What is the advantage of having 8x8 DCT in jpeg instead of 4x4 or 16x16 ?

[amith]

HI All,
what is the advantage of having 8x8 DCT in jpeg instead of 4x4 or 16x16
other than computaion expensive .

 

[mmelek1]

JPEG -DCT

With DCT you convert the 8*8 block into very few values to store, may be less than 10 values (instead of 64)
I believe that 4*4 is too small, you won't achieve good compression.
16*16 would probably cause the resulting image to not sharp or smooth enough (bad reconstruction).