Contrast describes the relationship between light and dark values. To understand contrast, make a value scale. Draw ten squares, making the first one white and the last one black. Then create a range of eight grays between them, progressing from light to dark. It is the distance between values on such a scale by which we measure degrees of contrast. The farther apart two values are on the scale, the stronger the contrast between them. Black is farthest from white; thus, when juxtaposed, these two extremes create the greatest possible value contrast. Less contrast exists between a light gray and a dark gray, and still less between a dark gray and black, which are very close to each other on the scale. Contrasting values placed side by side will accentuate each other; lights will appear lighter and darks will appear darker.
As you will discover, a skillful use of contrast can help you establish the illusion of distance and define the quality of light in your drawings.
This is a value scale. Contrast is the relationship of two or more values on the value scale.
The two cubes at left contrast less with each other than the two on the right.