Unit 1introduction to computer graphics & scan conversion

Computer graphics application & softwareCAD (Computer Aided Design)Used in design of buildings, automobiles, aircrafts, spacecrafts, computers, textiles, etc.Objects are displayed in a wireframe structure

ConWireframe structure of a building

ConInterior of the vehicle and Effects of adjustments in design are visible

Behavior of the inner components during motion can be seen

Multi-window environment

After the completion of design realistic lighting applied to produce final product

ConAnimation in VR environments are used to determine how vehicle operators are affected by certain motions.

Standard shapes for electrical, electronic and logic circuits are supplied. Eg: diode, resistor

Architects used to design the buildings.

Electrical designer design the arrangements of wiring, electrical layout, etc

Presentation graphicsProduce illustration for reportsEg: charts (bar,pie), graphs (line,surface,2D,3D) Computer artFine art and commercial artEntertainment Making motion pictures, music videosCG works in moviesEducation and training Flight simulator, military tank simulator

Flight simulator

Visualization Scientists, engineers, medical personnel business analysts using large set of information to study a behavior of certain process

Super computer gives million data files after its computation.

To study and analyze large set of data is difficult, so data are converted into visual form

2 types of visualization

Scientific visualizationProduce graphical representations for scientific engineering and medical data sets.Business visualization Produce graphical representations for data sets related to commerce, industry and other nonscientific areasMethods for visualizationColor coding, graphs, charts, etc

Image processing Used to modify or interpret the existing picture 2 PrinciplesImprove picture qualityMachine perception of visual information which is used in roboticsGUI (Graphical User Interface)Window manager allows a user to display multiple window areas. Each window contain different process that contain graphical or nongraphical displays Icon is a graphical symbol that is designed to look like the processing option it represents

Cathode Ray Tube (CRT)

ConElectron gun emits the beam of electrons which passes through focusing and deflection system and reaches phosphor-coated screen.Phosphor-coated screen emits small spot of light at each position which is contact with electron beamRefresh CRT Redraw the picture repeatedly by quickly directing the electron beam back over the same points .Refresh rate of CRTNo. of times per second the image is redrawn

Con

ConElectron gun is heated metal cathode and control gridHeat is supplied to the cathode by directing a current through coil of wire called filament and the electron beam is emittedIntensity of the electron beam is controlled by setting voltage levels on control gridHigh ve voltage will shut off the beamSmall ve voltage will decreases no. of electrons passes through.

ConAmount of light emitted by the phosphor coating depends on the no. of electrons striking the screenControl the brightness of the display by varying the voltage on control gridFocusing system force the electron beam to converge into a small spot as it strikes the phosphor, otherwise electrons would repel each other and beam would spread outFocusing , deflection of the electron beam can be controlled either using electric or magnetic fields, CRT commonly use magnetic deflection coils

Con

Con2 pairs of coils used, one pair mounted on the top and bottom of the neck, and another pair is mounted on the opposite sides of the neck

Horizontal deflection made by one pair and vertical deflection by another pair of coils

In electrostatic deflection is used, 2 pairs of parallel plates are mounted inside the CRT envelope

ConPersistence How long phosphor continue to emit light after the CRT beam is removedResolutionMaximum no. of points that can be displayed without overlap on a CRT No. of points per centimeter that can be plotted horizontally and verticallyAspect RatioRatio of vertical points to horizontal points necessary to produce equal-length lines in both directions

Con

Storage Tube Graphics Displays A CRT with a long persistence phosphor

Line or character will remain visible up to a hour until erased

Intensity of electron beam is increased sufficiently to cause the phosphor to assume its permanent bright storage

Display is erased by flooding the entire tube with a specific voltage which causes the phosphor to assume its dark state

Con FeaturesIt is flicker freeResolution is 10241024Display of dynamic motion or animation is not possibleEasier to program than calligraphic or raster scan refresh displayLevel of interactivity is lower than with either a refresh or raster scan display

Raster Scan or Calligraphic Refresh Graphics Displays

ConElectron beam swept (move) across the screen, one row at a time from top to bottom

Picture definition is stored in a memory area called refresh buffer or frame buffer

Memory area holds intensity values for all screen points

Stored intensity values retrieved and painted

Each screen point referred as pixel

ContIn black and white system each pixel is represented as either 0 or 1, so one bit required to store pixel value in frame buffer which is called bitmap

Bit value 1-> Electron beam on

Bit value 0-> Electron beam off

Frame buffer which requires multiple bits to represent one pixel called pixmap

Con

Horizontal retrace After refreshing each scan line , electron beam returns to left end of the screen

Vertical retraceAt end of each frame electron beam returns to the top of the screen to begin next frame

ConInterlaced refresh procedure Display each frame in two passes1st pass even numbered (solid) lines are displayed2nd pass odd numbered (doted) lines are displayed

Random-Scan Displays

ConElectron beam is directed to only the parts of the screen where a picture is to be drawn

Picture components can be drawn in any order

Refresh display filePicture definition is stored as a set of line drawing commends in an memory called refresh display file or display list or display program