Tag: lossy compression file formats

Data compression: lossless and lossy


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Data compression: lossless and lossy

In computer science and telecommunications, the term data compression (data compression) will indicate the data processing techniques that allow the reduction of the quantity of bits necessary for the representation of the information in digital form. In practice, for example, data compression makes it possible to reduce the number of bits required for the transmission of a video transmission, allowing it to be viewed on the Internet even in the presence of a connection that is not fast enough.

losseless compression

For files, data compression allows you to reduce the size (number of bits) of the file – this is advantageous because it reduces the space occupied by the file on disk and allows you to transfer the file more quickly (for example, by email).

Compression techniques fall into two main categories:

lossless compression (lossless):

in this case it is possible to rebuild the file from the compressed without loss of information;

lossy compression (loss)

compression occurs to the detriment of information quality, for example, through loss of image definition or sound quality of an audio file; in this case it is not possible to rebuild the file from the compressed file before compression.

how mp3 workslosseless compression

The two techniques are used in different areas. As already mentioned, lossy compression is often applied to images, sounds and videos as it enables significant reductions to be made from the original data, at the price of an often negligible loss in quality. In addition, lossy techniques can be applied during data transmission (runtime), that is, it is not necessary to know all the data to be compressed to apply them: this is obviously an advantage in the transmission of transmissions over the Internet . Among the best known lossless algorithms, we mention jpeg for images and mp3 for audio and mpeg for videos.

In contrast, lossless compression is used when you want to compress text documents, programs, databases, circuit diagrams, etc. and in any case where the loss of the original data is not accepted. The lossless compression category includes .zip and .rar formats, often used to compress files and file folders.

Later we will discuss lossy compression techniques, talking about multimedia formats. Here, instead, we want to deepen the understanding of lossless compression.

Lossless compression algorithms

Lossless compression techniques (algorithms) can be divided into two main categories:

statistical compression;

replacement compression

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Statistical compression is based on the input study to be compressed. Statistical studies are carried out on the input format to obtain a good compression. For example, in a text file to compress, the relative frequency of each character is studied and then the shortest code is associated with the character present several times in the text; vice versa, characters present with low frequency are associated with a longer code. Codes like Huffman’s are part of this class, which we will discuss in the next lesson.

As for substitution compression, this is based on the idea of ​​replacing, in a file, all occurrences of repeated strings with pointers to previous copies of the same string. Compression is due to the fact that the length of a pointer is usually less than the length of the string being replaced. As a result, the higher the repetitions of string occurrences in the file to be compressed, the greater the degree of compression achieved.


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Files without compression, lossless and lossy formats

Files without compression, with compression but without loss and with compression and with loss … what does that mean?

There is currently a huge confusion in most people about audio formats and that is why we are going to give an explanation that is as simple and clear as possible so that most of the people who read can understand enough to be able to make decisions about it. .

We will not try to get into technicalities or knowledge What are for specialists or connoisseurs or programmers, such as those who developed the mp4gain, but rather we will talk about general concepts at the beginner level but that can allow a correct understanding of the matter.

So the first thing we must understand is that the quality of an audio file depends on the amount of details it contains and for it to contain many details, it takes up a lot of space on the hard disk.

We could say that there are three groups of audio file formats:

– audio formats that do not have compression such as WAV, AIFF, etc.

– formats that compress audio but do not have a loss of information. FLAC, MPEG-4 SSL, WAV PACK, etc.

– There are also the formats that the audio compresses but that do have a loss of information, for example MP3, Ogg, HERE, ETCÉTERA

Now let’s clarify what it means that some formats do have compression but do not have loss of information while others also have compression but do have loss of information.

The formats that are compressed but have no loss of information what they do is something very similar to zip the file. In other words, they simply compress.

The original information but they do not discard anything, therefore when unzipping the file the original file is obtained again that had all the details and therefore is of very high quality.

On the other hand there are files such as MP3 that are compressed but also to achieve greater compression what they do is that they get rid of some part of the information. For example, those frequencies that are not audible to the human ear also get rid of that information that is redundant and they also use the method called masking which part of the idea that a sound that is very loud and is very forward It will be able to mask other sounds and the human brain will not perceive those other sounds. Therefore, according to this theory, they can get rid of these sounds that have been masked and the file will sound more or less the same to the human ear.

This concept of sound masking was one of the great milestones that made MP3 become so popular because it could compress files a lot, at a time when disk space was not superfluous, and yet they sounded pretty good to that ear. era and those people.

Also the programs that made the normalization of the audio volume, achieved results that at that time sounded good, but at this time the listening ear as a has become much more demanding and sophisticated. And so we need much more modern normalizers with much more algorithms. more powerful like mp4gain.