I've been stumped on this techinque for several years in the absence of examples I'll try to describe

If a greyscael gradient was to be converted to a dot pattern
with, the size of the dots ( combining dots into "blobs") the size of the individual dot and their their frequency
corresponding to that greyscale.

how would one go about it?
I've been racking my brain over this one for years and haven't figured out how to acomplish the effect.
It was fairly common for many "hip" adverts in the years past although its not seen too much anymore I wold like to use it for several things

I'll try a manual version to show what I'm talking about
any pointers would be great as itis not in any of the tutorals.

thanks