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  • Hello and welcome everybody to the series of lectures on computer graphics. Today we have the introductory

  • and the first lecture on computer graphics and this is a series of 40 lectures. So we

  • start with the introduction on computer graphics.

  • Well, computer graphics is an area of computer science and engineering which play a very

  • important role in almost every applications of computer software and use of computer science.

  • Computer graphics involves display, manipulation and storage of pictures and experimental data

  • for proper visualization using a computer. Typically a graphics system comprises of a

  • host computer which must have a support of a fast processor, a large memory and frame

  • buffer along with a few other crucial components. The first of them is the display devices.

  • Color monitors are one example of such display device. We need a set of input devices. Typical

  • examples are the mouse, keyboard, joystick, touch screen, trackball etc. Through these

  • input devices you provide input to the computer and display device is an output device which

  • shows you the image. There are other examples of output devices

  • like LCD panels, laser printers, color printers, plotters etc.

  • You can also have interfacing devices for a computer graphic system such as video input

  • output to a system or an interface to the TV. So these are some of the basic requirements

  • necessary to build a computer graphic system.

  • Well as u see now this flowchart gives the conceptual framework of interactive graphics

  • system. On left hand side you see an application model which the designer of computer graphics

  • system or software engineer will put his design. That is he will model the object he is planning

  • to display. Then he writes the program based on the application model. This application

  • program will run on the computer graphic system the output will come out to the screen and

  • inputs could be obtained from keyboard or from the mouse, so that is the typical framework.

  • There are lots of applications of computer graphics. So we will see just a few examples

  • of application areas of computer graphics. The first and most important of them is the

  • GUI as it is called. What is a Graphical User Interface or GUI as it is called? It has various

  • components. A graphical interface is basically a piece of interface or a program which sits

  • between the user and the graphics application program. It helps the graphics system to interact

  • with the user both in terms of input and output. Let us see few examples.

  • Typical components which are used in a Graphical User Interface are menus, icons, cursors,

  • dialog boxes and scrollbars. We will see the few examples of these in the next slide.

  • There are few other components which also could be used like buttons, valuators, grids,

  • sketching and 3D- interface. Let us take an example to see what these different components

  • are in typical graphical interface.

  • As u see in the next slide what I have done here is taken an example of Graphical User

  • Interface from software called Adobe Acrobat reader which is used for reading adobe documents

  • or PDF files.

  • Now this is an example which has various components of the graphical user interface which we have

  • talked about. You see the list of menus on the top in terms of the components on the

  • top screen bar and of course this is an example of what is called as a pull down menu. You

  • can click one of these and then what will happen is you will get a pull down menu and

  • adobe reader is one other example.

  • You can try this with various other menus and Linux based software starting from Word,

  • PowerPoint users, Linux, X fig and Paint Brush in Windows also so these are some of the menus.

  • Let us go back and see the next example is the icons and the cursor. Of course you can

  • see probably we can make out the cursor floating around to a point to a particular location.

  • These are certain examples of icons in terms of the options which will help you. The icons

  • are small representative pictures of tasks of computer graphics application program which

  • you are using. So these are certain examples of the icons, cursors, the dialog boxes.

  • Well, the next example does not have a dialog box. The dialog box is an example of a small

  • window which is used by a computer graphic system to interact with the user by sending

  • error or text messages. A typical dialog box is used to send an error message to the user

  • that you have provided the wrong input let us say. So that is an example of a dialog

  • box.

  • The scroll bar is an example, on the right hand side you can see of this window of the

  • example of this image which I have put here is a scroll bar which could be used to scroll

  • up and down.

  • Anything which you need to move within the screen right to left, up and down you can

  • use scroll bars and it will give you the current status or position of where you are in terms

  • of the screen location or the amount of data you are viewing. In this case the part shows

  • here that you are somewhere on the top part of the page or top part of the document which

  • you are viewing. The other examples of the graphical user interface

  • which is probably not in the example I have taken such as buttons, valuators, grids and

  • sketching. Just to give an example buttons could be considered equivalent to small icons.

  • Valuators could be used to control the particular value which could be linear or circular you

  • can assume it be a knob on a radio or a TV set which you control to control the volume

  • or tune it to a certain frequency or it could be in the form of a slide which you could

  • move from left to right or top to bottom to control a particular value to give as a input

  • to the computer graphic system.

  • Grids are used in two dimensional graphics packages to align your objects along a set

  • of specific coordinates or positions those are called the grids. You can switch it on

  • and off and display them on the screen. Sketching is an example which is used to draw lines,

  • arcs, poly lines and various other objects.

  • The most difficult part of the Graphical User Interface is at the bottom of your screen

  • is what is given as a three dimensional interface. It is easy to interact and handle with two

  • dimensional objects but when you are interacting with the three dimensional objects you need

  • a three dimensional interface to pick up one of the 3D objects from a two dimensional screen.

  • Essentially the computer monitor is just a two dimensional ray of pixels where the entire

  • picture is projected and the picture could represent a three dimensional scene. So you

  • need special type of interfaces to pick up or manipulate objects in 3D using a two dimensional

  • interface. So you need special facilities for 3D interface to handle or manipulate three

  • dimensional objects. The 3D interface is one of the hard topics of research in active areas

  • and the part of the Graphical User Interface.

  • Let us come back to other typical application areas of computer graphics. Plotting in business

  • we need to plot various curves in the form of pi-charts or 2D or 3D graphs.

  • And probably in business applications you need to show the growth rate of the company,

  • the expenditure, the profit and the various other types of work forces that you have been

  • using, various economical types of data for business applications and so you need plotting.

  • You need to provide for office automation which are the standard packages of Word in

  • Microsoft and the Microsoft Excel and PowerPoint are examples of office automation. Almost

  • all software has Graphical User Interface along with desktop publication for designing

  • documents, for designing PowerPoint slides like these you also need the help of graphical

  • user systems.

  • Plotting in science and technology, we discussed about plotting in business and plotting in

  • science and technology is absolutely necessary in almost all areas of study, any branch of

  • science and engineering and technology and I was talking of 2D or 3D graphs in the form

  • of line drawings, surface plots, contour plots, ISO contour plots, pi charts, so various types

  • of plotting are necessary in science and technology. And you probably cannot do without computer

  • graphic systems which has replaced the traditional draftsmen which are to take the help about

  • one or two decades ago for the help of plotting.

  • Web business, commercial publishing and advertisements you need to design very good advertisements

  • on the web or on the TV shows and for the commercial shoot outs may be post certain

  • banners outside in the city and you do take the help of computer graphics to make your

  • advertisement and very attractive and with that you can get a wide amount of publicity.

  • Coming to engineering applications we talk of CAD/CAM design when we expand those terms

  • it means computer aided design and computer aided manufacturing and typical example of

  • CAD/CAM is a vast scope in many fields of engineering and technology.

  • But I have taken three examples in this case VLSI Very Large Scale Integration constructions

  • in the area of architecture and civil engineering and circuits designs in the area of electrical

  • engineering. And these are the areas of CAD/CAM designs where we actually manufacture a particular

  • chip in VLSI or a printed circuit board let us say in a circuit or an architecture, a

  • bridge or road or it could be a building or a complex, a multi-storey complex we would

  • like to design it in a computer graphic system to have a view and provide the interface and

  • show what sort of design you have come up with. So there are various utilities of CAD/CAM

  • designs in computer graphics which play a very crucial role.

  • Scientific visualization is almost similar to what we talk of plotting in science and

  • technology. But we need to visualize something we can say as multi-dimensional data, something

  • which requires animation.

  • Let us say you would like to visualize the effect of a nuclear explosion so those sorts

  • of visualizations and you need to understand certain patterns in data, it could be in genetic

  • engineering, biological sciences or mechanical sciences or anywhere else. You would also

  • like to have a visualization of the scientific data and you demonstrate the activity which

  • is going on in a system using a typical Graphical User Interface.

  • Entertainment, very important, a huge market in the industry where you need computer graphics

  • system to design movie, TV advertisements, video games in fact almost a majority of the

  • market economy in computer graphic systems probably revolves around the entertainment

  • world where we create not only animation or carton movies but we also make real time movies

  • in between the real time characters.

  • You make advertisements with the help of real characters and merge it with various types

  • of steel frames, cartoon characters and things like that to create good advertisements. And

  • of course, video games it is a very lovely market not only for young children but even

  • adults get attracted to lots of video games and similar kinds of entertainment.

  • Simulation studies and simulators I will put both of these together. Well this is another

  • application I will say close to scientific visualization where you need to create a system

  • with a good graphical interface for various applications.

  • Simulation studies and simulators include areas such as computation, fluid dynamics,

  • heat and mass transfer, various other mechanical and chemical processors, it could include

  • even studies about nuclear explosion and disaster management, damage prediction in a certain

  • area, flight simulators. If we talk of simulators, flight simulators car racing, docking of a

  • naval ship or a space shuttle, you would like to train your pilots and engineers before

  • going on to a particular mission and you can use simulators to really test the skill of

  • a particular person. It could be even in the field of sports one would like to use simulators

  • to study the reaction time of a particular individual.

  • Cartography is an area which is connected to drawing, manipulation and creation of maps

  • as I would say. It is an area in civil engineering, geology, geography, applied geophysics and

  • Cartography is involved in the design of maps, creation of maps in geographical engineering

  • systems and for other geographical applications. Basically it has to do with the creation of

  • maps.

  • Multimedia is vast area again it combines text, audio images, video, computer graphics

  • everything together and the presentation must be very synchronized and computer graphics

  • is a very important and integrated part of any multimedia presentation.

  • Virtual reality, well we discussed about video games. That is probably a very classical example

  • of virtual reality. Or even animation movies or movies synthesized with the help of computer

  • graphic systems which takes you to a completely different world and you can acquire big set

  • of movies which have come out in the last decade based on virtual reality. Either the

  • movie shows itself or it can help you to design good simulators and training kids for people

  • before like the pilot of an aircraft, before they go on to actually test a system you can

  • test their skills using virtual reality systems.

  • Process monitoring again in chemical and mechanical processors you can have a large plans where

  • several activities are going simultaneously and we can have sensors fitted at various

  • points which monitors the health and the flow of a particular assembly line or a system

  • is going on and we need online monitoring to find out that the entire team is working

  • true and in a correct form. The sensors are giving feedback simultaneously from different

  • locations and if there is any wrong signal coming out from the sensor you can generate

  • an alarm using a Graphical User Interface and alert the person who is probably monitoring

  • it. So GUI could be used for process management as well.

  • Digital management processing is a vast area by itself. But I will probably like to mention

  • areas connected to computer graphics which involves manipulations, storage and editions

  • of pictures, enhancing the quality of the pictures, the contrast of the pictures, removing

  • the noise, the blurriness and all those types of manipulations of digital pictures, saving

  • them in different types of formats starting from ENP, PGN, TIF, JPEG you name it sort

  • of a thing as all are coming under the field of computer graphics.

  • The last and not the least of for what we are also here, the computer graphics is also

  • playing a major role in education and training not only in giving lecture series like the

  • topics but today we are discussing but for any sort of education and training to individuals,

  • professionals, students and may be even bureaucrats and politicians mainly where computer graphics

  • systems could really become very helpful in training certain professionals and educating

  • people.

  • So we come out of computer graphics applications and move over to certain application packages

  • and standards available in computer graphics. As we see here computer graphics packages

  • and standards have evolved over time before of course we go on to tell you what is the

  • standard we will name a few of these; core graphics was the traditional standard of computer

  • graphics and then we had the GKS and then the SRGP, I will expand these terms and then

  • we had PHIGS SPHIGS AND PEX 3D and currently we have the OpenGL with or without ActiveX

  • and Direct3D and the OpenGL is also available on X11 based system on Linux operating system.

  • We will try to see the expansion of GKS. It is a Graphics Kernel System which was defined

  • as a standard, almost the first in computer graphics by ISO and ANSI you can see the expansion

  • of the word ISO International Standards Organization and ANSI stands for American National Standards

  • Institute. Why are we taking about standards?

  • We are taking because you need, a programmer needs a certain set of rules, constraints,

  • procedures, syntax and function cause within his programming environment to build a graphic

  • system. We have not come across to learn how to build a graphic system but if every person

  • comes up with his own different type of syntax, formats and function cause, then when you

  • design a system nobody else will be able to use your system and build another system on

  • top of it so we need to talk of standards. And ISO and ANSI came up with the first standard

  • of the Graphic Kernel System and it was very popular till it was probably replaced for

  • a very short while by SRGP or Simple Raster Graphics Package as it is called.

  • SRGP was very simple but was soon replaced by the standard called PHIGS Programmers Hierarchical

  • Interactive Graphics System. I repeat PHIGS stands for Programmers Hierarchical Interactive

  • Graphics System. This was quite popular I should say probably up to the late 90s and

  • then currently we have the OpenGL, let us go back, the PHIGS replaced by current standard

  • as industry has accepted today called OpenGL graphics available on almost all system of

  • Windows and Linux which are the most popular system used all over the world in industry

  • as well as in educational institutions.

  • And what you have to do is to download the device drivers, download the libraries, download

  • the header files for OpenGL corresponding to your operating system and also the display

  • adapter chord which you are using and then once you have the compiler when you talk about

  • visual environment or dot net in windows system or in new environment or X11 graphics system

  • is available on Linux you should be able to use OpenGL as a standard and write your own

  • graphics, programs or packages.

  • So this is how it has probably evolved over time, you do not need to know all of them,

  • we will stick to OpenGL standards whenever you use comments and syntax for giving examples

  • of graphic system. Sometimes you may use PHIGS also because just a few years back that was

  • one of the popular standards.

  • And I was saying sometime back these standards are available in almost all systems of course

  • we have almost forgotten the use of the DOS or

  • Distributed Operating System, most commonly used operating systems based on Windows or

  • Linux and the OpenGL and PHIGS are available on both. You also have graphic systems and

  • operating systems such as OS/2, silicon graphic system, SunOS, Solaris, HP-UX these are the

  • old systems and Mac and DEC-OSF.

  • But the most common platform are Linux and Windows but we should not forgot the silicon

  • graphic systems and the Solaris which have been also quite popular in many parts of the

  • world. Various utilities and tools which are available for computer graphic systems and

  • specially for web-based design which includes Java, XML, VRML and GIF animators.

  • These are mostly examples of tools which help you to create nice web pages I should clarify

  • here. But when you are designing a graphic system you are not probably only interested

  • in a web page design but you are interested to come up with say a computer game or demonstrate

  • certain facts through virtual reality or simulators or simulate a certain scenario through animations.

  • So you need an operating system with graphics library support and pick up a standard to

  • use it. So most compilers starting from the current visual CC++ visual basic, the Borland’s

  • turbo C Pascal, even new CC in Linux and java provide their own graphics libraries, API

  • or Application programming environment and support and help for programming for both

  • 2D as well as in 3D graphics. So you have to ensure that the proper operating systems,

  • the proper compilers and correspondingly the proper libraries and APIs are all installed

  • for your use to help you to design the computer graphic system.

  • Well, you must be careful with some of these systems there are basically two types, some

  • of them are device independent and some are device dependent. I should clarify here the

  • difference between the two examples of device independent or X11 systems or OpenGL systems.

  • Device dependent systems are the SGI systems and the old Hewlett Packard or advanced graphics

  • packages probably which nobody uses these days.

  • Device dependent systems had a drawback in the sense that once you design your own graphical

  • computer graphic application program on a particular system it is almost impossible,

  • it is very difficult to take that program and run it on any other system. So those are

  • examples of device dependent system where if you program it on one particular platform,

  • on one particular system which will run almost entirely on identical platforms, identical

  • machines, identical systems. This is not the case for device independent systems. In device

  • independent systems if you design a computer graphics program in a X11 system or an OpenGL

  • system either it is Linux or Windows almost with very little change or no change in certain

  • occasions you should be able to take that program and run it on any platform, any machine

  • which has windows or Linux with OpenGL support, X11 supports OpenGL as well. You should be

  • able to run such programs anywhere on a device independent system. So that is the difference

  • between a device dependent one where you cannot run on any system, you have to run it on only

  • that system or exactly identical systems whereas device independent you should be able to run

  • it on any system. You can change your keyboard, your mouse, your monitors, you can change

  • your operating system on platforms you should be able to run the device independent programs

  • on any system independent of whatever type of devices you have been using.

  • Well, what you draw? We are talking of standards, platforms, device dependent, device independent

  • and all that. There are basically four basic output primitive elements for drawing pictures.

  • You can draw a very complicated picture, you need to draw of course for most applications.

  • But you basically draw almost any picture with a very few fundamental operation or what

  • we call as output primitives. We will clarify output primitives later on but assuming for

  • the time being that you hold on and look at these examples of what are called primitives.

  • A few points to be clear, poly lines, you can draw a line from a point x1y1 to a point

  • x2 y2. Take a graph paper plot a point x1 y1 and plot a point x2 y2 and then what you

  • do draw a line so that is the simple example of drawing a line. What is a poly line? Well,

  • you can have a set of n points with coordinates x1 y1 x2 y2 x3 y3 and so on up to xnyn in

  • any order does not matter and the poly line command or the output primitive will draw

  • lines from the first point x1y1 to a point x2y2 and then connect x2y2 to x3y3 and so

  • on and it will connect the last set of pair of points basically connecting the points

  • in that order as given in the function and that is an example of a poly line.

  • The next feature or next output primitive which we see after poly line is called the

  • filled polygon or also filled region you can call. But the technical term is a polygon

  • or a filled polygon. Well, a polygon can be filled or it may not be filled. But what is

  • the difference between the poly line and a polygon? Well, the difference is the following;

  • in a poly line we discussed about a set of n points being joined by lines.

  • The same set of n points could be for a polygon line. But in the case of a polygon the last

  • and first point are joined together to enclose the region. You remember, in a polygon we

  • started from x1y1 to x2y2 and we stopped at xnyn to draw a line. We kept on drawing lines

  • and in the case of a polygon we take the last point also and connect it or join it with

  • the first point so that will be the enclosed region. That is why it is also called a region

  • but polygon is probably the proper terminology and then you can also fill it.

  • Of course you will see in the algorithms how to fill the polygons with certain shades,

  • textures and colors when the particular topic of drawing polygons and scanning polygons

  • will come but that is also the functionality which is provided as an output.

  • The next primitives are we talked of lines that we should be able to draw curves. And

  • if we go back the output primitive for drawing curves is basically to draw an arc or a ellipse.

  • So you should be able to draw a arc or a ellipse and remember you should bother about drawing

  • a circle where geometrically if you see the equation of a circle and ellipse, the circle

  • is a very special case of drawing an ellipse.

  • So once you are given the option of drawing a ellipse or part of the ellipse as an arc

  • you should be able to draw any arc, you should be able to draw a circle as well as ellipses.

  • So that primitive must be there. In addition you should also be provided an option to text.

  • Text with various kinds of fonts, various types of sizes, various types of scalable

  • fonts and it could be in bold, italic font and all that with various such options.

  • You should be provided an option to draw text and position it anywhere in any arbitrary

  • orientation that option should be there in a computer graphics system. And the last but

  • not the least is to draw a Raster IMAGE.

  • You should have the option to open a Raster IMAGE, a digital image, it could be stored

  • in any format. We discussed about a few of these examples format in applications of computer

  • graphics or image processing where the format could be JPEG format a DMT format, a PGM or

  • TIF but you should have the provision to read a particular digital image, display it on

  • the screen, edit it, manipulate it, colors, give shades and whatever it is and then you

  • can save it back, save it back to the disc or file. These options must be there as output

  • primitives and once you have these I can almost assure that you can draw any picture which

  • includes animation. That is of course a special feature but let us talk of static feature.

  • Now, actually you should able to draw any complicated static picture once you have all

  • these five basic primitives available on any computer graphics package or standard. Well

  • the four major areas of computer graphics you will discuss in various lectures in a

  • sequence later on but not necessarily in this sequence and they will be display of information,

  • design and modeling, simulation and user interface. Well, we discussed about user interface already.

  • Throughout the lecture we will talk about design and modeling which is the important

  • part and in fact in the next lecture we will talk about display devices and then display

  • of information. And of course to make the entire package work you must simulate it and

  • make the application program work. So these are the four major areas where people

  • work and also do research in the field of computer graphics.

  • Well, computer graphics system could be active or passive. That is another terminology which

  • you must know. Let us read the lines, as you see here

  • in both cases the input to the system is the scene description and the output is a static

  • or animated scene to be displayed. That is true for both active and passive systems.

  • Your input is the scene description and the output is some picture, a static picture or

  • animated picture. Then what is the difference? The difference is that in case of active systems

  • the user controls the display with the help of a graphical user interface using an input

  • device and that is only possible in active system. In passive system you do not have

  • any control, you have to watch whatever is shown to you. A typical example of a passive

  • system, whatever you see in your TV, well you can change the channel but you stick to

  • the particular channel, you are forced to see whatever is broadcasted by that particular

  • channel.

  • You can switch off the TV and go to another channel but you do not have control of what

  • is being viewed on the screen or what is being telecasted on the screen or projected on the

  • screen by the channel broadcaster. So that is the example of a passive system.

  • Example of an active system is very easy, the video games where almost you can decide

  • where you want to go by giving an input through the mouse, through the keyboard, through the

  • joystick so that is the example of an active system where the user play a prominent role

  • and the pictures are shown depending upon the inputs given to the user. Although, the

  • sequence is pre decided but you can provide many options for the games and quite a bit

  • of randomness in the animation and the task which the video games will actually ask the

  • user to do. It could be a very good active system in order to a passive one which you

  • might think.

  • Last but not the least of computer graphics introduction is, computer graphics is now-a-days

  • is a significant components of all system applications of computers in every field of

  • life. Right from the point the computer boots up the operating system comes up and the login

  • prompt is provided to you then you log in inside the screen see your desktop options

  • in windows and Linux everything is controlled by a computer graphics applications package

  • or computer graphics software it is there in every field of life now which involves

  • of course Computers, TVs, video shows and movies and one cannot think of systems without

  • computer graphics.

  • Well let us look at a list of the major concepts and principles of computer graphics which

  • we will go through this course. This is an introductory course but let us move on to

  • certain topics.

  • Almost in this order we will talk of displays system in the next introduction lecture and

  • in display systems we will talk of storage displays, random scan displays, raster refresh

  • displays, CRT basics, video basics and flat panel displays. We will try to cover as much

  • as possible with display devices and videos in the next lecture after introduction.

  • Then we will move on to transformations, manipulations of computer graphics and computer graphical

  • objects dealing with transformations which mean manipulation objects. And mathematically

  • we have to learn about affine transformations which involve rotation, translations, scaling,

  • reflection and shear then comes viewing transformations. The camera transformations in terms of various

  • types of perspective projection, various types of orthographic, isometric, stereographic

  • views the way we human beings see. And the corresponding quaternion of the mathematics

  • is associated with transformations. Then the next we will see on how to draw a line. We

  • discussed about an output primitive to draw a line or a curve as a function but actually

  • how it is implemented in a graphics package we must also know. You can use the command

  • to draw a line but you must know how the command is working inside the system to draw a line.

  • So it involves learning about scan conversion and clipping, drawing of points, lines, line

  • markers, curves, circles, ellipse, poly line, polygon, area filling, fill style, fill pattern,

  • clipping algorithm and anti-aliasing.

  • So there are various topics as you see on the board here for scan conversion and clipping.

  • It involves many of these options. So we will study those, the algorithms involved in scan

  • conversion algorithm. Well, hidden surface removal is the next task.

  • We are moving from 2D to 3D now where we talk of three dimensional structures and objects.

  • When you see a three dimensional object in front of you it is evident that you will be

  • able to only see the faces which are in front of you. You will not be able to see the face

  • which is on the back side. So how to come up with the algorithms using geometry, mathematical

  • model to find out which part of the surface of an object is facing you and which part

  • of the object is behind you. So those algorithms involve the concept of hidden surface removal.

  • There are various ways and means and by which you can do by it hidden surface removal. The

  • first and easiest is back face scaling. As you see on the board the next few algorithms

  • are Painter’s algorithm, scanline algorithm,

  • BSP-trees, Z buffer/sorting, Ray tracing etc. The most popular among these are the Z buffer

  • and Ray tracing. But people also use back face culling and BSP trees. After you remove

  • the hidden surfaces you need to shade and eliminate the surface facing the viewer or

  • facing the design. It involves shading and illumination. There are various shades of

  • model; Phong’s shading model, texture mapping, bump mapping, Gouraud shading, Shadows and

  • background, Color models etc. So when you move to that chapter of lecture you will study

  • the chapter of shading and illumination.

  • Solid modeling, we need to model a solid object. There are various types of methods and algorithms

  • and techniques by which you can model a solid object. I will give an example at the end

  • of the talk today about wire-frame object.

  • But we can use other representations like Octrees, Sweep representation, Boundary representation,

  • regularized Boolean set operations and constructive solid geometry or what is also known CSG.

  • In the last you also move towards curves and surfaces which involve special mathematical

  • functions like Bezier or Bernstein polynomials curves, B-Splines, Cubic-Splines Quadratic

  • surfaces, parametric and non-parametric forms, Hermite curves etc. Depending upon the time

  • I will also cover some advanced aspects such as concept of Animation, Fractals, Projection

  • and Viewing, Geometry, Modeling, Image File formats, Image Morphing, Interaction sample

  • and event-driven etc. Also, if you have some background of computer architecture you will

  • be able to follow the parts of my lecture which talks about Display Processors, Pipeline

  • and parallel architectures, multi-processor systems, hybrid architectures, you need some

  • good fantastic highly optimized high speed architectures to make your graphics program

  • work really fast so that the user doesn’t have to wait for a certain event to occur

  • after he provides the input. Well, these are the list of references or

  • books on computer graphics which I will ask you to go through as a part of this lecture.

  • You can at least purchase one of them. Well the most advance one is the first one which

  • is Computer Graphics Principles and Practice by J. Foley A. Van Dam and Hughes that uses

  • the fixed standard. The nest book is by Rogers and Adams which is taking about the Mathematical

  • Aspect of Computer Graphics. The third book in fact is the book by Computer Graphics C

  • Version Hearn and Baker which is simple and easy to read as it has lot of good illustrations

  • and you can use that book as well. Well, if you are talking about the current standard

  • of OpenGL I would recommend the fourth book. There are good examples and programs that

  • you can take on and try it on your system to see whether it works and which gives you

  • confidence. And the last but not the least is a book by Rogers on Procedure Elements

  • of Computer Graphics. It is a good mixture of mathematics as well as concepts and algorithms

  • on computer graphics. I do believe one should have one of these books, if possible two books

  • at your disposal also to have a reading material in addition to listening to these lectures

  • to understand computer graphics. Well, to wind up the lecture I have brought today some

  • examples and illustration of computer graphical objects. Well, I will not have time today

  • to tell you how these graphic objects are created but we will see examples of what computer

  • graphical systems can do or generate. I discussed of a 3D solid modeling in one of the course

  • contents. This is an example of wireframe model of a sphere which uses the sweep representation.

  • Well, if you see the sphere it looks like a sphere and how this has been created? Well,

  • assume the surface of the sphere is a perfect sphere. We have learnt that in basic school

  • geography and you can start to think of latitudes and longitudes on the surface of the earth.

  • Remember, the vertical circles on the surface and the horizontal lines which are equidistance

  • sort of a thing, and of course the vertical circle which intersects at the north and the

  • South Pole probably that is the best example. So you have to take those sort of lines, latitudes

  • and longitudes and the intersection points of those latitudes and longitudes

  • give the vertices of the wire-frame model or basically the 3D coordinates of these sphere.

  • Just to see an example of what I mean we will go to the next slide in the left hand side

  • which has come out now. As u see some of the vertices have been marked by a light red color,

  • a light reddish color and those are the vertices which are the intersection of the vertical

  • lines and the horizontal parallel lines or something like the latitudes and the longitudes

  • of the hard surface in the map of the earth. Of course it is a very fine grid but those

  • intersection points are the most crucial for storing or representing the sphere.

  • The 3D coordinates of the intersection points are basically stored to represent the wire-frame

  • model of a sphere using a sweep representation. What is a sweep representative, you do not

  • have to worry about this now. Just to give an example you can take a circle and rotate

  • the circle in 3D vertically that will give some example of the sweep representation.

  • But you can generate other types of objects as well.

  • Well, if you see the third figure I have joined a set of three vertices, a few of them to

  • show a set of triangles. now what you need is after you have the wire-frame model you

  • need to apply techniques like hidden surface removal, then you need to apply illumination

  • and shading and to do that you need to approximate the surface of a curved object like a sphere

  • or even a planer surface could be a rectangular parallelepiped or a cube with a set of triangles

  • or quadrilaterals or rectangles.

  • We have taken the rectangular, that is the best approximation and that smaller patch

  • which is curved is approximated basically by this triangle or linear patch. And once

  • the coordinates of the triangle are known you can apply the algorithm of hidden surface

  • removal, back face culling, illumination and shading to actually throw of the hidden surface

  • which is back side as viewed.

  • Now you do not need to shade the surfaces or the patches which are on the back side

  • of the object, not visible to the viewer from the front and then you need to shade. So,

  • all those shading algorithms and back face culling rely on the area, the surface normal

  • and the orientation of those rectangular or triangular patches. So, these are the examples

  • of the triangular patches which should be used for shading parts of this sphere, just

  • an example. Well, these are some examples of simple 3D objects.

  • This is an example of four objects here, well you can assume that at the bottom there is

  • a flat table type of structure or a small very thin rectangular parallelepiped and on

  • top of that there are three object a cube a sphere and a pyramid. Well, you can think

  • this pyramid to be a cone but it does not have a rectangular base. I will say this is

  • a pyramid with an octagonal base.

  • A highly approximated sphere and in a cube there are four such objects and these are

  • some examples of primitive objects that you can use, combine and manipulate to create

  • other objects. Well, these are simple objects and then you can of course shade them. But

  • to create complex objects let us take another example like this, this is a object which

  • is already shaded, it is a pyramid, a perfect pyramid with a triangle base but it has a

  • hole.

  • We will see an example of how to create such a hole within an object with different examples.

  • But this is an example of an object which is shaded it is slightly complex in the sense

  • that it has a hole and that is an example.

  • We will see the next example. These are another set of primitive objects which are very commonly

  • used to generate other complex 3D structures. Examples are; a cylinder, a cube, a sphere,

  • a perfect cone and a triad, a 3D triad. And these are examples of five objects which are

  • used and combined and manipulated to generate other complicated structures.

  • And in this case you can use sweep representation or a wire -frame to have the model of the

  • object and then shade it. As you can see here it is shaded with a constant color and it

  • gives an effect of the shadow as well. All these objects on the right hand side bottom

  • as you see probably tells you that the light is falling on the object from the right hand

  • side of the screen somewhere from the right hand side of the screen, the object. Now this

  • is an example where the objects are shaded with textures. In the left hand side top wire-frame

  • diagram that object is shaded with texture mat and four different textures on four different

  • objects. And sometimes the texture gives a good feeling, it gives an idea of good shape

  • of the object but sometimes it does not. It looks very nice but it does not give you the

  • shape.

  • To my feeling the texture gives a good revealing shape for the cone but I am not satisfied

  • whether you are able to perceive the shape of the structure of the cube with the help

  • of texture mapping which has been done. The texture sometimes reveals the shape sometimes.

  • I will give another good example where the shape information is perceived by the viewer

  • much better with the help of a texture than the normal flat type of uniform color shade.

  • Before that we talked with a simple example to create a hole using CSG or constructive

  • solid geometry. I am now interested to take to create a hole within a sphere. A small

  • cylindrical hole within a sphere is my target so I basically I picked up an object which

  • is a union or a combination of two parts where a sphere and a cylinder is passing through

  • it. In virtual reality the computer graphics does not stop you from creating complicated

  • structures or put a structure within another structure. So what I have done is I have started

  • with a structure which is a union of a sphere and a cylinder through it. I start with a

  • structure then what I need to do is basically take out this cylinder out of this sphere.

  • Once I take, it is something like an object subtraction not mathematically but in terms

  • of object structures. If you look into this screen I would like to subtract this cylinder

  • from this sphere. So I have displayed with two colors so I am taking out that greenish

  • cylinder out of that purple type sphere and if you can do that the resultant structure

  • will be as shown on the right hand side bottom of the screen. You will be able to obtain

  • a sphere with a cylindrical hole inside. The last couple of examples here are the shading

  • effects of texture mapping and shadows.

  • We will take the example of a simple parallelepiped, a linear patch at the bottom and some sort

  • of the curve irregularly curved object on the top and that is the simple example again

  • of a wire-frame or sweep representation and this is an example of constant uniform color

  • shading. Now it is good for the platform which is rectangular patch at the bottom, uniform

  • red color absolutely no problem. But I do not think you will be able to perceive the

  • structure or the 3D shape of the curved object nicely with the help of shading information

  • as given here in the grey shade. In this case it is better to put a texture mapping like

  • this.

  • As you can see both on the planar surface and curved object once I map it with the texture,

  • the texture reveals the shading along with the shading effects the curvature or the structure

  • of the objects both in planar and as well as definitely in the curved objects the shape

  • information is revealed much more in a satisfactory and better manner with the help of texture.

  • This is a very good example why texture is better than normal shading in terms of revealing

  • the structure of an object, the structure is good. I did say it helps to visualize the

  • shape and structure of objects, typical examples of geometrical structures being mapped on

  • artificial object synthesized by computer graphics are given on the left hand side of

  • the screen.

  • Two examples I do not think there is any problem in visualizing the 3D structure of these objects.

  • Well, we have to end the sphere on the top as you can see forgot the color of the scene

  • part of it. Even if it is in black and white there is no problem, you need to visualize

  • the structure and at the bottom you typically have four curved parts of the structure. It

  • could be a structure on a wall, or a ceiling, or a roof of a particular building which could

  • have these particular shapes and this texture helps you to understand the shape in formation

  • of the structure of the object much more basically.

  • Textures are good, it helps to reveal this shape in formation, makes the picture very

  • attractive but there are some textures which are in fact very difficult to draw. Stochastic

  • textures, real world textures, not the texture which you see on a garment, or in cleaning,

  • or in a table top, or on my cloth, or the garment which you are wearing because all

  • are having textures in general but in real world Stochastic textures occur in almost

  • every part of the world makes the computer graphics scene or picture more appealing or

  • realistic. It is very difficult to draw and that is the typical example of Stochastic

  • texture.

  • Here is an example of a water image. As you can see here, you can stand on the banks of

  • the river or even on the sea shore and keep watching the water as it goes away from you,

  • this is the example of such an image which is put on the screen now. It is not generated

  • by computer graphics system. This is a real digital picture or a digital image taken by

  • a camera. It also has a texture but you can see, I will say that this texture has a random

  • effect. I will call this texture as a Stochastic texture, difficult to draw or difficult to

  • implement using computer algorithms. In most cases you will find such examples of Stochastic

  • or real world textures.

  • If you look around in a street, go out and see in a garden, in a bed of roses or go to

  • the mountain top and keep watching the scenario around, go to a high raised building, look

  • at the clouds, walk around a field and you can see various types of examples of real

  • world textures and to incorporate that in a scene to give it a realistic effect is probably

  • the most challenging task in computer graphic system.

  • What we are trying to do in computer graphics?

  • We are trying to generate pictures and make it look almost like real life so that people

  • will not be able to discriminate and find out whether you have actually taken the picture

  • or generated that picture using a computer graphics application or a program. If you

  • can do that you have almost become a real professional or a good expert in computer

  • graphics systems.

  • We will see one example of what is called visual realism, trying to create the visual

  • effects of real pictures or realistic effects of real world picture around you on to your

  • computer graphics system. From the previous example we had seen the case where synthetic

  • pictures look alright but they are not that realistic. They do not appear that realistic.

  • You will often be able to discriminate realistic pictures as to whether you are being shown

  • an animation picture, a static picture, or real world picture taken by a camera and shot

  • like what is being done now. That is the difference between synthetic and real world pictures.

  • And the task of computer graphics programmers, systems designers is to make pictures, animation

  • pictures and static pictures as close as possible to real world. But of course, we must first

  • learn the basics and then try to put in effects of real world scenarios or visual realism

  • as it is called into the picture to make it look almost real world. Well, we wind up the

  • talk today with these examples and we will start the next lecture with the talk on display

  • devices and video basics, thank you very much.

Hello and welcome everybody to the series of lectures on computer graphics. Today we have the introductory

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Lecture - 1 Introduction to computer graphics電腦 + graphics

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    Why Why 發佈於 2013 年 03 月 26 日
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