Lossy Image Compression
The topic of image compression is a
very involved and decribes a wide range of methods.
Our goal here is to provide a sufficient background
for understanding the most common compression
techniques used. In particular those used on the WWW.
There are generally two types of images that
are widely used on the WWW, gifs and jpegs. As you are
probably aware, each method has its own strengths and
weaknesses. Both methods also use some form of image
compression.
Some of the highlights of these compression methods
are summarized in the table shown on the right.
|
|
GIF |
JPEG |
| Colors |
256 |
224 |
| Compression |
Dictionary-based
(LZW) |
Transform Based |
| Processing Order |
Quantize, Compress |
Transform, Quantize |
| Primary Use |
Graphics, Line Art |
Photos |
| Special Features |
Transparency, Interleaving |
Progressive |
|
