An example image would help, but are you looking for something like this?

http://www.evilmadscientist.com/2012/stipplegen-weighted-voronoi-stippling-and-tsp-paths-in-processing/

YES!
exactly (almost)

thank you very much for the example.

i would like the white area to have a random pattern as well, but lighter than the dark areas... of course. but that could be probably managed by adjusting the gradient of the original pixel image.

so a random dot pattern that still gives an image by changing the random dot sizes according to the halftone of the pixel image. as a plugin in illustrator

thanks for help

You could implement this in Scriptographer, but I doubt you'll be able to achieve the efficiency of the tools mentioned in the link provided above. Since javascript is single-threaded, you would not be able to compute the areas and centroid of each cell in parallel.

Some folks were looking into this a few years ago, but I don't think anyone ended up generating a Sg based script:
http://scriptographer.org/forum/wish-list/stippling-effect/