Re: RLE for DC/AC-coefficients separately for the blocks or at whole?

> I think that coding for DC/AC-coefficients for blocks separately gives lesser RLE-compression ratio.
> It is right?

Whether or not it's "right", the format does not give you the option. 
The token system defined in the specification has two ways of exploiting 
runs: runs of zeros _within_ a single block, and runs of EOB tokens 
_across_ multiple blocks. You can't code runs of zeros which span 
blocks, except through EOB tokens.