Babylon University
College of Computer Technology
Department of Information Network
Introduction to Computer Graphics
Second Stage
Lecture1
General introduction on computer graphics
By
Lecturer Assistant
Alaa Shawqi Jaber
2015-2016
1. What is computer graphics?
Computer graphics provides a set of tools to create pictures and to interact with them in natural ways. The tools consist of specialized graphical hardware and software, and together they permit programmers to fashion programs with a strong graphics capability. Therefore, computer graphics is the field that concerned with the generation, manipulation, and storage of digital graphical data. This includes images in two- and three-dimensional, animated graphics, and interactive images (virtual reality). In fact, most digital data that is not text, software, or audio, is graphics data.
Data are presented visually through shapes, colors, and texture rather than by tables of numbers. Words and numbers are replaced whenever possible by pictures, because the eye-brain system is better at recognizing and interpreting visual representations. With interactive graphics a person instructs the computer using natural hand movements, such as pointing and drawing.
Computer graphics has become an important technical discipline within computer science and engineering, with its own set of fascinating ideas, techniques, and sometimes astonishing graphics devices.
2. History of Computer Graphics
In the 1950’s, typical source of input was a typewriter-like machine called a teletype terminal or TTY. Output was provided by a line printer that operated by means of a mechanical arrangement of small pins that noisily produced an approximate rendering of the alphabetic characters. The Cathode Ray Tube (CRT) found its way from television into computers. CRT consists of a glass tube whose inside is coated with a specially formulated phosphor. When the phosphor-coated surface is hit by an electron beam it becomes fluorescent. Figure 1 shows the CRT display.
Figure 1 The CRT display
In the 1960’s, beginnings of modern interactive graphics, output are vector graphics and interactive graphics. One of the worst problems was the cost and inaccessibility of machines. In the early 1970’s, output start using raster displays, graphics capability was still fairly chunky. In the 1980’s output are built-in raster graphics, bitmap image and pixel. Personal computers costs decrease drastically; trackball and mouse become the standard interactive devices. In the 1990’s, since the introduction of VGA and SVGA, personal computer could easily display photo-realistic images and movies. 3D image renderings became the main advances and it stimulated cinematic graphics applications.
3. Raster versus Vector graphics
Before an object can be shown on a computer monitor or a printer, a model describing the object’s geometry is required, unless the object is an image itself. Modelling of geometrical objects is usually done in the framework of vector-oriented or vector graphics. A more complex object is modelled as a combination of elementary objects like lines, rectangles, circles, ellipses or arcs. Each of these elementary objects can be defined by a few coordinates, describing the location of the object, and some parameters like the radius for a circle.
Raster graphics uses a pixel matrix of fixed size. A color can be assigned to each pixel of the raster. In the simplest case of a black-and-white image a pixel takes one of the two values black or white. In order to display vector-oriented graphics in the form of raster graphics, all geometrical shapes must be converted into pixels. This procedure is called scan conversion. Figure 2 shows a very simple description of the house in vector and raster graphics.
Figure 2 vector and raster graphics
4. Applications of computer graphics
• Entertainment: Movies, Video games
• Computer-aided design and manufacturing (CAD/CAM)
• Scientific visualization / simulation
• Virtual Reality
• Education
• E-commerce
• Computer art
• Engineering Analysis
• Medical applications
5. Terms and Concepts
Here are a few informal definitions of the graphics field and its “relatives”:
Image processing: (more precisely, digital image processing) is the field that deals with methods, techniques, and algorithms for image manipulation, enhancement, and interpolation. Therefore, it is requiring methods, techniques, algorithms and the more important some understanding of Human Visual System (HVS). Among the major topics are:
• Image Restoration - taking an image with some known or estimated degradation and restore it back to original appearance Example, defect in telescope lens, blurring effect due to imperfect focusing, etc.
• Image Enhancement - improve an image visually by taking advantage of HVS. Example: improve contrast, image sharpening and image smoothing.
• Image Compression - reduce the amount of data required to represent an image by removing unnecessary. Example: JPEG, MPEG, etc.
Computer Vision: is a field that includes methods for acquiring, processing, analysing, and understanding images. In general, high-dimensional data from the real world processed in order to produce numerical or symbolic information. Computer vision does not involve a human in the visual loop. One of the major topics within this field is image analysis. Image analysis involves the examination of image data to solve a vision problem. Example: auto hand-written character recognition, auto biometrics verification (fingerprint, retina, signature, DNA etc.), auto speed tracking, robot fighter, auto satellite image processing (map making, predicting weather etc.), auto skin tumour diagnostic, etc.
Pixel: (Pel or picture element) is the fundamental display element of an electronic screen or bitmapped image and also considered the smallest unit of a digital image. In computer, a pixel is represented by its color code, which is either a gray scale value or the three components of a color. We tend to think of a pixel as a small dot, circular or square. Screen resolution is rated by the number of horizontal and vertical pixels; for example, 1024x768 means 1,024 pixels are displayed in each row, and there are 768 columns (lines). Likewise, bitmapped images are sized in pixels: a 350x250 image has 350 pixels across and 250 down.
Pixel Structures: In storage, pixels are made up of one or more bits. The greater this "bit depth," the more shades or colors can be represented. The most economical system is monochrome, which uses one bit per pixel (on/off). Gray scale and color typically use from 8 to 24 bits per pixel, providing from 16 to 16 million colors.
On a display screen, pixels are either phosphor or liquid crystal elements. For monochrome, the element is either energized fully or not. For gray scale, the pixel is energized with different intensities, creating a range from light to dark. For color displays, the red, green and blue sub pixels are each energized to a particular intensity, and the combination of the three-color intensities creates the perceived color to the eye.
6. Introduction to Computer Algorithm
An algorithm is any well-defined computational procedure that takes some values as input and produces some values as output. Like a cooking recipe, an algorithm provides a step-by-step method for solving a computational problem. Unlike programs, algorithms are not dependent on a particular programming language, machine, system, or compiler (usually described using natural language and pseudo code). They are mathematical entities, which can be thought of as running on some sort of idealized computer with an infinite random access memory and an unlimited word size. Algorithm design is all about the mathematical theory behind the design of good programs. The process of writing an algorithm is just taking your problem, and breaking it down, abstracting it to be able to be solved without a computer. Then you can translate those steps into code.
Computer algorithm has the following terminology clarification:
• Computer algorithm is detailed step-by-step instruction.
• ”No ambiguity” , no fuzz!
• Careful specification of the input and the output.
• A program is a formal representation of an algorithm, which can be executed by a computer
• A process is the activity of executing an algorithm (or equivalently, a program)
• The same algorithm may be represented in many different ways
• Several [different] algorithms may exist for solving a particular problem
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المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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