Fundamental of Computer graphics Flashcards
What are input devices?
It is an Electro mechanical Device that can be used to enter data and instructions to the computer
What are output devices?
That are used to receive information from the computer either in soft copy or hard copy
Video Display devices
Output in a visual way
When the input information is an electrical signal it then changes into an electronic display
CRT’s Raster Scan Displays ,Color CRT monitors Direct view Storage tube ,Flat Panel Displays ,Light emitting Diode,Liquid Crystal Displays
What Does A CRT do?
Convert electrical signals to visual signals
What happens in a CRT?
Beam of electrons directed from cathode(-) to phosphor-coated (fluorescent) screen
(anode(+))
Directed by magnetic focusing and deflection coils(anodes) in vacuum filled tube.
Phosphor emits photon of light, when hit by an electron, of varied persistence
What are the characteristics of a CRT?
Intensity: It is proportional to the number of electrons repelled in beam per second (brightness).
Resolution: It is the maximum number of points that can be displayed without overlap. It is expressed as
number of horizontal points by number of vertical points. These points are called pixels (picture
elements). Example: resolution 1024 x 768 pixels. Typical resolution is 1280 x 1024 pixels.
High-definition systems means high resolution systems.
Aspect Ratio: It is the ratio of vertical points to horizontal points necessary to produce equal- length
lines in both directions on the screen.
An aspect ratio of ¾ means that the vertical line plotted with three points has the same length as a
horizontal line plotted with four points.
Do you know some categories of CRT?
Based on tech: Raster Scan System Random Scan System Based on Color: Beam Penetration System Shadow mask system
What is Raster Scan System?
In a raster scan system the viewing screen is divided into large number of discrete phosphor picture elements,called pixels/dots
Define pixel and scan line in raster?
Pixel: one dot or picture element of the Raster
Scan line: A row of pixels
ON a black and white system with one bit per pixel,the frame buffer is called ___________
For a system with multiple bits per pixel,the frame buffer is referred to a ______
Bitmap
Pixmap
The return to the left side of the screen after a refreshing scan line is called the
Horizontal Retrace of the electron beam
At the end of each frame the electron beam return to the top left corner of screen to begin the next frame is called
vertical retrace
Define interlacing
It is the scanning of every other line and on the next scan scanning every opposite line.
Interlacing allows for a faster fresher rate by having less information during each scan at ta lower cost
What is a Random Scan System?
Refresh rate depends on the number of scan lines
Picture definition is stored in as a set of line drawing applications not realistic for shaded ones
Since the picture definition is stored as a set of line drawing instructions as ,vector displays generally have a higher resolution than a raster system
Difference between Raster and Random Scan
Resolution: poor and later High resolution
Electron Beam: directed from top to bottom and One line at a time in vector display
Cost: cheap expensive
Refresh rate:60-80 frame per second and latter 30-60 frame per second
line: Zigzag and Smooth
Realism in the display: Realistic display of, scenes, latter cannot give a realistic display of scenes
what are the types of Color CRT’s
Beam penetration
shadow mask
Shadow masks
Commonly used in Raster systems usually TV
Three color dots at each point on the screen(RGB)
one phosphor dot emits red light, another emits green and the third one emits blue light
three electron guns, controlling each of the display RGB
We obtain color variations by varying the intensity levels of the three electron
beam
High-quality raster graphics system have 24 bits per pixel in the frame buffer (a
Full-Color System or a True Color System)
When the three beams pass through a hole in the shadow mask, they activate a dot
triangle, which appears as a small color spot on the screen.
The phosphor dots in the triangles are arranged so that each electron beam can activate
only its corresponding color dot when it passes through the shadow mask.
what are 2 methods of implementation of shadow masks:
Delta and inline
Beam penetration method
Use Random Scan Monitors
Two layers of phosphor (red and green) are coated inside of the CRT screen
The display color depends on how far the electron beam penetrates into the phosphor
A beam of very fast electrons penetrates through the red layer and excites the green layer
At intermediate beam speeds, combinations of red and green light Orange and yellow
The speed of the electrons, and the screen color at any point, is controlled by the
beam acceleration voltage
4 colors are possible of beam penetration
Red Green orange Yellow
Colors of Shadow mask?
Yellow: red and green dots
Magenta blue and red dots
Cyan: blue and green dots
