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Difference Between Raster Scan and Random Scan
Raster scan and random scan are two of the most popular approaches used to display the pictures and images of objects on the screen. Raster scan is a technique in which a rectangular pattern of the image is captured on screen, whereas random scan is one in which the picture is constructed through an electron beam.
Read through this article to find out more about raster scan and random scan and how they are different from each other.
What is Rater Scan?
In raster scan, the electron beam is swept across the screen, one row at a time from top to bottom. When this electron beam moves across each row, the beam intensity is turned on and off to create a pattern of illuminated spots on the screen.
The picture definition in a raster scan is stored in a memory area called the Refresh Buffer or Frame Buffer. This memory area holds the set of intensity values for all the screen points. Each screen point is known as a pixel. Finally, at the end of each scan line, the electron beam returns to the left side of the screen to begin displaying the next scan line. The pen plotter is an example of raster scan system.
What is Random Scan?
In random scan, the electron beam is directed only to the part of the screen where the image is to be displayed rather than scanning from left to right and top to bottom as in the case of raster scan. The random scan system is also called vector display, stroke-writing display, or calligraphic display.
In a random scan, the picture definition is stored as a set of line-drawing commands in an area of memory known as the refresh display file. In order to display a specified image, the system cycles through the set of commands in the display file, drawing each component line in turn. The system cycles back to the first line command in the list once all the line drawing commands are executed.
Difference between Raster Scan and Random Scan
The following table highlights all the significant differences between raster scan and random scan −
| Random Scan | Raster Scan |
|---|---|
| The resolution of random scan is higher in comparison raster scan. | The resolution of raster scan is lower in comparison to random scan. |
| It is expensive in comparison to raster scan. | It is inexpensive in comparison to random scan. |
| Any alterations can be done easily. | Alterations are difficult to make. |
| The concept of interweaving is not used. | The concept of interweaving is used. |
| A mathematical function is used to render an image or a picture. | To render image or picture, pixels are used. |
| It is suited for applications that require polygon drawings. | It is suitable to create realistic scenes. |
| An example of random scan is a pen plotter. | A TV set is an example of raster scan. |
| Random scan has lower refresh rate about 30 to 60 times per second. | Raster scan has higher refresh rate about 60 to 80 times per second. |
Conclusion
The most significant difference between the two is that the random scan has higher resolution, while the resolution of raster scan is relatively less.
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