Afterimages

If one's attention is focused on an area of a single color for thirty to sixty seconds and then shifted to a field of white (Figure 4.3), the eye will sense a color other than the first one covering the white field. The second color is complementary to the first color. For example, red will produce an afterimage of green, and blue will produce an orange afterimage. The complementary afterimage appears as a luminous transparency. The effect is similar to that obtained by viewing the white surface through a colored filter. Because the color does not reside

LINE OF SIGHT

Fig. 4.3A,B. Color A is viewed for 30 to 60 seconds. The eye then focuses on a spot some distance away. A different color will be perceived in the same shape as A. Color B is the complement of A.

Fig. 4.4A,B. Color A is located on a white field. Retinal fatigue produces the color B halo surrounding A. Color B is the complement of A.

on the white surface, we can assume that it is a sensation generated in the eye (See Section 5.6 The Eye and Color Sensation).

The afterimage phenomenon affects many of the choices made by a painter. An optically generated complementary color will not only fill a prescribed white field; it will spill out in all directions from the primary color source (Figure 4.4). If two areas of color, one the complement of the other, are placed adjacent to each other, an optically generated complement of some de-ree of intensity will overlie each of the areas (Figure 4.5). Think again of the afterimage as a color filter suspended before the eye. Since the overlay will be of the same color as that lying beneath it, and because the afterimage appears as a colored light, we will sense that the field of color has become more luminous and intense. Complementary colors are always more intense when they are in close proximity to one another than when they are isolated or surrounded by other colors. Note how the complementary colors red and green in van Gogh's La Berceuse (Color Plate 13) amplify each other to create a brilliant, intense, and massive foreground.

Value relationships are affected in the same complementary way as hue relationships. White will look lighter and black darker if they are placed next to each other. When colors that are not complementary are placed adjacent to one another, the same optical behavior will bring about a different effect. An area of yellow in a field of red will appear more greenish than the same yellow residing in a field of blue-violet. The yellow is being altered by the complement of red, which is green. The blue-violet intensifies the yellow with the overlay of its complement, which is yellow. The manipulation of one color by another through complementary overlay is known as simultaneous contrast.

Fig. 4.5A,B. Two areas of color A and B, a complementary pair, are viewed adjacent to each other. Complementary afterimages A' and B' are also present due to the effect illustrated in Figure 4.4.

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