Encoding data to take up less storage space and less bandwidth for transmission. Digital data are compressed by finding repeatable patterns of binary 0s and 1s. The more patterns can be found, the more the data can be compressed. Text can typically be compressed to approximately 40% of its original size, and graphics files from 20% to 90%. Some files compress very little. It depends entirely on the type of file and compression algorithm used. See archive and archive formats.
Compression Sparked a Revolution
Data compression is an important part of the digital world. For example, MPEG compression allowed a two-hour movie to fit on a DVD disc. Compression enables voice and video calls over the Internet. MP3 compression sparked a revolution by enabling people to download a song from the Internet 10 times faster than the original CD format. See codec.
Dictionary and Statistical Methods
Two major ways to compress data are the dictionary and statistical methods. The widely used dictionary method creates a list of repeatable phrases. For example, GIF images and ZIP and JAR archives are compressed with this method (see LZW). The statistical method converts characters into variable length strings of bits based on frequency of use (see Huffman coding).
Lossless Vs. Lossy
When text and financial data are compressed, they must be decompressed back to a perfect original, bit for bit. This is known as "lossless compression." However, audio and video can be compressed down to as little as 5% of its original size using "lossy compression." Some of the data are actually lost, but the loss is not noticeable to the human ear and eye. See lossless compression, codec examples and capacity optimization.
