The process of reducing the overall number of bits in a file so that it can be transmitted faster and occupy minimal disk space.
What is file compression?
File compression is the process of reducing the overall number of bits in a file so that it can be transmitted faster and occupy minimal disk space.
Once the file is downloaded to the computer, it is expanded back to its original size using expansion programs like WinZip or Stuffit.
How It Works
The basic principles and systems used in file compression are as follows:
- Redundant information in files is listed only once; when the same information appears when the file is expanded, the program refers back to this list.
- An algorithm called LZ (refers to Lempel and Ziv) Adaptive Dictionary-Based Algorithm is utilized by most compression programs. Dictionary is the method of cataloging bits of information. There are different systems in arranging dictionaries. One example of this system is using a numbered list.
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Numbers are used to the represent a word. To reconstruct the original file, the expansion programs refer back to the number pattern in the dictionary.
File reduction is not maximized using this system especially in smaller files.
- Compression programs identify patterns and do not pick out repeated words in particular. To reduce the file size, compression programs selects patterns to include in the dictionary. If there is a repeated pattern of a certain letter or character in a sentence, it will be included in the dictionary; but if the pattern is isolated and does not reoccur in subsequent sentences, the program will overwrite it.
- Programs can rewrite the dictionary according to the “adaptive” part of the dictionary-based algorithm.
- The size of text files are reduced optimally because of its high rates of data redundancy unlike files that include non-text data for they don’t repeat much patterns.
Thus, the extent of file reduction depends on a number of factors including file types, file size and the compressions systems being utilized.
The systems described above falls under the category of lossless compression. As explained, these systems break the file into smaller form, recreating it for ease in transmission and storage. The file is then restored to its original size and form using an expansion program.
Lossy compression as its name implies, eliminate bits of information that are considered unnecessary in order to minimize the file size. This is commonly used in compressing bitmap images which are usually bulky.