Figure 3 shows the effect surrounding color or intensity has on perception. Note the relative brightness of the smaller gray squares in the center of the black and white squares. The small square surrounded by black seems brighter and closer than when it is surrounded by white, but both gray squares are in the same place and are the same color. It's all a part of how you make sense of the world around you. The visual surroundings of an object give you valuable clues about its size and distance from you.
Lines can show perspective, which is an indicator of distance.
The brightness of an object is another attribute the brain takes into account when determining the nearness of an object. We perceive dimmer objects to be farther away than bright ones. Night perils Pilots have recognized since the early days of aviation that flying at night is more dangerous than flying in the daylight. The low level of light means that the rod cells in the retina of the eye are going to be doing most of the work since they are more sensitive to very weak light energy. Unfortunately, the rods permit seeing only black, white, and grays.