Differences Between a Raster Scan and a Random Scan Display

Raster Scan vs Random Scan Display

Most of our displays nowadays use raster scanning, where the entire display is changed one by one from the top left down to the bottom right. But there is also another method of displaying images on a screen, and it is called random scan. The main difference between a raster scan and a random scan is the way they output to the screen. Unlike a raster scan, a random scan doesn’t have a set pattern, thus the name. The images are stored as vectors, and the electron gun is used like a pen to draw the images on the tube.  Random scanning saves on memory as you do not need to store the contents of the entire screen. Only the details of the primitive shapes are stored. You can easily relate a raster scan to Photoshop and a random scan to Coreldraw.

Raster scan displays have a set refresh rate, and they constantly refresh the display even when nothing is changed. That does not happen with a random scan. Only when there are changes needed the screen will be refreshed.

Another difference between a raster scan and a random scan is what they can display. Raster scan displays, as you may have already figured out, can output full color images. In contrast, random scan displays are typically monochromatic. This is not a hardware limitation as color random scan displays are possible, but the associated cost is too much to really be practical. Random scan displays are also not capable of showing realistic images on the screen like photos. Photos cannot be easily broken down into basic shapes for the display to recreate.

Raster scanning grew in popularity very quickly because of its superior capability. On the other hand, random scanning went the way of the dinosaur. There may be certain fields where random scanning may still prove useful, like in oscilloscopes. But in most other applications, raster scan displays are much better. Raster scanning is also the only technology that applies to newer display technologies like LCD and LED.

Summary:

1. A raster scan draws on the entire screen while a random scan does not.
2. Random scan images are stored as vectors.
3. Raster scans have a constant refresh rate while random scans do not.
4. Raster scan displays are typically colored while random scan displays are monochromatic.
5. Raster scan displays can achieve realism while random scan displays cannot.

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