Creating the Illusion of Distance and Depth
One of the innate clues we use in our perception of distances is this: The greatest degree of contrast will be in the foreground, the least in the distance. Imagine two identical white horses standing in a field at midday, each at a different distance from you. The light and dark areas on the near horse will appear slightly more pronounced than on the distant horse. Likewise, the cast shadow of the near horse will appear darker than that of the far horse. This type of contrast relationship establishes distance even without the additional clues of scale, perspective, or placement in the environment.
The shadows and cast shadows of the horse in the foreground are darker than those of the background horse. This contrast relationship indicates each horse's distance from the picture plane.
These two spheres are the same size and have the same placement in space. The sphere on the right appears closer to the viewer because it contrasts more with the white background than the sphere at left.
The corner of the screen that comes forward does so because the contrast between the planes that form it is greater than that between the planes of the corner that recedes. If we isolate the middle of the screen so that we see no perspective, these corners still advance and recede.
When you are dealing with vast areas, it is easy to see the reduction of contrast between the light and dark sides of objects. When you are viewing distant mountains, you may see so little contrast between the light and shadow on them that they can appear as a single-value silhouette. Contrast is also important in distinguishing small distances, such as in a portrait, where a subtle contrast of light and shadow between the tip of the nose and the planes of the cheeks will define the distance between those features.
Strong value contrast in the foreground of your drawing is very useful in the depiction of foreshortened objects. It works this way: When you draw an object on a flat surface like paper, you are limited to working in two dimensions, height and width. To express depth, you foreshorten the object-shorten the parts that come forward-thus creating the illusion of projection or extension in space. Contrast is used to enhance this illusion; an object seems to come forward in space when the contrast between light and shadow is strong, and seems to recede when this contrast is weak.
The contrast between light and shadow is stronger on the rock formations in the foreground of the picture plane than on those that recede into the background.
The light and dark contrasts on the hand, and between the hand and the background, are stronger than those on the face. This shows how, even in comparatively shallow space, contrast differences are used to establish spatial relationships.
The value of the background in your composition can enhance the illusion of depth. For example, depicting a light object against a dark background (or a dark object against a light background) sets up a strong contrast that makes the object appear closer to the viewer. And, because strong contrast naturally attracts the eye, it is an important tool when you want to draw the viewer's attention to a particular area of a composition.
Although the perspective implies two receding planes, only the one on the right appears to recede. The example at left appears to stand upright because the contrast between the shape's light top and the dark background is equal to the contrast between the shape's dark bottom and the light background.
Placing a subject against a contrasting background is a good way to call attention to it. If these rabbits were reversed in compositional placement, both would disappear.