The main difference between Random Scan and Raster scan is that Random Scan produces a high resolution images because it stores pictures as a set of line commands rather than storing as a intensity value.
Random scan System :-
- In Random scan system , the electron beam in CRT draws the image only in that part of the screen where the image is to be drawn.
- Picture definition is now stored as a set of line commands.
- Memory areas required for the storage of line commands is called as refresh display list.
- Random scan systems are designed for line-drawing applications and cannot used to display realistic shaded scenes.
- Refresh rate of Random scan system is 30 to 60 times each second.
- It is costlier than the Raster Scan system as it produces a high resolution image.
In this figure , the electron beam points to that point on the screen where the image is to be drawn. It does not start from the starting of the frame.
Difference between Raster Scan and Random Scan Display
|Raster Scan||Random Scan|
|1. Low Resolution image is generated.||1. High Resolution Image is generated.|
|2. Picture definition is stored in memory area called frame buffer/ refresh buffer.||2. Picture definition is stored in memory area called frame refresh display file.|
|3. Image spot is stored as pixels.||3. Image is stored as a set of line commands.|
|4. A zig-zag line is produced when electron beam strikes on phosphor surface.||4. A smooth line is produced when electron beam strikes on phosphor surface.|
|5. Refresh rate of raster scan display is 60 to 80 frames per second.||5. Refresh rate of raster scan display is 30 to 60 times per second.|
|6. Electron beam is directed to whole screen i.e from left to right and top to bottom.||6. Electron beam is directed to only that part of the screen where image is to be drawn.|