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.