Thursday, June 6, 2019

Raster Scan Display

Raster Scan Display

In raster scan display the beam is affected all over the screen one scan line at a time from top to bottom and then back to top. In this the refresh process is independent. Raster Scan Display mathematically smooths lines, polygon and boundaries. Its cost is low. Raster scan has ability to display areas filled with sailed colors or patterns. Raster display stores the display printers (such as line, characters sailed) in a refresh buffer in the form of pixel.
Architecture of a raster display.
It consists of display controller, central processing unit, refresh buffer, keyboard, mouse and the CRT. In raster scan display a special space of memory is dedicated to graphics only. This memory is called frame buffer. It holds a set of values for all the screen points. The store values are retrieving from frame buffer and display on the screen one row at a time. Each screen point referred to as a pixel. Each pixel on the screen are often specific by its row and column range. Thus, by specifying row and column number. We can specify the picture element position on the screen. The raster screen display system is the most common method of displaying images on the CRT screen. In this method, the horizontal & vertical deflection signals are generating to move the beam all over the screen in a pattern shown in figure. Picture def. in a memory area hold the set of intensity values for all screen point stored intensity value are then retrieve from the refresh buffer and “pointed” on the screen one row at a time. Each screen point is noted as a pixel. Home television sets and printers are examples of other system using raster scan methods.

Image result for raster scan display diagram


1. Realistic image
2. 2Million Different colors to be generated
3. Shadow scenes are possible


1. Low resolution
1. Expensive
2. Electron beam directed to entire screen and only to that part of the screen where picture is to be draw.
In the raster scan approach the viewing screen is divided into a large no. of discrete phosphor picture elements, called pixels. The matrix of pixels constitutes the raster the no. of separate pixels in the raster display might typically range from 256*256 (total 65000) to 1024*1024 (total 1,000,000) each pixel on the screen can be made to glow with a different brightness. During operation an electromagnetic wave creates the image by sweeping along a horizontal line on the screen from left to right and provides the energy to the pixels in that line during the sweep. When the sweep of one line is completed, the electron beam moves to the next line below & proceeds in affixed pattern as in directed.

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