archive, the Zip is opened and its content is compressed into the SITx archive. Upon expansion, the Zip archive is recreated. The recreated Zip archive and the original Zip archive may have different compression attributes and are therefore not identical, but if each of the Zips is expanded the resulting output will be identical. This example also applies to image formats that contain compressed information as part of the structure. This is commonly referred to as "pixel-perfect". Identical output is commonly referred to as "bit-perfect".
StuffIt 12 includes custom recompressors for these file formats:
- JPEG (.jpg, .jpeg) - Always bit-perfect
- JPEG lossless (.jls) - pixel-perfect
- JPEG 2000 (.j2k) - pixel-perfect
Note - recompression is only applied when a j2k file is lossless encoded
- Bitmap (.bmp) - Always bit-perfect
- GIF (.gif) - pixel-perfect
- TIFF (.tif, .tiff) - depends on data
- PSD (.psd) - depends on data
- PNG (.png) - pixel-perfect
- PICT (.pict, .pct) - pixel-perfect
- PXM (.pbm, .pgm, .ppm) - Always bit-perfect
- MP3 (.mp3) - Always bit-perfect
- Zip (.zip, .cbz) - pixel-perfect
- PDF (.pdf) - depends on data
Why compress?
Compression makes files smaller so they take up less storage space and can be transferred faster from machine to machine. Combined with archiving, it becomes a useful way to organize files and projects.
Compressing vs. Archiving
Compression is typically applied to a single file. Compressed Formats contain only one item. Gzip, BZip2, UNIX Compress, and SpaceSaver are examples of Compressed Formats.
Archiving allows a hierarchy of files and folders to be grouped together for compression. Archive Formats can contain one, or many items, and preserve the hierarchy of nested folders. Most archive formats include compression as part of the archiving process. The UNIX Tape Archive (tar) format does not and it typically post-compressed with Gzip, BZip2, UNIX Compress. Compressed TAR archives are often referred to as "tarballs". StuffIt (.sit), StuffIt X (.sitx), Zip, TAR, and LHa are examples of Archive Formats.
What is Expansion vs. Extraction? What is Browsing?
Archives can be accessed in two modes. In Expansion mode, the entire contents of an archive are expanded out at once. In Browse mode, the archive is accessed like a folder. The hierarchical structure can be navigated and individual files can be extracted without having to expand the entire contents of the archive. In some cases, archive content can be manipulated: items can be renamed, moved, deleted, added, etc..
What is Encryption?
Similar to compression, encryption is the process of obfuscating a file using various schemes for security purposes. Access to the file (ie: decoding the encrypted data) requires the correct "key" or passphrase. The more complex the encoding key, the more difficult it is to "break". RC4 uses a 512-bit method, Blowfish uses a 448-bit method, AES uses a 256-bit method and DES uses a 64-bit method. StuffIt X allows you to choose any of the above encryption schemes.
What is Encoding?
Encoding is the process of converting files to allow them to be transferred intact from one platform via another platform. For example, pre-OS X Macintosh files typically have two parts: a resource fork and a data fork. Since no other platform use this dual-fork format, older Macintosh files need to be encoded to preserve the resource forks before being transferred to a non-Mac. Typically this is done with MacBinary (.bin) encoding.
Files transferred as email attachments across the Internet must pass through gateways to get to their final destination. Up until a few years ago, nearly all gateways only supported 7-bit files. Meaning, if you sent an 8-bit file through the 7-bit email gateway, the resulting file would become damaged. File encoding was created to convert these 8-bit files into 7-bit files so they would be transferred intact. Files that are represented with an 8-bit character set (ie: binary files) sometimes still need to be converted to a 7-bit character set (ie: text files) to be attached to emails or posted to UseNet news groups. Typically this is done with BinHex for older Mac files and UUencoding for non-Mac specific files.
Note: Encoding does not compress a file. Often it actually makes a given file larger!
Like the older StuffIt 5 format, the StuffIt X format is a single-part file (ie: no critical data is stored in the resource fork) and as a result MacBinary encoding is not necessary. If the resource fork of a StuffIt 5 or StuffIt X archive is stripped off, the data contained in the archive will still be completely intact.
StuffIt X includes text encoding options within its own format to allow for text encoding at the time of compression without post-processing.
What are the different methods of encoding?
Below are the most common forms of file encoding:
UU encoding takes only the 8-bit data fork and converts it into a 7-bit file. This format is normally used for Windows files because it only recognizes the file's data fork. It can be used for Mac files that do not store crucial information in their resource fork (i.e., '.jpg' files, text files without formatting), however most Mac files store crucial information in the resource fork, such as applications, some word processing documents, and control panels. This method of encoding typically produces the largest file of any of these encoding methods. Files that have been UU-encoded typically have a '.uu' extension in the name.
MIME (Multipurpose Internet Mail Extensions) is not a method of encoding, but rather a map. It maps a particular method of encoding to an application that can decode that file. You may be most familiar with this as your Netscape Navigator or Internet Explorer helper applications. If you choose to change or add a helper application, you must specify the MIME type. As part of the encoded file, the MIME type maps to, or uses, a particular application to decode, or read, a file. For example, Expander is the typical application mapped to decode files whose MIME type is application/mac-binhex40. Microsoft Word is the application that is mapped to decode, or read, files whose MIME type is application/msword.
Base64 encoding takes an 8-bit file and converts it into a 7-bit file. You can use this format to transfer files through any method.
BinHex encoding takes the 8-bit resource and data forks of a Macintosh file and converts them into a single 7-bit file. This is useful for transferring files in any method, including via email. Files that have been BinHex encoded typically have an '.hqx' extension in the name.
MacBinary encoding takes the 8-bit resource and data forks of a Macintosh file and converts them into a single 8-bit file. This method should normally be used for transferring files to and from Macintosh computers. Files that have been MacBinary-encoded typically have a '.bin' extension in the name, although not all files with .bin extensions are MacBinary encoded files.
AppleSingle encoding, like MacBinary, takes the 8-bit resource and data forks of a Macintosh file and converts them into a single 8-bit file.
AppleDouble encoding takes the 8-bit resource and data forks of a Macintosh file and converts them into a single 8-bit file, then uses Base64 encoding to convert that file to a 7-bit file.
StuffIt products support these encoding formats, and more. For a complete list of file formats supported by StuffIt products, see the File Formats page.
What is the best archive solution for sharing files?
Exchanging files with Windows, Macintosh and Unix-based computer users is simple with StuffIt. StuffIt products are designed to provide easy solutions for your communication needs. These compression utilities provide a complete solution: compression, decompression, encoding and decoding of all popular file formats found online.
Here's a summary of format options:
StuffIt - The older StuffIt 5 (.sit) format is a legacy format. It has been replaced with the StuffIt X (.sitx) format, a modern archive format, designed from the ground up to be extendable, support Mac OS X, Windows, and UNIX/Linux file permissions, long file names, and very large data sets. Optimized compressors give it the edge for getting files as small as possible. It is a truly cross-platform format with full support for native file properties and free Expander utilities are available for most platforms.
Zip - A venerable format, common on Windows and now more common on OS X, that has been extended if various ways to support features such as encryption, or large numbers of files (Zip64). These extended Zip features are not supported by many Zip utilities including the Zip tool integrated with Windows and Apple's integrated ArchiveHelper.
Tarballs - Common on UNIX/Linux-based machines. They are usually created by first "tarring" a selection of files, then post-compressing with ".gz", ".bz2", or ".Z". Stuffit can create tarballs in one step. StuffIt can also browse the content of tarballs.
Self-Extracting Archives - Self-extracting archives provide Windows or Mac users convenient file expansion without requiring a decompression utility. All the recipients do is double-click to expand the file. These SEAs can also be configured to present the user with dialogs, graphics, and can install files to particular locations on the user's machine. You can create "self-extracting" archives using StuffIt Deluxe's SEA Builder on Windows, or SEA Maker on the Mac.
Only the StuffIt product line creates and expands the formats of choice for all popular platforms. StuffIt products are available for Macintosh, Windows, Windows Mobile Edition, Linux and Solaris.
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