is a free cross-platform file compression utility that provides an
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export job definition as script.
Lossy and lossless compression
What is file compression,
types of algorithms
File compression is the process of
creating a smaller output from a larger input, in order to sparing
storage space, or saving bandwidth to share the data, or reduce the
input to a suitable size for a media of distribution (CD, DVD, mail
attachment size limit...).
How lossy and lossless compression works
Data compression can be defined lossy
in terms of
reversibility of the compression process due loss (or preservation) of
original information in the process. The two types of algorithms have
different pros and cons, and different field of application.
Lossless compression definition, file archiving
statistical models to map the input to a smaller
output eliminating redundancy in the data.
In this way the output carry
exactly all the information featured by the input in less bytes, and
can be expanded when needed to a 1:1 copy of the original data
(restoring exactly the original content), which
is a fundamental property for storing some types of data - i.e. a
software, a database.
For this reason
lossless compression algorithms are used for data backup and for archive
used in general
purpose archive manager utilities, like 7Z, RAR,
and ZIP, where an
exact and reversible image
of the original data must be saved.
Some graphic file fomats (notably, PNG files and deflated TIFF) uses
lossless compression, which usually results in less compression but no
image quality degradation after multiple cycles of modification and
saving of the picture, making this kind of image format suitable as
intermediate save files for image editing tools.
|Lossless compression is fully invertible,
as 1:1 copy of original content input is stored in the smaller,
efficiently encoded output, so it is usually suitable for backup, file
archiving and other applications where any loss of information is not
Lossy compression definition, multimedia data
or less relevant information (not just redundant data) and removing it.
The loss of information / content is irreversible, and depending from
the nature of the algorithm, will likely happen each time the content
is modified and saved to a lossy file format - e.g. when editing a
lossy jpeg images, and saving it multiple times to intermediate work
In this way data
compression is improved but at the cost of making lossy compression a
non reversible process - as it comes at the cost of losing part of the
information - and making it a suitable choice only when it is not
intended, by design, to restore the original content again.
is consequently not suitable for general purpose file
(as in example losing a single byte of an executable file would make it
not working), but it works very well when loss of less relevant
information is acceptable, as for graphic and multimedia files
- in example for MP3
losing audio information below the audibility threshold, or losing not
visible details in JPEG
images, or both in compressed video formats such as MPEG (MPG, MP4...).
Most common lossy compression algorithms are consequently usually fine
tuned for the specific pattern of a multimedia data type.
loss is destructive for the ability of 1:1 reversal of
the algorithm (the information is permanently lost), but it is not
prejudicial for the ability of end users to receive meaningful
information - intelligible audio, clear picture or video.
Due the lossy nature of those compression schemes, however, usually
professional editing work is performed on non compressed data (i.e. WAV
audio, or TIFF images) or data compressed in a lossless way (i.e. FLAC
audio, or PNG images) every time it is feasible so saving the work in
progress multiple times does not result in losing bits of the
information each time, with progressive degradation of quality -
reserving use of lossy compression to final step for creating a
reasonably sized output to distribute for media consumption.
compression and lossy
definitions on Wikipedia.
> Archiving > What are lossy & lossless compression
Topics and search suggestions about how lossy compression and lossless
compression works, what are reversible and non reversible algorithms,
invertible file compressio / archiving and non-invertible destructive
multimedia compression, compare definitions and compressed file types:
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classification of compression algorithms,
loss of information,
file compression utility,
| what is
lossy / lossless differences,
non invertible algorithms,
how file compression works,
application of lossless compression,
and disadvantages of
lossy & lossless compression,
types of compression strategies,
what are invertible functions,
what is file compression,
file compression applications,
applications of lossy compression,
file compression software,
compression algorithm families,
classification of compression