Introduction to Computer Graphics

Computer Graphics

• Computer graphics is the field of informatics that studies methods and tools for creating and processing images using software and hardware computing systems.
• The representation of data on a computer monitor in graphical form was first implemented in the mid-1950s for most computers used in scientific and military research.
• Computer graphics are now at the forefront of computer technology, with commercial applications using modern image processing technologies for just over a decade.
• Andries van Dam is considered one of the fathers of computer graphics, and his books are fundamental textbooks on the entire spectrum of technologies underlying computer graphics.
• Areas like automated training with simulators, modeling, and animation, the creation of educational materials based on computer layout and the use of scientific and artistic works, and the performance of research work are closely related to computer graphics.
• In all these areas, it is easy to present the operations of scaling images (compression and expansion) of geometric models, consisting of separate elementary parts - graphic primitives (segments, points, solid and dotted straight lines, arcs of circles and ellipses, rectangles, polygons) and bringing them into action with the help of technical means of computer graphics (graphic displays of graph plotters, Coordinatographs-encoders of graphic information).
• The boundaries of computer graphics have expanded so much that they have lost their clear outlines, however, there are still several classes of its applications: business graphics, illustration, engineering (design) and scientific, each of which should be kept in mind when solving problems of representing historical knowledge.
• Business graphics systems are designed to illustrate data, the values of which are most often extracted from databases and electronic tables.
• Most of its packages allow you to quickly present this data directly after entering it into the computer and choosing the type of representation.
• Working with them is simple, efficient and does not require large preparation costs.
• The displayed data is most often represented by a two-dimensional array.
• The most common forms of graphical representation of data are bar charts (histograms) with vertical or horizontal orientation, pie charts and line graphs.
• Graphs and charts can have different colors and scalings.
• Most packages allow you to combine different forms of data representation, supply the image with additional decorative elements, apply various transformations of individual elements of the image (obtaining a mirror image, stretching along one of the axes, rotation, cutting out individual parts), superimpose images one on top of the other, all these things make them diverse, emphasize some aspects and shade others.
• The purpose of illustrative graphics is to create machine images that play the role of illustrative material, it can be images in the form of diagrams, sketches, historical maps, drawings, etc.
• At the same time, the efforts of developers of illustrative graphics packages are aimed at ensuring that the generation and transformation of graphic images is as easy as operating on groups of numbers.
• The packages are equipped with a wide range of tools for creating graphic images based on regular structures (graphic primitives: circles, rectangles, ellipses, lines, etc.) and tools for manipulating them.
• Figures can be moved, scaled, colored, rotated, superimposed on each other, deformed (compressed, stretched, etc.) their way of image is comparable to drawing such figures on paper with compasses, stencils, rulers; this type of image refers to the so-called vector or coordinate graphics, since each object is defined by the coordinates of the reference points and certain parameters.
• Another type of graphics is images based on irregular structures that are comparable to paintings created by an artist or designer.
• To build such images, the packages have tools for so-called free drawing that simulate working with a pencil, brushes and paints.
• They also include tools for cutting, erasing and gluing fragments of an image, composing their separate blanks taken from the database of fragments, some editors have tools for "reviving drawings" (animation), as a rule, such editors have a set of their own scalable fonts.
• Packages and systems of engineering (design) graphics are mainly focused on automating drawing and design work, they are used in the so-called computer-aided design systems (CAD) in the design of mechanical, electrical, electronic devices and the performance of similar work in construction and architecture.
• Packages of engineering are used to create both sketches and accurate drawings, they contain their own databases of standardized graphic images in automated areas of activity, powerful tools for scaling, editing and performing calculations, software systems for layout and optimization.
• In the field of scientific research, computer graphics has found the same wide application as in engineering.
• Scientific graphics start to develop with some delay compared to the above types of graphics, is currently rapidly developing and improving, and integrates the capabilities of business and engineering graphics to some extent.
• Graphic packages of scientific graphics manipulate a much larger number of classes of displayed objects.
• Images can be represented in the form of line graphs, maps, isolines, three-dimensional wireframe, halftone and color diagrams, vector fields, current lines, etc.
• Scientific graphics systems are combined with packages of mathematical support and modeling, or are part of such packages and systems.
• Computer graphics, in turn, are divided into two-dimensional and three-dimensional graphics, the main object of two-dimensional raster graphics is a discrete plane (more precisely, its rectangular area), and the main object of three-dimensional raster graphics is a three-dimensional discrete space.
• The elements of this space (usually cubic in shape) are called voxels.
• Two-dimensional raster graphics is often called simply raster graphics, and three-dimensional raster graphics is called volumetric graphics and vector graphics are also two-dimensional and three-dimensional.
• These sections deal, respectively, with flat or volumetric geometric models.
• The term raster graphics is quite obvious, if you learn the concepts related to raster images.

Raster Graphics

• Raster images resemble a sheet of graph paper, on which any cell is painted either black or white, forming a drawing in combination.
• A pixel is the main element of raster images, it is these elements that make up a raster image
• In the digital world of computer images, the term pixel refers to several different concepts.
• It can be a separate point on a computer screen, a separate point printed on a laser printer, or a separate element of a raster image.
• These concepts are not the same, so to avoid confusion, they should be called as follows: a video pixel when referring to an image on a computer screen; a point when referring to a separate point created by a laser printer.
• There is a rectangularity coefficient of the image, which is introduced specifically for displaying the number of pixels of the image matrix horizontally and vertically.
• Returning to the analogy with a sheet of paper, we can notice that any raster image has a certain number of pixels in horizontal and vertical rows.
• The following rectangularity coefficients exist for screens: 320x200, 320x240, 600x400, 640x480, 800x600 etc.
• This coefficient is often called the image size, the product of these two numbers gives the total number of pixels in the image.
• There is also a concept such as the rectangularity coefficient of pixels in contrast to the rectangularity coefficient of the image, it refers to the real dimensions of the video pixel and is the ratio of the real width to the real height.
• This factor depends on the size of the display and the current resolution, and therefore takes different values on different computer systems.
• The color of any pixel of a raster image is stored in the computer using a combination of bits.
• The more bits used for this, the more shades of colors can be obtained.
• The number of bits used by the computer for any pixel is called the bit depth of the pixel.
• The simplest raster image consists of pixels having only two possible colors black and white, and therefore images consisting of pixels of this type are called one-bit images.
• The number of available colors or shades of gray is equal to 2 to the power equal to the number of bits in a pixel.
• Colors described by 24 bits provide more than 16 million available colors and are often referred to as natural colors.
• Raster images have many characteristics that must be organized and fixed by the computer.
• The size and location of pixels in it are two main characteristics that a raster image file must save in order to create a picture.
• Even if the color information of any pixel and any other characteristics are corrupted, the computer will still be able to recreate the version of the drawing, if it knows how all its pixels are located.
• A pixel in itself does not have any size, it is just an area of the computer's memory that stores color information, so the rectangularity coefficient of the image does not correspond to any real dimension.
• Knowing only the rectangularity coefficient of the image with some resolution, you can determine the real size of the drawing.
• Since the image sizes are stored separately, the pixels are stored one after the other, as a regular data block, the computer does not have to store separate positions, it only creates a grid by the sizes specified by the rectangularity coefficient of the image, and then fills it pixel by pixel.
• This is the easiest way to store this raster image, but not the most efficient in terms of computer time and memory usage.
• A more efficient way is to save only the number of black and white pixels in any row this method compresses the data that raster images use; in this case, they take up less computer memory.
• Since pixels do not have their own size, they only acquire them when output to some types of devices, such as a monitor or printer.
• In order to remember the real size of a raster drawing, raster graphics files sometimes store the resolution of the raster.
• Resolution is simply the number of elements in a given area.
• When we talk about raster graphics, the minimum element is usually a pixel, and the given area is inches.
• Therefore, the resolution of raster graphics files is usually specified in pixels per inch.
• Raster graphics files take up a large amount of computer memory.
• Some pictures take up a large amount of memory due to the large number of pixels, each of which takes up a certain amount of memory.
• The three facts have the greatest impact on the amount of memory occupied by a raster image: the size of the image, the bit depth of the color, and the file format used to store the image.
• There is a direct relationship between the size of a raster image file: the more pixels in the image, the larger the file size, the resolution of the image has no effect on the file size.
• The resolution affects the file size only when scanning or editing images: the relationship between the bit depth and the file size is direct, the more bits used in a pixel, the larger the file.
• The size of a raster graphics depends heavily on the format chosen for storing the image.
• Under otherwise equal conditions, such as image size and bit depth, the compression scheme of the image is essential.
• For example, a BMP file usually has a larger size compared to PCX and GIF files, which in turn are larger than a JPEG file.
• Many image files have their own compression schemes and may also contain additional data for a brief description of the image for previewing.
• Raster graphics has both advantages and disadvantages, this type of graphics effectively represents real images.
• The real world consists of billions of tiny objects, and the human eye is just adapted to perceive a huge set of discrete elements that form objects.
• At its highest level of quality, the image looks quite realistic, similar to how photographs look in comparison with drawings.
• This is only true for very detailed images, usually obtained by scanning photos.
• In addition to the natural look, raster images have other advantages, output devices, such as laser printers, use sets of dots to create images.
• Raster images can be easily printed on such printers because it is easy for computers to control the output device to represent individual pixels with the help of dots.
• The disadvantage of raster graphics is that it takes up a large amount of memory.
• There is also the problem of editing raster images, since large raster images take up significant amounts of memory, to ensure the operation of editing functions of such images, the same significant amounts of memory and other computer resources are needed.
• One of the first raster graphics formats is the BMP format (file extension *.bmp) and is familiar to everyone who works in the Windows operating system, developed by Microsoft and is widely used for displaying raster images in Windows.
• In the BMP format, you can save images with the number of bits per pixel: 1, 4, 8 and 24, you can use the BMP format both without compression and with compression.
• The group coding (RLE) method is used to compress files in BMP format, which can achieve quite a high degree of compression of homogeneous pictures with a small number of colors, however, many application programs do not support the compression of BMP files.
• Compressed BMP files may have the extension *.rle.
• The GIF format (file extension *.gif) was developed by CompuServe as a platform-independent raster format, which is intended for storing raster images with compression.
• The LZW method, which has already been considered, is used for compression.
• The original format was developed in 1987 and is called "GIF87a", it supports images up to 65536x65536 and those color depth values that lie in the range from 1 to 8 bits per pixel, that is, a pixel can take 256 values.
• The GIF format was specially developed by CompuServe specialists for working on the network, due to the compactness of files, it quickly replaced a number of other formats such as PCX and is currently the most popular format on the Internet.
• However, like any format, GIF has several significant drawbacks.
• First, it supports no more than 256 colors, so it is completely unsuitable for printing and transmitting high-quality images.
• Secondly, it did not support alpha channels, that is, transparency which made it difficult to develop more or less decent Web pages.
• Finally, due to the slowness of data transmission channels, users spent a lot of time downloading most of the image, after which it would be possible to understand what this image is.
• In this regard, in 1989, a new standard "GIF89a" was developed, which was designed to alleviate these problems, or rather, to mitigate the last two.
• Note two features of this format: the first is the support of interlaced scanning, in the new format, it was possible to save image lines not only sequentially one after another, but also in a different order.
• First every eighth line, then every fourth, then every second and, finally, all the rest this allowed users, having downloaded only one eighth of the image already present it and decide whether to download it further.
• The second feature of the new format is the support of transparent color, but is unfortunately only one.
• When saving images in the GIF89a format in the Adobe PhotoShop package, you can specify a transparent color in the dialog box that appears when you call the appropriate menu item.
• Another format is the JPEG format with the *.jpg file extension, despite the fact that this format supports full-color photorealistic images and provides a very high compression of files, it does not solve all the problems of graphics on the Web.
• First of all, it is not very suitable for the general design of web pages, in which there are clear lines, frames, non-rectangular images, etc.
• Therefore, along with JPEG, the GIF format is widely used on the Web and will continue to be used for a long time, despite all its shortcomings.

Vector Graphics

• Vector graphics are different from raster graphics, in that vector graphics images are constructed using mathematical descriptions of objects, circles, and lines.
• Although at first glance this may seem more difficult than using raster arrays, for some types of images, the use of mathematical descriptions is a simpler method.
• The key point of vector graphics is that it uses a combination of computer commands and mathematical formulas for an object.
• This allows computer devices to calculate and place real points in the right place when drawing these objects.
• This feature of vector graphics gives it several advantages over raster graphics, but at the same time it is the cause of its shortcomings.
• Vector graphics are often called object-oriented graphics or drawing graphics.
• Simple objects such as circles, lines, spheres, cubes, and the like are called primitives, and are used to create more complex objects.
• In vector graphics, objects are created by combining different objects.
• Simple descriptions are used to create primitive objects.
• A straight line, arcs, circles, ellipses and areas of uniform or varying light are two-dimensional drawings used to create detailed images.
• In three-dimensional computer graphics, elements such as spheres and cubes can be used to create complex drawings.
• Commands that describe vector objects may never have to be seen by most users, determining how to describe objects will be a computer program that is used to prepare vector objects.
• To create vector drawings, you need to use one of the many illustration packages.
• The main logical element of vector graphics is a geometric object.
• Geometric figures (so-called primitives rectangle, circle, ellipse, line), composite figures, or figures built from primitives, color fills, including gradients, are taken as objects.
• An important object of vector graphics is a spline which is a curve through which one or another geometric figure is described, modern fonts TrueType and PostScript are built on splines.
• Different vector formats have different color capabilities.
• The simplest formats, which may not contain any color information at all, use the default color of the devices to which they are output, other formats are able to store data about the full thirty-two bit color.
• No matter what color model a vector format uses, it does not affect the file size, except in cases where the file contains raster images.
• In ordinary vector objects, the color value refers to the entire object as a whole, the color of the object is stored as part of its vector description.
• Some vector files can create a raster sketch of the images stored in them, these raster images, sometimes called short descriptions of the images, are usually sketches of vector drawings as a whole.
• A short description of the image is especially useful in situations when you do not want to open the entire file to see what it contains or when you cannot see the vector drawing during its use.
• The first situation arises when you need to find a file using one of the many programs specifically designed for this purpose.
• To facilitate the search for the vector file, such programs can read the raster sketch of the image and other characteristics, for example, the vector format, creation time, bit depth of the image, and so on.
• The second situation arises when a vector drawing is placed on a page in some publishing package.
• The image that you see will be a raster sketch of the real vector drawing, which cannot be resized, cropped, or otherwise processed.
• For the sketches of images have to pay with memory, because sketches are a raster version of the drawings, and raster data uses a lot of computer memory.
• Vector graphics have many advantages, being economical in terms of disk space required for storing images.
• This is because it does not save the image itself, 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 can be easily transformed and modified, which has almost no effect on the image quality, scaling, rotation, curvature can be reduced to a couple of three elementary transformations over vectors.
• In those areas of graphics, where it is important to preserve clear and distinct outlines, for example, in font compositions, in creating logos, etc., vector programs are indispensable.
• Nature avoids straight lines, unfortunately, they are the main components of vector drawings.
• Until recently, this meant that the object of vector graphics were images that never tried to look natural, for example, two-dimensional drawings and pie charts created with special CAD programs, two- and three-dimensional technical illustrations, stylized drawings and icons, consisting of straight lines and areas painted in one color.
• Vector drawings consist of various commands sent from the computer to the output devices (printer), the printers contain their own microprocessors that interpret these commands and try to translate them into points on a sheet of paper.
• Sometimes, due to communication problems between the two processors, the printer cannot print individual parts of the drawings.
• Depending on the type of printer, problems can occur, and you may end up with a blank sheet of paper, a partially printed drawing, or an error message.
• Vector graphics programs are able to create raster images as one of the types of objects: this is possible because the raster drawing is just a set of instructions for the computer, and since these instructions are very simple, vector graphics are able to perceive raster images on a par with other objects, although you can place raster images in the form of a vector format object, but it is not possible to edit and change individual pixels in it.

Fractal Graphics

• Fractal graphics, like vector graphics, are calculated, but differ in that the computer stores formulas rather than objects.
• An image is built by an equation or a system of equations.
• If you change the coefficients in the equation, you get a completely different picture.
• The ability of fractal graphics to simulate the images of living nature by computational means is often used for the automatic generation of unusual illustrations.
• The main property of fractals is self-similarity: any microscopic fragment of a fractal in one way or another reproduces its global structure.
• In the simplest case, part of the fractal is simply a reduced whole fractal.
• Fractal files typically ends with a .fif extension.
• Typically .fif files are smaller than .jpg files, but not always.
• Files in .jpg usually shows its discrete nature almost immediately: when the size changes, the infamous ladder appears; whereas .fif files, with increasing, shows an increasing degree of detail of the structure, preserving the aesthetics of the image.

Software for Working with Graphics

• The need to input graphics, diagrams, and drawings in text has created the need for graphical processors.
• A graphical processor is an instrumental tool that allows you to create and modify graphical images using illustrative, commercial, scientific, or other graphics.
• Most graphics processors meet the WIMP (Windows Image Menu Pointer) user interface standard, which is based on the following: the panel includes a menu of actions, a ruler of tools, and a color palette.
• Graphical symbols used to construct the image are located on the tool ruler, a color palette contains a color scheme of the PC monitor.
• There are raster graphics image editors and applications, vector-graphic applications, and fractal-graphic applications.
• Packs of the first type are designed to work with drawings and photographs and include a set of tools for encoding the image for example, Adobe PhotoShop, PhotoWorks Plus, Aldus Photo Styler, Picture Publisher.
• For example, using Adobe PhotoShop it is possible to carry out electronic restoration of the historical source, including scaling, transformation and filtering, focusing and contrasting images, remove hidden and obvious defects, change color, work with details and fragments.
• Vector graphics packages are designed for professional work related to artistic and technical illustrations, occupy an intermediate position between CAD systems and desktop publishing systems.
• Software for creating fractal graphics is also available.

Presentation Graphics

• Presentation is a speech, report, or project presentation.
• Any presentation should be effective, as efficient as possible.
• The use of computers allows for the use of automated, interactive, and multimedia tools.
• Presentation Graphics packages are used to create images for science, educational information in a dynamic form.
• A very popular tool is MS PowerPoint to create presentations.
• A presentation is the .ppt object.
• The software also allows working with ready made templates.
• Such an electronic document consists of two parts: the main (slide) and additional (notes) information.
• Slide order and numbering are found in the doc.
• The slide is based on a layout: a diagram featuring construction elements.
• The elements are text, logos, OLE objects (graphics, videos, and music), key management, and background.
• Each element has an animation tag.
• Animation parameters are selected individually for each element of the slide.
• There are four modes of working in presentation software like MS PowerPoint:
  • General
  • Slide Sorcer
  • Page Note
  • Slide Show.

Other Key Points:

• The representation of data on a computer monitor in graphical form was first implemented in the mid-1950s.
• Objects of vector graphics are easily transformed and modified.
• Scalability and vector graphics are related.
• Nature's objects can not be represented well by basic vector graphics.
• BMP type of graphics file has .bmp.
• Pixel is the most basic element of raster images.
• A slide needs to be laid out.
• Vector graphics can have more realistic images.
• Three-dimensional images use elements.