|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
VISUAL (OPTICAL) ILLUSIONS
Illusions of color vision. Encyclopedia of visual illusions
At leisure / Visual (optical) illusions << Back: Illusions when an object moves >> Forward: Other illusions and effects The most important property of our eye is its ability to distinguish colors. As mentioned earlier, only color-sensitive elements of the retina - cones - have this ability. One of the first remarkable discoveries related to color vision can be considered the phenomenon of shifting the maximum of relative visibility during the transition from daytime to twilight vision, discovered by the famous Czech biologist J. Purkinė. Purkin's phenomenon lies in the fact that during twilight vision (at low illumination) not only the sensitivity of the eye to the perception of colors in general decreases, but also that under these conditions the eye has a reduced sensitivity to colors of the long-wavelength region of the visible spectrum (red, orange), but it has hypersensitivity to colors of the short-wavelength part of the spectrum (blue, violet). Red poppy and cornflower in fig. II in daylight seem to be close to each other in brightness. At dusk, the poppy seems completely dark, and the cornflower is lighter. In the art gallery at dusk, colors gradually begin to disappear, first red, then yellow and green.
It is possible to point out a number of cases when, when looking at colored objects, we also encounter visual errors or illusions. First, sometimes we mistakenly judge the color saturation of an object by the brightness of the background or by the color of other objects surrounding it. In this case, the laws of brightness contrast also apply: the color brightens on a dark background and darkens on a light one. The great artist and scientist Leonardo da Vinci wrote: “From colors of equal whiteness, that one seems lighter, which will be on a darker background, and black will seem more gloomy against a background of great whiteness. And red will seem more fiery on a darker background, as well as all colors surrounded by their direct opposites. Secondly, there is the concept of actual color or chromatic contrasts, when the color of the object we observe changes depending on the background against which we observe it. Illusions of color vision of this kind we meet in the following forms. The black circle shown in Fig. III appears slightly reddish against a green background, but when we cover this circle with thin transparent paper, the illusory red color becomes even more noticeable. Obviously, transparent paper erases the sharpness of the borders and reduces the difference in the brightness of the field and background, and thus enhances the manifestation of the effect. Similarly, a black circle on red will appear greenish, on a violet-blue background greenish-yellow, and on blue a copper-red.
The same phenomenon of involuntary coloration of gray stripes can be observed through transparent paper in fig. IV.
It turns out that the color in which the black circle or gray stripe is painted is the so-called complementary color to the background color. For each color there is such another color, the optical shift with which gives an achromatic color (white or gray). Such colors are called complementary. The circle or stripe does not have to be black or grey, for example a yellow stripe appears greenish on a red background, but orange on a green background; in this case, these three colors, when mixed, will give white or gray. It is noted that this illusory coloring of black and gray objects occurs in a color that is only approximately complementary, but does not coincide exactly with it. The most visual representation of optical color mixing can be obtained as follows. If a disk (Fig. V) with sectors having such angles and colors as shown in the figure is brought into rapid rotation, then due to the rapid alternation of various excitations, the colors of the sectors will merge into a common gray tone. This illusion of color vision is explained by the following properties of our eye.
The retina of the human eye is most adapted to undecomposed sunlight, and, perhaps, the nerve endings of the retina, when irritated with one color, seem to make up for the color missing from white, giving us the illusion of seeing an additional color. There is an older hypothesis that explains the phenomenon of these color illusions by the fatigue of the perceiving nerves, but it is hardly more justified than the one above. Based on the fact that our organ of vision is most adapted to the perception of white sunlight, this illusion can also be explained. If we look at the red spot for a few seconds, and then look at the white paper, we will see a green spot on the paper. If we consider the yellow circle, then we will see blue on paper, and vice versa. Other illusions of color vision are also associated with color contrast. Let's take a few more examples. On fig. VI the area of the inner square on the left and the strip on the right are equal, but the perimeter of the strip is twice the perimeter of the square. Peering into this pattern, we see a strip that is brighter than the inner square.
The phenomenon of general psychological contrast can explain the illusion of the so-called trimming of colors, which consists in the following. If you look at fig. VII, then on it you can see a figure in the form of a green cross, then the middle circle also seems greenish; if you focus on the yellow circles, then the central circle will also appear yellowish.
Also interesting is the illusion of color accompaniment, which appears after examining the upper part of Fig. VIII. If you look closely at the black circle at the top of the picture for several minutes, and then quickly look at the black circle at the bottom, then in a few seconds, color images of all four spots surrounding the upper black circle will appear on a white background. What color will these spots appear?
Note here that in the transition from one color of a given surface to another color of the same surface, its apparent brightness will also change. Consequently, the brightness contrast will also change if we, say, simultaneously change the brightness of the object and the background, or we consider the same object against a less bright, and then against a brighter background. This is why luminance contrast is related to color contrast for our vision. The more the object color differs from the background color, the more the object is visible and the more clearly its outline and shape are visible. There are many examples of the effect of color contrasts on the eye. Goethe, for example, writes: "The grass growing in a courtyard paved with gray limestone seems to be of an infinitely beautiful green color, when the evening clouds throw a reddish, barely noticeable reflection on the stones." The complementary color of dawn is green; this contrasting green, when mixed with the green of the grass, produces an "infinitely beautiful green". Goethe also describes the phenomenon of so-called "colored shadows". "One of the most beautiful cases of colored shadows can be observed on a full moon. Candlelight and moonlight can be completely equalized in intensity. Both shadows can be made of the same strength and clarity, so that both colors will be completely balanced. Set the screen so that the light of the full moon falls directly on it, the candle is placed somewhat to the side at a proper distance, and some transparent body is held in front of the screen.Then a double shadow appears, and the one cast by the moon and which at the same time illuminates the candle seems to be of a pronounced reddish-dark color , and, conversely, the one that the candle casts, but the moon illuminates, is of the most beautiful blue color. Where both shadows meet and merge into one, a black shadow is obtained. The fact that some colors are perceived by us as "protruding" and others as "receding" is illustrated here in Fig. IX.
Looking at the top figure in this figure, we tend to think that it is a truncated pyramid with its apex facing us. Looking at the bottom figure, we are ready to imagine a tunnel with an exit opening in the distance. "Protruding" colors usually appear to be red-orange-yellow (or "warm") colors, while "receding" colors appear to be green-blue (or "cold"). Saturated and light colors usually seem closer to us than dark and desaturated ones. Chromatic colors usually "come forward" against grays. It should be noted that many properties of the eye that cause the appearance of illusions of color vision, at the same time, turn out to be very useful for obtaining visual sensations that more fully reflect objective reality. That is why, for example, on signboards and advertisements assembled from luminous gas-light tubes, words written with red glow tubes approach the observer and seem to be hanging in the air, while words written with green or blue glow tubes recede. However, it turns out that for some people the illusion of different distances of different colors is the opposite, i.e., blue colors seem closer (in some people, the illusion is not observed at all). Among the various explanations for this illusion, the following deserves attention. The visual line crosses the plane of the pupil not in its center, but somewhat from the side, i.e., the lens is not strictly centered in relation to the visual line. Therefore, when the eye fixes some blue dot, the image of the red dot adjacent to it will give a known circle of light scattering on the retina, and this circle will not be concentric with the image of the fixed point, but is somewhat shifted towards the temporal or nasal part of the retina. This shift in binocular vision creates the same impression that we get from irritated retinal areas equally distant from the axes of the eyes, if the red dot is actually closer or farther than the blue one. Author: Artamonov I.D. << Back: Illusions when an object moves >> Forward: Other illusions and effects
Machine for thinning flowers in gardens
02.05.2024 Advanced Infrared Microscope
02.05.2024 Air trap for insects
01.05.2024
▪ Road signs with E Ink displays ▪ New synchronous boost converter chipsets ▪ superMHL/HDMI 2.0 port processor
▪ site section Lightning protection. Article selection ▪ article Found a scythe on a stone. Popular expression ▪ article What is the longest bus in the world? Detailed answer ▪ article Observation of the activity of the stomach and intestines. Health care ▪ article Photorelay on a triac. Encyclopedia of radio electronics and electrical engineering
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
Latest news of science and technology, new electronics:
All languages of this page