Value, which refers to the relative lightness or darkness of a color, is the second layer of composition. Works of art rendered in only black, white, and tones of gray rely especially on a skillful handling of value composition. Even pictures executed in full color are visualized as black-and-white photographs to assess value composition. Usually, line dominates over value, color, and texture in composition, but the power of value contrasts can sometimes mean value is the dominant layer.
You can use value to alter linear elements in a composition. For example, if your subject makes it necessary to run a line into a corner (which we've learned is not good compositional practice), value can correct this mistake. The border between two neighboring values is a line. By making those values similar, you make the line less important. If you want to emphasize a line, you instead exaggerate the value differences.
Value contrasts can affect apparent size relationships. If a gray square and a black square of the same size are placed on a white background, the black square will appear larger and more important. This is because the contrast between black and white is stronger than that between gray and white. Also thanks to contrast, a small dark object and a large light object seen together against a light background will appear to be in balance; conversely, a small light object can balance a large dark object on a dark background.
In a linear composition, areas of equal size can be uninteresting. But introducing a high contrast between two areas can create the appearance that one is of a different size, thus making the proportions seem more interesting. By the same token, compositional areas that are well balanced in terms of line can lose their balance when a strong value contrast is introduced too close to the edge or corner of the composition.
Thus, what is wrong with the linear aspects of a composition could actually be right when adjusted with value. And, what is right with line could actually be wrong if the value contrasts are out of balance.
When you wish to emphasize a particular area or object in a composition, create strong value contrast near it. You can also arrange the edges of values to guide the eye to the area of greatest importance. These kinds of devices can be used to guide the eye in a specific sequence. To make a point quickly, draw the viewer's attention to the most important thing first. Other areas of emphasis are then used to augment the first. If you want to begin by setting the mood and then reveal the main point, you draw the viewer's attention through a series of areas of interest that lead to the significant part.
Value can be used to alter linear compositional elements. In this example, the awkwardness of the line running to the corner is minimized by reducing the value contrast in that area (A). Another part of the line is emphasized by exaggerating the value contrast around it (B).
Value contrasts can affect apparent size relationships. Although it is the same size as the gray square, the black square appears larger and more important because it is in higher contrast with the white background.
Because of its greater contrast with the background, the small dark circle balances with the large light circle.
Although the proportions of its linear elements are good, this composition is out of balance because the value contrast at right is too strong.
In this example, although the upper two shapes are the same size (which would be undesirable if the composition were solely linear), the value contrast creates the illusion that they are different and thus makes the composition more interesting.
Artists use value to call attention to important details in a composition. Here the light column of smoke and the dark triangle of the trees draw our attention to the two small figures.
If it is desirable to set the a mood of a picture first and then reveal the meaning, you can create a series of areas of interest that lead to the significant part. Here the flowers are the first things we see, and they set the mood. Only after a moment or two do we see the romantic snakes.
By using just value and line you can direct the viewer's eye through a composition. If you want the viewer to understand the picture quickly, make most lines point to, and value contrast greatest at, the important area, as in this example.