Color attributes in computer graphics. Color systems in computer graphics. Color model CMY (K)

To describe the color shades that can be reproduced on a computer screen and on a printer, special tools have been developed - color models(or color systems). To successfully apply them in computer graphics, you must:

Understand the features of each color model;

Be able to identify a particular color using different color models;

Understand how different graphics programs deal with color coding;

Understanding why color casts displayed on a monitor are difficult to accurately reproduce when printed.

We see objects because they emit or reflect light.

Light- electromagnetic radiation.

Color characterizes the effect of radiation on the human eye. Thus, the rays of light falling on the retina of the eye produce a sensation of color.

Emitted light - it is light coming from a source such as the sun, a light bulb, or a monitor screen.

Reflected light is light that bounces off the surface of an object. This is what we see when we look at any object that is not a source of light.

The emitted light, coming directly from the source to the eye, retains all the colors from which it was created. But this light can change when reflected from an object or if a person has vision diseases

Like the sun and other light sources, the monitor emits light. The paper on which the image is printed reflects light. Since color can be obtained in the process of radiation and in the process of reflection, there are two opposite methods of describing it: systems of additive and subtractive colors.

2.1. Additive color system - RGB color model

If you look at the screen of a working monitor or TV from a close distance (or even better with a magnifying glass), then it is not difficult to see many tiny dots of red (Red), green (Green) and blue (Blue) flowers. The fact is that on the surface of the screen there are thousands of phosphorescent color dots, which are bombarded by electrons at high speed. Color dots emit light when exposed to an electron beam. Since the dimensions of these dots are very small (about 0.3 mm in diameter), adjacent multi-colored dots merge, forming all other colors and shades, for example:

red + green = yellow,

red + blue = magenta,

green + blue = blue,

red + green + blue = white.

In the figure (fig. 3) you can see the receipt of different colors in the RGB system.

Figure 3. RGB color rendering system

The computer can precisely control the amount of light emitted through each point on the screen. Therefore, by changing the intensity of the glow of the colored dots, you can create a wide variety of shades.

Thus, the additive (add) color is obtained by combining (summing) the rays of the three primary colors - red, green and blue. If the intensity of each of them reaches 100%, then a white color is obtained. The absence of all three colors results in black. The system of additive colors used in computer monitors is usually denoted by the abbreviation RGB.

2.2. Subtractive color system - color model

During the printing process, light is reflected off the sheet of paper. Therefore, for printing graphic images, a color system that works with reflected light is used - a system of subtractive colors (subtract - subtract).

White is made up of all the colors of the rainbow. If you pass a beam of light through a simple prism, it decomposes into a color spectrum. Red, orange, yellow, green, cyan, blue and violet colors form the visible spectrum of light. White paper reflects all colors when illuminated, while colored paper absorbs some of the colors and reflects the rest. For example, a piece of red paper illuminated with white light looks red precisely because such paper absorbs all colors except red. The same red paper illuminated in blue will appear black as it absorbs the blue.

In the system of subtractive colors, cyan is the main (Cyan), purple (Magenta) and yellow (Yellow). Each of them absorbs (subtracts) certain colors from white light falling on the printed page. Here's how the three primary colors can be used to create black, red, green, and blue:

cyan + magenta + yellow = black,

cyan + magenta = blue,

yellow + magenta = red,

yellow + blue = green.

By mixing primary colors in different proportions on white paper, you can create a wide variety of shades.

White is obtained when all three primary colors are absent. High percentages of cyan, magenta, and yellow produce black. More precisely, the black color should turn out theoretically, but in reality, due to some peculiarities of the printing inks, the mixture of all three primary colors gives a dirty brown tone, so when printing the image, black ink is added. (Black).

In the figure (fig. 4) you can see the receipt of different colors in the CMYK system.

Figure 4. CMYK color rendering system

The CMYK system, by its nature, cannot display all shades, as the RGB model "can". Therefore, do not scold the printer, which printed a faded picture instead of a color and bright one, as it was on the monitor. Translating an image into this color model also requires some knowledge in the field of printing. The same picture, converted with different parameters, looks different.

The subtractive color system is denoted by the abbreviation CMYK(to avoid confusion with Blue, to denote Black the symbol is used TO).

2.3. System "Hue - Saturation - Luminance" - HSB color model

Color systems RGB and CMYK are based on constraints imposed by hardware (computer monitors and printing inks). A more intuitive way to describe a color is to represent it as a tone. (Hue), saturation (Saturation) and brightness (Brightness). This color system uses the abbreviation HSB. Tone - specific shade of color: red, yellow, green, magenta, etc. NS. Saturation characterizes the "purity" of the color: by decreasing the saturation, we "dilute" it with white. Brightness it also depends on the amount of black paint added to a given color: the less blackness, the greater the brightness of the color. To be displayed on a computer monitor, the system HSB converted to RGB, and for printing on a printer - to the system CMYK... You can create an arbitrary color by specifying in the input fields H, S and V values ​​for hue, saturation, and lightness from 0 to 255.

There are other color models used in various video devices.

Bibliography

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In certain forms of color blindness, green can be perceived as equivalent to bright blue, and red as very dark, or even indistinguishable. People with dichromic red perception, for example, are unable to see red traffic lights in bright sunlight. With deythanopia - a violation of the perception of green, at night, the green traffic signal becomes indistinguishable from the light of street lamps.

In television, PAL uses the YUV color model, SÉCAM uses the YDbDr model, and NTSC uses the YIQ model. These models are based on the principle that the main information is carried by the brightness of the image - the Y component (important - Y in these models is calculated completely differently than Y in the XYZ model), and the other two components responsible for color are less important.

Similar information.

The practice of displaying information in a graphical form has many synonyms, but recently two are most often used - data visualization and infographics. Data visualization is a display of large arrays of numerical and semantic information in the form of graphical objects. Data visualization products are intended for further integration into information systems and decision support systems.

Data visualization is used in a wide variety of areas of human activity. For example, let's call medicine (computed tomography), scientific research (visualization of the structure of matter, vector fields and other data), modeling of fabrics and clothing, experimental design, statistics and reports, etc.

COMPUTER GRAPHICS

There is a special area of ​​informatics that studies methods and means of creating and processing images using software and hardware computing systems - computer graphics, which were developed in the mid-50s for large computers used in scientific and military research. Since then, the graphical method of displaying data has become an integral part of the vast majority of computer systems, especially personal ones. Graphical user interface (GUI) is the standard for different classes of software today, starting with operating systems.

Graphics editor- a program (or software package) that allows you to create and edit two- and three-dimensional images using a computer. Modern graphic image editors are used as programs for drawing from scratch and as programs for editing photos.

Depending on the method of forming images, it is customary to subdivide computer graphics on raster, vector and fractal.

Rice. 1. Various types of graphics.

A separate subject is three-dimensional (3D ) graphics studying techniques and methods for constructing volumetric models of objects in virtual space. As a rule, it combines vector and raster imaging methods.

Features of color gamut characterize concepts such as black and white and color graphics. Specialization in certain areas is indicated by the titles of some sections: engineering graphics, scientific graphics, Web-graphics, computer printing and others.

At the intersection of computer, television and film technologies, a new field of computer graphics and animation has arisen and is rapidly developing.

Computer graphics is one of the most rapidly developing branches of informatics and in many cases acts as a "locomotive" pulling the entire computer industry.

Color rendering

To transfer and store color in computer graphics, various forms of its representation are used. In general, a color is a set of numbers, coordinates in a certain color system.

The standard methods for storing and processing color in a computer are due to the properties of human vision. The most common systems RGB (Red-Red,Green- green,Blue- blue) for displays and CMYK for work in the typographic business. Sometimes a system with more than three components is used. The reflectance or emission spectrum of the source is encoded to more accurately describe the physical properties of the color. Such schemes are used in photorealistic 3D rendering.

Rice. 2. Color rendering system RGB. Rice. 3. Scheme of subtractive synthesis in CMYK

Raster graphics

Raster graphics- a rectangular matrix consisting of many very small indivisible points ( pixels). Each such pixel can be colored in any one color. For example, a monitor with a resolution of 1024x768 pixels has a matrix containing 786432 pixels, each of which (depending on the color depth) can have its own color. Because pixels are very small, then such a mosaic merges into a single whole and with good image quality (high resolution) the human eye does not see the “pixelization” of the image.

When the image is reduced, the opposite process occurs - the computer simply "throws away" the extra pixels. Hence, the main disadvantage of raster graphics is the dependence of the image quality on its size.

Raster graphics should be used for photographic quality images that have many color transitions. The size of the file that stores the bitmap depends on two factors: the size of the image; on the color depth of the image (the more colors are presented in the picture, the larger the file size).

Rice. 3... Changing the bitmap when enlarged.

For raster images consisting of dots, the concept of resolution, which expresses the number of dots per unit length, is of particular importance. In this case, one should distinguish: the resolution of the original; screen resolution; resolution of the printed image.

Original resolution. Original print resolution is measured in dots per inch ( dots per inch - dpi) and depends on the requirements for image quality and file size, the method of digitizing and creating the original illustration, the selected file format, and other parameters. The higher the quality requirement, the higher the resolution of the original should be.

Screen resolution... For screen copies of an image, the elementary raster point is called a pixel. Pixel size varies depending on the selected screen resolution (from a range of standard values), original resolution and display scale. Monitors for image processing with a diagonal of 20-21 inches provide standard screen resolutions 640x480, 800x600, 1024x768,1280x1024,1600x1200,1600x1280, 1920x1200, 1920x1600 pixels. The distance between adjacent dots of the phosphor in a high-quality monitor is 0.22–0.25 mm. For a screen copy, a resolution of 72 is sufficient dpi, for printing on a color or laser printer 150-200 dpi, for displaying on a photoexposing device 200-300 dpi... Typically, when printed, the resolution of the original should be 1.5 times the screen frequency of the output device.

Intensity of tone(the so-called lightness) is usually divided into 256 levels. A large number of gradations are not perceived by human vision and are redundant. A smaller number worsens the perception of the image (the minimum acceptable value for a high-quality halftone illustration is 150 levels). It is easy to calculate that to reproduce 256 tone levels, it is enough to have a raster cell size of 256 = 16x16 pixels.

Relationship between image parameters and file size... By means of raster graphics, it is customary to illustrate works that require high accuracy in rendering colors and halftones. However, bitmap file sizes grow rapidly with increasing resolution. Photo intended for home viewing (standard size 10x15 cm, digitized with a resolution of 200-300 dpi, 24-bit color resolution), occupies in the format Tiff with the included compression mode about 4 MB. A high-resolution digitized slide takes 45-50 MB. Separated color image of A4 format occupies 120-150 MB.

Scaling bitmaps... One of the disadvantages of raster graphics is the so-called pixelation of images when they are enlarged (unless special measures are taken). Once in the original there is a certain number of dots, then at a larger scale their size also increases, raster elements become noticeable, which distorts the illustration itself. To counteract pixelation, it is customary to digitize the original in advance with a resolution sufficient for high-quality rendering when scaling. Another trick is to use a stochastic raster to reduce the pixelation effect within certain limits. Finally, when scaling, the interpolation method is used, when the increase in the size of the illustration is not by scaling the points, but by adding the required number of intermediate points.

A certain class of raster graphic editors is not intended for creating images "from scratch", but for processing finished drawings in order to improve their quality and implement creative ideas. Such programs, in particular, include Adobe photoshop, Photostyler, Picture Publisher and others. The initial information for processing on a computer can be obtained in different ways: by scanning 1 ton of color illustrations, loading an image created in another editor, or by inputting an image from a digital photo or video camera.

Color concept

Colour- an extremely difficult problem, both for physics and physiology, since it has both psychophysiological and physical nature. The perception of color depends on the physical properties of light, i.e., electromagnetic energy, on its interaction with physical substances, as well as on their interpretation by the human visual system. In other words, the color of an object depends not only on the object itself, but also on the light source illuminating the object and on the human vision system. Moreover, some objects reflect light (board, paper), while others transmit it (glass, water). If a surface that only reflects blue light is illuminated with red light, it will appear black. Likewise, if a green light source is viewed through glass that only transmits red light, it will appear black as well.

The simplest is achromatic color, i.e. such as we see on a black and white TV screen. At the same time, objects look white if they achromatically reflect more than 80% of the light from a white source, and black - less than 3%. The only attribute of such a color is intensity or quantity. A scalar can be associated with intensity, defining black as 0 and white as 1.

If the perceived light contains wavelengths in arbitrary unequal quantities, then it is called chromatic .

When subjectively describing this color, they usually use three quantities such as hue, saturation, and brightness. Color tone allows you to distinguish between colors such as red, green, yellow, etc. (this is the main color characteristic). Saturation characterizes purity, i.e. the degree of weakening (dilution, lightening) of a given color with white light, and allows you to distinguish pink from red, emerald from bright green, etc. In other words, saturation is used to judge how soft or harsh the color seems. Brightness reflects the idea of ​​intensity as a factor independent of hue and saturation (intensity (power) of color).

Usually not clean monochromatic colors, but mixtures thereof. The three-component theory of light is based on the assumption that there are three types of color-sensitive cones in the central part of the retina. The first perceives green, the second red, and the third blue. The relative sensitivity of the eye is maximum for green and minimum for blue. If all three types of cones are affected by the same level of energy brightness, then the light appears white. The sensation of white can be obtained by mixing any three colors as long as neither is a linear combination of the other two. These colors are called basic. .

The human eye is capable of distinguishing about 350,000 different colors. This number has been obtained as a result of numerous experiments. Approximately 128 color tones are clearly visible. If only saturation changes, then the visual system is able to distinguish not so many colors: we can distinguish from 16 (for yellow) to 23 (for red and violet) such colors.

Thus, the following attributes are used to characterize the color:

· Color tone ... It is possible to determine the predominant wavelength in the emission spectrum. Allows you to distinguish colors.

· Saturation or purity of tone. It is expressed by the proportion of the presence of white. In a perfectly pure color, there is no impurity of white. If, for example, white is added to a pure red color in a certain proportion, you will get a light pale red color.

· Brightness ... Determined by energy, intensity of light radiation. Expresses the amount of light perceived.

These three attributes describe all colors and shades. The fact that there are exactly three attributes is one of the manifestations of the three-dimensionality of color properties.

Most people distinguish between colors, and those who are engaged in computer graphics should clearly feel the difference not only in colors, but also in the subtlest shades. This is very important, since it is color that carries a large amount of information, which is in no way inferior in importance to either form, or mass, or other parameters that determine each body.

Factors affecting the appearance of a particular color:

§ Light source;

§ information about the surrounding objects;

§ your eyes;

Correctly selected colors can both draw attention to the desired image and repel it. This is due to the fact that depending on what color a person sees, he has different emotions that subconsciously form the first impression of the visible object.

Color in computer graphics is necessary for the following reasons:

§ it carries certain information about objects. For example, trees are green in summer and yellow in autumn. It is almost impossible to determine the season of the year in black and white photography, unless some other additional facts indicate it.

§ color is also necessary to distinguish objects.

§ with its help, you can bring some parts of the image to the fore, while others take them into the background, that is, focus on the important - compositional - center.

§ Without enlarging the size, some details of the image can be conveyed with the help of color.

§ in two-dimensional graphics, and this is exactly what we see on the monitor, since it does not have a third dimension, it is with the help of color, more precisely shades, that volume is imitated (transmitted).

§ color is used to grab the viewer's attention, create a colorful and interesting image.

Any computer image is characterized, in addition to geometric dimensions and resolution (the number of dots per inch), by the maximum number of colors that can be used in it. The maximum number of colors that can be used in a given type of image is called color depth.

In addition to full color, there are types of images with different color depths - black and white line, in grayscale, with an indexed color. Some types of images have the same color depth, but differ in color model.

3.1. Additive color model

3.2. Formation of own color shades in the RGB model

3. Color in computer graphics

Those who are engaged in computer graphics must clearly distinguish not only colors, but also the subtlest shades. This is very important, since it is color that carries a large amount of information, which is no less important than the shape, mass and other parameters of each physical object.

Correctly selected colors can both draw attention to the image and repel it. Depending on what color a person sees, he has different emotions that form the first impression of the object. There is even a whole science that studies the effect of color on humans.
So, why do you need color in computer graphics?

• Color carries certain information about objects. For example, trees are green in summer and yellow in autumn. It is almost impossible to determine the time of the year in black and white photography, unless some other additional facts indicate it.
• Color is needed to distinguish objects.
• With its help, you can bring some parts of the image to the foreground, others - to take away into the background, thus focusing attention on the most important thing - the compositional center.
• Without enlarging the size, using color can convey some of the details of the image.
• In two-dimensional graphics (we see this on the monitor, since it does not have a third dimension), it is with the help of color, more precisely shades, that volume is imitated.
• Finally, color is used to grab the viewer's attention and create a colorful and interesting image.
• Of course, you can create gorgeous black and white creations, but since we live in a colored world, it is much more familiar to see colored objects.

Colour is a subjective characteristic of an object. Color only exists when there is an observer. Real light (for example, daylight) is electromagnetic radiation, a mixture of different light waves, that is, it has a different spectrum. The human eye catches light waves in a certain range of lengths and intensities (visible spectrum of radiation). Then the brain processes the incoming signals, perceiving objects in different ways, depending on the combination of wavelengths and their intensity. Thus, in reality, color refers not only to the object itself, but also to the features of the physiological perception of a particular observer. Similar to taste, smell, hearing and other senses, color perception also varies from person to person. We can perceive a color as warm, cold, heavy, light, soft, strong, energizing, relaxing, shiny, or dull. However, in each case, the perception depends on the culture of the person, language, age, gender, living conditions and previous experience. Two people will never perceive the same physical color in the same way. People differ from each other even in their sensitivity to the range of visible light. The perception is also influenced by the size of the object.

The world around us is full of all kinds of colors and shades of color. With the development of many industries, including printing, computer technology, there is a need for objective methods of describing and processing color.

Colors in nature are rarely simple. Most colors are obtained by mixing some others. For example, a combination of red and blue produces magenta, blue and green produces cyan. Thus, by mixing, from a small number of simple colors, you can get a lot (and quite a lot) of complex (composite) ones. Therefore, to describe the color, the concept is introduced color model- as a way of representing a large number of colors by decomposing it into simple components.

In each model, a certain range of colors is represented as 3D space. In this space, each color exists as a set of numerical coordinates. This method makes it possible to transfer color information between computers, programs and peripherals.

A natural question arises: why do we need all this? Wasn't it easier to take and present in the color model not the main, but all possible colors? Of course not! It is very difficult to describe each color separately, especially now, when on the monitor screen we have the opportunity to see not hundreds, not thousands, but 4 billion colors (more precisely, colors and color shades)! Try to describe each color individually. Thus, color models are an almost perfect way to describe colors, especially in computer technology and printing. Why almost? The fact is that not every color can be represented as a combination of the main ones. This is the main problem with color models.

3.1. Additive color model

Emitted color - it is light emitted from a source such as the sun, light bulb, or monitor screen. The emitted color, coming directly from the source to the eye, retains all the colors from which it was created. When reflected from an object, the light may change. Any object that is not a light source partially reflects and partially absorbs light falling on it.

Like the sun and other light sources, the monitor emits light. The paper on which the image is printed reflects light. Since color can be obtained in the process of radiation and in the process of reflection, there are two opposite methods of describing it: additive and subtractive color models.

The emitted light is described using an additive color model.

If you look at the screen of a working monitor or TV from a close distance (or even better - with the help of a magnifying glass), then it is not difficult to see many tiny dots of red, green and blue colors, the so-called primary, basic or primary colors. The fact is that each video pixel on a color screen is a collection of three points of different colors: red, green, and blue. Since they are very small, our eyes blend three colors into one. Thus, adjacent multi-colored dots merge, forming other colors. An example of this is a rotating disc, half of which is colored yellow and the other blue. When the disk spins quickly, we see green, but we don't see blue and yellow.

Red + green = yellow

red + blue = magenta

green + blue = cyan

red + green + blue = white

By changing the intensity of the glow of the colored dots, you can create a wide variety of shades.

Thus, the additive (from the English add - attach) color is obtained by combining (summing) the three primary colors - red, green and blue. If the intensity of each of them reaches 100%, then a white color is obtained. The absence of all three colors results in black.

The additive color model used in computer monitors is usually denoted by the abbreviation RGB (rgb OR rzhb) (Red (red) - red, Green (Green) - green, Blue (blue) - blue).

3.2. Formation of own color shades in the RGB model

The RGB model describes the emitted colors. The basic components of the model are three colors of the rays - red, green, blue. When a person perceives color, it is they that are perceived by the eye. The rest of the colors are a mixture of the three base colors in different proportions. When adding (mixing) two rays of the primary colors, the result is lighter than the components. Colors of this type are called additive. RGB is a three-channel color model. In RGB model, the scanner encodes the image and displays the monitor screen.

The concepts of light and color are fundamental in computer graphics. Usually, light is a continuous stream of waves of different lengths and amplitudes. Such light can be characterized by an energy spectral curve (Fig. 2.2), where the value of the function itself is the contribution of waves with a wavelength  to the total wave flux.

Rice. 2.2. Light spectral curve

The sensation of color occurs in the brain during excitation and inhibition of color-sensitive cells - receptors of the human eye retina, cones. In humans, there are three types of cones - "red", "green" and "blue", respectively. The light sensitivity of the cones is low, therefore sufficient illumination or brightness is required for good color perception. Each color sensation in a person can be represented as the sum of the sensations of these three colors.

The main characteristics of color are hue, saturation, brightness.

Definition 2.6.Color tone - an attribute of visual perception, according to which the area seems to have one of the perceived colors (red ( R), green ( G) or blue ( V)). It is the main color characteristic.

Definition 2.7.Saturation - a characteristic expressed by the proportion of the presence of white. In a perfectly pure color, there is no impurity of white. If, for example, white is added to a pure red color in a certain proportion, you will get a light pale red color.

Definition 2.8.Brightness - characteristic determined by energy, intensity of light radiation. Expresses the amount of light perceived.

An ordinary color (sun, light bulb) consists of all the colors of the rainbow. If you pass it through a prism, then it decomposes into the color spectrum of the rainbow. These colors represent the frequencies of electromagnetic waves that appear to the naked eye.

A distinction is made between emitted and reflected light. Radiated Light - Light emitted from an active source contains all colors. Reflected light can contain all colors, a combination of them, or just one color. Since color can be obtained in the process of radiation and absorption, there are two opposite methods of describing it:

Additive color system;

Subtractive color system.

RGB color model. An additive color is obtained by combining rays of light of different colors. The absence of all colors in this system is black. The presence of all colors is white. This system works with emitted color, for example, from a computer monitor. This system uses three primary colors: red, green, blue (RGB). RGB color system. The most common and popular. Used in monitors.

CMY color model. In the system of subtractive colors, the opposite process takes place. A specific color is obtained by subtracting other colors from the total light beam. White appears as a result of the absence of all colors, while their presence gives black. This system works with reflected color.

In the system of subtractive colors, the main ones are cyan, magenta, yellow (CMY - Cyan, Magenta, Yellow). When mixing them, it is assumed that you should get black. In reality, printing inks do not completely absorb light, and therefore the combination of the three primary colors appears dark brown. This system is mainly used in the printing industry. Converting pictures from RGB to CMYK faces a number of challenges. The main difficulty is that colors can change in different systems. In these systems, the nature of obtaining colors is different, and therefore what is displayed on the monitor screen can never be exactly repeated when printed. The conversion process is complicated by the need to correct imperfections in printing ink.

HSV color model. The color models discussed above in one way or another use a mixture of some primary colors. The HSV color model can be classified as an alternative type.

Rice. 2.3. HSV color model

In the HSV model (Fig. 2.3), the color is described by the following parameters: hue H (Hue), saturation S (Saturation), brightness, lightness V (Value). The H value is measured in degrees from 0 to 360, since here the colors of the rainbow are arranged in a circle in this order: red, orange, yellow, green, cyan, blue, purple. The S and V values ​​are in the range (0 ... 1).

Examples of color coding for the HSV model. When S = 0 (i.e. on the V-axis) - gray tones. V = 0 corresponds to black. White is coded as S = 0, V = 1. Colors located in a circle opposite each other, i.e. differing in H by 180 º are additional. Specifying a color using HSV parameters is often used in graphics systems, and usually shows a sweep of a cone.

The HSV color model is convenient for use in those graphic editors that are focused not on processing finished images, but on creating them with your own hands. There are programs that allow you to imitate various artist's tools (brushes, pens, felt-tip pens, pencils), paint materials (watercolor, gouache, oil, ink, charcoal, pastel) and canvas materials (canvas, cardboard, rice paper, etc.).

There are other color models built similar to HSV, for example HLS (Hue, Lighting, Saturation) models and HSB also uses a color cone. The HSB model also has three components: Hue, Saturation, and Brightness. By adjusting them, you can get as many arbitrary colors as when working with other models.

Lab color model. All of the above models describe the color with three parameters and in a fairly wide range. Now let's consider a color model in which a color is specified by one number, but for a limited range of colors (shades).

In practice, grayscale images are often used. Gray colors in the RGB model are described by the same component values, i.e. r i = g i = b i. Thus, for gray images there is no need to use triplets of numbers - just one number is enough. This simplifies the color model. Each gradation is determined by the brightness Y. The Y value = 0 corresponds to black, the maximum Y value to white.

To convert color images presented in the RGB system to grayscale, use the ratio

Y = 0.299R + 0.587G + 0.114B,

where the coefficients for R, G and B take into account the different sensitivity of vision to the corresponding colors and, in addition, their sum is equal to one.

Obviously, the inverse transformation R = Y, G = Y, B = Y will not give any other colors than grayscale.

The variety of models is due to different areas of their use. Each of the color models has been designed to efficiently perform individual operations: image capture, screen rendering, printing on paper, image processing, saving to files, colorimetric calculations and measurements. Converting from one model to another may distort the colors in the image.

Control questions and tasks

1. What types of presentation of video information do you know?

2. What is bit depth?

3. What is raster resolution?

4. What characteristics affect the size of the image?

5. What is the peculiarity of scaling raster and vector images?

6. What are the main characteristics of color?

7. What color systems do you know?

8. Define the additive color system. What devices is it used in?

9. What is the subtractive color system?

10. List alternative color systems.