Computer Graphics Lecture 3

Graphics Output Devices A- VIDEO DISPLAY DEVICES 1.Refresh cathode-ray tube (CRT) 2.Raster-Scan Displays 3.Random-Scan Displays B- Flat-Panel Displays 1.Flat CRTs 2.Plasma panels. 3.Thin-film electroluminescent displays. 4.light-emitting diode (LED). 5.Liquid – crystal display (LCDs).

Graphics Output Devices C- printers (HARD-COPY DEVICES) 1.Impact printers( Dot – Matrix) 2.non--Impact printers (Laser techniques) 3.Laser-device :- plotters(ink-jet plotters, pen plotters)

A- Video Display Devices 1-Refresh Cathode-Ray Tubes (CRT) Component : electronic gun - focus control deflection coil - electronic beam

A- Video Display Devices Illustrates the basic operation of a CRT(CRT operation ): 1.A beam of electronic (cathode rays), emitted by an electron gun. 2.pass through focusing and electronic systems that direct the beam to word specified positions on the phosphor coated screen. 3.The phosphor then emits a small spot of light at each position contacted by the electron beam.

A- Video Display Devices Because the light emitted by the phosphor fades very rapidly,some method need for maintaining.the screen picture this method are:- 1-Store picture information as a charge distributed with CRT,this can be keep the phosphor active 2-The most common method today is redraw the picture repeatedly by quickly directing the electron beam back over the same screen points This type called refresh CRT The frequency at which picture is redraw on the screen is (Refresh Rate).

A- Video Display Devices 2-Raster -Scan Displays: Base on television technology. - Operation:- Electronic beam is swept a cross the screen,on row at a time,from top to down. As electronic beam moves a cross a scan line and beam turn on and off. Each row is referred to as scan line.

A- Video Display Devices Bitmap: A frame buffer with one bit per pixel is commonly called bitmap Pixmap : A frame buffer with multiple bits per pixel is Pixmap

A- Video Display Devices A raster image stored in computer as rectangle array of numerical value Raster system Characterize by their resolution, Which is the number of pixel position that can be plotted. Another property is : aspect ratio, which is the number of horizontal points to vertical points