Data and Image Compression

Compression is a way of encoding digital data so it takes up less storage space and requires less network bandwidth to be transmitted. There are two basic types of compression: lossy methods, in which some data is lost when the files are decompressed, and lossless methods, in which no data is lost when the files are restored to their original format.

By Lee Copeland

August 21, 2000 12:00 PM ET

Recommended

Computerworld - As long as bandwidth is expensive and people are impatient, data compression is here to stay. Simply put, compression methods crunch data - text, graphics, audio or video - into a computer-decipherable shorthand that's 10% to 99% of its original size. The data takes up less storage space and requires less bandwidth to be transmitted over the Internet. In addition, many methods can squeeze multiple files into a single file called an archive.

There are two basic methods for compressing data: lossy and lossless. Lossless techniques compress data without destroying or losing anything during the process. When the original document is decompressed, it's bit-for-bit identical to the original. Lossy techniques let the file be compressed even smaller, but some data is lost forever.

			Compression Standards Joint Photographic Experts Group (JPEG): A still-image, lossy compression method that uses discrete cosine transform equations to compress images at a ratio of up to 20-to-1, without noticeable loss. Lempel-Ziv-Welch: This algorithm, used in many compression formats, including graphics interchange format and Tag Image File Format, takes each input sequence of bits of a given length and creates an entry in a lookup table, along with a shorter code. Lookup entries are part of the compressed file, enabling the decoding program to rebuild the table. Moving Pictures Experts Group (MPEG): A lossy compression method for video. MPEG-1 is used for CD-ROMs and video CDs. MPEG-2 compresses video for regular and high-definition television. MPEG Audio Layer 3 (MP3): An audio compression technology that's part of MPEG-1 that uses perceptual audio coding to compress CD-quality audio by a factor of 12. Fractal: A lossy compression method for color images that's well suited for natural objects, with compression ratios up to 100-to-1. PKZip: A popular lossless compression shareware program from PKWare Inc. The program uses an algorithm and a data library to encode or archive multiple date files. PKUnzip decompresses the files to their original states. Wavelet: This form of lossy compression uses a mathematical function that can compress images to a greater extent than other methods - sometimes to only one-fourth the size of a similar image compressed with JPEG. Windows Media Technology: This Microsoft Corp. product delivers better sound quality than MP3 for same-size files, as well as near-DVD-quality video. - Lee Copeland and Russell Kay

"Lossy compression makes a trade-off: You give up accuracy for higher compression," says Steve Hoffenberg, director of product management at Sound Vision Inc., a digital imaging firm in Framingham, Mass. "If you're compressing bank records, you want to be sure they're identical before and after. But with an image or audio or video files, it's generally not crucial to restore every bit of data."

Recommend Digg Twitter ShareThis

Email Print Send Feedback Reprints

Jump to comments

Operating Systems

Additional Resources

WHITE PAPER

Do You Know the 7 Steps to Successful Data Migration?

Approximately 60 percent of data migration projects overrun time or budget, while some fail completely. Download this white paper, "Enhancing Your Chance for Successful Data Migration," to learn the critical steps you need to take to execute a data migration project with minimum cost and risk to your business.

WHITE PAPER

Total Cost of Ownership of Server Computing Vs. PCs

Read the Gartner research note to learn why the TCO of a server-based computing deployment used to deliver all applications to users is around 50% lower than that of an unmanaged desktop deployment.

WHITE PAPER

IDC White Paper: Linux in a Global Recession

Economic downturns have a tendency to accelerate emerging technologies, boost the adoption of effective solutions, and punish solutions that are not cost competitive or that are out of synch with industry trends. This IDC White Paper presents the results of an IDC survey of 330 companies in Western Europe, Asia/Pacific and the Americas that measures the receptiveness to Linux and takes into consideration changing views driven by the disruptive economic environment that businesses face today.