Photoshop :: Image As Dots In One Color

I want to make this effect on a photo. Its abit difficult to explain, but I'll try:

The image only contains one color, say black or red, and is put together by dots in different sizes and with different space between them, not sure, might just me different space between them. In the dark areas they are close to each other and in lighter areas they have a greater distance between each other.

I also wonder how to make the same kinda dot effect, but not with only one color. like magazies and newspaper use when they print photos. Im not reffering to the halftone filters. I tried to define a dot pattern, and delete the inverted pattern in the image, but im not satisfied with the results...