Which color absorbs the least light? Color properties (scientific data for artists). From light to color and back
Item colors. Why do we see a sheet of paper as white and leaves of plants as green? Why do objects have different colors?
The color of any body is determined by its substance, structure, external conditions and processes occurring in it. These various parameters set the body's ability to absorb rays of one color incident on it (the color is determined by the frequency or wavelength of light) and reflect rays of a different color.
Those rays that are reflected enter the human eye and determine the color perception.
A sheet of paper appears white because it reflects white light. And since white light consists of violet, blue, cyan, green, yellow, orange and red, a white object must reflect all these colors.
Therefore, if only red light falls on white paper, then the paper reflects it, and we see it as red.
Similarly, if only green light falls on a white object, then the object must reflect green light and appear green.
If the paper is touched with red paint, the property of absorbing light by the paper will change - now only red rays will be reflected, all the rest will be absorbed by the paint. The paper will now appear red.
The leaves of trees and grass appear green to us because the chlorophyll contained in them absorbs red, orange, blue and violet colors. As a result, the middle of the solar spectrum is reflected from the plants - green.
Experience confirms the assumption that the color of an object is nothing but the color of the light reflected by the object.
What will happen if the red book is illuminated with green light?
At first it was assumed that the green light of the book should turn into red: when the red book is illuminated with only one green light, this green light should turn into red and be reflected so that the book should appear red.
This is contrary to experiment: instead of appearing red, in this case the book appears black.
Because the red book does not turn green to red and does not reflect green light, the red book must absorb green light so that no light is reflected.
Obviously, an object that does not reflect any light appears black. Further, when white light illuminates a red book, the book must reflect only the red light and absorb all other colors.
In fact, a red object reflects a little orange and a little purple, because the colors used in the production of red objects are never completely pure.
Similarly, a green book will reflect mostly green light and absorb all other colors, and a blue book will reflect mostly blue and absorb all other colors.
Recall that red, green and blue are the primary colors. (About primary and secondary colors). On the other hand, since yellow light is a mixture of red and green, a yellow book must reflect both red and green light.
In conclusion, we repeat that the color of a body depends on its ability to absorb, reflect, and transmit (if the body is transparent) light of different colors in different ways.
Some substances, such as clear glass and ice, do not absorb any color from the composition of white light. Light passes through both of these substances, and only a small amount of light is reflected from their surfaces. Therefore, both of these substances appear almost as transparent as the air itself.
On the other hand, snow and soap suds appear white. Further, the foam of some drinks, such as beer, may appear white, despite the fact that the liquid containing air in the bubbles may have a different color.
This foam appears to be white because the bubbles reflect light off their surfaces so that the light does not penetrate deep enough into each of them to be absorbed. Due to reflection from surfaces, soap suds and snow appear white instead of colorless like ice and glass.
Light filters
If you pass white light through an ordinary colorless transparent window glass, then white light will pass through it. If the glass is red, then light from the red end of the spectrum will pass through, and other colors will be absorbed or filtered out.
In the same way, green glass or some other green filter transmits mainly the green part of the spectrum, and a blue filter transmits mainly blue light or the blue part of the spectrum.
If two filters of different colors are attached to each other, then only those colors will pass that are passed by both filters. Two light filters - red and green - when added together, they practically do not let any light through.
Thus, in photography and color printing, by applying color filters, you can create the desired colors.
Theatrical effects created by light
Many of the curious effects we see on the stage are simple applications of the principles we have just been introduced to.
For example, you can make a figure in red on a black background almost completely disappear by switching the light from white to the appropriate shade of green.
The red color absorbs the green so that nothing is reflected, and hence the figure appears black and blends into the background.
Faces painted with red grease paint or covered with red blush appear natural under red spotlight, but appear black under green spotlight. The red will absorb the green so nothing will be reflected.
Similarly, red lips appear black in the green or blue light of a dance hall.
The yellow suit will turn bright red in the crimson light. A crimson suit will appear blue under a bluish-green spotlight.
By studying the absorbing properties of various paints, many different color effects can be achieved.
A team of scientists from the UK has pleased with a new scientific discovery, presenting to the general public the latest form of matter. Until recently, this kind of black shade was not known to anyone.
The discovered substance is called vantablack and, according to British discoverers, can once and for all change people's understanding of the universe.
The blackest material absorbs 99.965% of visible light, microwaves and radio waves
The ultra-black material has the ability to successfully absorb 99.96% of the light, and in this case we are talking only about the radiation that is visible to the human eye. Scientists from the UK led by Ben Jenson took up research on the original scientific phenomenon.
According to one of the researchers, the material is made up of a collection of carbon nanotubes. Such a phenomenon can be confidently compared with a human hair cut into 8-10 thousand layers - one such layer is the size of a carbon nanotube. The general composition can be represented as a field overgrown with grass, where a particle of light that has fallen begins to confidently bounce from one blade of grass to another. These peculiar “blades of grass” absorb light particles to the maximum, reflecting only a small part of the light.
The Secret of Vantablack - Vertically Oriented Nanotubes
The technology for creating this kind of tubes cannot be called innovative, however, Ben Jenson and his associates have only now managed to find worthy ways to use it. They invented a way to combine carbon nanotubes with materials used in modern telescopes and satellites. An example of such a material is aluminum foil. This fact means that photographs of the Earth and the Universe from space can be made clearer.
“The presence of stray light inside the telescope contributes to the increase in noise, resulting in a lack of sharp images,” Ben Jenson explains. “By using new materials to cover the interior baffles of the telescope as well as the aperture plates, stray light is reduced and the image is much sharper.”
Given the laws of physics, creating a material that absorbs 100% of light is almost impossible. For this reason alone, Jenson's invention today can be called a breakthrough on the verge of fantasy.
The US military has already become interested in a new type of material. After all, it can be used in "Stealth" technologies to reduce the visibility of aircraft for radar or create photographs during special reconnaissance missions. In addition, scientists are confident that even more opportunities for using vantablack will open up over time.
The colors that we attribute to objects are the result of the radiation reflected by them reaching our eyes. When illuminated with white light, a red brick appears red because it reflects radiation from the red part of the spectrum. It can reflect a lot of yellow and orange, some green, some purple and even blue. But most of the blue, violet and green radiation will be absorbed. You can accurately measure the color (spectral) reflection and absorption of any surface. Any color has its own spectral composition, whether it is an artificial dye or a natural color. Two colors that look almost the same to the eye may well have completely different spectral compositions.
The standard Kodak test chart allows the photographer to control the reproduction of bright and pastel colors, as well as the contrast and effect of color filters.
Pure (bright) colors are usually the result of selective (highly selective) absorption and reflection. They are characteristic of surfaces that reflect almost all radiation of certain wavelengths and absorb the rest, usually in the usual way. Desaturated (pastel or pale) colors are due to less selectivity; they are characteristic of surfaces with low absorptivity, reflecting in a wide range of wavelengths, with the dominant role of certain wavelengths. They are like bright colors mixed with a predominant amount of white.
Dimmed colors are the result of generally low reflectivity, with almost all wavelengths absorbed and only a few reflected. Such colors can be considered as some kind of pure colors mixed with black. From a photographic point of view, neither a muted nor a pastel color can be turned into a bright or saturated color. A color heavily saturated with white light can be dimmed, then it will turn into a muted gloomy shadow. A color with an excess of neutral density (an admixture of "gray") can be made lighter, but at the same time it becomes a faded shadow. When dealing with any color, we meet with a specular reflection or surface brilliance in the form of a dazzling glow. A pure rich red color may appear pale pink if it has a polished object that is exposed to light. Surface reflection adds unwanted white light impurities.
Relative illumination also has a strong influence. In the shade, the color looks less bright than the same color next to it in full sunlight. In the photograph for both cases separately, you can achieve the same color saturation by individual selection of exposure. If you shoot a plot that has both lights and deep shadows at the same time, then when transferring color, you will have to give preference to one of the options - either lights or shadows. The reason that many colored surfaces look less vibrant on overcast days is surface reflection, not light levels. A cloudy sky is reflected, and a completely diffused light gives a completely diffused sheen. Direct sunlight does not cause glare over a wide range of incidence angles and does not form a dazzling bright spot when looking at the surface "against the light."
Chapter 3. Optical properties of paints
Chiaroscuro in painting
Sunlight consists of seven main rays, which differ from each other by a certain wavelength and place in the spectrum.
Rays with a wavelength of 700 to 400 mµ, acting on our eyes, cause sensations of one of the colors that we see in the spectrum.
Infrared rays with a wavelength above 700 mµ. do not affect our eyes, and we do not see them.
Ultraviolet rays below 400 mµ. are also invisible to our eyes.
If a glass prism is placed in the path of a sunbeam, then on a white screen we see a spectrum consisting of simple colors: red, orange, yellow, green, blue, indigo and violet.
In addition to these seven colors, the spectrum consists of many different shades located between the bands of these colors and forming a gradual transition from one color to another (red-orange, yellow-orange, yellow-green, green-blue, blue-blue, etc.).
Spectral colors are the most saturated colors and the purest. Of the art paints, ultramarine, cinnabar and chrome yellow are comparatively higher in tone purity than the others and to some extent approach spectral colors, while most colors seem pale, whitish, cloudy and weak.
Refraction and reflection of light in the ink layer
When light falls on the surface of the paintings, part of it is reflected from the surface and is called reflected light, part is absorbed or refracted, that is, deviates from the original direction by a known angle, and is called refracted light. Light, falling on a flat and smooth surface of the ink layer, creates a sensation of brilliance when the eye is located in the path of the reflected light.
When the position of the picture changes, that is, when the angle of incidence of the light changes, the brilliance disappears, and we can see the picture well. Pictures with a matte surface reflect light diffusely, evenly, and we do not see glare on them.
The rough surface reflects the rays with its cavities and protrusions in all possible directions and at different angles from each part of the surface, in the form of tiny shines, of which only a small part enters the eye, creating a feeling of dullness and some whitishness. Varnish-oil paints and a thickly laid topcoat give the surface of the picture a sheen; excess wax and turpentine - haze.
As you know, when passing from one medium to another, depending on their optical density, color rays do not remain straight, but at the boundary that separates the medium, they deviate from their original direction and refract.
Rays of light, passing, for example, from air into water, are refracted in different ways: red rays are refracted less, violet rays are more.
The refractive index of any medium is equal to the ratio of the speeds of light in air and the speed in this medium. Thus, the speed of light in air is 300,000 km/s, in water about 230,000 km/s, therefore, the numerical index of water refraction will be 300,000/230,000 = 1.3, air - 1, oil -1.5.
A spoon in a glass of water seems broken; glass in air shines more than under water, since the gel shows a refraction of glass more than air. A glass rod placed in a vessel with cedar oil becomes invisible due to the almost identical refractive index of glass and oil.
The amount of reflected and refracted light depends on the refractive indices of the two media separated by the surface. The color of paints is explained by their ability, depending on the chemical composition and physical structure, to absorb or reflect certain rays of light. If the refractive indices of two substances are the same, then there is no reflection, with different indices, part of the light will be reflected, and part will be refracted.
Art paints are made up of a binder (oil, resin and wax) and pigment particles. Both have different refractive indices, so the reflection inside the paint layer and the color of the paint will depend on the composition and properties of these two substances.
The ground of paintings can be neutral, white or tinted. We already know that light, falling on the surface of the paint layer, is partially reflected, partially refracted and passes into the paint layer.
Passing through the pigment particles, the refractive indices of which differ from the refractive indices of the binder, the light is divided into reflected and refracted. In this case, the reflected light will be colored and come to the surface, and the refracted light will pass inside the paint layer, where it will meet pigment particles and will also be reflected and refracted. Thus, the light will reflect off the surface of the painting in a color complementary to that absorbed by the pigment.
We see a variety of colors and shades in nature due to the fact that objects have the ability to selectively absorb different amounts of light falling on them or selectively reflect light.
Any paint light has certain basic properties: lightness, hue and saturation.
Colors that reflect, all the rays that fall on them in the proportion in which they constitute light, appear white. If some of the light is absorbed and some is reflected, the colors appear gray. Black colors reflect the minimum amount of light.
Objects from which more light is reflected appear lighter to us, less light is reflected from dark objects. White pigments differ in the amount of reflected light.
Barite white has the whitest color.
Barite white reflects 99% of light, zinc white - 94%; lead white - 93%; gypsum - 90%; chalk - 84%.
White, gray and black colors differ from each other in lightness, i.e., the amount of reflected light.
Colors are divided into two groups: achromatic and chromatic.
Achromatic have no color tone, such as whites, grays, and darks; chromatic have a color tone.
Colors (red, orange, yellow, green, blue, etc.), except for white, gray and dark, reflect a certain part of the rays of the spectrum, mostly the same as its color, and therefore they differ in color tone. If white or black is added to red or green, they will be light red and dark red, or light green and dark green.
Lightly colored colors almost do not differ from gray, on the contrary, strongly colored colors (to which there is little or no achromatic admixture) differ significantly from gray in color.
The degree of difference between a chromatic color and an achromatic color equal to it in lightness is called saturation.
The colors of the spectrum do not contain white, so they are the most saturated.
Paints with fillers (blancfix, kaolin, etc.) and natural pigments (ocher, sienna, etc.), reflecting a large number of rays close in composition to white, have a soft and whitish, i.e., slightly saturated, tone.
The more fully the paint reflects certain rays, the brighter its color will be. Any paint mixed with white becomes paler.
There are no such colors that would reflect only a beam of one color, and absorb all the rest. Paints reflect composite light with a predominance of the beam that determines its color, so, for example, in ultramarine this light will be blue, in chromium oxide it will be green.
Additional colors
When the paint layer is illuminated, some of the rays are absorbed, some rays are larger, others less. Therefore, the reflected light will be colored in a color complementary to that which was absorbed by the paint.
If the paint from the rays falling on it absorbs orange, and reflects the rest, then it will be colored blue, when absorbing red - green, when absorbing yellow - blue.
By simple experience, we are convinced of this: if we put another prism in the path of decomposition of the rays by a glass prism and move it sequentially along the entire spectrum, deflecting individual rays of the spectrum to the side, first red, orange, yellow, yellow-green, green and bluish-green, then the color of the mixture of the remaining rays will be colored bluish-green, cyan, blue, violet, purple and red.
By mixing these two components (red and green, orange and blue, etc.), we again get white.
White color can also be obtained by mixing a pair of separate spectral rays, for example, yellow and blue, orange and blue, etc.
Colors simple or complex, which give white when optically mixed, are called complementary colors.
To any color, you can pick up another color, which, when optically mixed, gives an achromatic color in certain quantitative ratios.
Additional primary colors will be:
Red Green.
Orange - blue.
Yellow - blue.
In the color wheel, which consists of eight color groups, complementary colors are opposite each other.
When mixing two complementary colors in certain quantitative ratios, colors are obtained that are intermediate in tone, for example: blue with red gives purple, red with orange - red-orange, green with blue - green-blue, etc.
Intermediate colors: purple, crimson, red-orange, yellow-orange; yellow-green, green-blue, blue-blue.
The main and intermediate colors of the spectrum, we can arrange in order in the following row:
No. 1a Raspberry
No. 1 Red
No. 2a Red-orange
No. 2 Orange
No. For Yellow-Orange
No. 3 Yellow
No. 4a Yellow-green
No. 4 Green
No. 5a Green-blue
No. 5 Blue
No. 6a Blue-blue
No. 6 Blue
No. 7a Purple
Additional intermediate colors:
Violet and crimson-yellow-green.
Red-orange - green-blue.
Yellow-orange - blue-blue.
Additional primary and intermediate colors are three numbers apart.
Transparent and opaque paints.
Paints that absorb some of the light and transmit some are called transparent, and those that only reflect and absorb are called opaque or opaque.
Transparent or glazing paints include those paints whose binder and pigment have equal or similar refractive indices.
Transparent artistic oil paints usually have a refractive index of the binder and pigment of 1.4-1.65.
When the difference between the refractive indices of the pigment and the binder is not higher than 1, the paint reflects little light on the interface, most of the light passes deep into the paint layer.
Due to the selective absorption by the pigment particles, the light is intensively colored on its way and, falling on the ground, returns back to the surface of transparent substances.
The soil in this case is prepared white and matte so that it reflects the rays more fully.
Larger pigment particles in the paint give an increase in transparency.
Transparent paints are of great value for painting compared to opaque ones, since they have a deep tone and are the most saturated.
Transparent paints include:
Refractive indices
Kraplak 1.6-1.63
Ultramarine 1.5-1.54
Blue cobalt 1.62-1.65
Blancfix 1.61
Alumina 1.49-1.5
When, for example, a transparent green paint is illuminated with daylight, part of the mainly red, i.e. additional, rays will be absorbed, a small part will be reflected from the surface, and the remaining unabsorbed ones will pass through the paint and undergo further absorption. Light that is not absorbed by the paint will pass through it and then be reflected, come to the surface and determine the color of the transparent object - in this case, green.
Covering paints are those in which the refractive indices of the binder and the pigment have a large difference.
Light rays are strongly reflected from the surface of the opaque paint and are already slightly transparent in a thin layer.
Covering oil paints, when mixed with transparent mixtures, take on various shades, captivating artists with their depth and transparency compared to the cloudy whites of zinc or lead white.
The most opaque are adhesive paints - gouache, watercolor and tempera, since after the paint dries, the space in it is filled with air with a lower refractive index compared to water.
Covering paints include: lead white (refractive index 2), zinc white (refractive index 1.88), chromium oxide, cadmium red, etc.
Mixing colors.
Mixing paints is used to obtain different color shades.
Usually in practice three methods of mixing are used:
1) mechanical mixing of paints; 2) applying paint to paint; 3) spatial mixing;
Optical changes during mixing of colors can be well disassembled by the example of the passage of daylight successively through yellow and blue glasses.
Light, passing through yellow glass at first, will lose almost all blue and violet colors and pass through blue-green, green, yellow-green, yellow, orange and red, then blue glass will absorb red, orange and yellow and let green through, therefore, when passing through Light through two colored glasses absorbs all colors except for green.
As a rule, pigments absorb colors that are close to the complementary color.
If, having prepared a mixture of yellow cadmium with blue cobalt on the palette, we apply them to the canvas, then we will make sure that the light falling on the paint layer of this mixture, passing through yellow cadmium, will lose blue and violet rays, and passing through blue paint will lose red, orange and yellow rays. As a result, the reflected light and the color of the ink mixture will be green.
The mixed paint is darker than any one paint taken for mixing, since the mixed paints, in addition to green, contain other colors. Therefore, it is impossible to obtain a very intense light green - pol-veronese - by tinting.
Cinnabar with Prussian blue gives a gray dye. Kraplak with Prussian blue, cobalt blue and ultramarine form good violet hues, since kraplak contains more violet than cinnabar and, therefore, is more suitable for mixing with blues.
The method of applying one layer of transparent paint to another in order to obtain different shades is called glazing.
When glazed, the upper layers of paints must be transparent so that the lower layer or primer can be seen through them.
As in the case of a single layer, the light illuminating the picture with multilayer writing will have the same reflection and absorption phenomena as in the previous example with a mixture of yellow and blue paints.
It should be noted that depending on the covering properties of paints, the thickness of the paint layer and the order of application, one or another reflected light will prevail.
So, if the paints are yellow and blue transparent, then the largest part of the light will be reflected from the ground and the reflected light will be closer to green.
If the yellow topcoat is placed on top of the ink layer, then the predominant amount of light will be reflected from the top yellow layer and the color of the mixture will be closer to yellow.
By increasing the thickness of the upper yellow paint layer, the light, having traveled a long way, will become more intense.
By changing the ink stacking order (for example, blue paint will be on top and yellow paint on the bottom), the light reflected from the first layer will be blue, in the lower layer it will be blue-green, and from the ground it will be reflected green, as a result, the color of the entire paint layer will be blue-green.
Looking at two small surfaces of different colors at a great distance, our eye is not able to see each color separately, and they merge into one common color.
Thus, at some distance we also see sand of the same color, despite the fact that it consists of countless multi-colored grains of sand.
A mosaic is based on spatial mixing, which is made up of small pieces of colored stones (smalt). In painting, small specks and dashes of different colors give a variety of shades when viewed from a distance.
The method of spatial mixing increases the lightness of colors. So, if one or two thin strips of white are drawn in the red strip, then the red strip will receive bright illumination, which cannot be achieved by mixing with white. This technique significantly changes the intensity of colors (increases or decreases). Artists almost very easily get the desired tone from a mixture of paints.
Rays of light reflected by individual colored dots go so close to each other that our organ of vision perceives them with the same light-sensitive nerve ending (cone) and we see one common color, as if the colors were actually mixed.
When mixing colors, we get the impression of a common color from the reflection of various rays, since the eye does not distinguish between the individual components of the mixture due to their small size.
Color contrasts.
Considering two small painted surfaces lying side by side, one orange and the other gray, the latter will seem bluish to us.
It is well known that when combined, blue and orange colors, changing in tone, mutually reinforce in brightness, the same pairs of colors that increase in brightness will be yellow and blue, red and green, purple and yellow-green.
A change in color under the influence of colored surfaces lying nearby is called simultaneous contrast and is a consequence of the stimulation of three nerve centers of the eye independent of each other by light.
The paints placed on the canvas change their color depending on the color of the paints that are near them (for example, gray against a yellow background turns blue, and blue turns yellow). If we put the paint on a background that is lighter in color, then the paint will seem darker to us, and on the contrary, on a darker background, it will seem lighter. Green paint on a red background becomes brighter; while the same paint, placed on a greenish background, will appear dirty, due to the action of an additional colorful color. As a rule, paints that are close in color lower the intensity of the tone.
If, after a long examination of one color surface, the gaze is transferred to another, then the perception of the second will to a certain extent be determined by the color of the first surface (after a dark first surface, the second surface will appear lighter, after red, white will appear greenish).
In the eye, an impression of a contrasting color, close in hue to the complementary color, appears.
Additional to blue will be yellow, and contrasting orange, to purple additional yellow-green, and contrasting - yellow.
Changing the perception of color depending on what color acted on the eye before is called sequential contrast.
Placing separate pairs of colors side by side, their shades change as follows:
1. Yellow and green: yellow takes on the color that precedes it in the spectrum,
i.e. orange, and green is the color of the next, i.e. blue.
2. Red and yellow: red changes to magenta and yellow to yellow
3. Red and Green: Complementary colors do not change, but are enhanced in
brightness and saturation.
4. Red and Cyan: Red becomes orange and cyan approaches
green, that is, two colors that are two or more numbers apart in the spectrum take on color
additional neighbor.
Knowing and using color contrast techniques, you can change the tone of colors and color of the picture in the desired direction.
Along with the contrasts of colors, the reproduction of the space and depth of the picture is of great importance in painting.
In addition to perspective building, the depth of the picture can be achieved by the placement of colors: dark colors create the illusion of depth; bright colors, light places come to the fore.
To achieve a high light and color intensity of paints and obtain a variety of shades, artists use the method of mutual influence of the color of paints (color contrast), arranging them in certain spatial relationships.
If you put a small spot of white paint on a black background, then the white spot will appear the lightest, while the same white spot on a gray background will seem darkish. Such a contrast is more pronounced when the background is significantly different in lightness from the color of the paints. In the absence of such a contrast in lightness, adjacent paints that are close in hue appear dull. In the paintings of the great masters, glare of light, surrounded by dark tones, gives the impression of very bright and light colors.
In addition to the contrast in lightness, there is a color contrast. Two paints placed side by side influence each other, causing a mutual change in their shades towards a complementary color.
The influence of lighting on the color of paints.
The paint layer, depending on the lighting, takes on various shades during the day, since sunlight, under the influence of many reasons, modifies its spectral composition.
Depending on the nature of the light source, the color of the paints may vary. Cobalt blue under artificial lighting, due to the presence of yellow rays in the composition of the light, seems greenish; ultramarine - almost black.
The color of paints also depends on the shade of the light source, for example, in cold lighting, cold colors become brighter. The color of paints darkens when exposed to light of the opposite tone: orange from blue, purple from yellow.
Cobalt blue turns gray under artificial lighting and acquires brightness and color depth in daylight sunlight, on the contrary, cadmium yellow, kraplak red and cinnabar appear brighter under artificial lighting.
Based on a series of experiments, it was established that when illuminated with kerosene, yellow, orange, red, and in general all warm colors rose in tone, while cold colors (blue and green) decreased, i.e., darkened.
Chromium oxide becomes gray-green, cobalt blue takes on a purple hue, ultramarine becomes cloudy, Prussian blue turns green, etc.
Consequently, when the nature of the light source changes, such strong optical changes appear in the paintings that the relationships between tones and the overall color of the painting are completely violated, since artificial lighting has a different composition of rays (yellow and orange rays), which is very different from the composition of the rays of daylight. The influence of artificial light on the shade of paints is perfectly proved by the experiments carried out by prof. Petrushevsky. (S. Petrudpevsky. Paints and painting, St. Petersburg, 1881, pp. 25-36.)
Colors of translucent, hazy media
Dusty air, smoke, fog, turbid water, milk, foam, etc. are commonly called turbid media in which the smallest particles of a solid or gaseous substance are in suspension.
Dusty air and smoke are, as it were, a homogeneous mixture of air and solid particles; milk-water and the smallest drops of oil; mist-air and water droplets; foam - water and air. A characteristic property of such mixtures or turbid media is the ability to reflect some of the light and transmit some.
Short-wavelength rays of light (blue and violet), falling on the smallest suspended particles - solid (smoke), liquid (fog) or gaseous (foam) - almost the same size as the wavelength, are reflected and scattered in all directions, and we see blue or blue light.
Rays with a longer wavelength (red, orange and yellow) pass freely through the smallest suspended particles, coloring the light in dark colors.
A mass of tiny solid and liquid particles is carried in the air, therefore, in the evening, as the sun approaches the horizon, its rays (red, orange and yellow, that is, with a longer wavelength), passing through a large layer of polluted air, are colored in Orange color.
We also observe a similar phenomenon on foggy days:
high humidity enhances the color of the sun at sunset. By mixing a small amount of opaque paint with a binder (oil or varnish), we get translucent paints. Applied to a dark surface, they become cold, on a light surface they become warmer for the same reasons mentioned above.
reflexes.
Reflexes, or coloring of light, are the result of its reflection by illuminated objects standing close to each other.
Colored light reflected from the first object falls on another object, this produces a selective absorption and a change in color tone.
If light falls on the folds of matter, then the protruding parts, illuminated directly by the light source, acquire a color that differs from the color of the depressions.
Inside the folds, the colored light reflected by the fabric falls, it will be darker, while part of the light after reflection again penetrates deep into the folds, and the color of 1 folds in depth will be richer and darker than on the protruding parts.
Depending on the spectral composition of the light and selective absorption, the color tone changes (for example, yellow matter in the depths of the folds sometimes has a greenish tint).
Chiaroscuro in painting.
The location of light on objects in different strengths is called chiaroscuro. The phenomenon of chiaroscuro depends on the total strength of illumination and on the color of objects. If the lighting in the shade is ten times weaker, then all colors, regardless of color, while in the shade will reflect ten times less light than the same colors in the light.
The light reflected by objects in the shadow is reduced evenly, and the ratio between the colors of objects in the shadow does not change, only a general decrease in the brightness of the color occurs.
When transferring shadows, they sometimes use the admixture of black tones with paints, but then, instead of the impression of a shadow, an impression of dirt is created, since in the shadow a decrease in brightness occurs with a uniform darkening of all colors.
Light shadows in bright light are more noticeable on dark-colored objects, on light ones they are whitish and very weak in tone.
Light objects with deep shadows appear more saturated.
In very dense shadows, only the lightest objects retain color differences, while the darkest ones merge with each other.
In low light, colors lose their saturation.
Chiaroscuro plays a big role in building the volume of the form. Usually highlights are written in corpus, and shadows and penumbra are transparent.
With an excessive abundance of light or a lack of it, objects are almost indistinguishable, and the volume is almost not felt. Lighting in the picture is kept mainly in medium strength.
Some old masters used the techniques of double lighting: brighter for the main figures and weaker for the secondary ones, which made it possible to depict the main figures in relief and convex, in rich colors; the background is poorly lit, and there are almost no color shades in it.
The technique of double lighting allows the audience to focus on the main figures and create an impression of depth.
Skillful use of chiaroscuro gives a very effective result in painting practice.
Whether we realize it or not, we are in constant interaction with the outside world and take on the influence of various factors of this world. We see the space around us, we constantly hear sounds from various sources, we feel heat and cold, we do not notice that we are under the influence of natural background radiation, and we are constantly in the radiation zone that comes from a huge number of sources of telemetry, radio and telecommunication signals. Almost everything around us emits electromagnetic radiation. Electromagnetic radiation is electromagnetic waves created by various radiating objects - charged particles, atoms, molecules. Waves are characterized by repetition frequency, length, intensity, and a number of other characteristics. Here is just an introductory example. The heat emanating from a burning fire is an electromagnetic wave, or rather infrared radiation, and of very high intensity, we do not see it, but we can feel it. The doctors took an x-ray - irradiated with electromagnetic waves with a high penetrating power, but we did not feel and did not see these waves. The fact that electric current and all devices that operate under its influence are sources of electromagnetic radiation, of course, you all know. But in this article I will not tell you the theory of electromagnetic radiation and its physical nature, I will try to explain in a less simple language what visible light is and how the color of the objects that we see is formed. I started talking about electromagnetic waves to tell you the most important thing: Light is an electromagnetic wave that is emitted by a heated or excited state of matter. The role of such a substance can be played by the sun, an incandescent lamp, an LED flashlight, a fire flame, various kinds of chemical reactions. There can be quite a lot of examples, you yourself can bring them in much more than I wrote. It should be clarified that by the term light we mean visible light. All of the above can be represented in the form of such a picture (Figure 1).
Figure 1 - The place of visible radiation among other types of electromagnetic radiation.
Figure 1 visible radiation presented in the form of a scale, which consists of a "mixture" of different colors. As you may have guessed, this range. A wavy line (sinusoidal curve) passes through the entire spectrum (from left to right) - this is an electromagnetic wave that reflects the essence of light as electromagnetic radiation. Roughly speaking, any radiation is a wave. X-ray, ionizing, radio emission (radio receivers, television communications) - it does not matter, they are all electromagnetic waves, only each type of radiation has a different wavelength of these waves. A sinusoidal curve is just a graphical representation of radiated energy that changes over time. This is a mathematical description of the radiated energy. In figure 1, you can also notice that the depicted wave seems to be slightly compressed in the left corner and expanded in the right. This suggests that it has a different length in different areas. The wavelength is the distance between its two adjacent peaks. Visible radiation (visible light) has a wavelength that varies from 380 to 780nm (nanometers). Visible light is just a link of one very long electromagnetic wave.
From light to color and back
You know from school that if you put a glass prism in the path of a ray of sunlight, then most of the light will pass through the glass, and you can see the multi-colored stripes on the other side of the prism. That is, initially there was sunlight - a beam of white color, and after passing through a prism it was divided into 7 new colors. This suggests that white light is made up of these seven colors. Remember, I just said that visible light (visible radiation) is an electromagnetic wave, and so, those multi-colored stripes that turned out after the passage of the sun's ray through a prism are separate electromagnetic waves. That is, 7 new electromagnetic waves are obtained. Look at figure 2.
Figure 2 - The passage of a beam of sunlight through a prism.
Each wave has its own length. You see, the peaks of neighboring waves do not coincide with each other: because the red color (red wave) has a length of about 625-740nm, the orange color (orange wave) has a length of about 590-625nm, the blue color (blue wave) has a length of 435-500nm., I will not give figures for the remaining 4 waves, I think you understand the essence. Each wave is an emitted light energy, i.e. a red wave emits red light, an orange wave emits orange, a green wave emits green, and so on. When all seven waves are emitted at the same time, we see a spectrum of colors. If we mathematically add the graphs of these waves together, then we get the original graph of the electromagnetic wave of visible light - we get white light. Thus, it can be said that range visible light electromagnetic wave sum waves of different lengths, which, when superimposed on each other, give the original electromagnetic wave. The spectrum "shows what the wave consists of." Well, to put it quite simply, the spectrum of visible light is a mixture of colors that make up white light (color). I must say that other types of electromagnetic radiation (ionizing, X-ray, infrared, ultraviolet, etc.) also have their own spectra.
Any radiation can be represented as a spectrum, though there will be no such colored lines in its composition, because a person is not able to see other types of radiation. Visible radiation is the only type of radiation that a person can see, which is why this radiation is called visible. However, the energy of a certain wavelength does not have any color by itself. Human perception of electromagnetic radiation in the visible range of the spectrum occurs due to the fact that in the human retina there are receptors that can respond to this radiation.
But is it only by adding the seven primary colors that we can get white? Not at all. As a result of scientific research and practical experiments, it has been found that all the colors that the human eye can perceive can be obtained by mixing just three primary colors. Three primary colors: red, green, blue. If by mixing these three colors you can get almost any color, then you can get white! Look at the spectrum that was shown in Figure 2, three colors are clearly visible on the spectrum: red, green and blue. It is these colors that underlie the RGB (Red Green Blue) color model.
Let's check how it works in practice. Let's take 3 light sources (spotlights) - red, green and blue. Each of these spotlights emits only one electromagnetic wave of a certain length. Red - corresponds to the radiation of an electromagnetic wave with a length of approximately 625-740nm (the beam spectrum consists only of red), blue emits a wave of 435-500nm (the beam spectrum consists of blue only), green - 500-565nm (only green color in the beam spectrum ). Three different waves and nothing else, there is no multi-colored spectrum and additional colors. Now let's direct the spotlights so that their beams partially overlap each other, as shown in Figure 3.
Figure 3 - The result of overlaying red, green and blue colors.
Look, at the places where the light rays intersect with each other, new light rays have formed - new colors. Green and red formed yellow, green and blue - cyan, blue and red - magenta. Thus, by changing the brightness of the light rays and combining colors, you can get a wide variety of color tones and shades of color. Pay attention to the center of the intersection of green, red and blue: in the center you will see white. The one we talked about recently. White color is the sum of all colors. It is the "strongest color" of all the colors we see. The opposite of white is black. Black color is the complete absence of light at all. That is, where there is no light - there is darkness, everything becomes black there. An example of this is Figure 4.
Figure 4 - Lack of light emission
I somehow imperceptibly move from the concept of light to the concept of color and I don’t tell you anything. It's time to be clear. We have found out that light- this is the radiation that is emitted by a heated body or a substance in an excited state. The main parameters of the light source are the wavelength and light intensity. Colour is a qualitative characteristic of this radiation, which is determined on the basis of the resulting visual sensation. Of course, the perception of color depends on the person, his physical and psychological condition. But let's assume that you are feeling well enough, reading this article and you can distinguish the 7 colors of the rainbow from each other. I note that at the moment, we are talking about the color of light radiation, and not about the color of objects. Figure 5 shows color and light parameters that are dependent on each other.
Figures 5 and 6 - Dependence of color parameters on the source of radiation
There are basic color characteristics: hue, brightness (Brightness), lightness (Lightness), saturation (Saturation).
Color tone (hue)
- This is the main characteristic of a color that determines its position in the spectrum. Remember our 7 colors of the rainbow - in other words, 7 color tones. Red color tone, orange color tone, green color tone, blue, etc. There can be quite a lot of color tones, I gave 7 colors of the rainbow just as an example. It should be noted that such colors as gray, white, black, as well as shades of these colors do not belong to the concept of color tone, as they are the result of mixing different color tones.
Brightness
- A feature that shows how strong light energy of one or another color tone (red, yellow, violet, etc.) is emitted. What if it doesn't radiate at all? If it does not radiate, it means that it is not there, but there is no energy - there is no light, and where there is no light, there is black color. Any color at the maximum decrease in brightness becomes black. For example, a chain of reducing the brightness of red: red - scarlet - burgundy - brown - black. The maximum increase in brightness, for example, the same red color will give "maximum red color".
Lightness
– The degree of proximity of a color (hue) to white. Any color at the maximum increase in lightness becomes white. For example: red - crimson - pink - pale pink - white.
Saturation
– The degree of closeness of a color to gray. Gray is an intermediate color between white and black. The gray color is formed by mixing in equal amounts of red, green, blue with a decrease in the brightness of radiation sources by 50%. Saturation changes disproportionately, i.e. lowering the saturation to a minimum does not mean that the brightness of the source will be reduced to 50%. If the color is already darker than gray, it will become even darker as the saturation is lowered, and as the saturation decreases further, it will turn completely black.
Such color characteristics as hue (hue), brightness (Brightness), and saturation (Saturation) underlie the color model HSB (otherwise called HCV).
In order to understand these color characteristics, consider the color palette of the Adobe Photoshop graphics editor in Figure 7.
Figure 7 - Adobe Photoshop Color Picker
If you look closely at the picture, you will find a small circle, which is located in the upper right corner of the palette. This circle shows which color is selected on the color palette, in our case it is red. Let's start to figure it out. First, let's look at the numbers and letters that are located on the right half of the picture. These are the parameters of the HSB color model. The topmost letter is H (hue, color tone). It determines the position of a color in the spectrum. A value of 0 degrees means that it is the highest (or lowest) point on the color wheel - that is, it is red. The circle is divided into 360 degrees, i.e. It turns out that it has 360 color tones. The next letter is S (saturation, saturation). We have a value of 100% - this means that the color will be "pressed" to the right edge of the color palette and have the maximum possible saturation. Then comes the letter B (brightness, brightness) - it shows how high the point is on the color palette and characterizes the intensity of the color. A value of 100% indicates that the color intensity is at its maximum and the dot is "pressed" to the top edge of the palette. The letters R(red), G(green), B(blue) are the three color channels (red, green, blue) of the RGB model. In each, each of them indicates a number that indicates the amount of color in the channel. Recall the spotlight example in Figure 3, when we figured out that any color can be made by mixing three light beams. By writing numerical data to each of the channels, we uniquely determine the color. In our case, the 8-bit channel and the numbers range from 0 to 255. The numbers in the R, G, B channels indicate the light intensity (color brightness). We have a value of 255 in the R channel, which means that this is a pure red color and it has the maximum brightness. Channels G and B are zeros, which means the complete absence of green and blue colors. In the very bottom column you can see the code combination #ff0000 - this is the color code. Each color in the palette has its own hexadecimal code that defines the color. There is a wonderful article Color theory in numbers, in which the author tells how to determine the color by the hexadecimal code.
In the figure, you can also notice the crossed-out fields of numerical values with the letters "lab" and "CMYK". These are 2 color spaces, according to which colors can also be characterized, they are generally a separate conversation and at this stage there is no need to delve into them until you understand RGB.
You can open the Adobe Photoshop color palette and play around with the color values in the RGB and HSB boxes. You will notice that changing the numeric values in the R, G, and B channels will change the numeric values in the H, S, B channels.
Object color
It's time to talk about how it happens that the objects around us take on their color, and why it changes with different lighting of these objects.
An object can only be seen if it reflects or transmits light. If the object is almost completely absorbs incident light, then the object takes black color. And when the object reflects almost all the incident light, it receives White color. Thus, we can immediately conclude that the color of the object will be determined by the number absorbed and reflected light with which this object is illuminated. The ability to reflect and absorb light is determined by the molecular structure of the substance, in other words, by the physical properties of the object. The color of the object "is not inherent in it by nature"! By nature, it contains physical properties: to reflect and absorb.
The color of the object and the color of the radiation source are inextricably linked, and this relationship is described by three conditions.
- First condition: An object can take on color only when there is a light source. If there is no light, there will be no color! Red paint in a can will look black. In a dark room, we cannot see or distinguish colors because there are none. There will be a black color of the entire surrounding space and objects in it.
- Second condition: The color of an object depends on the color of the light source. If the light source is a red LED, then all objects illuminated by this light will have only red, black and gray colors.
- And finally, the third condition: The color of an object depends on the molecular structure of the substance that makes up the object.
Green grass looks green to us because, when illuminated with white light, it absorbs the red and blue wavelengths of the spectrum and reflects the green wavelength (Figure 8).
Figure 8 - Reflection of the green wave of the spectrum
The bananas in Figure 9 appear yellow because they reflect the waves in the yellow region of the spectrum (yellow spectrum wave) and absorb all other wavelengths of the spectrum.
Figure 9 - Reflection of the yellow wave of the spectrum
The dog, the one shown in Figure 10, is white. White color is the result of reflection of all waves of the spectrum.
Figure 10 - Reflection of all waves of the spectrum
The color of the object is the color of the reflected wave of the spectrum. This is how objects acquire the color we see.
In the next article, we will talk about a new color characteristic -