Saturday, March 22, 2008

Tech Tip: Compression for CDs and DVDs Part 2: Data

Written by Donald R.J. White

There are different compression techniques that can be used for compressing plain text languages such as English, latin-based, Slovak and the like. Two examples are (1) RLE for Run length encoding and (2) LZ encoding to cover entropy encoding and Lamped-Ziv compression. While impressive compressions are available for video, as described in the next section, the best that can be expected for plain text is about 3:1.

Thus, a strong argument can be used for not bothering to compress alphanumerics at all, especially if there is embedded video such as graphics, sketches, drawings, and photos. For example, assume a report has 80 % plain text and 20% graphics.

Read more at http://www.datadisc.com/

Friday, March 7, 2008

Tech Tip: Compression for CDs and DVDs Part 1: Music

Written by Donald R.J. White

One Byte = 8 bits = 28, or 256 options or quanta levels. CDs can store 670 MB of information and DVDs (single sided) store 4.7GB. DVDs store 4700MB/670MB = seven times more capacity. For example, 50 CDs of music can be stored on seven DVDs. Compression tools can compress disk space from about three to 200 times, depending on the stored information (i.e. text, music, video, etc). Music compresses from 1.2x to 3:1 times (MP3 format for 10:1 times), and text compresses only about three times. But, video can compress enormously, depending upon if is (1) stills, like a picture gallery or a power point presentation, or (2) movies which compress the best (roughly 100 times). The amount of compression of video depends upon the acceptability level (quality control) of lossy compression techniques.

Read more at http://www.datadisc.com