Data compression tutorial – codingpoint

Introduction of Data compression

In the last decade we have been witnessing a transformation—some call it a revolution—in the way we communicate, and the process is still under way. This transformation includes the ever-present, ever-growing Internet; the explosive development of mobile communications; and the ever-increasing importance of video communication. Data compression is one of the enabling technologies for each of these aspects of the multimedia revolution.

It would not be practical to put images, let alone audio and video, on websites if it were not for data compression algorithms. Cellular phones would not be able to provide communication with increasing clarity were it not for compression. The advent of digital TV would not be possible without compression.

Data compression, which for a long time was the domain of a relatively small group of engineers and scientists, is now ubiquitous. Make a long-distance call and you are using compression. Use your modem, or your fax machine, and you will benefit from compression. Listen to music on your mp3 player or watch a DVD and you are being entertained courtesy of compression.

So, what is data compression, and why do we need it? Most of you have heard of JPEG and MPEG, which are standards for representing images, video, and audio. Data compression algorithms are used in these standards to reduce the number of bits required to represent an image or a video sequence or music. In brief, data compression is the art or science of representing information in a compact form.

We create these compact representations by identifying and using structures that exist in the data. Data can be characters in a text file, numbers that are samples of speech or image waveforms, or sequences of numbers that are generated by other processes. The reason we need data compression is that more and more of the information that we generate and use is in digital form—in the form of numbers represented by bytes of data. And the number of bytes required to represent multimedia data can be huge.

For example, in order to digitally represent 1 second of video without compression (using the CCIR 601 format), we need more than 20 megabytes, or 160 megabits.

If we consider the number of seconds in a movie, we can easily see why we would need compression. To represent 2 minutes of uncompressed CD-quality music (44,100 samples per second, 16 bits per sample) requires more than 84 million bits. Downloading music from a website at these rates would take a long time

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