Lossy and lossless compression pdf

In information technology, lossy lossy and lossless compression pdf or irreversible compression is the class of data encoding methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data size for storage, handling, and transmitting content.

Different versions of the photo of the cat above show how higher degrees of approximation create coarser images as more details are removed. The amount of data reduction possible using lossy compression is much higher than through lossless techniques. Well-designed lossy compression technology often reduces file sizes significantly before degradation is noticed by the end-user. By contrast, lossless compression is typically required for text and data files, such as bank records and text articles.

10 kilobyte lossy copy can be made for a small image on a web page. It is possible to compress many types of digital data in a way that reduces the size of a computer file needed to store it, or the bandwidth needed to transmit it, with no loss of the full information contained in the original file.

A picture, for example, is converted to a digital file by considering it to be an array of dots and specifying the color and brightness of each dot. The original data contains a certain amount of information, and there is a lower limit to the size of file that can carry all the information. Basic information theory says that there is an absolute limit in reducing the size of this data. When data is compressed, its entropy increases, and it cannot increase indefinitely.

As an intuitive example, most people know that a compressed ZIP file is smaller than the original file, but repeatedly compressing the same file will not reduce the size to nothing. Most compression algorithms can recognize when further compression would be pointless and would in fact increase the size of the data. In many cases, files or data streams contain more information than is needed for a particular purpose. Developing lossy compression techniques as closely matched to human perception as possible is a complex task.

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