Use color in computer graphics. Color Systems in Computer Graphics Color Transfer Features in Computer Graphics
In this section:
- emitted I. reflected light in computer graphics; Formation of color shades on the monitor screen; Formation of color shades when printing images.
To describe the color shades that can be played on the computer screen and on the printer, developed special means - Color models (or flower systems). To successfully apply them in computer graphics, it is necessary:
Understand the features of each color model
Be able to determine this or that color using different color models
Understand how different graphic programs solve color coding
Understand why the color shades displayed on the monitor are quite difficult to reproduce exactly when printing.
We see objects because they emit or reflect light.
Light is electromagnetic radiation.
Color characterizes the effect of radiation on the human eye. Thus, the rays of the light, falling on the retina of the eye, make a feeling of color.
Emitted light- This is the light coming out of the source, such as the sun, light bulb or monitor screen.
Reflected light- This is the light, "bounced" from the surface of the object. It is his us that we see when we look at any item that is not.
The radiated light, which goes directly from the source to the eye, retains all the colors from which it is created. But this light may change when reflected from the object (Fig. 1).
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Like the Sun and other light sources, the monitor radiates light. The paper on which the image is printed reflects the light. Since the color may turn out in the process of radiation and in the reflection process, there are two opposite methods of its description: systems additive and subtractive colors.
Additive flower system
If from close distance (and even better with a magnifier) \u200b\u200blook at the screen of the working monitor or television, it is not difficult to see many smallest points of red (Red),green (Green)and blue (Blue)flowers. The fact is that thousands of phosphorent colors are located on the surface of the screen, which are bombarded by electrons at high speed. Color points emit light under the influence of the electron beam. Since the dimensions of these points are very small (about 0.3 mm in diameter), adjacent multicolored points merge, forming all other colors and shades, for example:
red + green \u003d yellow
red + blue \u003d purple,
green + blue \u003d blue
red + green + blue \u003d white.
The computer can accurately control the amount of light emitted through each point of the screen. Therefore, changing the intensity of the glow of color points, you can create a large variety of shades.
Thus, an additive (add-to attach) the color is obtained by combining the (summation) of the rays of the three main colors - red, green and blue. If the intensity of each of them reaches 100%, then the white color is obtained. The absence of all three colors gives black. The system of additive colors used in computer monitors is made to mark abbreviation RGB.
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Fig. 3. Dialog box for selecting color in the program Adobe Photoshop.
In most programs to create and edit images, the user has the ability to form its own color (in addition to the offered palettes), using red, green and blue components. As a rule, graphic programs allow combining the desired color of 256 shades of red, 256 shades of green and 256 shades of blue. As it is easy to calculate, 256 x 256 x 256 \u003d 16.7 million colors. Type of dialog box for setting arbitrary color shade in different programs may be different (Fig. 2,3,4).
Thus, the user can select the finished color from the built-in palette or create its own shade, specifying in the input fields R, G, and B for red, green and blue color components in the range from 0 to 255 (Fig. 2,3,4 ).
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Since the paper does not radiate light, color model RGB.cannot be used to create an image on a printed page.
System subtractive colors
In the process of printing, the light is reflected from the sheet of paper. Therefore, for print graphic images A system of colors operating with the reflected light is used - the system of subtractive colors (subtract - deduct).
White color consists of all colors of the rainbow. If you skip the ray of light through a simple prism, it will decompose in the color spectrum. Red, orange, yellow, green, blue, blue and purple colors form a visible spectrum of light. White paper when lighting reflects all the colors, the painted paper absorbs part of the colors, and the rest - reflects. For example, a red paper sheet illuminated with white light looks red precisely because such a paper absorbs all colors other than red. The same red paper lit by blue will look black, since the blue color it absorbs.
In the system of subtractive colors the main are blue (Cyan)Purple (Magenta) And Yellow (Yellow). Each of them absorbs (deducts) certain colors from white light falling on the printed page. This is how three basic colors can be used to obtain black, red, green and blue:
blue + purple + yellow \u003d black,
blue + purple \u003d blue,
yellow + purple \u003d red,
yellow + blue \u003d green.
Mixing the basic colors in different proportions on white paper, you can create a large variety of shades.
White color is obtained in the absence of all three main colors. High percentage of blue, purple and yellow forms black. More precisely, black should turn out theoretically, in reality, due to some features of typographical paints, a mixture of all three main colors gives a dirty brown tone, so there is still black paint when printing images (Black).
System subtractive colors are denoted by abbreviation CMYK.(so that no confusion with Blue,for notation Black.used symbol K).
The process of four-color printing can be divided into two stages.
1. Creation on the basis of the original pattern of four components of blue, purple, yellow and black flowers on the basis of the original pattern.
2. Print each of these images one after another on the same sheet of paper.
The separation of color drawings into four components performs special program Flowallements. If printers used the system CMY. (without adding black paint), converting images from the system RGB. in the system CMY. It would be very simple: flower values \u200b\u200bin the system CMY. - these are simply inverted system values RGB.The "Color Circle" scheme (Fig. 5) shows the relationship of the main colors of the models RGB. and CMY.. A mixture of red and green gives yellow, yellow and blue - green, red and blue - purple, etc.
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It is important that instead of solid colored areas, the flowering program creates rasters from individual points (Fig. 6), and these point rasters are slightly rooted with each other so that the points of different colors are not overlayed alone along the other, and were located nearby.
Small points of various colors, close to each other, seem merging together. That is how our eyes perceive the resulting color.
Thus, the system RGB.works with radiated light, and CMYK.- with reflected. If you need to print an image obtained on the monitor on the printer, a special program performs the conversion of one colors system to another. But in systems RGB.and CMYK.different nature of color reception. Therefore, the color that we see on the monitor is quite difficult to immediately repeat when printing. Usually, on the screen, the color looks somewhat brighter compared to the same color rendered to print.
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Fig. 7. Program dialog box CorelDraw.to form color in the system HSB.
In addition, the user can choose a color tone by clicking in the appropriate point of the color field (Fig. 3, 4, 7).
As a result of moving the label in the form of a small square (Fig. 7), the saturation and brightness of the selected tone are changed along the inside of the color rectangle. In the upper left corner of the rectangle, the color becomes the most blurred (almost white). In the lower right corner, the brightness of its color is minimal. IN Adobe Photoshop. (Fig. 3) Changing saturation and brightness is performed as a result of moving the label in the form of a circle inside the color field. In a graphic editor Paint. The color field allows you to choose tone and saturation (contrast), and the brightness is set using a special regulator (Fig. 4).
1. What is the difference between the emitted and reflected light?
2. What color description methods are known to you?
3. How is the color in the RGB colors system?
4. How to form your own color when working in some graphic package?
5. Why does RGB colors system cannot be used to create images on a printed page?
6. What basic colors are used to form color in the CMYK colors system?
7. What is the process of four-color printing?
8. Why are the colors created on the screen, can not always be reproduced when printing?
9. How is the color in the HSB colors system describe?
Color and light in computer graphics
A person is a trichromate - the retina of the eye has 3 types of light receptors responsible for color vision (columns). Each type of flashes responds to a certain range of the visible spectrum. The response caused in the columns with the light of a certain spectrum is called color stimulusAt the same time, light with different spectra can have the same color stimulus, and thus perceived the same person. This phenomenon is called metallic - two radiations with different spectra, but the same color incentives will be indistinguishable by a person. You can determine the color space of incentives as the Euclidean space, if you set the coordinates x, y, z as the values \u200b\u200bof incentives corresponding to the response
cabinges of long-wave (L), medium-wave (M) and short-wave (S) range of optical spectrum. The origin of the coordinates (S, M, L) \u003d (0, 0, 0) will be black.
The color model is a description of the color shades for viewing on the monitor screen and when printing on the printer.
Additive color model RGB
Additive (from the English. "Add -" attach ") the color is obtained by combining the (summation) of the three main colors - red, green and blue. If the intensity of each of them reaches 100%, then the white color is obtained. The absence of all three colors gives black.
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Computer geometry and graphics |
The additive color model used in computer monitors is made to designate the RGB abbreviation (Red - Red, Green - Green, Blue
Blue). By changing the intensity of color points, you can create a large variety of shades.
red + green - yellow; red + blue - purple; Green + blue - blue; Red + green + blue \u003d white.
The figure shows various combinations of red, green and blue.
Formation of own color shades in the RGB model
Graphic editors tend to combine the desired color of 256 shades of red, 256 shades of green and 256 shades of blue.
Thus, 16,777,126 color shades can be obtained on the computer screen.
Dialog box for forming colors in the RGB model
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Computer geometry and graphics |
Side colive color model
At the subtractive color model, the main colors are blue, purple and yellow. Each of them absorbs (deducts) certain colors of white light falling on the printed page. Hence the model name
Subtractive (from English. "Subtract * -" deduct "). Here's how three basic colors can be used to get black, red, green and blue:
blue + purple + yellow \u003d black; Blue + purple \u003d blue; Yellow + purple \u003d red; Yellow + blue \u003d green.
Spendtractive mixing of flowers
Sistemptive Color Model CMYK
The subtractive color model is denoted by the abbreviation CMYK (Cyan
Blue, Magenta - Purple, Yellow - Yellow, Black - Black. In order not to confuse the "Blue", the "K" symbol is used to designate "Black").
The relationship of additive and subtractive color models
The RGB model works with radiated light, a CMYK - with reflected. If you want to print an image received on the monitor on the printer, a special program performs the conversion of one color model to another.
CIE XYZ is a linear 3-component color model based on the results of measuring the characteristics of the human eye. Built on the basis of the visual capabilities of the so-called "standard observer", that is, a hypothetical viewer, whose capabilities were carefully studied and
x \u003d x / (x + y + z), y \u003d y / (x + y + z).
Usually, YXY diagram is used to illustrate the characteristics of the Hamuts various devices Play color - displays and printers.
Properties of diagram of a tonality
Properties:
– The diagram presents all colors visible to the average person.
– All colors that can be obtained by mixing any two are lying on a straight line between them.
– All colors that can be obtained by mixing three colors,
lying inside the triangle mixing three data of real light source, it is impossible to get all the colors visible by a person
Three-dimensional space
L * - Brightness (Lightness)
- L * \u003d 0 black
- L * \u003d 100 white
a * - position between violet and green
- but*< 0 фиолетовый
- A *\u003e 0 green
b * - position between yellow and blue
- b *< 0 желтый
- b *\u003e 0 blue
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Computer geometry and graphics |
Hsv (eng. Hue, Saturation, Value - tone, saturation, value) or HSB (eng. Hue, Saturation, Brightness - Tint, Saturation, Brightness) - Color model in which color coordinates are:
Scale Shades - Hue
Hue is a color tone, (for example, red, green or blue-blue). It varies within 0-360 °, but sometimes it is driven to the range of 0-100 or 0-1.
Saturation is a saturation. Varies in the range of 0-100 or 0-1. The greater this parameter, the "cleaner" color, so this parameter is sometimes called the color purity. And the closer this parameter to zero, the closer the color to the neutral gray.
Value (color value) or Brightness - brightness. Also set within
The model was created by Elvi by Smith, one of the founders of Pixar, in 1978. It is a nonlinear conversion of the RGB model.
It should be noted that HSV (HSB) and HSL are two different color models.
Three HSV space visualization
The simplest way to display HSV to three-dimensional space is to use the coordinate cylindrical system. Here the coordinate H is determined by the polar angle, S is a radius-vector, and V - z-coordinate. That is, the shade is changed when moving along the cylinder circle, saturation - along the radius, and the brightness - along the height. Despite the "mathematical" accuracy, this model has a significant disadvantage: in practice, the number of saturation and shades distinguishable by the eye is reduced by the brightness approach (V) to zero (that is, on shades close to the black). Also on small S and V, significant rounding errors appear when translating RGB in HSV and vice versa.
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Computer geometry and graphics |
Another way to visualize the color space is a cone. As in the cylinder, the shade changes around the circumference of the cone. Color saturation increases with a distance from the axis of the cone, and brightness - with an approach to its base. Sometimes instead of a cone, a hexagonal proper pyramid is used.
HSV visualization in applied
Color circle
This visualization consists of a color circle (that is, cross-section of the cylinder) and the brightness engine (cylinder height). This visualization gained wide fame according to the first versions of Corel. On the this moment It is extremely rarely used, the ring model is used more often.
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Computer geometry and graphics |
The HSV model is often used in computer graphics programs, as convenient for a person. Therefore, it is necessary to deploy a three-dimensional HSV space on a two-dimensional computer screen
Color Ring
The shade is represented as a rainbow ring, and the saturation and value of the color are selected using the triangle ring entered into this ring. Its vertical axis, as a rule, adjusts the saturation, and the horizontal allows you to change the color value. Thus, to select a color, you must first indicate the shade, and then select the desired color from the triangle.
Color spaces
Source (Reference) Color spaces:
- Cie Xyz.
- CIE L * A * B
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Computer geometry and graphics |
– Cie RGB (not used)
Color models:
- RGB.
- CMYK.
- HSV.
Derivatives Color spaces:
- SRGB (RGB)
- Adobe RGB (RGB)
SRGB space
Created by Microsoft, Hewlett-Packard
Standardized in 1996.
Currently used:
- Monitors
- cameras
If the image does not specify the color space, we can assume that it is srgb
Disadvantages: source colors strongly inside the visible man
ADOBE RGB space
Developed ADOBE in 1998
The goal is to be able to work on the monitor with most colors available in the CMYK model on printers
Wider range of colors (Gamut)
Problem: 8 bits per color may not be enough
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Computer geometry and graphics |
Colorful temperature
Color Temperature (TC) - Characteristics of the intensity of the radiation of the light source as a function of the wavelength in the optical range.
Units
Color temperature of the light source:
characterizes the spectral composition of the radiation of the light source;
it is the basis of objectivity of the impression of the color of reflective objects and light sources.
Scale color temperatures Commanded light sources
800 K - the beginning of the visible dark red glow of crack 2000 K - the light of the candle flame, 2360 K is an incandescent lamp, vacuum,
2800-2854 K - gas-filled (gas) incandescent bulbs with tungsten spiral, 3200-3250 K - typical film lamps,
5500 K - daylight, straight sunny, 6500 K - standard source of daylight light, it is close to the midday sunlight,
7500 K - daylight, with a large share of scattered from pure blue sky, 100000 K - color of the source with "infinite temperatures"
In order to avoid many errors and failures, it is necessary to understand the theory of color as well as the principles of reproduction and synthesis of colors using the palette and the dialogue of graphic editors. Color and light The effect of color per person is multifaceted. Properly selected colors can how to draw attention to the desired image and push it away from it.
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I.. Color Systems in Computer Graphics
1. Basic concepts of computer graphics ..................... 2 p.
2. Color and color models .......................................... ... 4 pp.
3. Color model RGB ................................................ 5 p.
4..systems of HSB and HSL colors ..........................................................
5. Color model HSB ................................................ 7 pp.
6. Color model Cie Lab .......................................... ..8 p.
7. CMYK color model, flowering .......................... 8 pp.
II.. Practical part
1.Practive question (creating a picture in the CorelDRAW program)
List of references used ..................................... 11pm.
Basic concepts of computer graphics
In computer graphics with the concept of permission, it usually happens the most confusion, because it is necessary to deal with several properties of different objects. It should be clearly distinguished: screen resolution, printing resolution and image resolution. All these concepts relate to different objects. With each other, these types of permissions are not connected yet until you need to find out what physical size will be picture on the monitor screen, print on paper or file on the hard disk.
Screen resolution is the properties of the computer system (depends on the monitor and video card) and operating system (Depends on Windows settings). The screen resolution is measured in pixels (points) and determines the size of the image that can fit on the entire screen.
The printer resolution is the printer property expressing the number of individual points that can be printed on a portion of a single length. It is measured in DPI units (points per inch) and determines the size of the image at a given quality or, on the contrary, the image quality at a given size.
Image resolution is the property of the image itself. It is also measured at dpi dpi and set when creating an image in a graphic editor or using a scanner. So, to view the image on the screen, it is enough for it to have a resolution of 72 DPI, and for printing on the printer - no less than 300 dpi. The image resolution value is stored in the image file.
The physical image size determines the size of the drawing vertical (height) and horizontal (width) can be measured both in pixels and in units of length (millimeters, centimeters, inches). It is set when creating an image and stored with the file. If the image is prepared to demonstrate on the screen, then its width and height is set in pixels to know what part of the screen it takes. If the image is prepared for printing, its size is set in units of length to know what part of the paper sheet it will take.
The physical size and image resolution is inextricably linked with each other. When changing the resolution, the physical size is automatically changing.
When working with color, concepts are used: the depth of color (it is also called the color resolution) and the color model.
To coding the color of the pixel of the image, a different number of bits can be allocated. It depends on how many colors on the screen can be displayed simultaneously. The larger length binary code Colors, the more colors can be used in the picture.
The color depth is the number of bits that are used to encode the color of one pixel. To encode two-color (black and white), the image is enough to highlight one bit to represent the color of each pixel. Selecting one byte allows you to coding 256 different color shades. Two bytes (16 bits) allow you to define 65536 different colors. This mode is called High Color. If three bytes are used for color coding (24 bits), it is possible to simultaneously display 16.5 million colors. This mode is called True Color. From the depth of color, the size of the file in which the image is saved.
Colors in nature are rarely simple. Most color shades are formed by mixing the main colors. The method of separating the color shade into components is called color model. There are many different types of color models, but in computer graphics, as a rule, no more than three are applied. These models are known as the names: RGB, CMYK, NSB.
Color and color models.
The color is additive and subtractive.
Additive color is obtained by connecting light different colors. In this scheme, the absence of all colors is black, and the presence of all colors is white. The diagram of additive colors works with radiated light, for example, a computer monitor.
In the system of subtractive colors there is a reverse process. Here it turns out any color when subtracting other colors from the common beam of light. In this scheme, the white color appears as a result of the lack of all colors, while their presence gives black. Scheme of subtractive colors works with reflected light.
In computer graphics, apply the concept of color permission (another name - color depth). It defines the color information encoding method for playing it on the monitor screen. To display a black and white image, two bits (white and black colors) are sufficient. Eight-bit encoding allows you to display 256 gradations of color tone. Two bytes (16 bits) define 65,536 shades (such a mode is called High Color). With a 24-bit encoding method, it is possible to determine more than 16.5 million colors (the mode is called from a practical point of view to the color resolution of the monitor closely the concept of color coverage. Under it means a range of colors that can be reproduced using a particular output device (monitor, printer, Printing machine and other). In accordance with the principles of image formation by additive or subtractive methods, methods for separating the color shade to components components, called color models, are developed. In computer graphs, the RGB and HSB models are used mainly (to create and process additive images) and CMYK ( To print a copy of the image on printing equipment). Color models are located in a three-dimensional coordinate system forming the color space, since the laws of the Grossman follows that the color can be expressed by a point in three-dimensional space.
The first law of Grassman (the law of three dimensions). Any color is uniquely expressed by three components if they are linearly independent. Linear independence is the inability to get any of these three colors by adding two other.
The second law of Grassman (the law of continuity). With continuous change in radiation, the mixture color also changes continuously. There is no such color to which it would be impossible to pick up infinitely close.
The third grassman law (the law of additivity). The color of the mixture of radiation depends only on their color, but not the spectral composition. That is, the color (C) of the mixture is expressed by the sum of the color equations of radiation:
Cysmm \u003d (R1 + R2 + ... + Rn) R + (G1 + G2 + ... + Gn) G + (B1 + B2 + ... + BN) b.
Color model RGB.
The computer monitor creates a color directly by light radiation and uses RGB colors scheme.
The RGB color model is additive, that is, any color is a combination in a different proportion of three main colors - red (Red), green (green), blue (Blue). It serves as the basis for creating and processing computer graphics intended for electronic playback (on the monitor, TV). If you look at the monitor screen from closely, it can be noted that it consists of the smallest points of red, green and blue. The computer can control the amount of light emitted through any painted point and, combining various combinations of any colors, can create any color. When applying one component of the primary color to another brightness of total radiation increases. Combining three components gives a sharm gray color, which, with an increase in brightness, approaches white color. With 256 gradation levels of tone, the black color corresponds to the zero values \u200b\u200bof RGB, and the white - maximum, coordinates (255,255,25).
Being determined by the nature of computer monitors, the RGB scheme is the most popular and common, but it has a disadvantage: computer drawings should not be present only on the monitor, sometimes you have to be printed, then you need to use another color system - CMYK.
HSB and HSL colors
HSB and HSL colors systems are based on restrictions imposed by hardware. In the HSB system, the color description is represented in the form of tone, saturation and brightness. Another HSL system sets tone, saturation and illumination. The tone is a specific shade of color. Color saturation characterizes its relative intensity or frequency. Brightness or illumination show the magnitude of the black shade added to the color, which makes it more dark. The HSB system is well coordinated with a model of color perception by man, that is, it is equivalent to the wavelength of light. Saturation is the intensity of the wave, and the brightness is the total amount of light. The disadvantage of this system is that to work on the computer monitors it must be converted to the RGB system, and for the four-color printing to the CMYK system.
Color model HSB.
The color model HSB is designed with the maximum consideration of the characteristics of the color perception by man. It is based on the color circle of Mansell. Color is described by three components: a tint (HUE), saturation (SATURATION) and brightness (BrigFitness). The color value is selected as a vector emanating from the center of the circle. The point in the center corresponds to white color, and points around the perimeter of the circle - clean spectral colors. The direction of the vector is set in degrees and determines the color shade. Vector length determines color saturation. On a separate axis, called achromatic, brightness is set, with a zero point corresponds to black color. The color coverage of the HSB model overlaps all known values \u200b\u200bof real colors.
The HSB model is customary to use when creating images on a computer with imitation of work techniques and tools of artists. There are special programs, imitating brushes, feathers, pencils. It provides imitation of work with paints and various canvases. After creating the image, it is recommended to convert to another color model, depending on the intended method of publishing.
Color model Cie Lab
In 1920, the color spatial model of Cie Lab (Communication International De I "EclaiRage was developed - the International Commission at the Meeting. L, A, B - references to the coordinate axes in this system). The system is hardware independent and therefore is often used to transfer data between devices . In the CIE LAB model, any color is determined by the light (L) and chromatic components: the parameter A varying in the range from green to red, and the B parameter B, varying in the range from blue to yellow. Color coverage of the model CIE LAB significantly exceeds the possibilities of monitors and printed Devices, so before the image output presented in this model, it is necessary to convert it. This model was designed to match color photochemical processes with polygraphic. Today it is the default standard for the Adobe Photoshop program.
Color model CMYK, Flowering
This system was widely known long before computers began to be used to create graphic images. To split colors of the image on CMYK colors, computers are used, and their special models have been developed for printing. Converting colors from the RGB system to the CMYK system faces a number of problems. The main difficulty lies in the fact that in different systems, color can change. These systems, the nature of the color is different from these systems and what we see on the monitors screen can never be immediately repeated when printing. Currently, there are programs that allow you to work directly in CMYK colors. Vector graphics programs have already reliably have this ability, and raster graphics programs have only recently become to provide users with CMYK colors and accurate management how the drawing will look like when printing.
The color model CMYK refers to a subtractive, and it is used in preparing publications to print. CMY color components are colors obtained by subtraction of the main white:
blue (Cyan) \u003d white - red \u003d green + blue;
purple (Magenta) \u003d white - green \u003d red + blue;
yellow (Yellow) \u003d White - blue \u003d red + green.
This method corresponds to the physical essence of the perception of the rays reflected from printed originals. Blue, purple and yellow colors are called extra, because they complement the main colors to white. From here, the main problem of the color model CMY follows - the overlay on each other additional colors in practice does not give clean black. Therefore, the color model was included in the black black component. So the fourth letter appeared in the Abbreviation of the CMYK Color Model (Cyan, Magenta, Yellow, Black). For printing on printing equipment, a color computer image must be divided into components corresponding to the components of the color model CMYK. This process is called flowering. As a result, four separate images contain single-color content of each component in the original are obtained. Then in the printing house with forms created on the basis of flowered films, the multicolor image obtained by the applied of CMYK colors is printed.
Indexed color, working with palette
All colors described earlier were dealing with all spectrum of colors. Indexed colors palettes are sets of colors from which you can choose the desired color. The advantage of limited palettes is, they are that there are much less memory than full systems RGB and CMYK. The computer creates a color palette and assigns each color number from 1 to 256. Then, when saving the color of a separate pixel or an object, the computer simply remembers the number that has this color in the palette. To memorize the number from 1 to 256, you need only 8 bits. For comparison, the full color in the RGB system takes 24 bits, and in the CMYK system 32.
Bibliography:
1. Computer graphics. Porev VN,
2. Come on computer graphics. Sergeev A. P., Kushchenko S.V.
3. Computer graphics. Dynamics, realistic images. E.V.Shikin, A.V. Bestov
Computer graphics (11)Abstract \u003e\u003e Informatika
2 species Computer Graphics Three types are distinguished computer graphics. This is raster graphics, Vector graphics and fractal graphics. They differ ... three-dimensional systems coordinates. Each coordinate reflects the contribution of each component to the result color in...
The concepts of light and colors in computer graphics are fundamental. Usually the light is a continuous flow of waves with different lengths and various amplitudes. This light can be characterized by an energy spectral curve (Fig. 2.2), where the value of the function is the contribution of waves with a wavelength into a common wave flow.
Fig. 2.2. Spectral curve of light
The feeling of color occurs in the brain during the excitation and braking of the flower sensitive cells - the receptors of the eye retina of a person, kolodskok. In humans, there are three types of colums - "red", "green" and "blue", respectively. The photosensitivity of the colums is low, so for a good color perception requires sufficient illumination or brightness. Each color sensation in humans can be represented as the sum of the sensations of these three colors.
The main characteristics of the color are color tone, saturation, brightness.
Definition 2.6.Color tone - the attribute of visual perception, according to which the area seems possessing one of the perceived colors (red ( R.), green ( G.) or blue ( IN)). It is the main color characteristic.
Definition 2.7.Saturation - Characteristic, expressed fraction of the presence of white color.In perfectly clean color, there is no white admixture. If, for example, to pure red color add a white color in a specific proportion, then it turns out a light pale red color.
Definition 2.8.Brightness - Characteristic, determined by energy, intensity of light radiation.Expresses the amount of perceived light.
Ordinary color (sun, light bulbs) consists of all the colors of the rainbow. If you skip it through the prism, it will decompose in the color spectrum of the rainbow. These colors represent the frequencies of electromagnetic oscillations, which are submitted by the naked eye.
Distinguish emitted and reflected light. The emitted light is a light that leaves the active source contains all colors. Reflected light may contain all colors, their combination or only one color. Since the color may turn out in the process of radiation and absorption, there are two opposite methods of its description:
The system of additive colors;
System of subtractive colors.
Color model RGB.Additive color is obtained by connecting rays of light different colors. The absence of all colors in this system is black. The presence of all colors is white. This system works with radiated color, for example, from a computer monitor. This system uses three main colors: red, green, blue (RGB). RGB colors system. The most common and popular. Used in monitors.
Color model CMY.The system of subtractive colors is reverse. Defined color It turns out the subtraction of other colors from the overall beam of light. White color appears as a result of the lack of all colors, while their presence gives black color. This system works with reflected color.
In the system of subtractive colors the main are blue, purple, yellow (CMY - Cyan, Magenta, Yellow). When mixed, it is assumed that it should turn out black. In fact, printing paints absorb not completely completely, and therefore the combination of three main colors looks dark brown. This system is used mainly in printing. Converting drawings from the RGB system to the CMYK system faces a number of problems. The main difficulty is that in different systems, color can change. In these systems, the nature of color receiving color is different, and therefore what is displayed on the monitor screen can never be repeated when printing. The process of conversion is complicated by the need to adjust the imperfection of typographic paints.
Color model HSV.The color models considered above may somehow use the mixture of some basic colors. The color model HSV can be attributed to alternative type.
Fig. 2.3. Color model HSV.
In the HSV model (Fig. 2.3), the color is described by the following parameters: HUE color tone, saturation S (saturation), brightness, Svetlot V (Value). The value of H is measured in degrees from 0 to 360, because here the colors of the rainbow are located in a circle in this order: red, orange, yellow, green, blue, blue, purple. The values \u200b\u200bS and V are in the range (0 ... 1).
Examples of colors coding for the HSV model. For s \u003d 0 (i.e., on the axis V) - gray tones. V \u003d 0 value corresponds to black color. White color is encoded as s \u003d 0, v \u003d 1. Colors located in a circle opposite each other, i.e. Distinguished by H 180 º are additional. The color task using the HSV parameters is often used in graphic systems, Moreover, the cone sweep is usually shown.
The color model HSV is convenient for use in those graphic editorswhich are not focused on handling ready-made images, but for their creation with their own hands. There are such programs that allow imitate various artist's tools (brushes, feathers, markers, pencils), paint materials (watercolor, gouache, oil, mascara, coal, pastel) and materials of the canvas (canvas, cardboard, rice paper, etc.).
There are other color models built similarly to HSV, such as HLS and HSB and HSB models also uses the color cone. In the HSB model, too, three components: color shade (HUE), color saturation (SATURATION) and brightness of color (Brightness). Adjusting them, you can get as much arbitrary colors as when working with other models.
Color model Lab.All of the above models describe the color of three parameters and in a rather wide range. Now consider the color model in which the color is set by one number, but already for a limited range of colors (shades).
In practice, black and white (gray) semitone images are often used. Gray colors in the RGB model are described by the same components values, i.e. R i \u003d g i \u003d b i. Thus, for gray images, there is no need to use the top three numbers - enough and one number. This allows you to simplify the color model. Each gradation is determined by the brightness of Y. The value y \u003d 0 corresponds to black color, the maximum value of Y is white.
To convert color images represented in the RGB system, the ratio is used in gradation
Y \u003d 0.299r + 0.587g + 0.114b,
where the coefficients at R, G and B take into account various sensitivity of vision to the corresponding colors and, moreover, their amount is equal to one.
Obviously, the reverse transformation r \u003d y, g \u003d y, b \u003d y will not give any other colors, except grades.
A variety of models is due to various areas of their use. Each of the color models was designed to effectively perform individual operations: input images, visualizations on the screen, printing on paper, image processing, saving in files, colorimetric calculations and measurements. Converting from one model to another can lead to distortion of image colors.
Check questions and tasks
1. What types of video information do you know?
2. What is the bit depth?
3. What is the resolution of the raster?
4. What characteristics affect image size?
5. What is the feature of zooming raster and vector images?
6. Name the main characteristics of the color?
7. What color systems do you know?
8. Give the definitive colors system. What devices are it used?
9. What is a system of subtractive colors?
10. List alternative color systems.