A person perceives light using color receptors (the so-called cones) located on the retina of the eye. The cones are most sensitive to red, green and blue colors, which are the basic colors of human perception. The sum of red, green and blue colors is perceived by a person as white, their absence as black, and their various combinations as numerous shades of colors.

From a monitor screen, a person perceives color as the sum of the radiation of three basic colors: red, green and blue. This color rendering system is called RGB, after the first letters of the English color names (Red - red, Green - green, Blue - blue). The colors in the RGB palette are formed by adding the base colors, each of which can have different intensities. The color of the Color palette can be determined using a formula.

Color = R + G + B, where 0

With a color depth of 24 bits, 8 bits are allocated to encode each of the basic colors. In this case, for each color, N = 2 8 = 256 intensity levels are possible. Intensity levels are specified by codes: –decimal (from minimum – 0 to maximum – 255); –Binary (from to)

Color coding at 24-bit color depth Color Binary and decimal intensity codes for base colors Red Green Blue Black Red Green Blue Cyan Magenta Yellow White

When printing images on printers, a color palette in the CMYK system is used. The main colors in it are Cyan - blue, Magenta - purple and Yellow - yellow. The CMYK system, unlike RGB, is based on the perception of reflected light rather than emitted color. A person perceives an image printed on paper in reflected light. If paints are not applied to the paper, then the incident light is completely reflected, and we see a white sheet of paper. If paints are applied, then they absorb certain colors. CMYK colors are created by subtracting certain colors from white.

Cyan = W – R = G + B Cyan ink applied to paper absorbs red light and reflects green and blue light, and we see the color blue. Cyan = W – R = G + B Magenta = W – G = R + B Magenta ink applied to paper absorbs green light and reflects red and blue light and we see the color purple. Magenta = W – G = R + B Yellow = W – B = R + G Yellow ink applied to paper absorbs blue light and reflects red and green light, and we see the color yellow. Yellow = W – B = R + G Red = Y + M = W – R - B If you apply magenta and yellow paints to paper, the green and blue colors will be absorbed, and we will see red. Red = Y + M = W – R - B Green = Y + C = W – R - B If you apply blue and yellow paints to paper, the red and blue colors will be absorbed, and we will see green. Green = Y + C = W – R - B If you apply magenta and cyan inks to paper, the green and red colors will be absorbed, and we will see blue. Blue = M + C = W – R - G

Formation of colors in the SMUK color rendering system Color Formation of color Black Black = C + M + U = W – G – B - R White White = (C = 0, M = 0, U = 0) Red Red = U + M = W – R - B Green Green = U + C = W – R - B Blue Blue = M + C = W – R - G Cyan = W – R = G + B Purple Magenta = W – G = R + B Yellow Yellow = W – B = R + G

Mixing three colors - cyan, yellow and magenta should lead to complete absorption of light, and we should see black. However, in practice, instead of black, the result is a dirty brown color. Therefore, the color model contains one more, true black color. Since the letter “B” is already used to denote the color blue, the last letter in the English name for the color black “Black” is adopted to denote the color black, i.e. “K” In the CMYK color rendering system, the color palette is formed by superimposing cyan, magenta, yellow and black.

CMYK model The CMYK model is subtractive, i.e. To obtain a new shade, you need to remove the primary colors in certain proportions. Cyan = white – red = green + blue Magenta = white – green = red + blue Yellow = white – blue = red + green Black white + red + green + blue

The RGB color rendering system is used in computer monitors, televisions and other light-emitting technical devices. The CMYK color rendering system is used in printing because... printed documents are perceived by humans in reflected light. Inkjet printers use four cartridges containing base colors to produce high-quality images.

The HSB color rendering system uses Hue, Saturation and Brightness as basic parameters. The Hue parameter allows you to select a color hue from all colors of the optical spectrum, starting from red and ending with violet (H = 0 - red, H = green, H = 240 - blue, H = 360 - violet). The Saturation parameter determines the percentage of “pure” tint and white color (S = 0% - white color, S = 100% - “pure tint”). The Brightness parameter determines the intensity of the color (the minimum value B = 0 corresponds to black, the maximum value B = 100 corresponds to the maximum brightness of the selected color).

Model HSB The HSB model is tuned to human color perception. In it, all the primary colors are located at the top, decreasing in brightness down. To more accurately determine the desired shade, use the gradation bar on the right to make the selected color brighter or darker. There is also a choice of color by name and its coordinates translated into RGB or CMYK model.

Chapter Textbook: Ugrinovich N.D. Computer Science and ICT. Basic course: Textbook for 9th grade. – 4th ed. –M.: BINOM. Knowledge Laboratory

1. In what color rendering system is the color palette formed by adding red, green and blue? 1) HSB 2) RGB 3) WBRK 4) CMYK

2. In what color rendering system is the color palette formed by superimposing cyan, yellow, magenta and black? 1) HSB 2) RGB 3) WBRK 4) CMYK

3. How much information (in kilobytes) is contained in a screen image with a resolution of 512 × 768 pixels and 16 colors? 16= 2 i , i = 4, I = 512,768 4 = 1572864 bits / 8 = 196608 bytes / 1024 = 192 KB.

4. How much information (in kilobytes) is contained in a screen image with a resolution of 256 × 1280 pixels and 256 colors? 256= 2 i , i = 8, I = 256 1280 8 = 2621440 bits / 8 = 327680 bytes / 1024 = 320 KB.

5. To store a raster image of 64 × 128 pixels, 8 kilobytes of memory were allocated. What is the maximum possible number of colors in the image palette? 8 KB = 8 * 1024 = 8192 bytes * 8 = 65536 bits 64 * 128 = 8192 65536 /8192 = 8 bits per point 28 = 256 Answer: 256 colors.

6. To store a raster image of 128 × 256 pixels, 4 kilobytes of memory were allocated. What is the maximum possible number of colors in the image palette? 4 KB = 4 * 1024 = 4096 bytes * 8 = 32768 bits 256 * 128 = 32768 /32768 = 1 bit per point 21 = 2 Answer: 2 colors.

7. A raster file containing a black and white image has a volume of 1.5 kilobytes. What size will the image be in pixels? 1.5 KB = 1.5*1024 = 1536 bytes *8 = 12288 bits 2= 2 i , i = 1 bit (black and white picture) 12288/1= 12288 pixels.

Number of points along the entire horizon vertical or number of informational colors bits per screen point volume 800 600 480000 256 8 3840000 bits 640 480 307200 2 1 320 200 102400 16 4 307200 bits 409600 bits

| Planning lessons for the school year (according to the textbook by N.D. Ugrinovich) | Color palettes in RGB, CMYK and HSB color rendering systems

Lesson 12
Color palettes in RGB, CMYK and HSB color rendering systems

§ 2.2.3. Color palettes in RGB, CMYK and HSB color rendering systems

2.2.3. Color palettes in RGB, CMYK and HSB color rendering systems

White light can be decomposed using optical instruments, such as a prism, or water droplets in the atmosphere (rainbow) into various colors of the spectrum: red, orange, yellow, green, cyan, indigo and violet (Fig. 2.4).

Rice. 2.4. Decomposition of white light into a spectrum

There is a well-known phrase that helps you easily remember the sequence of colors in the visible light spectrum: « Every hunter wishes know , Where is sitting pheasant ».

A person perceives light using color receptors, the so-called cones, located on the retina of the eye. The cones are most sensitive to red, green and blue colors, which are the basic colors of human perception. The sum of red, green and blue colors is perceived by a person as white, their absence as black, and their various combinations as numerous shades of colors.

Color palette in the RGB color rendering system. From a monitor screen, a person perceives color as the sum of the radiation of three basic colors: red, green and blue. This color rendering system is called RGB, after the first letters of the English color names ( Red - red, Green - green, Blue - blue).

Colors in the palette RGB are formed by adding basic colors, each of which can have different intensities.

The color of the Color palette can be determined using the formula (2.1).

At the minimum intensities of all basic colors, black is obtained, and at maximum intensities, white is obtained. The maximum intensity of one color and the minimum of the other two are red, green and blue. The overlay of green and blue colors forms cyan (Cyan), the overlay of red and green colors forms yellow (Yellow), the overlay of red and blue colors forms magenta (Magenta) (Table 2.4).

Table 2.4. Formation of colors in the RGB color rendering system

In the RGB color rendering system, the color palette is formed by adding red, green and blue.

With a color depth of 24 bits, 8 bits are allocated to encode each of the basic colors. In this case, for each color, N = 2 8 = 256 intensity levels are possible. Intensity levels are specified in decimal (from minimum - 0 to maximum - 255) or binary (from 00000000 to 11111111) codes (Table 2.5).

Color palette in the CMYK color rendering system. When printing images on printers, the color palette in the system is used CMY. The main colors in it are Cyan - blue, Magenta - purple and Yellow - yellow.

Colors in the CMY palette are formed by applying paints of base colors. The color of the Color palette can be determined using formula (2.2), in which the intensity of each paint is specified as a percentage:

A person perceives an image printed on paper in reflected light. If no paint is applied to the paper, then the incident white light is completely reflected and we see a white sheet of paper. If paints are applied, they absorb certain colors of the spectrum. Colors in the CMY palette are created by subtracting certain colors from white light.

When applied to paper, blue ink absorbs red light and reflects green and blue light, giving us the color blue. When applied to paper, purple ink absorbs green light and reflects red and blue light, giving us the color magenta. Yellow ink applied to paper absorbs blue light and reflects red and green light, giving us the color yellow.

By mixing two CMY paints, we get a base color in the RGB color rendering system. If we apply magenta and yellow inks to paper, the green and blue light will be absorbed and we will see red. If you apply blue and yellow paints to paper, the red and blue light will be absorbed and we will see green. If you apply magenta and cyan paints to paper, green and red light will be absorbed, and we will see blue (Table 2.6).

Mixing three colors - blue, yellow and purple- should lead to complete absorption of light, and we should see a black color. However, in practice, instead of black, the result is a dirty brown color. Therefore, another true black color is added to the color model. Since the letter “B” is already used to denote the color blue, the last letter in the English name for the color Black, i.e. “K,” is adopted to denote the color black. The extended palette is called CMYK (see Table 2.6).

In the CMYK color system, the color palette is created by combining cyan, magenta, yellow and black.

The RGB color rendering system is used in computer monitors, televisions and other light-emitting technical devices. The CMYK color rendering system is used in printing, since printed documents are perceived by humans in reflected light. Inkjet printers use four cartridges containing base inks of the CMYK color rendering system to produce high-quality images (Fig. 2.5).

Rice. 2.5. Using RGB and CMYK color rendering systems in technology

Color palette in the HSB color rendering system. The HSB color rendering system uses as basic parameters Hue(color shade), Saturation(saturation) and Brightness(brightness).

Hue setting allows you to select a color shade from all colors of the optical spectrum: from red to violet (H = 0 - red, H = 120 - green, H = 240 - blue, H = 360 - violet).

Saturation parameter determines the percentage of “pure” tint and white color (S = 0% - white color, S = 100% - “pure” tint).

Brightness parameter determines the intensity of the color (the minimum value B = 0 corresponds to black, the maximum value B = 100 corresponds to the maximum brightness of the selected shade of color).

In the HSB color rendering system, the color palette is formed by setting the values ​​of hue, saturation and brightness.

Graphic editors usually have the ability to switch from one color rendering model to another. This can be done either using the mouse, moving the pointer across the color field, or by entering the parameters of color models from the keyboard into the corresponding text fields.

Control questions

1. In what natural phenomena and physical experiments can one observe the decomposition of white light into a spectrum? Prepare a report.

2. How the color palette is formed in the color rendering system RGB? In the color rendering system CMYK? In the HSB color rendering system?

Tasks for independent completion

2.8. Short answer task. Define colors if the intensities of the base colors in the color rendering system are given RGB. Fill the table.

2.9. Short answer task. Determine colors if paints are applied to paper in a color rendering system CMYK. Fill the table.

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, there is an increased risk of under-registration in elements printed in black, as well as waterlogging of the material (paper).

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.