Rasterise with squares (or other) instead of dots

[AlsoStarring]

Hi,
I've seen once this app that allowed you to rasterise any image you wanted with selected forms.
I'm not sure it is called rasterization in this case, but does the same effect: takes the average luminosity of a group of pixels and turns it in a square (or dot, or anything else) with the appropriate size.

I've seen it with letters, looks really nice

And I can't find the app any more....
Any Idea what this is???

Thanks
GB