Need for data compression

Multimedia data (audio, image, video) is very large, while storage capacity and network bandwidth are limited. Data compression reduces the number of bits needed, so such data can be stored and sent practically.

Reasons

1. Large data volume. Uncompressed CD-quality stereo audio needs 44,100 x 16 x 2 = 1.41 Mbps. A 1024 x 768 true colour image is 1024 x 768 x 3 bytes = 2.36 MB. Uncompressed video at 640 x 480, 24 bit, 25 fps needs about 184 Mbps (23 MB/s).
2. Limited storage. A CD (about 700 MB) would hold only about half a minute of such video without compression.
3. Limited bandwidth. A typical home connection or mobile network cannot carry raw video in real time.
4. Faster transmission and lower cost. Smaller files download and upload faster and use less data.
5. Real-time delivery. Video conferencing, streaming and broadcasting need data rates that fit the channel.
6. Efficient use of devices. Mobile phones and cameras can store more photos and videos.

Why it works: media contains redundancy (neighbouring pixels are alike, successive video frames are similar) and irrelevance (details humans cannot see or hear). Compression removes both.