Orange sky

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QUANTUM LABORATORY

G. I. Kosourov

ORANGE SKY

In this article we present several experiments on color vision. All of them are associated with various color illusions caused by unusual operating conditions of the eye or its color fatigue.

The mechanism of color perception by the eye is very complex and has not yet been fully studied. It is known that the retina of the eye contains two kinds of light-sensitive cells, which are called rods and cones. The rods contain phototympeschi floral pigment - visual purple, or rhodopisin. When exposed to light, rhodopisin supplies and acts on nerve fibers that transmit stimulation to the brain. In bright light it ensures that the sticks become completely blind. Walking in the dark

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the reverse process is the restoration of the visual cortex. Rod, twilight vision has very high sensitivity, but it is achromatic. Rods do not sense color. At sufficiently high brightness, the cone mechanism of vision comes into force. Cone vision is color sensitive. There are many convincing experiments leading to the conclusion that cones contain three types of photochemical sensitive pigments with maximum sensitivity in the red, green and blue regions of the spectrum. Varying degrees of expression of all three pigments give our consciousness the sensation of color and allow us to see the world in all its diversity of colors, shades, halftones and transitions.

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The three-color nature of color vision is the basis for color reproduction in film, television, color photography, and printing. Quantitative color measurement methods are also based on the three-color principle.

However, color errors can be caused not only by paints, but also, for example, by excessive lighting. Draw the black and white disks shown in Figures 1 (a, 6, c, d) using ink on drawing paper. It is enough for the disks to have a diameter of 8-12 cm. Cut the disks and rotate them not very quickly, about 1-3 revolutions per second. To do this, you can put them on the winder axis of a film projector, player, tape recorder, or simply make tops out of disks. Instead of black arcs, you will see colored circles. The color depends on the speed of rotation, illumination and the nature of figure. For example, for a disk at figure 1,a, the arcs following the black sector (in the direction of rotation) appear red in low light, and yellow in bright light. At certain rotation speeds and bright lighting, black sectors appear blue. There is no complete explanation for this phenomenon yet.

Paints differ not only in color, but also in saturation. If you gradually add white to red paint, the color will become more and more pink. In paintings, and even more so in printed copies from paintings, it is difficult to obtain rich tones and a greater gradation of brightness. The ratio of the rage of the whitest paint to the rage of the blackest is barely one hundred, but in nature we are dealing with a difference in rage of many thousands of times. Therefore, copies from paintings seem too pale or, conversely, too dark. This violates one of the elements of illumination reproduction - the impact respectrum. The image of a landscape or genre scene appears flat. This means a wider range of transmitted rages when projected onto the screen. This is why photographs on color reversible film—slides—are so expressive and three-dimensional.

The perception of a painting can be significantly improved by lighting it in a special way. Take a color inclusion from Ogonyok, shape it and print it using contact method from film to film of contrasting black and white ranges. Insert the slides into a projector with a large luminous flux (a “Light” type projector is suitable) and project the slides onto the original so that the contours of the projection and the original exactly match. The result will not make you regret the work expended. The painting will become animate, acquire volume and special expressiveness. Turn off the projector, and you will see how dull and inexpressive the picture is under uniform lighting.

The following experiments relate to the so-called sequential color image. This phenomenon is due to the fact that complete restoration of color-sensitive pigmenta is a relatively slow process. If you look at a single-color figure for a long time, and then turn your gaze to white paper, a wall or a ceiling, then the white color will be perceived as if it lacks color, which tires the eye. On a white surface the same figure will be visible, but rendered in a color that is called complementary. Cut out red, orange, yellow, green, blue and purple squares measuring 2x2 cm from colored paper. Place one of the colored squares in front of you on a sheet of white paper and look at it without straining your eyes for about thirty seconds. You need to look, as they say, at one point, so that the image of the square does not move across the retina. Turn your gaze to the white field, and after a second or two you see on the paper a clear image of a square in a complementary color. So are you

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Fig. 2. The complementary colors of squares in one row are green, blue is orange, and yellow is violet (Fig. 2). Each pair of complementary colors in the mixture should produce a white or gray achromatic color.

To mix additional colors, place two additional squares next to each other and place a glass plate between them (Fig. 3). Position your eye so that one square is visible through the glass, and the other is reflected in the glass. By changing the inclination of the glass and thereby the correspondence between the light fluxes coming from the squares, it is possible to ensure that the coloring in the place where the image overlaps almost disappears. To completely achromatize an image, you need precise selection of colors. Most often the result is a brown color. But if you take two clearly non-complementary colors, for example green and yellow or red and violet, any mixture of them will produce a bright color. Even more vibrant color images arise if the squares are placed not on white paper, but on an additional background.

After you have made observations on simple figures, try making an applique from colored paper similar to the one shown at figure in front of the statue, that is, replacing the colors in it with additional ones.

Fig. 3.

body By looking at the pictures in the same way as you looked at the squares, you will very soon learn to see landscapes in natural colors on a white background. For success, only bright enough lighting is needed.

The most striking and most incomprehensible color iliosis is provided by our latest experience. We have already said that the basis for color reproduction is a three-color system. If you repeatedly photograph the same scene through three light filters: red, green and blue - and, having printed positive copies, project them with three projectors onto the same place on the screen through the same light filters, then a color image with correct color reproduction will appear on the screen. In this case, the light filters must be selected so that in total they give a white color. You can limit yourself to two photographs through two additional light filters, for example, red and green. This also produces good color rendition, although not as perfect as in the three-color method. But it turns out that during projection you can limit yourself to just one color filter.

Shoot the same color scene, without moving the camera, twice on panchromatic film through red and green filters.