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