What color models exist. Color models. What are they and why do you need to know about them?

A color TV or your computer monitor is based on the principle of this division of light. To put it very roughly, the monitor you are looking at now consists of a huge number of dots (their number vertically and horizontally determines the resolution of the monitor) and three “lights” shine at each of these dots: red, green and blue. Each “light bulb” may shine with different brightness, or may not shine at all. If only the blue “light” shines, we see a blue dot. If only red, we see a red dot. Same with green. If all the light bulbs shine with full brightness at one point, then this point turns out to be white, since all the gradations of this white again come together. If no light bulb is shining, then the point appears black to us. Because black is the absence of light. By combining the colors of these “light bulbs”, glowing with different brightness, you can get different colors and shades.

The brightness of each such light bulb is determined by the intensity (division) from 0 (the “light bulb” is turned off) to 255 (the “light bulb” shining with full “power”). This division of colors is called the RGB color model from the first letters of the words “RED” “GREEN” “BLUE” (red, green, blue).

Thus White color our point in the RGB color model can be written in the following form:

R (from the word "red", red) - 255

G (from the word "green", green) - 255

B (from the word "blue", blue) - 255

A "rich" red would look like this:

The yellow color will look like this:

Also, to record colors in rgb, the hexadecimal system is used. The intensities are shown in #RGB order:

White - #ffffff

Red - #ff0000

Black - #00000

Yellow - #ffff00

CMYK color model

So, now we know in what cunning way our computer conveys to us the color of a particular point. Let's now use our acquired knowledge and try to get white using paints. To do this, we’ll buy gouache at the store, take jars of red, blue and green paint, and mix them. Happened? Neither do I.

The problem is that our monitor emits light, that is, it glows, but in nature many objects do not have this property. They simply reflect the white light that falls on them. Moreover, if an object reflects the entire spectrum of white light, then we see it as white, but if part of this light is absorbed by it, then not completely.

Something like this: we shine white light on a red object. White light can be thought of as R-255 G-255 B-255. But the object does not want to reflect all the light that we directed at it, and brazenly steals all the shades of green and blue from us. As a result, only R-255 G-0 B-0 is reflected. That is why it appears red to us.

So for printing on paper it is very problematic to use the RGB color model. For this, as a rule, the CMY (tsmi) or CMYK (tsmik) color model is used. The CMY color model is based on the fact that the sheet of paper itself is white, that is, it reflects almost the entire RGB spectrum, and the colors applied to it act as filters, each of which “steals” its own color (either red or green, or blue). Thus, the colors of these paints are determined by subtracting RGB colors from white one at a time. The resulting colors are Cyan (something like blue), Magenta (one might say pink), Yellow (yellow).

And if in the RGB color model the gradation of each color occurred according to brightness from 0 to 255, then in the CMYK color model the main value for each color is “opacity” (the amount of paint) and is determined by percentages from 0% to 100%.

Thus, white color can be described as follows:

C (cyan) - 0%; M (magenta) - 0%; Y (yellow) - 0%.

Red - C-0%; M-100%; Y-100%.

Green - C-100%; M-0%; Y-100%.

Blue - C-100%; M-100%; Y-0%.

Black - C-100%; M-100%; Y-100%.

However, this is only possible in theory. But in practice, it’s impossible to get by with CMY colors. And the black color when printed turns out to be more of a dirty brown, the gray does not look like itself, and it is problematic to create dark shades of colors. Another paint is used to adjust the final color. Hence the last letter in the name CMYK (TsMIK). The decoding of this letter may be different:

It may be short for blacK (black). And in the abbreviation it is the last letter that is used so as not to confuse this color with the Blue color in the RGB model;

Printers very often use the word "Outline" in relation to this color. So it's possible that the K in CMYK is short for the German word "Kontur";

It can also be an abbreviation for Key-color (key color).

However, it is difficult to call it key, since it is rather additional. And this color doesn’t quite look like black. If you print only with this ink, the image turns out to be rather gray. Therefore, some are of the opinion that the letter K in the CMYK abbreviation stands for “Kobalt” (dark gray, German).

Typically, the term "black" or "black" is used to refer to this color.

Printing using CMYK colors is called "full color" or "process".

*It’s probably worth saying that when printing CMYK (CMIK) paints do not mix. They lie on the paper in “spots” (raster patterns) one next to the other and mix in the person’s imagination, because these “spots” are very small. That is, the image is rasterized, because otherwise the paint, falling on one another, blurs and moiré or dirt is formed. There are several different rasterization methods.

Grayscale color model

Many people mistakenly call an image in the grayscale color model black and white. But that's not true. A black and white image consists of only black and white tones. While grayscale (grayscale) has 101 shades. This is a Kobalt color gradation from 0% to 100%.

Device-dependent and device-independent color models

The CMYK and RGB color models are device-dependent, meaning they depend on the way color is transmitted to us. They tell a specific device how to use their corresponding dyes, but have no knowledge of how the final color is perceived by humans. Depending on the brightness, contrast and sharpness settings of the computer monitor, the room illumination, and the angle at which we look at the monitor, color with the same RGB parameters is perceived differently by us. And a person’s perception of color in the “CMYK” color model depends on an even larger number of conditions, such as the properties of the printed material (for example, glossy paper absorbs less paint than matte paper, so the colors on it are brighter and more saturated), characteristics of the paint, air humidity , at which the paper dried, the characteristics of the printing press...

To convey more reliable information about color to a person, so-called color profiles are attached to device-dependent color models. Each of these profiles contains information about a specific method of transmitting color to a person and regulates the final color by adding or subtracting parameters from any component of the original color. For example, when printing on glossy film, a color profile is used that removes 10% Cyan and adds 5% Yellow to the original color, due to the characteristics of the particular printing machine, the film itself and other conditions. However, even attached profiles do not solve all the problems of transmitting color to us.

Device-independent color models do not carry information to convey color to humans. They mathematically describe the color perceived by a person with normal color vision.

HSB and HLS color models

This color space is based on the familiar RGB rainbow ring. Color is controlled by changing parameters such as:

Hue- shade or tone;

Saturation- color saturation;

Brightness- brightness.

The hue parameter is the color. Determined in degrees from 0 to 360 based on the colors of the rainbow ring.

The saturation parameter - the percentage of white paint added to this color has a value from 0% to 100%.

The Brightness parameter - the percentage of adding black paint also varies from 0% to 100%.

The principle is similar to one of the representations of light from a fine art perspective. When white or black paint is added to existing colors.

This is the easiest color model to understand, which is why many web designers love it. However, it has a number of disadvantages:

The human eye perceives the colors of the rainbow ring as colors that have different brightnesses. For example, spectral green has greater brightness than spectral blue. In the HSB color model, all colors in this circle are considered to have a brightness of 100%, which, unfortunately, is not true.

Since it is based on the RGB color model, it is still hardware-dependent.

This color model is converted to CMYK for printing and converted to RGB for display on a monitor. So guessing what color you will end up with can be quite problematic.

The HLS color model is similar to this model (interpretation: hue, lightness, saturation).

Sometimes used to correct light and color in an image.

LAB color model

In this color model, a color consists of:

Luminance - illumination. This is a combination of the concepts of brightness (lightness) and intensity (chrome)

A- this is a color range from green to purple

B- color range from blue to yellow

That is, two indicators together determine the color and one indicator determines its illumination.

LAB - This is a device-independent color model, that is, it does not depend on the way color is transmitted to us. It contains both RGB and CMYK colors, and grayscale, which allows it to convert an image from one color model to another with minimal loss.

Another advantage is that, unlike the HSB color model, it corresponds to the peculiarities of color perception by the human eye.

Often used to improve image quality and convert images from one color space to another.

Good day, dear readers, acquaintances, visitors, passing individuals and other strange creatures! Today we will talk about a slightly specific, but undoubtedly important thing for any user, namely this thing: the representation of color in a computer.

Whatever one may say, sooner or later everyone will be faced with the practical need to understand what a color model is, and simply this knowledge is useful from the point of view of broadening one’s horizons and awareness of what and how it works in a computer and what it consists of, both software and and from a physical point of view.

What is a color model

In general color model- this is some abstract thing in which color is represented as a collection of numbers. And each such model has its own characteristics and disadvantages. Essentially, it’s like with a language, for example, if a color is the word “house,” then in different languages ​​it will be written and sounded differently, but the meaning of the word will be the same everywhere. It's the same with color.

We will look at the most basic models. Their 5 . As a rule, several different models are used simultaneously, because some are best used visually, while others are best used numerically.

RGB

This is the most common color representation model. In it, any color is considered as shades of three primary (or basic) colors: red, green (Green) and blue (Blue). There are two types of this model: eight-bit representation where the color is specified by numbers from 0 before 255 (for example color will correspond to blue, and - yellow), and sixteen-bit, which is most often used in graphic editors and html, where the color is specified by numbers from 0 before ff(green - # 00ff00, blue - # 0000ff, yellow - # ffff00).

The difference in ideas is that in eight-bit form, a separate scale is used for each base color, and in sixteen-bit color is immediately introduced. In other words, eight-bit presentation - three scales with each primary color, sixteen-bit- one scale with three colors.

The peculiarity of this model is that here a new color is obtained by adding shades of primary colors, i.e. "mixing".

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In the picture above you can see how the colors mix with each other to form new colors (yellow - [ 255,255,0 ], purple - [ 255,0,255 ], blue - [ 0,255,255 ] and white [ 255,255,255 ]).

Moreover, this model is most often used in numerical form, and not in visual form (when the color is set by entering its value in the corresponding field, and not selected with the mouse). Other models are used to visually adjust color. Because visually the model RGB is a three-dimensional cube, which, as you can see in the picture above, is not very convenient to use :)

So this is the most common model among web designers (we send our warm regards css) and programmers.

The disadvantage of this model is that it depends on the hardware, in other words, the same picture will look different on different monitors (because monitors use a so-called phosphor - a substance that converts the energy it absorbs into light radiation, and therefore Depending on the quality of this substance, the basic colors will be determined).

CMYK

This is also a very common model, but many may not have heard anything about it at all :)

And all due to the fact that it is used exclusively for printing. It stands for Cyan, Magenta, Yellow, Black(or Key Color), i.e. Cyan, Magenta, Yellow And Black(or key color).

The use of this model in printing is due to the fact that mixing three shades for each new color is too expensive and dirty, because when one color is first applied to paper, then another on top of it, and then a third color on top of them, firstly, the paper gets very wet (if inkjet printing), and secondly, it is not at all a fact that you will get exactly the shade that you wanted. Yes, that's how physics works :)

The most attentive may have noticed that there are three colors in the picture, and black is obtained by mixing these three. So, why was he taken out separately? Again, the reason is that, firstly, mixing three colors is expensive in terms of using toner (special powder for a printer cartridge, which is used instead of ink in laser printers), and secondly, the paper gets very wet, which increases drying time, thirdly, the colors may not actually mix properly, but may be more faded, for example. The picture below shows this model in reality

Thus, the result will not be black, but dirty gray or dirty brown.

That’s why (and not only) they introduced black color, so as not to stain the paper, not to spend money on toners, and in general to make life easier :)

The following animation very clearly illustrates the whole point (opens by clicking, weight approx. 14 Mb):

The color in this model is specified by numbers from 0 before 100 , where these numbers are often called "parts" or "portions" of the selected color. For example, khaki color is obtained by mixing 30 pieces of blue paint, 45 - purple, 80 - yellow and 5 - black, i.e. khaki color will be .

The difficulties of this model lie in the fact that in harsh realities (or in real harsh conditions) color depends not so much on numerical data as on the characteristics of the paper, the ink in the toner, the method of applying this ink, etc. So the numerical values ​​will clearly indicate the color on the monitor, but they will not show the actual picture on paper.

HSV (HSB) and HSL

I combined these two color models because... they are similar in principle.

3D implementation HSL(left) and HSV(on the right) of the models is presented in the form of a cylinder below, but in practice it is not used in software (software), because .. because it is three-dimensional :)

HSV (or HSB) means Hue, Saturation, Value(may also be called Brightness), Where:

• Hue- color tone, i.e. color shade.
• Saturation- saturation. The higher this parameter, the “purer” the color will be, and the lower, the closer it will be to gray.
• Value(Brightness) - value (brightness) of color. The higher the value, the brighter the color will be (but not whiter). And the lower, the darker (0% - black)

HSL - Hue, Saturation, Lightness

• Hue- You already know
• Saturation- similar
• Lightness- this is the lightness of the color (not to be confused with brightness). The higher the parameter, the lighter the color (100% - white), and the lower, the darker (0% - black).

A more common model is HSV, it is often used together with the model RGB, Where HSV is shown visually, and numerical values ​​are specified in RGB. :

Here RGB- the model is circled in red and the shade values ​​are given by numbers from 0 before 255 , or you can immediately specify the color in hexadecimal form. And circled in blue HSV model (visual part in left rectangle, numeric - in right). You can also often specify opacity (called alpha channel).

This model is most often used in simple (or non-professional) image processing, because Using it, it’s convenient to adjust the basic parameters of photos without resorting to a bunch of different filters or individual settings.
For example, in everyone’s favorite (or cursed) Photoshop, both models are present, only one of them is in the color selection editor, and the other is in the settings window Hue/Saturation

Showing in red here RGB- model, blue - H.S.B., green - CMYK and blue Lab(more on her a little later), as can be seen in the picture :)
A HSL- The model is in a window like this:

Flaw HSB- model is that it also depends on the hardware. It simply does not correspond to the perception of the human eye, because... It perceives colors with different brightness (for example, blue is perceived by us as darker than red), but in this model all colors have the same brightness. U HSL similar problems :)

They wanted to avoid such shortcomings, so one well-known company CIE(International Illumination Commission - Commission Internationale de l'Eclairage) came up with a new model designed to be independent of hardware. And they named her Lab(no, this is not an abbreviation for Laboratory).

Lab or L,a,b

This model is one of the standard ones, although it is little known to the average user.

It is deciphered as follows:

• L - Luminance- illumination (this is a combination of brightness and intensity)
• a- one of the components of color, changes from green to red
• b- the second of the color components, changes from blue to yellow

The figure shows the component ranges a And b For illumination 25% (left) and 75% (right)

The brightness in this model is separated from the colors, so it is convenient to use it to adjust contrast, sharpness and other light indicators without touching the colors :)

However, this model is not at all obvious to use and is quite difficult to use in practice. Therefore, it is used mainly in image processing and for converting them from one color model to another without loss (yes, this is the only model that does this without loss), but for ordinary mortal suffering users, as a rule, it is enough HSL And HSV plus filters.

Well, as an example of how the model works HSV, HSL And Lab here is a picture from Wikipedia (clickable)

Very often, people who are not directly involved in print design have questions: “What is CMYK?”, “What is Pantone?” and "why can't you use anything other than CMYK?"

In this article we will try to understand a little what color spaces are. CMYK, RGB, LAB, HSB and how to use paints Pantone in layouts.

Color model

CMY(K), RGB, Lab, HSB is a color model. Color model- a term denoting an abstract model for describing the representation of colors as tuples of numbers, usually three or four values, called color components or color coordinates. Together with the method for interpreting this data, the set of colors in a color model defines a color space.

RGB- abbreviation of English words Red, Green, Blue- red, green, blue. Additive (Add, English - add) color model, usually used to display images on monitor screens and other electronic devices. As the name implies, it consists of blue, red and green colors, which form all the intermediate ones. Has a large color gamut.

The main thing to understand is that the additive color model assumes that the entire color palette is made up of luminous points. That is, on paper, for example, it is impossible to display color in the RGB color model, since paper absorbs color and does not glow on its own. The final color can be obtained by adding percentages from each of the key colors to the original black (non-luminous) surface.

CMYK - Cyan, Magenta, Yellow, Key color- subtractive (subtract, English - subtract) color formation scheme used in printing for standard process printing. It has a smaller color gamut compared to RGB.

CMYK is called a subtractive model because paper and other printed materials are surfaces that reflect light. It is more convenient to calculate how much light was reflected from a particular surface rather than how much was absorbed. Thus, if we subtract three primary colors - RGB - from white, we get three additional CMY colors. "Subtractive" means "subtractive" - ​​the primary colors are subtracted from white.

Key Color(black) is used in this color model as a replacement for mixing equal parts of the CMY triad colors. The fact is that only in the ideal case, when mixing the colors of the triad, a pure black color is obtained. In practice, it will turn out, rather, dirty brown - as a result of external conditions, the conditions of paint absorption by the material and the imperfection of dyes. In addition, the risk of non-registration in elements printed in black, as well as waterlogging of the material (paper), increases.

In color space Lab the value of lightness is separated from the value of the chromatic component of color (hue, saturation). Lightness is specified by the L coordinate (varies from 0 to 100, that is, from the darkest to the lightest), the chromatic component is specified by two Cartesian coordinates a and b. The first denotes the color position in the range from green to purple, the second - from blue to yellow.

Unlike RGB or CMYK color spaces, which are essentially a set of hardware data for reproducing color on paper or on a monitor screen (color may depend on the type of printing machine, brand of ink, humidity in production, or the manufacturer of the monitor and its settings) ,Lab uniquely identifies the color. Therefore, Lab has found widespread use in image processing software as an intermediate color space through which data is converted between other color spaces (for example, from the RGB of a scanner to the CMYK of a printing process). At the same time, the special properties of Lab made editing in this space a powerful color correction tool.

Due to the nature of the color definition in Lab, it is possible to separately influence the brightness, contrast of the image and its color. In many cases, this allows for faster image processing, for example during prepress. Lab provides the ability to selectively influence individual colors in an image, enhancing color contrast, and the capabilities that this color space provides for combating noise in digital photographs are also irreplaceable.

H.S.B.- a model that is, in principle, an analogue of RGB, it is based on its colors, but differs in the coordinate system.

Any color in this model is characterized by Hue, Saturation and Brightness. Tone is the actual color. Saturation is the percentage of white paint added to the color. Brightness is the percentage of added black paint. So, HSB is a three-channel color model. Any color in HSB is obtained by adding black or white to the main spectrum, i.e. actually gray paint. The HSB model is not a rigorous mathematical model. The description of colors in it does not correspond to the colors perceived by the eye. The fact is that the eye perceives colors as having different brightnesses. For example, spectral green has greater brightness than spectral blue. In HSB, all colors in the main spectrum (hue channel) are considered to have 100% brightness. This is actually not true.

Although the HSB model is declared as hardware-independent, in fact it is based on RGB. In any case, HSB is converted to RGB for display on the monitor and to CMYK for printing, and any conversion is not without losses.

Standard paint set

In the standard case, printing is carried out using cyan, magenta, yellow and black inks, which, in fact, makes up the CMYK palette. Layouts prepared for printing must be in this space, since in the process of preparing photo forms, the raster processor unambiguously interprets any color as a CMYK component. Accordingly, an RGB pattern that looks very beautiful and bright on the screen will look completely different on the final product, but rather gray and pale. The CMYK color gamut is smaller than RGB, so all images prepared for printing require color correction and correct conversion to the CMYK color space!. In particular, if you use Adobe Photoshop to process raster images, you should use the Convert to Profile command from the Edit menu.

Printing with additional inks

Due to the fact that the CMYK color gamut is not enough to reproduce very bright, “poisonous” colors, in some cases CMYK printing + additional (SPOT) paints. Additional colors are usually called Pantone, although this is not entirely true (the Pantone catalog describes all colors, both included in CMYK and not contained in it) - it is correct to call such colors SPOT (spot), in contrast to spot colors, that is, CMYK.

Physically, this means that instead of four printing units with standard CMYK colors, more are used. If there are only four printing sections, an additional run is organized, during which additional colors are imprinted into the finished product.

There are presses with five printing units, so all colors are printed in one pass, which undoubtedly improves the quality of color registration in the finished product. When printing in 4 CMYK sections and additionally running through a printing machine with spot inks, color matching may suffer. This will be especially noticeable on machines with less than 4 printing sections - you’ve probably seen advertising leaflets more than once, where a yellow frame may protrude slightly beyond the edges of, for example, beautiful bright red letters, which is nothing more than yellow paint from the layout this beautiful red color.

Preparation of layouts for printing

If you are preparing a layout for printing in a printing house and you have not agreed on the possibility of printing with additional (SPOT) inks, prepare the layout in the CMYK color space, no matter how attractive the colors in the Pantone palettes may seem to you. The fact is that to simulate Pantone colors on screen, colors that fall outside the CMYK color space are used. Accordingly, all your SPOT inks will be automatically converted to CMYK and the result will not be at all what you expect.

If your layout (with an agreement to use a triad) still contains non-CMYK paints, be prepared for the layout to be returned to you and asked to be remade.

Why are different color models needed and why the same color can look different

Providing design services both in the field of web and in the field of printing, we often come across a question from the Client: why do the same corporate colors in the design layout of the website and in the design layout of printed products look different? The answer to this question lies in the differences between color models: digital and printed.

The color of a computer screen varies from black (no color) to white (the maximum brightness of all components of color: red, green and blue). On paper, on the contrary, the absence of color corresponds to white, and the mixing of the maximum number of colors corresponds to dark brown, which is perceived as black.

Therefore, when preparing for printing, the image must be converted from additive ("folding") flower models RGB into subtractive (“subtractive”) CMYK model. The CMYK model uses the opposite colors of the original colors - the opposite of red is cyan, the opposite of green is magenta, and the opposite of blue is yellow.

Digital RGB color model

What is RGB?

The abbreviation RGB means the names of three colors used to display a color image on the screen: Red (red), Green (green), Blue (blue).

How is RGB color formed?

The color on the monitor screen is formed by combining rays of three primary colors - red, green and blue. If the intensity of each of them reaches 100%, then the color white is obtained. The absence of all three colors produces black.

Thus, any color that we see on the screen can be described by three numbers indicating the brightness of the red, green and blue color components in the digital range from 0 to 255. Graphics programs allow you to combine the required RGB color from 256 shades of red, 256 shades of green and 256 shades of blue. The total is 256 x 256 x 256 = 16.7 million colors.

Where are RGB images used?

RGB images are used to display on a monitor screen. When creating colors for viewing in browsers, the same RGB color model is used as a basis.

Printing color model CMYK

What is CMYK?

The CMYK system is created and used for typographic printing. The abbreviation CMYK stands for the names of the primary inks used for four-color printing: cyan (Cyan), magenta (Magenta) and yellow (Yellow). The letter K stands for black ink (BlacK), which allows you to achieve a rich black color when printing. The last letter of the word is used, not the first, to avoid confusion between Black and Blue.

How is CMYK color formed?

Each of the numbers that define a color in CMYK represents the percentage of paint of that color that makes up the color combination. For example, to obtain a dark orange color, you would mix 30% cyan paint, 45% magenta paint, 80% yellow paint and 5% black paint. This can be expressed as follows: (30/45/80/5).

Where are CMYK images used?

The scope of application of the CMYK color model is full-color printing. It is this model that most printing devices work with. Due to color model mismatches, there is often a situation where the color you want to print cannot be reproduced using the CMYK model (for example, gold or silver).

In this case, Pantone inks are used (ready-made mixed inks of many colors and shades), they are also called spot inks (since these inks are not mixed during printing, but are opaque).

All files intended for printing must be converted to CMYK. This process is called color separation. RGB covers a larger color range than CMYK, and this must be taken into account when creating images that you later plan to print on a printer or printing house.

When viewing a CMYK image on a monitor screen, the same colors may appear slightly differently than when viewing an RGB image. The CMYK model cannot display the very bright colors of the RGB model; the RGB model, in turn, is not able to convey the dark, dense shades of the CMYK model, since the nature of the color is different.

The color display on your monitor screen changes frequently and depends on lighting conditions, monitor temperature, and the color of surrounding objects. In addition, many colors seen in real life cannot be output when printed, not all colors displayed on screen can be printed, and some print colors are not visible on a monitor screen.

Thus, when preparing a company logo for publication on the website, we use the RGB model. When preparing the same logo for printing in a printing house (for example, on business cards or letterhead), we use a CMYK model, and the colors of this model on the screen may be visually slightly different from those we see in RGB. There is no need to be afraid of this: after all, on paper, the colors of the logo will closely match the colors that we see on the screen.

CIE Lab color model.

In 1920, the CIELab color spatial model (Communication Internationale de I"Eclairage - International Commission on Illumination. L, a, b - designations of the coordinate axes in this system) was developed. The system is hardware independent and is therefore often used to transfer data between devices. In the CIELab model, any color is determined by lightness (L) and chromatic components: the a parameter, which varies in the range from green to red, and the b parameter, which varies in the range from blue to yellow. The color gamut of the CIELab model significantly exceeds the capabilities of monitors and printing devices, therefore. The image presented in this model must be converted before output. This model was developed to harmonize color photochemical processes with printing. Today it is the default standard for Adobe Photoshop.

RGB color model.

The RGB color model is additive, that is, any color is a combination in varying proportions of three primary colors - red (Red), green (Green), blue (Blue). It serves as the basis for the creation and processing of computer graphics intended for electronic reproduction (on a monitor, TV). When one component of the primary color is superimposed on another, the brightness of the total radiation increases. The combination of the three components gives an achromatic gray color, which, with increasing brightness, approaches white. With 256 gradational tone levels, black corresponds to zero RGB values, and white - maximum, with coordinates (255,255,255).

HSB (HSL) color model.

The HSB color model was developed with maximum consideration for the characteristics of human color perception. It is based on the Munsell color wheel. Color is described by three components: Hue, Saturation and Brightness. Initially, instead of the term “brightness,” the term “lightness” was used. The color value is chosen as a vector emanating from the center of the circle. The dot in the center corresponds to the color white, and the dots along the perimeter of the circle correspond to pure spectral colors. The direction of the vector is specified in degrees and determines the color shade. The length of the vector determines the color saturation. On a separate axis, called the achromatic axis, brightness is set, with the zero point corresponding to the color black. The color gamut of the HSB model covers all known values ​​of real colors.

The HSB model is used to create images on a computer simulating the working techniques and tools of artists. There are special programs that imitate brushes, pens, and pencils. Provides an imitation of working with paints and various canvases. After creating an image, it is recommended to convert it to a different color model, depending on how you intend to publish it.

CMYK color model, color separation.

The CMYK color model is subtractive and is used when preparing publications for printing. CMY color components are colors obtained by subtracting primary colors from white:

cyan (cyan) = white - red = green + blue; magenta = white - green = red + blue; yellow = white - blue = red + green.

This method corresponds to the physical essence of the perception of rays reflected from printed originals. Cyan, magenta, and yellow are called complementary colors because they complement the primary colors to white. This leads to the main problem of the CMY color model - overlapping additional colors in practice does not produce pure black. Therefore, a pure black component was included in the color model. This is how the fourth letter appeared in the abbreviation of the CMYK color model (Cyan, Magenta, Yellow, BlaK).

To print on printing equipment, a color computer image must be divided into components corresponding to the components of the CMYK color model. This process is called color separation. The result is four separate images containing the same color content of each component in the original. Then, in a printing house, from plates created on the basis of color-separated films, a multi-color image is printed, obtained by overlaying CMYK colors.

Indexed color.

Indexed colors are so called because in this mode, each pixel in the image is assigned an index pointing to a specific color from a special table called a color palette. Changing the order of the colors in the palette will have a dramatic effect on the appearance of the image represented by the indexed colors. Indexed palettes do not contain more than 256 colors, but there may be much less. The fewer colors in the palette, the fewer bits required to represent the color of each pixel and, therefore, the smaller the image file size.

Indexed colors are usually encoded with four or eight bits in the form of so-called color tables. Indexed color depth can be 2-8 bits. For example, the Windows 95 graphics environment supports a color table of eight bits per pixel, called the system palette. In this table, the colors are already predefined, so only those colors can be used.