Law of proximity
Multiple elements, interpreted as shapes.
It is easier for us to recognize elements if they are in close proximity. They are interpreted as a whole shape.
For example, the dots in this image are perceived as a row of dots, not just as individual dots.
Because of this interpretation in our minds, we are able to recognize rasterized, printed images as such.
This principle is also used in embossed printing. The letters of this so-called "braille" are extruded through the back of the sheet, and can be read with the finger.