➤ Random Scan Display
Random Scan Display uses an electron beam which operates like a pencil to create a line image on CRT screen.
The picture is constructed out of a sequence of straight line segments.
Each line segments is drawn on the screen by directing the beam to move from one point on the screen to the next, where its x & y coordinates defines each point.
After drawing the picture, the system cycles back to the first line and design all the lines of the image 30 to 60 times each second.
Random scan monitors are also known as Vector display or Stroke-Writing display or Calligraphic displays.
➺ Advantages:
- A CRT has the electron beam directed only to the parts of the screen where an image is to be drawn.
- Produce smooth line drawings.
- High Resolution.
- Less Memory Required
➺ Disadvantages:
- Random Scan monitors cannot display realistic shades scenes.
- Color limitations.
➤ 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 & off to create a pattern of illuminated spots.
Picture definition is stored in memory area called the Refresh Buffer or Frame Buffer.
This memory area holds the set of intensity values for all the screen points.
Stored intensity values are then retrieved from the refresh buffer and "Pointed" on the screen one row(scan time) at a time.
Each screen point is referred as a pixel (picture element). At end of each line, the electron beam returns to the left side of the screen to begin displaying the next scan line.
➺ Types of Scanning or Traveling of beam in Raster scan
- Interlaced scanning
- Non Interlaced scanning
- Interlaced scanning: Here, each horizontal line of the screen is traced from top to bottom, due to which fading of display of object may occur. This problem can be solved by non-interlaced scanning. In this first of all odd number of lines are traced or visited by an electron beam, then in the next circle, even number of lines are located
- Non Interlaced Scanning: Non-Interlaced display refresh rate of 30 frames per second used. But it gives flickers. For interlaced display refresh rate of 60 frames per second is used.
➺ Advantages of using Raster Scan
- Realistic image
- Million different colors to be generated
- Shadow scenes are possible
➺ Disadvantages of using Raster Scan
- Low Resolution
- Expensive
➤ Difference between Random Scan and Raster Scan
| Random Scan | Raster Scan |
|---|---|
| It has high resolution | Its resolution is low |
| It is more expensive | It is less expensive |
| Any modification if needed is easy | Modification is tough |
| Solid pattern is tough to fill | Solid pattern is easy to fill |
| Refresh rate depends on resolution | Refresh rate does not depend on the picture |
| only screen with view on area is displayed | Whole screen is scanned |
| Beam penetration technology come under it | Shadow mark technology came under it |
| It does not use interlacing method | It uses interlacing |
| It is restricted to line drawing application | It is suitable for realistic display |
Tags:
computer graphics