Data Compression IV: Irreversible Compression Techniques
Irreversible Compression is based on the assumption that some information can be sacrificed. [Irreversible compression is also called Entropy Reduction].
Example: Shrinking a raster image from 400-by-400 pixels to 100-by-100 pixels. The new image contains 1 pixel for every 16 pixels in the original image.
There is usually no way to determine what the original pixels were from the one new pixel.
In data files, irreversible compression is seldom used. However, it is used in image and speech processing.