In Section $4\mathrm{.}2\mathrm{.}2,$ we describe lossless compression schemes, such as run$-$length encoding and variable$-$length codes. However, most compression schemes in use today are lossy and only achieve extremely high rates of compression at the expense of losing some

of the detail contained in the sound or image. Often they base their compression techniques on specific knowledge of the characteristics of the human ear or eye. For example, it is well known that the eye is much more sensitive

to changes in brightness $($luminance$)$ than to changes in color $($chrominance$).$ The JPEG compression algorithm exploits this fact when it is compressing a photographic image.

Read about the JPEG image compression algorithm to learn how it is able to achieve compression ratios of $10$:$1$ or even $20$:$1.$ A good place to start would be the JPEG home page, located at www$.$jpeg.org.