2. What is CRT? Explain its types.
Ans: -
The CRT stands for Cathode Ray Tube.
The electron gun emits a beam of electrons called cathode ray. The electron
beam passes through focusing and deflection systems that direct it towards
specified positions on the phosphor-coated screen. When the beam hits the
screen, the phosphor emits a small spot of light at each position contacted by
the electron beam. It redraws the picture by directing the electron beam back
over the same screen points quickly.
The
two basic techniques for producing colour displays with a CRT are the
beam-penetration method and the shadow-mask method. These use three colours,
Red, Green and blue (RGB) and their combinations.
Types of CRT’s
Ø Raster-Scan Display: -
In
a raster scan system, the electron beam is swept across the screen, one row at
a time from top to bottom. As the electron beam moves across each row the beam
intensity is turned on and off to create a pattern of illuminated spots.
Picture definition is stored in memory. Stored intensity values are painted on
the screen one row at a time as shown below.
Refreshing on Raster-Scan display is carried out at the rate of 60
or higher frames per second. Most of display devices are based on this
technology. For e.g. CRT colour CRT, LCD and LED etc.
Horizontal retrace/Vertical retrace: -
Returning
of electron beam from right end to left end after refreshing each scan line is
horizontal retrace. At the end of each frame, the electron beam returns to the
top left corner to being next frame called vertical retrace.
Raster-Scan
system consists of several processing units. CPU is the main processing unit of
computer system. Architecture of Raster-Scan consist of system bus that helps
to access peripheral devices. It consists of video controller which is used to
control the operation of display devices. A fixed area of system memory is
reserved for the frame buffer. The content of frame buffers are used to control
the CRT beam’s intensity or colour.
Advantages: -
*
Shows Realistic pictures.
*
Millions unique hues can be performed.
*
Shadow scenes are conceivable. (i.e. Capable
of being imagined)
Hues = Colour.
Disadvantages: -
*
Low resolution.
*
Electron beam co-ordinated to whole screen not
exclusively to those parts of screen where picture is drawn so long when drawn picture
is longer then whole screen.
*
Expensive.
Ø Random-Scan (Vector) Display System: -
In this technique, the electron beam is directed only to the part of the
screen where the picture is to be drawn rather than scanning from left to right
and top to bottom as in raster scan. It is also called vector display ore
calligraphic display. Picture definition is stored as a set of line-drawing
commands in an area of memory referred to as the refresh display file. Random-scan
display are designed to draw all the component line of a picture 30 to 60 times
each second.
The refresh rate of vector display depends
upon the number of lines to be displayed for drawing all component lines 30 to
60 times per second. Plotter is the best example of this system.
Random
display system consists of additional processing unit along with CPU which is called
the display processor. Picture definition is stored as a set of line drawing
commands in an area of memory called display list. This display list is then
accessed by the display processor to create an image.
Advantages:
-
*
High resolution.
*
Produced smooth line drawing.
Disadvantages: -
*
Expensive.
*
Just does wire frame.
*
Complex scene cause-visible flicker.
3.
What is Random scan system? Draw
it’s block diagram and explain it in detail.
Ans: - Random-Scan (Vector) Display System: -
In this technique, the electron beam is directed only to the part of the
screen where the picture is to be drawn rather than scanning from left to right
and top to bottom as in raster scan. It is also called vector display ore
calligraphic display. Picture definition is stored as a set of line-drawing
commands in an area of memory referred to as the refresh display file. Random-scan
display are designed to draw all the component line of a picture 30 to 60 times
each second.
The refresh rate of vector display depends
upon the number of lines to be displayed for drawing all component lines 30 to
60 times per second. Plotter is the best example of this system.
Random
display system consists of additional processing unit along with CPU which is called
the display processor. Picture definition is stored as a set of line drawing
commands in an area of memory called display list. This display list is then
accessed by the display processor to create an image.
Advantages:
-
*
High resolution.
*
Produced smooth line drawing.
Disadvantages: -
*
Expensive.
*
Just does wire frame.
*
Complex scene cause-visible flicker.
4.
What is Raster scan system,
explain it in detail?
Ø Ans: -
Raster-Scan Display: -
In
a raster scan system, the electron beam is swept across the screen, one row at
a time from top to bottom. As the electron beam moves across each row the beam
intensity is turned on and off to create a pattern of illuminated spots.
Picture definition is stored in memory. Stored intensity values are painted on
the screen one row at a time as shown below.
Refreshing on Raster-Scan display is carried out at the rate of 60
or higher frames per second. Most of display devices are based on this
technology. For e.g. CRT colour CRT, LCD and LED etc.
Horizontal retrace/Vertical retrace: -
Returning
of electron beam from right end to left end after refreshing each scan line is
horizontal retrace. At the end of each frame, the electron beam returns to the
top left corner to being next frame called vertical retrace.
Raster-Scan
system consists of several processing units. CPU is the main processing unit of
computer system. Architecture of Raster-Scan consist of system bus that helps
to access peripheral devices. It consists of video controller which is used to
control the operation of display devices. A fixed area of system memory is
reserved for the frame buffer. The content of frame buffers are used to control
the CRT beam’s intensity or colour.
Advantages: -
*
Shows Realistic pictures.
*
Millions unique hues can be performed.
*
Shadow scenes are conceivable. (i.e. Capable
of being imagined)
Hues = Colour.
Disadvantages: -
*
Low resolution.
*
Electron beam co-ordinated to whole screen not
exclusively to those parts of screen where picture is drawn so long when drawn picture
is longer then whole screen.
*
Expensive.
Numerical Method Book: -
1. Numerical_MathematicsandComputing_(Sixth_Edition)
