Check out this comic book style effect on the ESO images I uploaded. It is meant to mimic the tiny priinted circles you find in comic books and posters. It was made simply by duplicating layers in photoshop then using the colour halftone filter to darken the original layer. There are so many variables in this technique you can get it to look exactly how you want it to. I really like this technique of combining many splodges to form a bigger picture. It is sometimes reffered to as divisionism or pointillism as an impressionist movement practised by many painters in times past. It is still used in printing whereby varying densities of CMYK (Cyan, Magenta, Yellow and Key) dots are used.
