Why do humans have color vision? Development of color perception. Differences between human and animal vision. Metamerism in photography

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Features of human perception. Vision

A person cannot see in complete darkness. In order for a person to see an object, it is necessary that the light is reflected from the object and hit the retina of the eye. Light sources can be natural (fire, sun) and artificial (various lamps). But what is light?

According to modern scientific concepts, light is electromagnetic waves of a certain (rather high) frequency range. This theory originates from Huygens and is confirmed by many experiments (in particular, the experience of T. Jung). At the same time, in the nature of light, carpuscular-wave dualism is fully manifested, which largely determines its properties: when propagating, light behaves like a wave, when emitted or absorbed, like a particle (photon). Thus, the light effects that occur during the propagation of light (interference, diffraction, etc.) are described by Maxwell's equations, and the effects that appear during its absorption and emission (photoelectric effect, Compton effect) are described by the equations of quantum field theory.

Simply put, the human eye is a radio receiver capable of receiving electromagnetic waves of a certain (optical) frequency range. The primary sources of these waves are the bodies that emit them (the sun, lamps, etc.), the secondary sources are the bodies that reflect the waves of primary sources. Light from sources enters the eye and makes them visible to man. Thus, if the body is transparent to the waves of the visible frequency range (air, water, glass, etc.), then it cannot be registered by the eye. At the same time, the eye, like any other radio receiver, is “tuned” to a certain range of radio frequencies (in the case of the eye, this range is from 400 to 790 terahertz), and does not perceive waves that have higher (ultraviolet) or lower (infrared) frequencies. This "tuning" is manifested in the entire structure of the eye - from the lens and vitreous body, which are transparent in this particular frequency range, to the size of photoreceptors, which in this analogy are similar to radio receiver antennas and have dimensions that provide the most efficient reception of radio waves of this particular range.

All this together determines the frequency range in which a person sees. It is called the visible light range.

Visible radiation - electromagnetic waves perceived human eye, which occupy a portion of the spectrum with a wavelength of approximately 380 (violet) to 740 nm (red). Such waves occupy the frequency range from 400 to 790 terahertz. Electromagnetic radiation with such frequencies is also called visible light, or just light (in the narrow sense of the word). The human eye is most sensitive to light at 555 nm (540 THz), in the green part of the spectrum.

White light separated by a prism into the colors of the spectrum

When a white beam is decomposed in a prism, a spectrum is formed in which radiation of different wavelengths is refracted at different angles. The colors included in the spectrum, that is, those colors that can be obtained by light waves of one wavelength (or a very narrow range), are called spectral colors. The main spectral colors (having their own name), as well as the emission characteristics of these colors, are presented in the table:

What does one see

Thanks to vision, we receive 90% of the information about the world around us, so the eye is one of the most important sense organs.
The eye can be called a complex optical device. Its main task is to "transmit" the correct image to the optic nerve.

The structure of the human eye

The cornea is the transparent membrane that covers the front of the eye. It lacks blood vessels, it has a large refractive power. Included in optical system eyes. The cornea borders on the opaque outer shell of the eye - the sclera.

The anterior chamber of the eye is the space between the cornea and the iris. It is filled with intraocular fluid.

The iris is shaped like a circle with a hole inside (the pupil). The iris consists of muscles, with the contraction and relaxation of which the size of the pupil changes. It enters the choroid of the eye. The iris is responsible for the color of the eyes (if it is blue, it means that there are few pigment cells in it, if it is brown, there are many). It performs the same function as the aperture in a camera, adjusting the light output.

The pupil is a hole in the iris. Its dimensions usually depend on the level of illumination. The more light, the smaller the pupil.

The lens is the "natural lens" of the eye. It is transparent, elastic - it can change its shape, "focusing" almost instantly, due to which a person sees well both near and far. It is located in the capsule, held by the ciliary girdle. The lens, like the cornea, is part of the optical system of the eye. The transparency of the lens of the human eye is excellent - most of the light with wavelengths between 450 and 1400 nm is transmitted. Light with a wavelength above 720 nm is not perceived. The lens of the human eye is almost colorless at birth, but acquires yellowish color with age. This protects the retina of the eye from exposure to ultraviolet rays.

The vitreous body is a gel-like transparent substance located in the back of the eye. The vitreous body maintains the shape of the eyeball and is involved in intraocular metabolism. Included in the optical system of the eye.

The retina - consists of photoreceptors (they are sensitive to light) and nerve cells. Receptor cells located in the retina are divided into two types: cones and rods. In these cells, which produce the enzyme rhodopsin, the energy of light (photons) is converted into electrical energy. nervous tissue, i.e. photochemical reaction.

Sclera - an opaque outer shell of the eyeball, passing in front of the eyeball into a transparent cornea. Attached to the sclera are 6 oculomotor muscles. In it is a small amount of nerve endings and vessels.

Choroid - lining back department sclera, the retina is adjacent to it, with which it is closely connected. The choroid is responsible for the blood supply to the intraocular structures. In diseases of the retina, it is very often involved in pathological process. There are no nerve endings in the choroid, therefore, when it is ill, pain does not occur, usually signaling some kind of malfunction.

The optic nerve - with the help optic nerve signals from nerve endings are transmitted to the brain.

Man is not born with developed body vision: in the first months of life, the formation of the brain and vision occurs, and by about 9 months they are able to process incoming visual information almost instantly. To see, you need light.

Light sensitivity of the human eye

The ability of the eye to perceive light and recognize varying degrees its brightness is called light perception, and the ability to adapt to different brightness of lighting is called eye adaptation; light sensitivity is estimated by the value of the threshold of light stimulus.
Man with good eyesight able to see the light from a candle at a distance of several kilometers at night. The maximum light sensitivity is reached after a sufficiently long dark adaptation. It is determined under the action of a light flux in a solid angle of 50 ° at a wavelength of 500 nm (maximum sensitivity of the eye). Under these conditions, the threshold energy of light is about 10–9 erg/s, which is equivalent to the flux of several quanta of the optical range per second through the pupil.
The contribution of the pupil to the adjustment of the sensitivity of the eye is extremely insignificant. The entire range of brightness that our visual mechanism is capable of perceiving is enormous: from 10-6 cd m² for a fully dark-adapted eye to 106 cd m² for a fully light-adapted eye. The mechanism for such a wide sensitivity range lies in the decomposition and restoration of photosensitive pigments. in the photoreceptors of the retina - cones and rods.
The human eye contains two types of light-sensitive cells (receptors): highly sensitive rods responsible for twilight (night) vision, and less sensitive cones responsible for color vision.

Normalized graphs of the light sensitivity of cones of the human eye S, M, L. The dotted line shows the twilight, "black and white" susceptibility of the rods.

In the human retina, there are three types of cones, the sensitivity maxima of which fall on the red, green and blue parts of the spectrum. The distribution of cone types in the retina is uneven: "blue" cones are closer to the periphery, while "red" and "green" cones are randomly distributed. The matching of cone types to the three "primary" colors enables the recognition of thousands of colors and shades. Spectral sensitivity curves three types cones partially overlap, which contributes to the phenomenon of metamerism. Very strong light excites all 3 types of receptors, and therefore is perceived as blindingly white radiation.

Uniform stimulation of all three elements, corresponding to the weighted average daylight, also causes a sensation of white.

The genes encoding light-sensitive opsin proteins are responsible for human color vision. According to supporters of the three-component theory, the presence of three different proteins that respond to different wavelengths is sufficient for color perception.

Most mammals have only two of these genes, so they have black and white vision.

The red light-sensitive opsin is encoded in humans by the OPN1LW gene.
Other human opsins encode the OPN1MW, OPN1MW2, and OPN1SW genes, the first two of which encode proteins that are sensitive to light at medium wavelengths, and the third is responsible for the opsin that is sensitive to the short-wavelength part of the spectrum.

line of sight

The field of view is the space simultaneously perceived by the eye with a fixed gaze and a fixed position of the head. It has certain boundaries corresponding to the transition of the optically active part of the retina to the optically blind.
The field of view is artificially limited by the protruding parts of the face - the back of the nose, the upper edge of the orbit. In addition, its boundaries depend on the position of the eyeball in the orbit. In addition, in each eye of a healthy person there is an area of ​​​​the retina that is not sensitive to light, which is called the blind spot. Nerve fibers from the receptors to the blind spot go over the retina and are collected in the optic nerve, which passes through the retina to its other side. Thus, there are no light receptors in this place.

In this confocal micrograph, the optic disc is shown in black, the cells lining the blood vessels are in red, and the contents of the vessels are in green. Retinal cells appear as blue spots.

The blind spots in both eyes are in different places(symmetrical). This fact, and the fact that the brain corrects the perceived image, explains why, with normal use of both eyes, they are invisible.

To observe your blind spot, close your right eye and look with your left eye at the right cross, which is circled. Keep your face and monitor upright. Without taking your eyes off the right cross, bring (or move away) your face from the monitor and at the same time follow the left cross (without looking at it). At some point it will disappear.

This method can also estimate the approximate angular size of the blind spot.

Reception for blind spot detection

There are also paracentral divisions of the visual field. Depending on the participation in the vision of one or both eyes, a distinction is made between monocular and binocular fields of view. In clinical practice, the monocular field of view is usually examined.

Binocular and stereoscopic vision

Visual analyzer of a person in normal conditions provides binocular vision, that is, vision with two eyes with a single visual perception. Main reflex mechanism binocular vision is an image fusion reflex - a fusion reflex (fusion), which occurs with simultaneous stimulation of functionally dissimilar nerve elements retinas of both eyes. As a result, there is a physiological doubling of objects that are closer or further than the fixed point (binocular focusing). Physiological doubling (focus) helps to assess the distance of an object from the eyes and creates a feeling of relief, or stereoscopic vision.

When seeing with one eye, the perception of depth (relief distance) is carried out by Ch. arr. due to secondary auxiliary signs of remoteness (the apparent size of the object, linear and aerial perspectives, obstruction of some objects by others, accommodation of the eye, etc.).

Pathways of the visual analyzer
1 - Left half visual field, 2 - Right half of the visual field, 3 - Eye, 4 - Retina, 5 - Optic nerves, 6 - Oculomotor nerve, 7 - Chiasma, 8 - Optic tract, 9 - Lateral geniculate body, 10 - Superior colliculi, 11 - Nonspecific visual pathway, 12 - Visual cortex.

A person sees not with his eyes, but through his eyes, from where information is transmitted through the optic nerve, chiasm, optic tracts to certain areas occipital lobes the cerebral cortex, where the picture of the outside world that we see is formed. All these organs make up our visual analyzer or visual system.

Change in vision with age

Retinal elements begin to form at 6-10 weeks prenatal development, the final morphological maturation occurs by 10–12 years. In the process of development of the body, the color perception of the child changes significantly. In a newborn, only rods function in the retina, providing black and white vision. The number of cones is small and they are not yet mature. Color recognition in early age depends on the brightness, not on the spectral characteristics of the color. As the cones mature, children first distinguish yellow, then green, and then red (already from 3 months it was possible to develop conditioned reflexes for those colors). Cones begin to function fully by the end of the 3rd year of life. AT school age the distinctive color sensitivity of the eye is increased. The sensation of color reaches its maximum development by the age of 30 and then gradually decreases.

In a newborn, the diameter of the eyeball is 16 mm, and its weight is 3.0 g. The growth of the eyeball continues after birth. It grows most intensively during the first 5 years of life, less intensively - up to 9-12 years. In newborns, the shape of the eyeball is more spherical than in adults, as a result, in 90% of cases, they have far-sighted refraction.

Pupils in newborns are narrow. Due to the predominance of the tone of the sympathetic nerves innervating the muscles of the iris, pupils become wide at 6–8 years of age, which increases the risk sunburn retina. At 8-10 years old, the pupil narrows. At the age of 12–13, the speed and intensity of the pupillary reaction to light become the same as in an adult.

In newborns and children preschool age the lens is more convex and more elastic than in an adult, its refractive power is higher. This allows the child to clearly see the object at a shorter distance from the eye than an adult. And if in a baby it is transparent and colorless, then in an adult the lens has a slight yellowish tint, the intensity of which may increase with age. This does not affect visual acuity, but may affect the perception of blue and purple colors.

Touch and motor functions vision develop at the same time. In the first days after birth, eye movements are not synchronous, with the immobility of one eye, you can observe the movement of the other. The ability to fix an object with a glance is formed at the age of 5 days to 3-5 months.

A reaction to the shape of an object is noted already in a 5-month-old child. In preschoolers, the first reaction is the shape of the object, then its size, and last but not least, the color.
Visual acuity increases with age, and stereoscopic vision improves. Stereoscopic vision reaches its optimum level by the age of 17–22, and from the age of 6, girls have a higher stereoscopic visual acuity than boys. The field of view is greatly increased. By the age of 7, its size is approximately 80% of the size of the adult visual field.

After 40 years, there is a drop in the level of peripheral vision, that is, there is a narrowing of the field of view and a deterioration in lateral vision.
After about 50 years of age, the production of tear fluid is reduced, so the eyes are less moisturized than at a younger age. Excessive dryness can be expressed in redness of the eyes, cramps, tearing under the influence of wind or bright light. This may not depend on ordinary factors (frequent tensions eye or air pollution).

With age, the human eye begins to perceive the surroundings more dimly, with a decrease in contrast and brightness. The ability to recognize color shades, especially those that are close in color, may also be impaired. This is directly related to the reduction in the number of retinal cells that perceive color shades, contrast, and brightness.

Some age-related visual impairments are caused by presbyopia, which is manifested by fuzziness, blurring of the picture when trying to see objects located close to the eyes. The ability to focus on small objects requires an accommodation of about 20 diopters (focusing on an object 50 mm from the observer) in children, up to 10 diopters at the age of 25 (100 mm) and levels from 0.5 to 1 diopter at the age of 60 years (possibility focusing on the subject at 1-2 meters). It is believed that this is due to the weakening of the muscles that regulate the pupil, while the reaction of the pupils to the light flux entering the eye also deteriorates. Therefore, there are difficulties with reading in dim light and the adaptation time increases with changes in illumination.

It also develops faster with age. visual fatigue and even headaches.

Color perception

The psychology of color perception is the human ability to perceive, identify and name colors.

The perception of color depends on a complex of physiological, psychological, cultural and social factors. Initially, studies of color perception were carried out within the framework of color science; later ethnographers, sociologists and psychologists joined the problem.

Visual receptors are rightfully considered "the part of the brain brought to the surface of the body." Unconscious processing and correction visual perception ensures the "correctness" of vision, and it is also the cause of "errors" in the evaluation of color in certain conditions. Thus, the elimination of the "background" illumination of the eye (for example, when looking at distant objects through a narrow tube) significantly changes the perception of the color of these objects.

Simultaneous viewing of the same non-luminous objects or light sources by several observers with normal color vision, under the same viewing conditions, makes it possible to establish a one-to-one correspondence between spectral composition compared radiations and color sensations caused by them. Color measurements (colorimetry) are based on this. Such a correspondence is unambiguous, but not one-to-one: the same color sensations can cause radiation fluxes of different spectral composition (metamerism).

There are many definitions of color as a physical quantity. But even in the best of them, from a colorimetric point of view, the mention is often omitted that the specified (not mutual) unambiguity is achieved only under standardized conditions of observation, illumination, etc., the change in color perception with a change in the intensity of radiation of the same spectral composition is not taken into account. (the phenomenon of Bezold - Brucke), the so-called. color adaptation of the eye, etc. Therefore, the variety of color sensations arising under real lighting conditions, variations in the angular sizes of elements compared in color, their fixation in different parts of the retina, different psychophysiological states of the observer, etc., is always richer than the colorimetric color variety.

For example, some colors (such as orange or yellow) are defined in the same way in colorimetry, which in everyday life are perceived (depending on lightness) as brown, “chestnut”, brown, “chocolate”, “olive”, etc. one of the best attempts to define the concept of color, due to Erwin Schrödinger, the difficulties are removed by the simple absence of indications of the dependence of color sensations on numerous specific conditions of observation. According to Schrödinger, Color is a property of the spectral composition of radiations, common to all radiations that are visually indistinguishable for humans.

Due to the nature of the eye, light that causes the sensation of the same color (for example, white), that is, the same degree of excitation of the three visual receptors, may have a different spectral composition. In most cases, a person does not notice this effect, as if “thinking” the color. This is because although the color temperature of different lighting may be the same, the spectra of natural and artificial light reflected by the same pigment can differ significantly and cause a different color sensation.

The human eye perceives many different shades, but there are "forbidden" colors that are inaccessible to it. An example is a color that plays with both yellow and blue tones at the same time. This happens because the perception of color in the human eye, like many other things in our body, is built on the principle of opposition. The retina of the eye has special neurons-opponents: some of them are activated when we see red, and they are suppressed by green. The same thing happens with the yellow-blue pair. Thus, the colors in red-green and blue-yellow pairs have opposite effects on the same neurons. When the source emits both colors from a pair, their effect on the neuron is compensated, and the person cannot see either of these colors. Moreover, a person is not only unable to see these colors in normal circumstances, but also to imagine them.

Such colors can only be seen as part of a scientific experiment. For example, scientists Hewitt Crane and Thomas Pyantanida from the Stanford Institute in California created special visual models in which stripes of "arguing" shades alternated quickly replacing each other. These images, fixed by a special device at the level of a person's eyes, were shown to dozens of volunteers. After the experiment, people claimed that at a certain point, the boundaries between the shades disappeared, merging into one color that they had never encountered before.

Differences between human and animal vision. Metamerism in photography

Human vision is a three-stimulus analyzer, that is, the spectral characteristics of color are expressed in only three values. If the compared fluxes of radiation with different spectral composition produce the same effect on the cones, the colors are perceived as the same.

In the animal kingdom, there are four- and even five-stimulus color analyzers, so colors that are perceived by humans as the same may appear different to animals. In particular, birds of prey see rodent tracks on burrow paths solely through the ultraviolet luminescence of their urine components.
A similar situation develops with image registration systems, both digital and analog. Although for the most part they are three-stimulus (three layers of film emulsion, three types of matrix cells digital camera or scanner), their metamerism is different from that of human vision. Therefore, colors perceived by the eye as the same may appear different in a photograph, and vice versa.

Sources

O. A. Antonova, Age anatomy and physiology, Ed .: Higher education, 2006

Lysova N. F. Age anatomy, physiology and school hygiene. Proc. allowance / N. F. Lysova, R. I. Aizman, Ya. L. Zavyalova, V.

Pogodina A.B., Gazimov A.Kh., Fundamentals of gerontology and geriatrics. Proc. Allowance, Rostov-on-Don, Ed. Phoenix, 2007 - 253 p.

color perception(color sensitivity, color perception) - the ability of vision to perceive and convert light radiation of a certain spectral composition into sensation different colors th shades and tones, forming a holistic subjective sensation (“chroma”, “color”, color).

Color is characterized by three qualities:

• color tone, which is the main feature of color and depends on the wavelength of light;
• saturation, determined by the proportion of the main tone among impurities of a different color;
• brightness, or lightness, which is manifested by the degree of proximity to white (the degree of dilution with white).

The human eye notices color changes only when the so-called color threshold (the minimum color change visible to the eye) is exceeded.

The physical essence of light and color

Visible electromagnetic vibrations are called light or light radiation.

Light emissions are divided into complex and simple.

White sunlight- complex radiation, which consists of simple color components - monochromatic (single-color) radiation. The colors of monochromatic radiation are called spectral.

If a white beam is decomposed into a spectrum using a prism, then a series of continuously changing colors can be seen: dark blue, blue, cyan, blue-green, yellow-green, yellow, orange, red.

The color of the radiation is determined by the wavelength. The entire visible spectrum of radiation is located in the wavelength range from 380 to 720 nm (1 nm = 10 -9 m, i.e. one billionth of a meter).

The entire visible part of the spectrum can be divided into three zones

• Radiation with a wavelength from 380 to 490 nm is called the blue zone of the spectrum;
• from 490 to 570 nm - green;
• from 580 to 720 nm - red.

A person sees different objects painted in different colors because monochromatic radiations are reflected from them in different ways, in different ratios.

All colors are divided into achromatic and chromatic

• Achromatic (colorless) are gray colors of various lightness, white and black colors. Achromatic colors are characterized by lightness.
• All other colors are chromatic (colored): blue, green, red, yellow, etc. Chromatic colors are characterized by hue, lightness and saturation.

Color tone- this is a subjective characteristic of color, which depends not only on the spectral composition of the radiation that enters the eye of the observer, but also on psychological characteristics individual perception.

Lightness subjectively characterizes the brightness of a color.

Brightness determines the intensity of light emitted or reflected from a unit surface in a direction perpendicular to it (the unit of brightness is candela per meter, cd / m).

Saturation subjectively characterizes the intensity of sensation of a color tone.
Since not only the source of radiation and the colored object, but also the eye and brain of the observer are involved in the appearance of the visual sensation of color, some basic information about the physical nature of the process of color vision should be considered.

Eye color perception

It is known that the eye is similar to a camera in which the retina plays the role of a light-sensitive layer. Emissions of different spectral composition are recorded by retinal nerve cells (receptors).

The receptors that provide color vision are divided into three types. Each type of receptor absorbs the radiation of the three main zones of the spectrum - blue, green and red in a different way, i.e. has different spectral sensitivity. If blue zone radiation enters the retina of the eye, then it will be perceived by only one type of receptors, which will transmit information about the power of this radiation to the brain of the observer. As a result, there will be a feeling of blue color. The process will proceed similarly in the case of exposure to the retina of the radiation of the green and red zones of the spectrum. With simultaneous excitation of receptors of two or three types, a color sensation will occur, depending on the ratio of the radiation powers of different zones of the spectrum.

With simultaneous excitation of receptors that detect radiation, for example, the blue and green zones of the spectrum, a light sensation can occur, from dark blue to yellow-green. The sensation of more blue shades of color will occur in the case of a higher power of the blue zone radiation, and green shades - in the case of a higher power of the green zone of the spectrum. The blue and green zones, equal in power, will cause the sensation of blue, the green and red zones - the sensation of yellow, the red and blue zones - the sensation of magenta. Cyan, magenta, and yellow are therefore called dual-zone colors. Equal in power radiation of all three zones of the spectrum cause a sensation gray color different lightness, which turns into a white color with sufficient radiation power.

Additive Light Synthesis

This is the process of obtaining different colors by mixing (adding) the radiation of the three main zones of the spectrum - blue, green and red.

These colors are called the primary or primary radiations of adaptive synthesis.

Various colors can be obtained in this way, for example, on a white screen using three projectors with blue (Blue), green (Green) and red (Red) color filters. On screen areas illuminated simultaneously from different projectors, any colors can be obtained. The change in color is achieved in this case by changing the ratio of the power of the main radiations. The addition of radiation occurs outside the eye of the observer. This is one of the varieties of additive synthesis.

Another type of additive synthesis is spatial displacement. Spatial displacement is based on the fact that the eye does not distinguish separately located small multi-colored elements of the image. Such, for example, as raster dots. But at the same time, small elements of the image move along the retina of the eye, so the same receptors are consistently affected by different radiation from neighboring differently colored raster dots. Due to the fact that the eye does not distinguish between rapid changes in radiation, it perceives them as the color of the mixture.

Subtractive color synthesis

This is the process of obtaining colors by absorbing (subtracting) radiation from white.

In subtractive synthesis, a new color is obtained using paint layers: cyan (Cyan), magenta (Magenta) and yellow (Yellow). These are the primary or primary colors of subtractive synthesis. Cyan paint absorbs (subtracts from white) red radiation, magenta - green, and yellow - blue.

In order to obtain, for example, red color in a subtractive way, you need to place yellow and magenta filters in the path of white radiation. They will absorb (subtract) respectively blue and green radiation. The same result will be obtained if yellow and purple paints are applied to white paper. Then only red radiation will reach the white paper, which is reflected from it and enters the eye of the observer.

• The primary colors of additive synthesis are blue, green and red and
• the primary colors of subtractive synthesis - yellow, magenta and cyan form pairs of complementary colors.

Additional colors are the colors of two radiations or two colors, which in the mixture make an achromatic color: W + C, P + W, G + K.

In additive synthesis, additional colors give gray and white colors, since in total they represent the radiation of the entire visible part of the spectrum, and in subtractive synthesis, a mixture of these colors gives gray and black colors, in the form that the layers of these colors absorb radiation from all zones of the spectrum.

The considered principles of color formation also underlie the production of color images in printing. To obtain printing color images, the so-called process printing inks are used: cyan, magenta and yellow. These colors are transparent and each of them, as already mentioned, subtracts the radiation of one of the spectral bands.

However, due to the imperfection of the components of subactive synthesis in the manufacture printed matter use the fourth additional black paint.

It can be seen from the diagram that if process colors are applied to white paper in various combinations, then all primary (primary) colors can be obtained for both additive and subtractive synthesis. This circumstance proves the possibility of obtaining colors of the required characteristics in the manufacture of color printing products with process inks.

The color reproduction characteristics change differently depending on the printing method. In gravure printing, the transition from light areas of the image to dark areas is carried out by changing the thickness of the ink layer, which allows you to adjust the main characteristics of the reproduced color. In gravure printing, color formation occurs subtractively.

In letterpress and offset printing, the colors of different areas of the image are transmitted by raster elements of various areas. Here, the characteristics of the reproduced color are regulated by the sizes of raster elements of different colors. It was already noted earlier that colors in this case are formed by additive synthesis - spatial mixing of colors of small elements. However, where raster dots of different colors coincide with each other and paints are superimposed on one another, a new color of the dots is formed by subtractive synthesis.

Color Rating

To measure, transmit and store color information, a standard measurement system is required. Human vision can be considered one of the most accurate measuring instruments, but it is not able to assign certain colors to colors. numerical values nor memorize them exactly. Most people don't realize how significant the effect of color is on their everyday life. When it comes to repeated reproduction, a color that appears "red" to one person is perceived as "reddish-orange" by others.

The methods by which an objective quantitative characterization of color and color differences is carried out are called colorimetric methods.

The three-color theory of vision allows us to explain the appearance of sensations of different color tone, lightness and saturation.

Color spaces

Color coordinates
L (Lightness) - color brightness is measured from 0 to 100%,
a - color range on the color wheel from green -120 to red +120,
b - color range from blue -120 to yellow +120

In 1931, the International Commission on Illumination - CIE (Commission Internationale de L`Eclairage) proposed a mathematically calculated color space XYZ, in which the entire spectrum visible to the human eye lay inside. The system of real colors (red, green and blue) was chosen as the base, and the free conversion of some coordinates into others made it possible to carry out various kinds measurements.

The disadvantage of the new space was its uneven contrast. Realizing this, scientists conducted further research, and in 1960 McAdam made some additions and changes to the existing color space, calling it UVW (or CIE-60).

Then in 1964, at the suggestion of G. Vyshetsky, the space U*V*W* (CIE-64) was introduced.
Contrary to the expectations of experts, the proposed system was not perfect enough. In some cases, the formulas used in the calculation of color coordinates gave satisfactory results (mainly with additive synthesis), in others (with subtractive synthesis), the errors turned out to be excessive.

This forced the CIE to adopt a new equal contrast system. In 1976, all disagreements were eliminated and the spaces Luv and Lab were born, based on the same XYZ.

These color spaces are taken as the basis for independent colorimetric systems CIELuv and CIELab. It is believed that the first system meets the conditions of additive synthesis to a greater extent, and the second - subtractive.

Currently, the CIELab (CIE-76) color space serves international standard color work. The main advantage of space is independence both from color reproduction devices on monitors and from information input and output devices. With CIE standards, all colors that the human eye perceives can be described.

The amount of measured color is characterized by three numbers showing the relative amounts of mixed radiation. These numbers are called color coordinates. All colorimetric methods based on 3D i.e. on a kind of volumetric color.

These methods give the same reliable quantitative characterization of color as, for example, temperature or humidity measurements. The difference is only in the number of characterizing values ​​and their relationship. This interrelationship of the three primary color coordinates results in a consistent change as the color of the illumination changes. Therefore, "tricolor" measurements are carried out under strictly defined conditions under standardized white illumination.

Thus, color in the colorimetric sense is uniquely determined by the spectral composition of the measured radiation, while the color sensation is not uniquely determined by the spectral composition of the radiation, but depends on the observation conditions and, in particular, on the color of the illumination.

Physiology of retinal receptors

Color perception is related to the function of cone cells in the retina. The pigments contained in cones absorb part of the light falling on them and reflect the rest. If some spectral components of visible light are absorbed better than others, then we perceive this object as colored.

Primary color discrimination occurs in the retina; in rods and cones, light causes primary irritation, which turns into electrical impulses for the final formation of the perceived hue in the cerebral cortex.

Unlike rods, which contain rhodopsin, cones contain the protein iodopsin. Iodopsin is the common name for the visual pigments in cones. There are three types of iodopsin:

• chlorolab ("green", GCP),
• erythrolab ("red", RCP) and
• cyanolab ("blue", BCP).

It is now known that the light-sensitive pigment iodopsin, found in all cones of the eye, includes pigments such as chlorolab and erythrolab. Both of these pigments are sensitive to the entire region of the visible spectrum, however, the first of them has an absorption maximum corresponding to the yellow-green (absorption maximum of about 540 nm.), And the second yellow-red (orange) (absorption maximum of about 570 nm.) parts of the spectrum. Attention is drawn to the fact that their absorption maxima are located nearby. This does not correspond to the accepted "primary" colors and is not consistent with the basic principles of the three-component model.

The third, hypothetical pigment sensitive to the violet-blue region of the spectrum, previously called cyanolab, has not been found to date.

In addition, it was not possible to find any difference between the cones in the retina, and it was not possible to prove the presence of only one type of pigment in each cone. Moreover, it was recognized that the pigments chlorolab and erythrolab are simultaneously present in the cone.

The non-allelic genes for chlorolab (encoded by the OPN1MW and OPN1MW2 genes) and erythrolab (encoded by the OPN1LW gene) are located on the X chromosomes. These genes have long been well isolated and studied. Therefore, the most common forms of color blindness are deuteronopia (a violation of the formation of chlorolab) (6% of men suffer from this disease) and protanopia (a violation of the formation of erytolab) (2% of men). At the same time, some people who have impaired perception of shades of red and green, better people with normal color perception perceive shades of other colors, such as khaki.

The cyanolalab OPN1SW gene is located on the seventh chromosome, so tritanopia (an autosomal form of color blindness in which the formation of cyanolalab is impaired) is a rare disease. A person with tritanopia sees everything in green and red colors and does not distinguish objects at dusk.

Nonlinear two-component theory of vision

According to another model (nonlinear two-component theory of vision by S. Remenko), the third “hypothetical” pigment cyanolab is not needed, the rod serves as a receiver for the blue part of the spectrum. This is explained by the fact that when the illumination brightness is sufficient to distinguish colors, the maximum spectral sensitivity of the rod (due to the fading of the rhodopsin contained in it) shifts from the green region of the spectrum to blue. According to this theory, the cone should contain only two pigments with adjacent sensitivity maxima: chlorolab (sensitive to the yellow-green region of the spectrum) and erythrolab (sensitive to the yellow-red part of the spectrum). These two pigments have long been found and carefully studied. At the same time, the cone is a non-linear ratio sensor that provides not only information about the ratio of red and Green colour, but also highlighting the level of yellow in this mixture.

The fact that with a color anomaly of the third type (tritanopia), the human eye not only does not perceive the blue part of the spectrum, but also does not distinguish objects at dusk ( night blindness), and this indicates precisely the lack of normal operation of the sticks. Proponents of three-component theories explain why always, at the same time as the blue receiver stops working, the sticks still cannot work.

In addition, this mechanism is confirmed by the long-known Purkinje effect, the essence of which is that at dusk, when the light falls, red colors turn black, and whites appear bluish. Richard Phillips Feynman notes that: "This is because the rods see the blue end of the spectrum better than the cones, but the cones see, for example, dark red, while the rods cannot see it at all."

At night, when the photon flux is insufficient for the normal functioning of the eye, vision is provided mainly by rods, so at night a person cannot distinguish colors.

To date, it has not yet been possible to come to a consensus on the principle of color perception by the eye.

Man and many species of animals with daytime activity distinguish colors, i.e., feel differences in the spectral composition of visible radiation and in the color of objects. The visible part of the spectrum includes radiation with different wavelengths, perceived by the eye in the form of different colors.

color vision due to the joint work of several light receivers, i.e. photoreceptors (See Photoreceptors) of the retina of different types, differing in spectral sensitivity. Photoreceptors convert the radiation energy into physiological excitation, which is perceived by the nervous system as different colors, because. The radiations excite the receivers to different degrees. The spectral sensitivity of photoreceptors of different types is different and is determined by the absorption spectrum of visual pigments (See Visual pigment).

Each light detector individually is not capable of distinguishing colors: all radiations for it differ in only one parameter - apparent brightness, or lightness, because. Light of any spectral composition has a qualitatively identical physiological effect on each of the photopigments. In this regard, any radiation at a certain ratio of their intensities can be completely indistinguishable from each other by one receiver. If there are several receivers in the retina (See retina), then the conditions for equality for each of them will be different. Therefore, for a combination of several receivers, many radiations cannot be equalized by any selection of their intensities.

Basics contemporary ideas about human color vision were developed in the 19th century by the English physicist T. Jung and the German scientist Hermann Helmholtz in the form of the so-called. three-component, or trichromatic, theory of color perception. According to this theory, there are three types of photoreceptors in the retina (cone cells (See Cone Cells)), sensitive to varying degrees to red, green, and blue light. However, the physiological mechanism of color perception makes it possible to distinguish not all radiations. Thus, mixtures of red and green in certain proportions are indistinguishable from yellow-green, yellow and orange radiations; mixtures of blue and orange can be equated with mixtures of red and cyan or blue-green. Some people hereditarily lack one (see) or two out of three light detectors, in the latter case there is no color vision.

Color vision is characteristic of many animal species. In vertebrates (monkeys, many species of fish, amphibians), and among insects in bees and bumblebees, color vision is trichromatic, like in humans. In ground squirrels and many species of insects, it is dichromatic, that is, it is based on the work of two types of light detectors, in birds and turtles, perhaps four. For insects, the visible region of the spectrum is shifted towards short-wave radiation and includes the ultraviolet range. Therefore, the world of insect colors is significantly different from the human one.

The main biological significance of color vision for humans and animals that exist in the world of non-luminous objects is the correct recognition of their color, and not just the discrimination of radiation. The spectral composition of the reflected light depends both on the color of the object and on the incident light and is therefore subject to significant changes with changing lighting conditions. Ability visual apparatus to correctly recognize (identify) the color of objects by their reflective properties in changing lighting conditions is called the constancy of color perception (see Color).

color vision - important component visual orientation of animals. In the course of evolution, many animals and plants have acquired a variety of signaling means, designed for the ability of animal "observers" to perceive colors. Such are the brightly colored corollas of flowers of plants that attract insects and pollinating birds; bright color of fruits and berries, attracting animals - seed distributors; warning and frightening coloration of poisonous animals and species that imitate them; "poster" coloring of many tropical fish and lizards, which has a signal value in territorial relationships; bright wedding attire, which is seasonal or permanent, characteristic of many species of fish, birds, reptiles, insects; finally, special means signaling that facilitates the relationship between parents and offspring in fish and birds.

Read more about color vision in the literature:

• Nyuberg N. D., Course of color science, M. - L., 1932;
• Kravkov S. V., Color vision, M., 1951;
• Kanaev II, Essays on the history of the problem of the physiology of color vision from antiquity to the 20th century, L., 1971;
• Physiology of sensory systems, part 1, L., 1971 (Guide to physiology);
• Orlov O. Yu., On the evolution of color vision in vertebrates, in the book: Problems of evolution, volume 2, Novosibirsk, 1972. O. Yu. Orlov.

COLOR VISION(synonym: color perception, color discrimination, chromatopsia) - the ability of a person to distinguish the color of visible objects.

Color has an impact on the general psycho-physiological state of a person and to a certain extent affects his ability to work. That's why great importance give color design of premises, equipment, instruments and other objects surrounding people at work and at home. Most favorable influence vision is affected by low-saturated colors of the middle part of the visible spectrum (yellow-green-blue), the so-called optimal colors. For color signaling, on the contrary, saturated (safety) colors are used.

Color - the property of light to cause a certain visual sensation in accordance with the spectral composition of the reflected or emitted radiation. There are seven primary colors: red, orange, yellow, green, blue, indigo and violet. Depending on the wavelength of light, three groups of colors are distinguished: long-wave (red, orange-red, orange), medium-wave (yellow, yellow-green, green) and short-wave (blue, indigo, violet).

Colors are divided into chromatic and achromatic. Chromatic colors have three main qualities: color tone, which depends on the wavelength of light radiation; saturation, depending on the proportion of the main color tone and impurities of other color tones; the brightness of the color, that is, the degree of its proximity to white. A different combination of these qualities gives a wide variety of shades of chromatic color. Achromatic colors (white, gray, black) differ only in brightness.

When two spectral colors with different wavelengths are mixed, the resulting color is formed. Each of the spectral colors has an additional color, when mixed with which an achromatic color is formed - white or gray. A variety of color tones and shades can be obtained by optical mixing of only three primary colors - red, green and blue. The number of colors and their shades perceived by the human eye is unusually large and amounts to several thousand.

The physiology of color vision is not well understood. Of the proposed hypotheses and theories of color vision, the most widespread is the three-component theory, the main provisions of which were first expressed by M. V. Lomonosov in 1756. Later these provisions were confirmed and developed by Jung (T. Young, 1802) and G. Helmholtz (1866). According to the Lomonosov-Jung-Helmholtz three-component theory, there are three perceiving apparatuses (receptors, elements) in the retina of the eye, which are excited to varying degrees under the action of light stimuli of different wavelengths (spectral sensitivity of the eye). Each type of receptor is excited mainly by one of the primary colors - red, green or blue, but to a certain extent it also reacts to other colors. Therefore, the curves of the spectral sensitivity of certain types of color-perceiving receptors partially overlap each other. Isolated excitation of one type of receptor causes a sensation of the primary color. With equal stimulation of all three types of receptors, a sensation of white color occurs. In the eye, a primary analysis of the radiation spectrum of the objects under consideration takes place with a separate assessment of the participation of the red, green and blue regions of the spectrum in them. In the cerebral cortex, the final analysis and synthesis of light exposure takes place, which are carried out simultaneously. Thanks to such a device of the visual analyzer, a person can distinguish quite well many color shades.

The three-component theory of color vision is confirmed by the data of morphophysiological studies. Spectrophotometric studies made it possible to determine the absorption spectra various types single photoreceptor cells. According to Dow (N. W. Daw, 1981), visual pigments(see) human retinal cones have the following absorption spectrum maxima: red-sensitive - 570-590 nm, green-sensitive - 535-555 nm and blue-sensitive - 440-450 nm. Modern electrophysiological studies of the organ of vision, conducted by L. P. Grigorieva and A. E. Fursova (1982), also confirmed the three-component theory of color vision. They showed that each of the three color stimuli corresponds to a certain type of biopotential of the retina and the visual area of ​​the cerebral cortex.

There are also other theories of color vision, which, however, have not received wide recognition. According to Hering's theory of color vision, three pairs of opposite colors are distinguished: red and green, yellow and blue, white and black. Each pair of colors in the retina corresponds to special - red-green, yellow-blue and white-black substances. Under the action of light, these substances are destroyed (dissimilation), and in the dark - restoration (assimilation). Various combinations processes of dissimilation and assimilation create a variety of color impressions. Hering's theory does not explain a number of phenomena, in particular color vision disorders. The ionic theory of Lazarev (1916) links color perception with the release of ions that excite color-recognizing receptors. According to his theory, the cones of the retina contain three light-sensitive substances: one of them absorbs mainly red light, the other - green, the third - blue; when light is absorbed, these substances decompose with the release of ions that excite color-recognizing receptors. Hartridge's polychromatic theory suggests that there are seven types of receptors.

A person distinguishes between night, or scotopic, vision, twilight, or mesopic, and daytime, or photopic, vision (see). This is primarily due to the presence in the retina (see) of the human eye of two types of photoreceptors - cones and rods, which served as the basis for substantiating the theory of duality of vision put forward by Schultze (M. J. Schultze, 1866) and further developed by M. M. Voinov (1874), Parino (H. Pari-naud, 1881) and Chris (J. Kries, 1894). Cones are located mainly in the central part of the retina and provide photopic vision - they perceive the shape and color of objects in the field of view; rods are located in the peripheral region, provide scotopic vision and detect weak light signals at the periphery of the visual field.

The maximum spectral sensitivity for cones is in the zone of 556 nm, and for rods - in the zone of 510 nm. This difference in the spectral sensitivity of cones and rods explains the Purkinje phenomenon, which consists in the fact that in low light conditions green and blue colors appear lighter than red and orange, while in daylight conditions these colors are approximately the same in lightness.

Color perception is influenced by the strength of the color stimulus and color contrast. For color discrimination, the brightness (lightness) of the surrounding background matters. The black background enhances the brightness of the color fields, as they appear lighter, but at the same time slightly reduces the color. The color perception of objects is also significantly affected by the color of the surrounding background. Figures of the same color on a yellow and blue background look different. This is the phenomenon of simultaneous color contrast.

Consistent color contrast appears as the vision of a complementary color after exposure to the primary color on the eye. For example, after examining the green lampshade of a lamp, white paper at first seems to be colored reddish. With prolonged exposure to color on the eye, a decrease in color sensitivity is noted, due to color “fatigue” of the retina, up to a state where two different colors are perceived as the same. This phenomenon is observed in persons with normal color vision and is physiological. However, with damage to the macula of the retina, neuritis and atrophy of the optic nerve, the phenomena of color fatigue occur faster.

In accordance with the three-component theory of color vision, normal color perception is called normal trichromacy, and persons with normal color vision are called normal trichromats. Quantitatively, color vision is characterized by the threshold of color perception, that is, the smallest value (strength) of a color stimulus perceived as a certain color.

Color vision disorders

Color vision disorders can be congenital or acquired. Congenital color vision disorders are more common in men. These disturbances, as a rule, are stable and come to light in both eyes, sensitivity is more often lowered to red or green colors. In this regard, the group with initial color vision impairments includes persons, although they distinguish all the main colors of the spectrum, but have reduced color sensitivity, that is, increased color perception thresholds.

The Chris-Nagel classification of congenital color vision disorders provides for three types of color vision disorders: 1 - abnormal trichromasia, 2 - dichromasia, 3 - monochromasia. Depending on the wavelength of the light stimulus and its location in the spectrum, color-perceiving receptors are denoted by Greek words: red - protos (first), green - deuteros (second), blue - tritos (third). In accordance with this, with abnormal trichromasia, a weakening of the perception of primary colors is distinguished: red - protanomaly, green - deuteranomaly, blue - tritanomaly. Dichromasia is characterized by a deeper impairment of color vision, in which the perception of one of three colors is completely absent: red (protanopia), green (deuteranopia) or blue (tritanopia). Monochromasia (achromasia, achromatopsia) means the absence of color vision, color blindness; while retaining only black and white perception. In addition to this classification, E. B. Rabkin (1937) identified three degrees (types) of color vision disorders in protanomaly and deuteranomaly: severe impairment - type A, moderate - type B and mild - type C.

Congenital disorders of color vision are usually called color blindness, after the English scientist J. Dalton, who suffered from a violation of the perception of red and described this phenomenon.

The most common among congenital color vision disorders (up to 70%) is anomalous trichromasia. Congenital disorders of color vision are not accompanied by a disorder of other visual functions. Persons with a congenital color vision disorder usually do not complain, and color vision disorders are detected only with a special study.

Acquired color vision disorders occur in diseases retina(cm.), optic nerve(see) or central nervous system; they can be observed in one or both eyes, are usually accompanied by a violation of the perception of all 3 colors, occur in combination with other visual disorders. Acquired color vision disorders can manifest as xanthopsia(see), cyanopsia and erythropsia(cm.). Xanthopsia - vision of objects in yellow, observed with jaundice, poisoning with certain substances and medicines(picric acid, santonin, quinacrine, amyl nitrite). Cyanopsia - the perception of objects in blue, observed after removal cataracts(cm.). Erythropsia is a violation of visual perception, in which visible objects appear to be painted in a reddish color. It is observed in persons with normal color perception as a result of prolonged fixation of the eye on a bright light source rich in UV rays, as well as after cataract surgery. Unlike congenital disorders color vision that are permanent, color vision altered as a result of the diseases listed above is normalized as they are cured.

Since a number of professions require the preservation of normal color perception, for example, for persons employed in all types of transport, in some industries, military personnel of certain military branches, they undergo a mandatory study of color vision. For this purpose, two groups of methods are used - pigment and spectral. Pigmentary studies include studies using color (pigment) tables and various test objects (sets of multi-colored skeins of wool, pieces of cardboard, etc.), spectral studies include studies using spectral anomaloscopes. The principle of studying color vision using color tables was proposed by J. Stilling. Of the color tables, Rabkin's polychromatic tables are most widely used. The main group of tables is intended for differential diagnosis of the forms and degree of congenital color vision disorders and their difference from acquired ones; control group of tables - to clarify the diagnosis in complex cases. In the tables, among the background circles of the same color, there are circles of the same brightness, but of a different color tone, constituting some figure or figure that is easily distinguishable by normally seeing people. Persons with a color vision disorder do not distinguish the color of these circles from the color of the circles of the background and therefore cannot distinguish between curly or digital imaging(color. Fig. 1-2). Ishihara tables serve the same purpose, they are used to detect color blindness in red and green.

A more subtle method for diagnosing color vision disorders is anomaloscopy - a study using special device- anomaloscope. In the USSR, a mass-produced device is the AN-59 anomaloscope (Fig.). Abroad, for the study of color vision, the Nagel anomaloscope is widespread.

The principle of operation of the device is based on the three-component color vision. The essence of the method lies in the color equation of two-color test fields, one of which is illuminated with a monochromatic yellow, and the second, illuminated by red and green, can change color from pure red to pure green. The subject must choose, by optical mixing of red and green, a yellow color corresponding to the control (Rayleigh equation). A person with normal color vision correctly selects a color pair by mixing red and green. A person with a color vision disorder cannot cope with this task. The method of anomaloscopy allows you to determine the threshold (acuity) of color vision separately for red, green, blue, to identify color vision disorders, to diagnose color anomalies.

The degree of violation of color perception is expressed by the coefficient of anomaly, which shows the ratio of green and red colors when the control field of the device is equalized with the test one. In normal trichromats, the anomaly coefficient ranges from 0.7 to 1.3, with protanomaly it is less than 0.7, with deuteranomaly it is more than 1.3.

The Rabkin spectral anomaloscope allows you to explore color vision in all parts of the visible spectrum. Using the device, it is possible to determine both congenital and acquired color vision disorders, color vision thresholds and the degree of functional stability of color vision.

To diagnose color vision disorders, the Farnsworth-Menzell hundred-tone test is also used. The test is based on the poor color discrimination of protanopes, deuteranopes and tritanopes in certain areas of the color wheel. The subject is required to arrange in the order of shades a series of pieces of cardboard different color in the form of a color wheel; in violation of color vision, the pieces of cardboard are not arranged correctly, that is, not in the order in which they should follow each other. The test has high sensitivity and provides information on the type of color vision impairment. A simplified Farnsworth test is also used, consisting of 15 colored test objects.

Bibliography: Kravkov S. V. Color vision, M., 1951, bibliogr.; Multi-volume guide to eye diseases, ed. V. N. Arkhangelsky, vol. 1, book. 1, p. 425, M., 1962; PadhamCh. and Sonder with J. Perception of light and color, trans. from English, M., 1978; Sensor systems, Vision, ed. G. V. Gershuni and others, p. 156, JI., 1982; With about to about l about in E. N. and Iz m and y l about in Ch. A. Color vision, M., 1984, bibliogr.; Adler's physiology of the eye, ed. by R. A. Moses, p. 545, St Louis a. o., 1981; H u r v i c h L. M. Color vision, Sunderland, 1981; System of ophthalmology, ed. by S. Duke Elder, v. 4, p. 617, L.* 1968.

A. A. Yakovlev-Budnikov.