As you can see the edges of the canvas are not written left white canvas. We focus on the main subject, usually it is placed in the center, and everything else we see peripheral vision. If the eye does not see the edges, it seems that the object is not limited in space. But if eye natykaetsya on the edge of the canvas - the illusion disappears. To leave the illusion of space the author left the field of the canvas is blank. By the way - remember the drawings on a white sheet - poyal always present...
Location of the painting