A computer bitmap is represented as a rectangular matrix, each cell of which is represented by a colored dot.

When digitizing an image, it is divided into such tiny cells that the human eye does not see them, perceiving the entire image as a whole. The network itself is called raster map, and its unit element is called pixel.

Pixels are like grains in a photograph, and when zoomed in a lot, they become noticeable. A raster map is a set (array) of triples of numbers: two coordinates of a pixel on a plane and its color.

Unlike vector images, when creating raster graphics objects, mathematical formulas are not used, therefore, for the synthesis of raster images, it is necessary to set the resolution and dimensions of the image.

With the help of raster graphics, you can reflect and convey the whole gamut of shades and subtle effects inherent in a real image. A bitmap image is closer to a photograph, it allows you to more accurately reproduce the main characteristics of a photograph: illumination, transparency, and depth of field.

Most often, raster images are obtained by scanning photographs and other images, using a digital camera, or by "capturing" a frame of video. Raster images can also be obtained directly in raster or vector graphics programs by converting vector images.

There are many raster graphics file formats, and each has its own way of encoding image information. We list the features of only the most common formats.

Of the large number of image file formats on the Internet, only two are now widely used - GIF and JPEG. Let's talk about them in more detail.

GIF format

The popular GIF format was developed by CompuServe as being hardware independent. It is designed to store bitmap images with compression. Several images can be stored in one file of this format. Typically this feature is used to store animated images (as a set of frames).

GIF-format allows you to record the image "through the line" (Interlaced), so that, having only part of the file, you can see the entire image, but with a lower resolution. This feature is widely used on the Internet. At first, you see a picture with a rough resolution, and as more data comes in, its quality improves. The main limitation of the GIF format is that a color image can contain no more than 256 colors. For printing, this is clearly not enough.

jpeg format

JPEG file format ( Joint Photographic Experts Group - Joint Expert Group on Photography) was developed by C-Cube Microsystems as an efficient method for storing images with deep color depths, such as scanned photographs with numerous subtle (and sometimes subtle) color tints.

The biggest difference between the JPEG format and other formats is that JPEG uses lossy compression algorithm(not a lossless algorithm).

The lossless compression algorithm preserves image information in such a way that the decompressed image exactly matches the original. Lossy compression sacrifices some image information in order to achieve a higher compression ratio.

The compression used in the JPEG format permanently distorts the image. This is not noticeable when simply viewing it, but becomes apparent with subsequent manipulations. But the file size is 10 to 500 times smaller than BMP! If you decide to burn an image in JPEG format, it's best to do all the necessary operations before writing the file for the first time.

Comparison of GIF and JPEG

1. GIF format is convenient when working with hand-drawn pictures.
2. The JPEG format is best used for storing photos and images with lots of colors.
3. The GIF format is used to create animations and images with a transparent background.

Vector graphics

The main logical element of vector graphics is a geometric object. As an object, simple geometric shapes (the so-called primitives - rectangle, circle, ellipse, line), composite shapes or shapes built from primitives, color fills, including gradients, are accepted.

The advantage of vector graphics is that the shape, color and spatial position of its constituent objects can be described using mathematical formulas.

An important object of vector graphics is a spline. A spline is a curve that describes a particular geometric figure. Modern fonts are built on splines true type and postscript.

Vector graphics have many advantages. It is economical in terms of disk space required for storing images: this is due to the fact that not the image itself is saved, but only some basic data, using which the program recreates the image every time. In addition, the description of color characteristics almost does not increase the file size.

Vector graphics objects are easily transformed and modified, which has almost no effect on image quality. Scaling, rotation, curvature can be reduced to a couple of elementary transformations over vectors.

In those areas of graphics where it is important to maintain clear and distinct contours, for example, in font compositions, in creating logos, and so on, vector programs are indispensable.

Vector graphics can also include fragments of raster graphics: a fragment becomes the same object as all the others (though with significant limitations in processing).

An important advantage of vector graphics programs is the advanced means of integrating images and text, a unified approach to them. Therefore, vector graphics programs are indispensable in the field of design, technical drawing, drawing, graphic and design work.

However, on the other hand, vector graphics may seem overly rigid, "plywood". It is indeed limited in purely pictorial means: it is almost impossible to create photorealistic images in vector graphics programs.

And besides, the vector principle of image description does not allow you to automate the input of graphic information, as does a scanner for dot graphics.

Recently, 3D modeling programs, which also have a vector nature, are becoming more widespread.

Possessing sophisticated drawing methods (ray tracing method, radiation method), these programs allow you to create photorealistic bitmap images with arbitrary resolution from vector objects with moderate effort and time.

Computer graphics imperceptibly, but firmly entered our everyday life. It has long ceased to be the lot of the elite. Every time you transfer photos from a digital camera to a computer or simply click on the "save" button to add a picture you like to the collection, you are working with computer graphics.

Is it worth spending time on theory?

Knowing the basics of how the imaging method works will serve you well. Extensions after the file name will no longer be some kind of magical abracadabra for you, but will begin to supply important information regularly. You will be able to consciously decide which images to compress in order not to clutter up your hard drive space, and choose wisely in which way this can be done.

Editing your own photos will also move from being a "scientific poke method" to a whole new level. And for some, innocent fun with images on the screen gradually turned into a fairly profitable job.

The difference between raster and vector graphics

At the moment, in the computer environment, vector and raster graphics are mainly used. They are fundamentally different from each other in the way information is encoded.

It's no secret that all data in a computer is written using binary code. Thus, any information, be it text, picture or sound, is encrypted in a certain way. In order to save a vector image, it is divided into elementary geometric shapes, which, in turn, are described by the simplest mathematical formulas. Thus, for example, the letter "and" for a graphic editor will be described by two parallel segments of a given length, which are connected by a line at an angle of 45 degrees.

A raster image is split according to a different principle. The computer breaks down the picture into many dots, called pixels, and remembers the color and location of each pixel.

Advantages and disadvantages

If you are working with a vector drawing, then theoretically you can increase it indefinitely. Moreover, this will not affect the quality of the image in any way. Since the parameters are set in the form of geometric formulas, the computer simply processes them and fills all the voids with the desired colors. As a result, you have a clear image.

The disadvantages of raster graphics lie precisely in the fact that compression (which in the vast majority of cases occurs when saving a file) can significantly affect the quality. The so-called granularity appears. However, it is raster graphics that are used in complex images. In vector drawings, you can create only very simple pictures. So for now, we'll focus on where raster graphics apply.

Areas of use

Raster images perfectly convey the content of the scanned objects. With their help, you can work with halftones and smooth color transitions. Photos taken with a digital camera also use bitmap images exclusively. Also, this format serves as an indispensable tool in the field of web design.

Raster graphics formats

Recall that the information about the image in our case is encoded using dots. The unit of measurement in this encoding is a pixel. It is the smallest point that cannot be divided in terms of either size or color.

The number of these points per given unit area is called the resolution. On an image with a high resolution (a large number of individual dots), we will see a clear pattern and smooth color transitions. However, in the case when the resolution is low, the image quality can suffer greatly (after all, the computer simply displays the number of points available in its memory and stretches them to the requested size).

Can be roughly compared with language. In order to convey the same information in different languages, a different number of letters, sounds and words will be required. Also, in most cases, the grammatical structure will also differ. And the "translators" from these "languages" in our computers are specialized programs that either "read" it or convert it to the desired format.

The main difference between the formats is the way information is stored. Let's consider the most common.

BMP

This is one of the pioneers. When it was developed, raster graphics were, one might say, at the very origins of its existence. The creators did not particularly bother and programmed the BMP to sequentially memorize each pixel. In fact, this is just a copy, but with some loss of color, since the BMP format has only 256 colors at its disposal.

TIFF

Quite cumbersome on the scale of digital storage, but simply indispensable when printing information. Unlike BMP, it supports the information capability. And for this, you can use not one, but several different algorithms. However, if you do not work in the printing industry or at least some publishing house, you will not particularly need the serious power of this format.

gif

This is already a format closer to real use (for non-specialists). He is especially famous for his ability to use animation sequences. Computer graphics made in this format also allow the creation of translucent images. However, you will not be able to convey smooth color transitions. Most often, the use of raster graphics in GIF format can be seen in web design. It is compatible with all platforms and also compresses information quite compactly, which is an important factor in the speed of opening Internet pages.

JPEG

The most popular format. And it is well deserved. Any graphic editors of raster graphics undoubtedly support this format. It was developed with the specific goal of getting rid of the limitations imposed by GIF file compression. in this format reaches a factor of 100 units. This is a big indicator. However, such compression still has its drawbacks - there is some data loss, and it is possible that the saved image will become somewhat blurry. Since this format simply discards information it considers insignificant, there is always the risk of distorting some details.

JPEG 2000

An improved version of an earlier version. Image information is compressed even more compactly, and the loss in quality has become much less. Most often, this format is used to store photos on a computer hard drive and on the Internet. However, it should be remembered that if you repeatedly save the same image in JPEG or JPEG 2000 formats, each time it will lose bits of information, and in the end you will get a significantly distorted image compared to the original.

PNG

Significantly improved in quality counterpart of the GIF format. Having retained literally all the advantages of its predecessor, it is devoid of its shortcomings. It is used both for and in the design of web pages. In addition, PNG, unlike GIF, is officially in the public domain.

PSD

Raster graphics in PSD format are processed exclusively in Adobe Photoshop. This is the internal package of this program. It supports working with layers of the edited image.

CDR

It is also an internal package for the raster graphics program. Typically, this program is used by graphic designers to create images from scratch. But the editing function is undoubtedly supported.

Bitmap editors

And now a little about programs that work with image editing.

The most popular among users at the moment is the Adobe Photoshop program, commonly referred to simply as "Photoshop". This development, in fact, monopolized the work with bitmaps among design professionals. However, this program is paid and it costs not so little. Therefore, the development of other companies began to appear. Some of them are already widely used.

As for the "Photoshop" itself, this did not affect its popularity in any way. The program is quite simple, and there is no shortage of various video courses and tutorials.

In Photoshop, you can not only make a collage of photos or add built-in effects to an image. The simplest functions of this program can be mastered very quickly, and this will open the door for unbridled flight of fancy. You can correct appearance flaws, adjust colors, change the background and much, much more.

Graphic editor GIMP

As for free programs, here we can safely recommend GIMP. This graphic editor can easily replace the popular "Photoshop". It excels at all the tasks required for editing bitmaps and has some entry-level features for working with vector graphics.

The GIMP program allows you to make photos richer and more vibrant, it easily removes unnecessary elements from the image and can be used to prepare professional design projects. The computer graphics created with this program look natural and fit seamlessly into the overall picture.

Graphic editor CorelDRAW

It would be wrong to ignore Corel products. With CorelDRAW, you can easily work with both raster and vector images. The possibilities of this tool are so numerous that the study of CorelDRAW is included in the required training course for graphic designers in colleges.

This program is also paid, and the arsenal of its products is replenished with enviable regularity. But, despite the widest possibilities that this graphic editor provides to the user, its intuitive interface makes the workflow a pleasure.

Free graphic editors

And just a few more words about alternative programs for editing images. In most cases, they do an excellent job with the requests of the average user, and they take up much less space and resources on your computer. Yes, and working with them is by and large easier, since you will not be overwhelmed by the need to choose among all kinds of functions, the purpose of which remains not completely clear.

If you like unusual and mostly comical photos, try using the Funny Photo Maker program. There you will find many original frames and funny visual effects.

For more serious work, Picasa is suitable. This editor is tailored for use in computer networks. Its new features will make it even easier for you to design your pages on social networks. And the built-in effects for editing will not disappoint even a sophisticated specialist.

Another interesting program is Paint.NET. It is very similar in its functions and capabilities to Adobe Photoshop. And the tools used in Paint.NET can seriously compete with the mentioned commercial counterpart.

Introduction

The presentation of data on a computer monitor in graphical form was first implemented in the mid-50s for large computers used in scientific and military research. Since then, the graphical way of displaying data has become an integral part of the vast majority of computer systems, especially personal ones. The graphical user interface today is the de facto standard for software of various classes, starting with operating systems.

There is a special field of informatics that studies the methods and means of creating and processing images using software and hardware computing systems, - computer graphics. It covers all types and forms of representation of images available for human perception either on a monitor screen or as a copy on an external medium (paper, film, fabric, etc.). Without computer graphics, it is impossible to imagine not only a computer, but also an ordinary, completely material world. Data visualization finds application in various fields of human activity. For example, let's name medicine (computed tomography), scientific research (visualization of the structure of matter, vector fields and other data), modeling of fabrics and clothing, and experimental design.

Depending on the method of image formation, computer graphics are usually divided into raster, vector and fractal.

Figure 1 Figure 2 Figure 3

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

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

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

A prominent place in computer graphics is devoted to entertainment. There was even such a thing as a mechanism for graphical presentation of data ( graphics engine). The gaming software market has a turnover of tens of billions of dollars and often initiates the next stage in the improvement of graphics and animation.

Although computer graphics is just a tool, its structure and methods are based on the cutting-edge achievements of fundamental and applied sciences: mathematics, physics, chemistry, biology, statistics, programming, and many others. This remark is true for both software and hardware tools for creating and processing images on a computer. Therefore, computer graphics is one of the most rapidly developing branches of computer science and in many cases acts as a “locomotive” that pulls the entire computer industry with it.

1.Computer graphics

Computer graphics is a science, the subject of which is the creation, storage and processing of models and their images using a computer, i.e. This is a branch of computer science that deals with the problems of obtaining various images (drawings, drawings, animations) on a computer.

Computer graphics is usually understood as the automation of the processes of preparation, transformation, storage and reproduction of graphic information using a computer. Graphical information refers to models of objects and their images.

Computer graphics- This is a field of computer science that deals with the problems of obtaining various images (drawings, drawings, animations) on a computer. Working with computer graphics is one of the most popular areas for using a personal computer, and not only professional artists and designers are engaged in this work. At any enterprise from time to time there is a need to submit advertisements to newspapers and magazines, to issue an advertising leaflet or booklet. Sometimes enterprises order such work from special design bureaus or advertising agencies, but often they manage on their own and with available software.
Not a single modern program can do without computer graphics. Work on graphics takes up to 90% of the working time of programming teams that produce programs for mass use.
The main labor costs in the work of editorial and publishing houses are also artistic and design work with graphic programs.
The need for widespread use of graphic software has become especially noticeable in connection with the development of the Internet and, first of all, thanks to the World Wide Web service, which has linked millions of "home pages" into a single "web". A page designed without computer graphics has little chance of attracting a mass Attention.

The scope of computer graphics is not limited to artistic effects alone. In all branches of science, technology, medicine, in commercial and managerial activities, diagrams, graphs, diagrams built with the help of a computer are used, designed to visually display a variety of information. Designers, when developing new models of cars and aircraft, use 3D graphics to represent the final product. Architects create a three-dimensional image of the building on the monitor screen, and this allows them to see how it will fit into the landscape.

2. Types of computer graphics

There are three types of computer graphics:

Raster graphics

Vector graphics

fractal graphics

Bitmap, a digital image is a data file or structure representing a rectangular grid of pixels or dots of colors on a computer monitor, paper, and other display devices and materials. I.e, raster graphics is an image format that contains information about the location, number, and color of pixels.

The main advantage raster graphics is the creation (reproduction) of almost any drawing, regardless of complexity, unlike, for example, a vector one, where it is impossible to accurately convey the effect of transition from one color to another (in theory, of course, it is possible, but a 1 MB file in BMP format will be 200 MB in vector format).

Vector graphics(other name - geometric modeling) is the use of geometric primitives such as points, lines, splines, and polygons to represent images in computer graphics. The term is used in contrast to raster graphics, which represent images as a matrix of pixels (dots).

Initially, the human eye perceives the image as a raster image. The image is projected onto the retina, which is made up of individual cells that respond to light. Further, the eye-brain system recognizes individual objects in the image, geometric shapes, which are already easier to process and remember.

fractal graphics based on mathematical calculations. The basic element of fractal graphics is the mathematical formula itself, that is, no objects are stored in the computer's memory and the image is built solely on the basis of equations. In this way, both the simplest regular structures and complex illustrations that imitate natural landscapes and three-dimensional objects are built.

3.Graphic systems. WithRaster and vector graphics systems.

Raster graphics

For raster images consisting of dots, the concept of permissions, expressing the number of points per unit length. In doing so, one should distinguish between:

resolution of the original;

screen image resolution;

print image resolution.

original resolution. The resolution of the original is measured in dots per inch (dots per inch – dpi) and depends on the requirements for image quality and file size, the method of digitizing and creating the original illustration, the chosen file format and other parameters. In general, the rule applies: the higher the quality requirement, the higher the resolution of the original should be.

Screen resolution. For on-screen copies of an image, an elementary dot of the raster is usually called pixel. The pixel size varies depending on the selected screen resolution(from the range of standard values), original resolution and display scale.

Monitors for image processing with a diagonal of 20-21 inches (professional grade), as a rule, provide standard screen resolutions of 640x480, 800x600, 1024x768, 1280x1024, 1600x1200, 1600x1280, 1920x1200, 1920x1600 pixels.

The distance between adjacent phosphor dots on a high-quality monitor is 0.22–0.25 mm.

For a screen copy, a resolution of 72 dpi is sufficient, for printing on a color or laser printer 150-200 dpi, for output on a photographic device 200-300 dpi. A rule of thumb has been established that, when printed, the resolution of the original should be 1.5 times greater than screen lineature output devices. In case the hard copy will be enlarged in comparison with the original, these values ​​should be multiplied by the scaling factor.

Resolution of the printed image and the concept of lineature. The size of a raster image dot both on a hard copy (paper, film, etc.) and on the screen depends on the applied method and parameters. screening original. When screening, a grid of lines is superimposed on the original, the cells of which form raster element. The raster grid frequency is measured by the number lines per inch (lines per inch - Ipi) and called lineature.

The screen dot size is calculated for each element and depends on the tone intensity in the given cell. The greater the intensity, the denser the raster element is filled. That is, if absolutely black color is in the cell, the size of the raster dot will match the size of the raster element. In this case, we talk about 100% occupancy. For pure white, the fill value will be 0%. In practice, element occupancy on a print is typically between 3 and 98%. In this case, all dots of the raster have the same optical density, ideally approaching absolute black. The illusion of a darker tone is created by increasing the size of the dots and, as a result, reducing the white space between them with the same distance between the centers of the raster elements. This method is called screening with amplitude modulation (AM).

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

When outputting a copy of an image on a printer or printing equipment, the raster lineature is chosen based on a compromise between the required quality, the capabilities of the equipment and the parameters of the printed materials. For laser printers, the recommended lineature is 65-100 Ipi, for newspaper production - 65-85 lpi, for book and magazine production - 85-133 lpi, for art and advertising works - 133-300 lpi.

When printing images with overlapping screens, such as multi-color, each subsequent screen is rotated by a certain angle. Rotation angles are considered traditional for color printing: 105 degrees for cyan, 75 degrees for magenta, 90 degrees for yellow and 45 degrees for black. In this case, the raster cell becomes oblique, and to reproduce 256 tone gradations with a lineature of 150 lpi, the resolution of 16x150=2400 dpi is no longer enough. Therefore, the minimum standard resolution of 2540 dpi is adopted for professional-class photo-exposing devices, which ensures high-quality screening at different screen rotation angles. Thus, the coefficient that takes into account the correction for the angle of rotation of the raster for color images is 1.06.

dynamic range. The quality of reproduction of tone images is usually evaluated dynamic range (D). This is optical density, numerically equal to the decimal logarithm of the reciprocal of transmittance (for originals viewed through the light, such as slides) or reflection coefficient(for other originals such as printed copies).

For optical media that transmit light, the dynamic range ranges from 0 to 4. For surfaces that reflect light, the value of the dynamic range is from 0 to 2. The higher the dynamic range, the more halftones are present in the image and the better the quality of its perception .

Relationship between image parameters and file size. By means of raster graphics, it is customary to illustrate works that require high accuracy in the reproduction of colors and halftones. However, file sizes for bitmap illustrations grow exponentially as resolution increases. A photograph intended for home viewing (standard size 10x15 cm, digitized with a resolution of 200-300 dpi, color resolution 24 bits), takes in the format TIFF with the compression mode turned on, about 4 MB. A high-resolution digitized slide takes up 45-50 MB. Separated color image of A4 format occupies 120-150 MB.

Scaling bitmaps. One of the disadvantages of raster graphics is the so-called pixelization images when they are enlarged (unless special measures are taken). Since there is a certain number of points in the original, then at a larger scale their size also increases, raster elements become visible, which distorts the illustration itself (Fig. 4). To counteract pixelation, it is customary to pre-digitize the original with a resolution sufficient for high-quality visualization when scaling. Another technique is to use a stochastic raster to reduce the pixelation effect within certain limits. Finally, when scaling, the interpolation method is used, when the illustration size is increased not by scaling the points, but by adding the required number of intermediate points.

concept

72. Resolution: 800*600, 1024*768. 1280*1024. 4. Vector and bitmap graphic arts: essence, differences, areas of application. Principles... where and how the drawing is stored/displayed. 6. concept graphic primitive. The most common graphic...

In computer graphics, the concept of resolution is usually the most confusing, because you have to deal with several properties of different objects at once. It should be clearly distinguished: screen resolution, printer resolution and image resolution. All these concepts refer to different objects. With each other, these types of resolution are not related in any way, until you need to know what physical size the picture on the monitor screen, print on paper or file on the hard drive will have. Screen resolution is a property of the computer system (depending on the monitor and video card) and the operating system. Screen resolution is measured in pixels and defines the size of an image that can fit on the entire screen.

Printer resolution is a property of a printer that expresses the number of distinct dots that can be printed in a unit length area. It is measured in units of dpi (dots per inch) and determines the size of an image at a given quality, or vice versa, the quality of an image at a given size.

Image resolution is a property of the image itself. It is also measured in dots per inch and is set when creating an image in a graphics editor or using a scanner. The resolution value of an image is stored in the image file and is inextricably linked to another property of the image, its physical size. The physical size of an image can be measured both in pixels and in units of length (millimeters, centimeters, inches). It is set when the image is created and is stored with the file. If the image is being prepared for display on the screen, then its width and height are set in pixels to know how much of the screen it occupies.

If the image is being prepared for printing, then its size is given in units of length in order to know what part of the sheet of paper it will occupy. It is easy to convert the size of an image from pixels to units of length, or vice versa, if the resolution of the image is known.

Table 1. Relationship between artwork linear size and file size

Table 2. Relationship between illustration size (in pixels) and print size (in mm)

Color resolution and color models

When working with color, the concepts of color resolution (it is also called color depth) and color model are used. Color resolution defines how color information is encoded and determines how many colors can be displayed on the screen at the same time. To encode a two-color (black and white) image, it is enough to allocate one bit per color representation of each pixel. The allocation of one byte allows you to encode 256 different color shades. Two bytes (16 bits) allow you to define 65,536 different colors. This mode is called High Color. If three bytes (24 bits) are used for color encoding, 16.5 million colors can be displayed simultaneously. This mode is called True Color.

Colors in nature are rarely simple. Most color shades are formed by mixing primary colors. The method of dividing a color hue into its constituent components is called a color model. There are many different types of color models, but in computer graphics, as a rule, no more than three are used. These models are known under the names: RGB, CMYK and HSB. The RGB color model is the easiest to understand and most obvious. Monitors and household TVs work in this model. Any color is considered to consist of three main components: red (Red), green (Green) and blue (Blue). These colors are called primary. It is also believed that when one component is superimposed on another, the brightness of the overall color increases. The combination of the three components gives a neutral color (gray), which tends to white at high brightness. This corresponds to what we observe on the monitor screen, so this model is always used when preparing an image intended for display on the screen. If the image undergoes computer processing in a graphics editor, then it should also be presented in this model. Graphic editors have tools for converting images from one color model to another.

The method of obtaining a new hue by summing the brightness of the constituent components is called the additive method. It is used wherever a color image is viewed in transmitted light ("through"): in monitors, slide projectors, etc.

It is easy to guess that the lower the brightness, the darker the shade. Therefore, in the additive model, the central point, which has zero values ​​of the components (0, 0, 0), is black (the absence of a glow on the monitor screen). The white color corresponds to the maximum values ​​of the components (255, 255, 255). The RGB model is additive, and its components - red, green and blue - are called primary colors.

The CMYK color model is used to prepare not screen, but printed images. They differ in that they are seen not in transmitted, but in reflected light. The more ink is placed on the paper, the more light it absorbs and the less it reflects. The combination of the three primary colors absorbs almost all the incident light, and from the side the image looks almost black. Unlike the RGB model, an increase in the amount of paint does not lead to an increase in visual brightness, but rather to its decrease. Therefore, for the preparation of printed images, not an additive (summing) model is used, but a subtractive (subtractive) model. The color components of this model are not primary colors, but those that result from subtracting primary colors from white:

* blue (cyan)=white? red=green+blue;

* magenta (magenta)=white? green=red+blue;

* yellow (yellow)=white? blue=red+green.

These three colors are called complementary because they complement the primary colors to white.

A significant difficulty in printing is the black color. Theoretically, it can be obtained by combining three basic or additional colors, but in practice the result is unusable. Therefore, a fourth component, black, has been added to the CMYK color model. This system is obliged to him by the letter K in the name (blackK).

In printing houses, color images are printed in several steps. By imposing cyan, magenta, yellow and black prints in turn on paper, a full-color illustration is obtained. Therefore, the finished image obtained on a computer is divided into four components of a single-color image before printing. This process is called color separation. Modern graphic editors have the means to perform this operation. Unlike the RGB model, the center dot is white (no dyes on white paper). A fourth one has been added to the three color coordinates - the intensity of black paint. The black axis looks isolated, but it makes sense: adding color components to black will still result in black. Everyone can check the addition of colors in the CMYK model by picking up blue, pink and yellow pencils or felt-tip pens. A mixture of blue and yellow on paper gives green, pink and yellow - red, etc. When all three colors are mixed, an indefinite dark color is obtained. Therefore, in this model, black was also needed additionally.

Some graphics editors allow you to work with the HSB color model. If the RGB model is the most convenient for a computer, and the CMYK model for printers, then the HSB model is the most convenient for a person. It is simple and intuitive. The HSB model also has three components: color hue (Hue), color saturation (Saturation) and color brightness (Brightness). By adjusting these three components, you can get just as many arbitrary colors as with other models.

The HSB color model is convenient for use in those graphic editors that are focused not on processing ready-made images, but on creating them yourself. There are programs that allow you to imitate various artist's tools (brushes, pens, felt-tip pens, pencils), paint materials (watercolor, gouache, oil, ink, charcoal, pastel) and canvas materials (canvas, cardboard, rice paper, etc.). When creating your own artwork, it is convenient to work in the HSB model, and at the end of the work it can be converted to the RGB or CMYK model, depending on whether it will be used as a screen or print illustration.

A color palette is a data table that stores information about what code a particular color is encoded with. This table is created and stored along with the graphics file. The most computer-friendly color coding method is 24-bit True Color. In this mode, one byte (8 bits) is allocated for encoding each color component R (red), G (green) and B (blue). The brightness of each component is expressed as a number from 0 to 255, and a computer can reproduce any color from 16.5 million using three codes. In this case, the color palette is not needed, since three bytes already contain enough information about the color of a particular pixel.

The situation is much more complicated when the image has only 256 colors encoded in one byte. In this case, each color shade is represented by a single number, and this number does not express the color of the pixel, but the color index (its number). The color itself is searched for by this number in the accompanying color palette attached to the file. Such color palettes are also called index palettes. Different images may have different color palettes. For example, in one image, green may be encoded with index 64, and in another image, this index may be given for pink. If you reproduce an image with a "foreign" color palette, then the green Christmas tree on the screen may turn out to be pink. In cases where the color of the image is encoded in two bytes (High Color mode), an image of 65 thousand colors is possible on the screen. Of course, these are not all possible colors, but only one two hundred and fifty-sixth of the total continuous spectrum of colors available in True Color mode. In such an image, each two-byte code also expresses some color from the general spectrum. But in this case, you cannot attach an index palette to the file, in which it would be written which code corresponds to which color, since this table would have 65 thousand entries and its size would be hundreds of thousands of bytes. It hardly makes sense to attach a table to a file that can be larger than the file itself. In this case, the concept of a fixed palette is used. It does not need to be applied to the file, because in any graphic file that has a sixteen-bit color encoding, the same code always expresses the same color.

1. Raster graphics - basic concepts. Raster graphics software.

The main element of a bitmap is dot. If the image is a screen image, then this point is called a pixel. Depending on the graphical screen resolution of the computer's operating system, images with 640x480, 800x600, 1024x768 or more pixels can be placed on the screen.

The size of an image is directly related to its resolution. This parameter is measured in dots per inch (dotsperinch- dpi). When the monitor is set to 800x600 pixels, the screen image resolution is 72dpi.

When printing, the resolution should be much higher. Printing a full-color image requires a resolution of 200-300 dpi.

Disadvantages:

1. Large amounts of data is the main problem when using raster images.

2. The second drawback of raster images is related to the impossibility of enlarging them to see the details. Since the image is made up of dots, magnifying the image only makes the dots larger. Increasing the dots of the raster visually distorts the illustration and makes it rough. This effect is called pixelation.

The main parameters of a computer image are its physical size and resolution. They affect the screen dimensions of the image and the size of the print on paper, as well as the quality of the image.

The basic concepts associated with color are color resolution (color depth) and color model. The color resolution defines the maximum number of colors that can be reproduced at the same time. It depends on the number of bytes used to encode the color. Basic modes: 8-bit (256 colors), 16-bit (65K colors, HighColor) and 24-bit (16.5 million colors, TrueColor).

A color model defines how complex color hues are divided into their constituent components. Theoretically, to determine the color, it is enough to specify the brightness of the three components.

In the RGB model, primary colors are used as components: red, green and blue. In the CMYK model, additional colors are used as elementary components: cyan, magenta, yellow. In addition to them, the black component is considered separately (theoretically, it is not needed, but it is convenient for printing). The HSB color model considers hue, brightness, and saturation as components.

The operation of decomposing a color image into three or four images corresponding to the applied color components is called color separation.

The RGB color model corresponds to viewing an illustration in transmitted light and is additive (the brightnesses of the components add up and give white at maximum values).

The CMYK color model corresponds to viewing an illustration in reflected light and is subtractive (the brightness of the components is subtracted from white and at maximum values ​​gives black).

The HSB color model is the most consistent with the conventional understanding of color management.

A color palette is a data table that stores information about what code a particular color is encoded with. This table is created and stored along with the graphics file.

Raster graphics file formats. Raster image files are distinguished by a variety of formats (several dozen). Each format has its own positive qualities that determine the appropriateness of its use when working with certain applications.

For the Windows 9x operating system, the most typical format is WindowsBitmap. Files of this format have the extension .BMP. This format is versatile and is the de facto standard for Windows applications. A characteristic disadvantage of the Windows Bitmap format is the large file size due to the lack of image compression.

For Web documents circulating on the Internet, the size of the files is very important, since the speed of access to information depends on it. Therefore, when preparing Web pages, two types of graphic formats are used that provide the most dense compression.

To store multi-color irregular images (photos), use the JPEG format, the files of which have the JPG extension. This format differs in that it provides data storage with a huge degree of compression, but at the expense of losing some of the information. If the file was recorded in JPG format, then after unpacking the resulting file may not correspond to the original, although this is hardly noticeable in illustrations such as color photographs. The amount of information loss can be controlled when saving the file. When it comes to reproducing illustrations on the screen (but not on paper), the loss of up to 90% of information has little effect on the quality of photographs.

In addition to the JPEG format, the GIF format is used on the Internet. This is the most "dense" of the graphic formats that do not have information loss. Files of this format have the extension .GIF. This format stores and transmits low-color images, such as hand-drawn illustrations. (By the way, the fewer colors an image has, the worse the effect of using the JPEG format. JPEG shows the worst results on two-tone black and white images.) The GIF format has some very interesting features that allow you to create unusual effects: background transparency and image animation.

All advanced raster graphics editors are capable of loading and saving images in major graphic formats. Thus, they can be used to convert images from one format to another.

Special requirements for the quality of images are imposed in the printing industry. A special TIFF format is used in this area. Files of this format have the extension .TIFF. They provide not only a good degree of compression, but also the ability to store additional information in one file in invisible auxiliary layers - channels. So, in the standard Imaging program, which is part of Windows98, the most interesting possibilities for imposing annotations and notes on a picture are realized only when working with images that have the TIFF format. In the other listed formats, you cannot create a layer for storing information that is not directly related to the image.

Classes of programs for working with raster graphics:

Image creation tools. There are many programs designed to work with raster graphics. A number of graphic editors, such as Painter and Fauve Matisse, are focused directly on the drawing process. The simplest programs of this class also include the graphic editorPaint, which is part of the Windows95 operating system.

Image processing tools. Another class of raster graphic editors is designed not to create images from scratch, but to process finished drawings in order to improve their quality and implement creative ideas. Such programs, in particular, include Adobe Photoshop, Photostyler, PicturePublisher and others.

The source material for processing on a computer can be obtained in various ways by scanning a color illustration, loading an image created in another editor, or inputting an image from a digital camera or video camera.

Today, Adobe Photoshop is considered the most powerful tool for processing ready-made raster images.

The Photoshop raster editor works with graphic files of the main formats adopted in printing, in computer networks, and also used in the development of electronic documents and software.

The main purpose of the Photoshop editor is to retouch finished images (bringing them to printing quality), to assemble compositions from separate fragments taken from various images, and to apply special effects called filters.

The main technical operations when working with images are:

changing the dynamic range (controlling the brightness and contrast of the image);

image sharpening;

color correction (change of brightness and contrast in the channels of red, green and blue color components);

hillshade (changing the brightness of individual fragments);

feathering (smoothing the transition between the boundaries of individual fragments);

clipping (“cutting out” individual fragments from the overall composition);

stuffing (restoration of lost image elements by copying fragments from preserved areas);

montage (layout of an image from fragments copied from other images or imported from other editors).

The main tools of the Photoshop editor, used in technical operations, are concentrated on the toolbar. A feature of the toolbar is the availability of alternative tools.

To customize how tools work in the Photoshop editor, you use a special type of dialog box called a palette.

Some palettes are not related to editor tools, but to the image as a whole. They allow you to control the image parameters and its structure (channels and layers), as well as obtain the necessary information about the image.