Compression for CDs and DVDs

Written by Donald R.J. White
March 28, 2008

Warning: This article is fairly technical. If you're not looking to understand compression algorithms, then the following will probably hurt your brain!

As mentioned twice above, the real CD and DVD compression advantages are nearly all reserved for images. This is readily understood when looking at a typical photograph. If an outdoor landscape, note the blue sky may take up 20% of the photo. Why waste all the hundreds of thousands of pixels when a few bytes will describe the sky color and then its location, height and width take up a small amount more. Only when the neighboring pixels are exhibiting a change does that information need to be preserved. Thus depending upon the simplicity or complexity, video compression techniques may provide for lossy compressions from 5:1 to 200:1 with 50 being a typical order of magnitude.

The most ubiquitous compression program is that used by Adobe's PDF files. They give away free the Adobe pdf decompression algorithm reader, and charge the sender or manufacturer for their compression program. Typical storage compression a standard laptop or CD or memory stick back up range from 15:1 to 200:1 with a medium of about 50:1 with plain text occupying less than 20% of the stills.

Motion Picture compression methods enjoy some of the same frame-to-frame methods as for stills. However, recognize that the frame rate may be about 25 frames/sec to overcome the persistence of vision. This chews up loads of memory if additional compression techniques were not used. If the scene is changing slowly, enormous additional compression is done by sending only the delta or frame-to-frame changes which may take up little memory. If the event is a sports event in which large images are changing rapidly, then the delta compression may not be useful.