Shape, Value and Edge
If you stop to think about it for a minute, you will realize that when you look at anything, three parts are involved: shape, value, and edges. You will probably recognize the shape at once. Is it a pear, a box, or a silo (or, whatever)? The value is the color you would see if the image were reproduced in black and white. Is it inky black or almost white, or somewhere in between?
When looking at something nearby, you are probably aware of the sharp edge that exists between one shape and another. When looking at something far away, the edge between two shapes is less distinct.
In landscape paintings, what matters to the viewer is whether the distant mountains seem to be far away, and the objects in the foreground seem close. To the artist, it’s a matter of shape, value, and edge.