Compression technology is a continuing field of research. As better mechanisms are developed, more information can be carried in fewer and fewer bits. Plus, as processing power increases, these techniques can be implemented on ever faster, ever cheaper processors. So, compression is constantly being used in more and more applications. In this section, we'll look at the reasons for using compression, and the benefits and drawbacks of using it.

Figure 4-1 shows a simplified block diagram of a compression system. The input can either be a computer file, such as a document, an image, and/or a video/audio recording. Or, the input can be a continuous stream of data, such as a digital video or audio signal. Either way, this information is fed into the compression engine. The output of the compression engine is a second data file or data stream that is smaller (i.e., contains fewer bits) than the input file or stream. This output can be stored, or it can be transmitted over a network. Before the data file can be used, it must be restored to its original size, using a decompression engine. Note that a compression engine is often implemented in a device commonly called an encoder, and the device housing the decompression engine is commonly called a decoder.

Figure 4-1: Simplified Compression Block Diagram

The goal of compression is to reduce the size of the incoming data file without removing useful information. In most real-world data files, some data patterns will repeat. For example,...