Raster Scan Display

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 • Raster can be explained as a rectangular collection of dots or points plotted. i.e (Grid of rows and columns)

   


1) 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 as below:


2) In a simple black-and-white system, each screen point is either on or off, so only one bit per pixel is needed to control the intensity of screen positions. For a bit level system,
•  A bit value of 1 indicates that the electron beam is to be turn ON at that position. 

• A bit value of 0 indicates that the beam intensity is to be turn OFF. 

•Additional bits are needed when color and intensity variations can be displayed.

3) Picture definition(Data about image) is stored in a memory area called the refresh buffer or frame buffer. 

4)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 "painted" on the screen one 
row (scan line) at a time.

5) PIXEL: Each screen point is referred to as a pixel or pel (shortened forms of picture element).

6) So in Raster scan Display, screen is divided into grid that is rows and columns and here electron beam scan the screen line by line from left-right and top-bottom to print the output.

7) I know you might be little confused in both the display techniques, don't worry in next post we will see there difference.

*You can leave a comment if you have doubt in it.



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